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Friday, July 12, 2019

Why inflate Motorhome tires differently than Trailer tires?

Found the following in a thread on an RV owner's forum. This came after there were comments about the advantages of inflating trailer tires to the tire sidewall inflation number but inflating Motorhome tires based on the measured load on the tires.

 "Such a hard concept for most to understand."

As an actual tire design engineer, not just someone that has used a lot of tires or bought or sold a lot of tires, I feel I might have a slightly better understanding of the science behind why tires fail.
I try and make the information easy to understand but I find that many simply refuse to accept the fact that my 40 years experience that includes thousands of failed tire "autopsies" might qualify me to give sound advice.
If you simply look at the experience of three groups of tire users. Excluding punctures or pothold impact breaks.
1. Regular motor vehicles. People get about 40 to 50,000 miles before the tires "wear out"  less than 1% experience tire failures.
2. Class-A and Class-C motorhome users. Many only drive 5 to 8,000 miles a year. It is recommended that starting at 5 years of age, tires be professionally inspected. This does not mean a simple walk around to look at the tread depth but close inspection with good lighting. Maybe even using a pit to allow the inner sidewalls to be inspected. Annual ispections thereafter are recommended and replacement at 10 year tire age "no matter how good a tire looks" This group also has a low structural failure rate not tracable to air leak or impact.

3. RV Trailer users "Towables". Based on numerous reports of higher structural failures i.e. belt/tread separations, and some strange patterns left in lose gravel where a trailer was turned 180 degrees I had some computer simulations run and the numbers provided an explination for the "why" towables have a mush worse structural failure rate. The forces inside the tire structure are significantly higher (+24%) in trailer application (i.e. towables) than in motor vehicle applications This force is identified as Interply Shear and it shows up as trying to separate the top steel belt from the bottom steel belt in radial tires.

While it would be possible for RV Trailer companies to make design changes to trailer suspension to allow for "passive steering" as seen on large cement trucks with a tag axle, I doubt they would go to the expense simply to extend tire life.

While lowering the actual load on a tire in trailer service can lower the Interply Shear force I doubt that it is possible to lower the load by 40 to 50%. One thing trailer owners can do to lower this force is to increase the cold inflation to the tire sidewall "max" Sorry to say you can not reduce the Interply Shear to zero as this is the nature of radial tires.

Friday, July 5, 2019

Modern radial tire assembly -Worldwide

A very good 10 min video from a number of different companies on how modern radials tires are "built," how some of the material is processed, tires are cured, handled in the warehouse and even how some retreads are made.

There isn't a tire plant worker in the world (China, Europe, or the US) that would not recognize what the equipment is doing.

Yes, the machines are painted different colors and the robotic handling of the tires is done with different equipment but the end result is almost identical.

This uniformity in the process is why, I have so much difficulty in accepting the idea that because a tire is built in one country, it is automatically more likely to fail than when it is made in another country.


Friday, June 28, 2019

Critical tire temperature ?

Received another question
Hi Roger, I just read your article on sidewall strength and “blowouts”. You mentioned that if the temperature rises too high the sidewall cords may melt. I have a 2017 Winnebago Grand Tour with a built in TPMS system with pressure and temperature sensors. Most RVers know (or should know) to keep their tires at the proper inflation level. The one thing I haven’t seen addressed is tire/air pressure temperature. As I drive down the road I can watch the pressure rise with a corresponding temperature increase. Is there a critical temperature to watch out for exclusive of tire pressure? If so, I’m sure it would be different for each make/model and tire size. Do manufacturers publish any specific data for their tires (i.e. a critical do not exceed temperature)?
Thanks for all you do to keep us in the loop.

Ken

Ken, If you check out the posts on my blog you will find numerous posts on tire temperature and pressure.

RE Critical temp.  For short term (MInutes or seconds) I would consider structural temperatures in the 205 - 230F to be critical. Size, brand or design, doesn't make much difference. The problem is there is no way to measure the temperature as the location of the hottest location is at the edges of the radial belts. In racing, like at Indy we use a needle probe and stick this into the tire about 1/4 to 3/8" deep. External surface temperatures are much cooler because of external air moving over the surface. With rubber being such a good insulator the heat does not travel to the surface fast enough (minutes) relative to the ability of the temperature to rise (seconds) at the critical location we see it possible to have internal rubber failure before the surface temperature gets to a critical point.
I think you can understand that the rubber can get softer with an increase in temperature. As it gets softer, it stretches more, as it stretches more it gets hotter, etc. Up to about 210F, this increased softness can be managed with construction and thickness design changes but each of those changes can result in some other property getting worse. Also, that 210F point, changes with time and temperature history. Tire design is a balancing act and a series of trade-offs. One thing that happens with a loss of strength and increase bending is the potential for tearing of the rubber at the molecular level which can result ultimately with the tearing to grow to the width of the belts which in turn results in a belt separation.

BUT

The key thing to understand is that temperature damage is cumulative and the chemical reaction that occurs can eventually result in a loss of elasticity at higher temperatures so the rubber tears which leads to a separation. The rate of these changes can itself change over time and the rate is also affected by the temperature.
Even for a single rubber compound, there is no exact temperature for it to "fail". The physical properties of rubber changes with temperature but here there is no exact point at which the strength goes from 100% to zero.

TPMS gives an approximate temperature of the air inside a tire which is also lower than the critical temperature. Most TPMS have a high-temperature warning set to 158F and if you see that reading then you do not have enough pressure for the load you have or are driving too fast. This does not mean you can lower pressure till you see a reading of 158 as you are still doing damage and "consuming" the finite life of the rubber in a tire.

Read my blog, Learn the actual load (when the RV is its heaviest) for each tire position (4 corner weights) Consult the tables, Learn the MINIMUM inflation pressure, add a +10% inflation margin to learn your "cold set pressure" for each axle based on the heaviest axle end, Adjust your TPMS low pressure level to never be lower than the minimum. The go and enjoy your RV

Friday, June 21, 2019

Tire sidewall "strength". What does that mean?

I note that on many RV forum posts on the topic of tire "Blowouts," there many times are posts on the "Strength" of the tire sidewall. Before I start, it's important that we have a shared definition of a few words.
"Blowout" is simply a statement that a tire failed catastrophically. It does not mean it simply exploded as if it were a bomb.

Belt or Tread Separation is the detachment of the belts and or tread in a radial tire. This can lead to a rapid loss of air which can make a loud noise, surprising the driver and leading to the idea that there was an explosion or "Blowout". But not all tires that have belt separations end up with a rapid loss of air. Here is an example of a tire with tread & top belt detached from the rest of the tire. It is shiny as I sprayed water on the tire while inflated on a wheel to inspect for punctures or leaks as I had suspected the tire had been run with low inflation. I "redacted" identifying marks as that information is not important for this discussion.

Sidewall Failure for this discussion means a failure of the tire sidewall not related to a sidewall cut or impact. many times when a tire loses air but is still being driven at highway speeds, the body cord or "body ply" material can fail due to excessive heat.  A more technically accurate term used by tire engineers would be "RLOF" which stands for Run Low Sidewall Flex Failure. Most Passenger, Light Truck and ST type tires made today use Polyester cords the sidewall ply.  With excessive flexing and bending from low inflation, the cord can overheat.








If the temperature gets high enough (300°F to 350°F) the cord can lose half its strength and high temperatures can result in the cord melting just as you have seen when you melt the end of a piece of Nylon or Polyester rope with a match.
 Here is what melted tire cord looks like.

I have shown this condition in a few posts, but probably the one with the best example is my post "Blowout- Real Life Example"

So why does this engineering stuff make a difference? You still had a "Blowout," and are not happy. Probably want to blame someone and the tire company is an easy target. BUT as I have said before if you do not know the real reason for a tire failure you might not prevent another failure from happening.

Imagine you had an RLOF but did not bother to try and learn why the tire was low on air. Puncture, cut, leaking valve, leaking valve core, cracked wheel are all "suspects" and just replacing the tires on your RV with a different brand will not prevent another "Blowout".

So this leaves the question of Sidewall Strength. DOT has a specific test to confirm a minimum "strength" for tires. The test procedure. involves forcing a 34 inch diameter steel rod with a hemispherical end perpendicularly into the tread as near to the centerline as possible,  at the rate of  2 inches per minute. This is repeated 5 locations around the tire and there are published minimum energy requirements (inch-pounds force) that tires must exhibit. These minimums are based on the tire size, type, and Load Range.

Now you may ask: How does the sidewall material strength come into play? Well, the sidewall material runs under the belt material so is part of the total strength requirement. Tire companies also have their own "Burst" test requirements which involve mounting a tire on a special test wheel and increasing the pressure till the tread or sidewall or the bead fails. They use special wheels as most tires are stronger than regular production wheels. The minimum pressure is not published but in most cases, it is in excess of three times the inflation number molded on a tire sidewall. and in some cases, I have seen tires exceed six times the inflation number on the sidewall.

Tire Design engineers have a wide choice of sidewall ply material to choose from. Different types of cord, different sizes and even different amounts or cords per inch circumference can be selected as the engineer works toward the final design specification. Simply claiming that "Our tires have larger and stronger cord" while true doesn't address the question of how much of that cord is used in the tire.

Bottom Line. I hope you now understand how simply claiming the tire sidewall wasn't strong enough will not help you solve your tire failure issue.

Friday, June 14, 2019

Are some tires from China better than others?

Another question on China tires:
"Tireman - in the Post you linked further up the thread you commented on not expecting long life performance out of the lowest priced tires. There seems to be something in all of the reports for "China Bombs" in that there are a lot of reported failures. Is the hype bigger than the problem? Should well maintained OEM tires last better than what is being reported? Is it your assessment that the seemingly high percentage of failures is due to the OEM tires being cheap, low-cost tires?

Sailun tires seem to have a good reputation, even though they are China tires. So it would seem that it's really just an issue of quality of the build. A good tire is a good tire, regardless of where it's made?"

In general, I would consider steel body tires, like many Sailun items, "Commercial" grade, be they LT or ST type and as such I would expect them to perform better that lighter duty tires (both ST & LT type). This would apply to other steel body tires too.

A problem with "reports" of failures is that almost no owners have the knowledge or training necessary to properly identify the real cause for failure. So while there may be a dozen reports of "Blowouts", there could be a dozen different root cause reasons. Some might even not be tire related cause like valve or wheel failure or pothole or 10d nail through the sidewall.

RE quality. All tires sold in the US are required to be certified by the manufacturer to be capable of passing Federal DOT Regulations. If tires do not pass a test (random selection by DOT) or if there are sufficient complaints to get the attention of NHTSA they might initiate an investigation. If it is found that tires do not pass the required testing then a recall might be ordered and recalls would include all tires made since the last tire that passed the test were made. This could be many thousands or even tens of thousands of tires. There are also per-tire fines. So this is something tire companies really do not want to have happened.

I have written a number of times on my blog about "China" tires and how I disagree with the concept which I liken to claiming that RVs made in Indiana are bad because most of the complaints or problem reports are about RVs built in Indiana.

##RVT901

Friday, June 7, 2019

Why not just inflate to the Certification label level?

I continue to read RV forum posts from people asking about what inflation to use. Tire Sidewall?, Sticker? Owner's manual? The inflation used by a neighbor? There is also continued confusion on what the sticker inflation is.
"Vehicle Certification Label" AKA "Tire Placard" only considers one thing. The max tire load capacity (molded on the tire sidewall) when the tire is inflated to the level associated with the original tire Load Range (Ply Rating) as shown in the industry load & Inflation tables.

Federal DOT Regulations specify the label indicate the tire inflation level needed to support AT LEAST  50% of the GAWR. NOTE there is no margin or reserve load capacity specified or required by the DOT Regulations.

Starting in Nov 2017, the RVIA (RV Industry Association) required that trailers have a 10% margin on tire load capacity. Motorhomes do not have this margin requirement from RVIA as far as I know.

This Reserve Load margin for trailers is more important than on Motorhomes due to the significantly higher Interply Shear imposed in trailer application.
Tire companies, do not know the exact loading that will be placed on their tires in RV application so you have to do a little work to learn the MINIMUM inflation needs for your personal vehicle. You could simply use the inflation on the Tire Placard but you still need to confirm, with scale measurement, that no axle is loaded more than the stated GAWR. It is also strongly recommended that you confirm your side-to-side load split is close to 50/50 as the tires do not "know" what the other tires are supporting, so you could be unknowingly overloading one tire by hundreds or even 1,000#.
I have other posts in this blog on how to learn the individual tire loads.

##RVT900

Friday, May 31, 2019

Why no tire reviews?

I occasionally see people complaining about the lack of meaningful tire comparisons. I guess they think someone should be doing comparison testing. I covered the topic of the cost of testing tires in May 2016 and even offered to run a test if there was some financial support. FYI after the offer, I received the grans total of $0.00 so I can only guess people want someone else to do the work and spend the money.

Cost aside, I'm not exactly sure what people would want or expect in an un-bias comparison.

Cost:  This is difficult as there are many different outlets for tires and without some detailed research How would you establish the value of buying from a neighborhood tire store vs buying the tires mail-order. If you had a problem how would you like to have to pay to ship the problem tire back to the sales outlet vs just taking the tire to the local dealer?
Different outlets also have sales of specific sizes or type tire so a comparison of brand Q  vs brand U could be very misleading if the identical size wasn't involved, and how would you compare a tire that is on sale in Calif vs one not on sale but with a free 1-year warranty in Ohio?

Wear:  Now we are back to the cost associated with doing the testing, and we have already seen that apparently, no one is willing to finance this type of testing.

Durability: Again controlled testing is expensive. Even if tires were donated and you found some RV owners willing to do the testing how do you compare the durability of a set of tires driven in PA & NY vs tires on a different RV driven in TX & AZ. Would you be willing to sign up to do the driving if you had your route specified to be a 200 mile back and forth trip across Iowa on US RT 30 with the requirement to complete 1200 miles a week for ten weeks, with you paying the cost of fuel, etc?

If a reader has some specific questions or requests on what information they would expect to gain from such a comparison, My offer of setting up and overseeing the testing still stands but someone else still needs to come up with the money to buy the tires and pay for the testing.

So yes it still comes down to cost and who is willing to pay. One other thing to consider is that there is always the potential of setting up and running an expensive test only to have one of the tires being evaluates dropped from production just as you complete the evaluation.

Just think if we had somehow started a test that included the Goodyear Marathon ST tire in the fall of 2016 and it was finished a year later, only to learn the Marathon was being replaced by the Goodyear Endurance?

##RVT899

Friday, May 24, 2019

Is a "Plug" repair or "liquid sealant" an acceptable repair?


Got a reply to a post on an RV Forum on a discussion on the use of a "plug only" type repair. I had posted a couple of pictures of examples of tires that had been run when significantly under-inflated and the owner only used a "plug-only" type repair.
Here is a picture of a tire showing the cracks through the inner liner due to the tire being run severely under-inflated because of the air leak, and run for hundreds of miles.

Here is another tire that had significant damage from the puncturing object but the damage went undetected because the tire was not dis-mounted and inspected.








Here is an example of a tire that was "plugged" 3 times but apparently continued to leak and the owner put some type of liquid sealant into the tire trying to stop the leak. (Note I don't think this is Fix-A-Flat brand sealant but you understand what I am talking about here.


Would you feel comfortable driving on either of these tires?
These examples show why the proper method of repair is to Dismount, Inspect then if the tire is OK a patch and plug and be used to seal the air chamber and to protect the steel belts from rusting due to water entering the belts from the outside. If you don't inspect how would you ever know the extent of the damage that has been done to your tires?

The person was asking the initial question about the advisability of using a plug, I assume wanted to do plug repairs continued:

"I'm still not sure what point you are making, especially if the cracks and the puncture are unrelated.
If the plug repair was successful, as most are, OR if there had never been a puncture anyway, then a tire interior would never be inspected and so cracks caused by say, running over a curb or large rock, would never be noticed unless they caused air loss that resulted in testing or inspection.
Your second exhibit shows a tire with a plug repair that we don't know if successful or not and again, probably or possibly unrelated damage that could have been there for hours or years and may or may not have been the reason for the tire being dismounted, so again, your point? Tires get damaged, tires fail and as your photos clearly show, a simple sharp object penetration isn't the most serious injury tires are subjected to."
I agree it may be "possible" to do a "plug" repair that will allow a tire to hold air. The main problem is that most people who do a plug repair as a "temporary fix" to allow them to stop the leak, re-inflate the tire and continue to travel to get off the highway. Most will never go the next step to have the interior of the tire inspected.
Innerliner cracks come from operating a tire for many hundreds of miles with the excess deflection that is probably due to running significantly underinflated. Such operation can not only damage the inner liner but also compromise the belt integrity.
Many times if there is a belt separation later, the owner does not associate the decision to not have the tire inspected and replaced if the damage is discovered so simply blames the tire MFG for the failure.
The second picture shows the damage to the interior of the tire when the object (maybe a piece of wire) was left in the tire and it cut through the inner liner. This will result in high-pressure air being forced into the body of the tire and again possibly leading to a separation that again the owner does not associate with the puncture weeks or months previous.
Some points to consider:
1. The use of a plug only will void any tire warranty according to most tire companies (GY, MI, BS, etc)
2. The use of a plug only is specifically not approved by DOT so don't try and make a claim of a tire being "defective" to NHTSA or in any court of law
3. Unless you have personally inspected a few thousand tires and can provide evidence that tires with improper repairs do not suffer secondary catastrophic failures, I suggest you include a warning with your posts that your observations are only based on your experiences with a few tires.
I agree that we are all entitled to our personal opinion but not our own facts, especially when others may be relying on our statements for the safe operation of their vehicles and specifically their tires.
Go ahead and use a plug if the situation warrants but just be sure you have the tire dismounted, completely inspect and if possible properly repaired but please be clear that without a complete inspection it is possible that the tire has suffered irreparable damage and should be removed from service.

Friday, May 17, 2019

Do your Tow Vehicle and Trailer match?

Here is some good advice I found on the Interweb and agree with.

Here is a short video from the RV Safety Education Foundation. A longer in-depth video link available at the end of this post.

 You should always do your calculations based on the GVWR of the trailer, not the dry (shipping) weight. The dry weight is a number used by some manufacturers and some dealers to try to sucker people into purchasing a trailer that is too much for their truck

The same goes for tongue weight. The marketing brochure may provide the trailer weight based on the empty trailer (with no propane or batteries, etc.). You should figure your weight based on 15% of the GVWR of the trailer. But the real trailer weighs figure you should know is what the truck scale tells you once the trailer is fully loaded but not hooked to the tow vehicle.

You can not use the "paper" figures found in truck or trailer literature and certainly not the verbal information from the truck or trailer salesperson to calculate your towing capacity. You MUST have real numbers which mean actual scale weights.

Next, take the cargo capacity of your truck (from the payload sticker from the door jamb of the driver's door on the truck). It will say something like "cargo must not exceed ... lbs.". From this payload capacity, you need to be able to deduct all of the following:
- People in the truck
- Cargo in the truck
- Weight of the WD trailer hitch or of the hitch for the 5th wheel
- Total actual weight of the trailer


Then you should also consider the maximum or gross combined weight rating (GCWR) - this is the maximum weight you're allowed to have on the road, which combines the full weight of the truck and trailer combined. To get these, you can use the GVWRs of both the truck and trailer, but really you should go to the scales and have them weighed as YOUR truck and YOUR trailer almost certainly do not weigh what is shown in the literature.

When working all these numbers, you need to consider the following:
- Do I have enough truck (engine, transmission, etc.) to pull this load up and over the hills without causing undue stress on the engine/transmission, etc?
- Do I have enough truck (brakes) to stop this whole load in the event the trailer brakes fail without causing undue stress to the truck brakes?
- Do I have enough truck (suspension, tires, etc.) to control the trailer in heavy winds, while passing or being passed by semi trucks - and especially in the event of an emergency maneuver, like dodging a deer which just jumped out on the road in front of me or a tire failure (blow-out).
I hope you're getting the basic information before you purchase. You'd be way ahead of the game.


In-depth video at RVSEF web site on truck - trailer matching HERE.

##RVT897

Friday, May 10, 2019

Have you "tested" your TPMS?

Like anything mechanical or electrical, parts can die, wear out or malfunction. While I am not aware of a lot of reports of failures of TPM Monitors or sensors I would be surprised if the only problems were related to battery life or improper set-up.

This post is limited to TPMS that use externally mounted sensors. i.e. the ones that screw onto the end of your valve stem.

Batteries. They eventually will die. The early warning of loss of signal from a sensor that previously was working appears to be an occasional intermittent loss of signal, followed eventually by almost constant no signal on the display. This is easy to fix as most of these systems have user replaceable batteries.  I always carry a couple but also I don't stock up as batteries may lose power even sitting in their original packaging.

"O" ring:  Under the screw-on plastic cap there is a very small O-ring. As with any rubber component they can simply die ( crack or tear) just from normal use as rubber does "age-out" due to exposure to heat an Ozone in the atmosphere. I would suggest having a few "O" rings on hand as, unlike the batteries, you can't just pick up a replacement at CVS, Walmart, or Walgreens. You will probably have to get them from your TPMS dealer. When you screw the cap on the sensor don't overtighten the cap as that can distort the O-ring and shorten its life

Plastic cap. This part should last longer than the rubber O-Ring but plastic ages too. Again this is special and unique to your brand TPMS so having at least one on hand from your dealer is a good idea. Also, don't over tighten the cap. It might be possible to seal a cracked cap for a short time with Silicone seal or glue but be careful not to glue the cap to the sensor.

Sensor electronics. All you can do here is get a new replacement sensor. Some brand TPMS offer a longer-term warranty (Lifetime) others only 12 months. I do carry a spare sensor but not in my toolbox or parts box but I added a sensor to my spare tire. in my Class-C. This gives give me a replacement I could use on a ground tire if one of those sensors ever failed. It would only require a quick program change when I move the sensor from a spare position to the ground tire. I could do without a sensor on the spare for the week it might take to get a replacement sensor. The reputable dealers I have talked with all offer single sensor sales or replacement under warranty. A sensor on a spare tire would probably last longer than the other external sensors as it isn't exposed to potential strike from road debris or heat from the tire or brake drum. If I had a sensor fail I would plan on keeping the cap and O-ring if in good condition as a future spare part.

Monitor. Well if this part fails I don't know of any repair a user could do. You just need to get a new monitor from your dealer and hope you have a good warranty and that your dealer will sell the monitor by itself so you don't have to buy another complete system.  I have to admit that I did manage to damage my older monitor after four years of reliable use. I grabbed the wrong power cord and connected it to a 12v source which fried the monitor that only wanted 5V. My Bad. Luckily I was able to get just the sensor and didn't have to buy a bunch of new sensors at the same time.

Replacement parts: If you bought your TPMS from a dealer that specializes in the RV market and attends RV shows then you should be able to get individual parts with little problem. If on the other hand, you purchased mail order from Amazon or eBay or similar, I have no idea what parts or service you can expect.

Testing:  This is something I doubt any have done but after some consideration, I think I have an easy and workable plan.
I suggest at least once every 6 months when you are at a location where you have nice weather and a bit of time you conduct an operation test.
With the system on, I would record all the readings from for both pressure and temperature. With the Co-Pilot in the driver seat, I would go to each tire position and unscrew the sensor. The Co-Pilot should signal the tester as soon as a warning is given on the monitor. You might use your phone or walkie-talkie or maybe a 3rd person, as honking the horn as a signal might become bothersome for your neighbors. If all the sensors give a warning within a few seconds (read your manual on the claimed warning time) all is OK. If there is a delay or no warning after say 10 seconds then there may be a problem in either the sensor or monitor or programming and you MUST learn the why and take corrective action as you are depending on receiving prompt warning of air loss.
You can also use this opportunity to confirm your cold tire pressure with your calibrated hand gauge. (See THIS post on how to confirm your gauge is sufficiently accurate) and you can also "top-off your cold pressure with your normal margin of air.

##RVT896

Friday, May 3, 2019

Expected tire life

I Saw a question on tire life:
"I was wondering could some one cover a topic travel trailers ,5th wheel, bus , semi's and semi trailers, and anything recreational  W H A T   IS   T I R E   LIFE  FOR  THEM?  I have never seen this covered   HUM !"
I have covered this in a few different posts on this blog and some RV forums but this post may put it all in one place:
Generally, tire life for Bus and HD truck is based on wear, not time, as these vehicles may drive 50 to 100,000 miles a year with the tires wearing out at 50 to 80,000 miles.
Daily drivers (cars  & P/U) drive about 12,000 a year and may get 3 to 5 years life again most based on wearing out.

With RVs (Trailer & Motorhome) mileage might be as low as a few hundred miles a year to a few driving up to 20,000.  BUT if you consult your owner's manuals you will probably see them point out expected life to be 3 to 5 on trailers. Motorhomes probably hit 7 to the suggested max of 10 years, again before wear-out due to low miles driven in most cases.

 The primary reason for the earlier "end of life" on trailers is the result of the unique radial belt shear forces identified in this blog and in the industry technical papers as "Interply Shear" that comes from a combination of tires being dragged rather than steered around corners and tires "fighting" each other when going around corners as the tires on different axles are not all rotating around the same center of the turn. It is the Interply Shear that initiates the cracks between the belts and accelerated the crack growth that can end up as a belt separation before the tires wear out. The Interply Shear damage is augmented by damage from improper (low) inflation, improper (high) load and in some cases, excess heat due to speeds higher than the basic design called for.

 I hope this helps others why we have different tire life experiences on our RVs than with our cars.

##RVT895

Friday, April 26, 2019

ST tire speed rating

Point of clarification.

The Tire & Rim Association Load formula used by the industry for ST type tires is based on a 65 mph max operating speed. They even identified inflation increase and load capability reductions necessary to operate up to 75 mph.  Neither P or LT tires have stated max speed associated with their load formula or calculation as far as I can find. P-type do have the stated 1.10 "De-Rating" of load capacity when used on a trailer or P/U.

If you look at similar physical sized tires and include the P Derating you will see the de-rated P and LT tires give similar results for load capacity.

BUT the load capacity of the ST type is significantly higher. Why would that be if there were not some other limiting factor such as the 65 mph speed limit?
Some people would have us believe that ST tires all had some magic rubber or body cord added to them in 2017 when speed ratings higher than 65 were added. The reality is that the speed rating was added to avoid import tariffs. Maybe you think that all the different tire companies used this "magic" rubber to give them an overnight increase in speed capability.
Why isn't there a single tire company anywhere in the world using this "pixie-dust" in their LT or heavy truck tires to give them an extra 10% to 25% more load capacity?

I have seen a section of a GY Endurance and it clearly has "better" construction than some non-speed rated tires. Only time will tell if this new construction results in a better life, But I seriously doubt that you can go from 65 mph max to 99 or 106 mph with an ST tire and not suffer some negative consequences.   Yes, many will say they do not drive that fast but we have all been passed by trailers going faster than 75. Some even say they tow at 80+.

Going faster can do structural damage and we have covered how damage is cumulative.
What I have not seen is anyone changing their advice on tire life in RV usage.
What ST tire company now says up to 10 years life or even claims over 5-year life?  I have reviewed a few different owner's manuals and see 3 - 4-year life suggested.
I have previously written about Interply Shear and while the addition of a Nylon cap on top of the belts may extend the life of a tire and it may also improve the tire's ability to pass some speed test designed for passenger tires I still have serious reservations about any trailer being towed at any speed above 65 mph.

I'm not saying "Don't buy tires with higher speed symbol" What I am saying is that you should still stay to 65 mph max or you may end up paying the consiquences with shorter than expected tire life.

But that's just my opinion.
 

Friday, April 19, 2019

Tire Brand Confusion. This info may help Who makes it where?

QUOTE from RV owner on a forum

"I called the tire place (they do commercial truck tires) last week to order the Sumitomo tires, but I then asked him about Firestone FS561 tires, and then he said he’s been selling a lot of Dayton D520S for RVs and that they are a Firestone/Bridgestone owned company. I told him I’d do some research and am just more confused the more I look at tires"


Not sure about the confusion on where a tire is made or by which company. A quick Google search such as "who owns Sumitomo tire"  can get you background information as found HERE.

The where it is made can be answered by reading the first two characters of the DOT serial and then checking HERE.


Michelin. Bridgestone & Goodyear ( The BIG 3) all own a number of brand names. This is like GM owns Chevy, Cadilac, GMC, etc The engineers that design one brand may have designed a different brand last year but generally have the same or similar list of rubber compounds to choose from. Many times a single plant may make two or more brands using the same equipment.  Part of the difference is brand positioning or image in the focus (longer wear or softer ride or better mud traction).

Do you think Chevy uses different bolts when they put a car together than Cadilac? They probably even have the same suppliers making similar components such as tires or power steering pumps. Cadilac has an "image" of a better ride so may choose more expensive and better-performing shocks but the Chevy Corvette engineers would select firmer shocks.  Does this make one "brand" better than another? No, they have different target markets.

Same for tires. Bridgestone wants "Hi-Tech" & Premium image for tires with the Bridgestone name on the sidewall. Firestone brand is aimed at Mid-America solid performance at a reasonable cost, while Dayton is aimed at a "value" image.  The expected wear is slightly different for the 3 brands, so is the price.

I see no reason to not consider the Dayton brand if you were considering the Firestone brand.   The same would apply if you were considering Fulda vs Dunlop as both brands are owned by Goodyear. Michelin owns BFG brand

Friday, April 12, 2019

Do you have "Big Wheels" on your car or tow vehicle? Why?

When people shop for cars/trucks very few pay attention to the tires other than to decide if they "look" good.
 A few years the ago "stylists" decided to start moving to ever larger wheel diameters. Now in a few cases, there was a reason to move from 15" to 16" due to increased brake rotor diameter. This increase does not apply to standard cars or pick-up trucks.
If you look at the clearance between the brakes and wheel sometimes that are many inches. This tells you that the reason for your "Big Wheels" is most likely just a styling gimmick.

The larger wheels are more expensive and the larger wheel diameter required a significant increase in tire mfg equipment in the tire plants to make the 18", 19" 20" and larger tires.
Why do people think big wheels "look" better?  I have no idea other than they might have liked the "Big Wheel" look on their toy cars as a kid?

  My Chevy 3500 and 4500 trucks work just fine with 16" tires so other than styling looks I have no idea why people think they would need anything larger on their 1/2 to 1 ton TV.

There is a definite downside to having a vehicle with larger than 16" diameter wheels. That is a higher cost and fewer choices when it comes to buying replacement rubber.

If you do a little research you will discover the more limited selection. Your tow vehicle has a job to do so it is probably to your advantage to not get the truck because it looks "Hot" as you may end up paying the price for excesses of the "stylists".

Just one man's opinion.

Friday, April 5, 2019

Do you need an external spare tire cover?

Reading a forum where the owners of one specific brand of trailers were complaining about the $21 the RV company wanted to charge for a spare tire cover.

I have previously covered, in detail the advantages and the "why" we should be storing our tires inside or under our RV or under light colored covers. It is the HEAT that kills tires and the aging effect on tires is exponential with an increase in temperature (doubles each 18°F) you could end up with a tire failure with ZERO miles as seen in this example.








 I pointed out, with temperature data, in my blog post on why white tire covers are good and much better than black covers.
This shot shows what can happen with a black cover that effectively places the spare in an "oven" where cooling air can't offset any of the Sun's heat.
You will note that in both the above examples the top side of the tire (location with most direct Sun heating) is the location of the failure.

These folks do it right.













I know of no tire shine or protectant spray that provided protection from heat.

Friday, March 29, 2019

It appears Goodyear agrees with me

I have written a number of times on the advisability of running trailer tires at the inflation molded on the tire sidewall.

Some posts dove deep into the Science behind the recommendation. I know this can make your eyes glaze over so how about just following what Goodyear says in their RV Tires information web page:

"Unless trying to resolve poor ride quality problems with an RV trailer, it is recommended that trailer tires be inflated to the pressure indicated on the sidewall of the tire. Trailer tires experience significant lateral (side-to-side) loads due to vehicle sway from uneven roads or passing vehicles. Using the inflation pressure engraved on the sidewall will provide optimum load carrying capacity and minimize heat build-up."

##RVT890

Friday, March 22, 2019

Valve stems, cores, and caps "Oh My", and how tight is tight enough?


Yes, some rubber valve stems have a metal center and some valves are all metal except for a rubber gasket. The metal part of valves is almost always brass. Sometimes Nickle plated to look like chrome or to match aluminum wheels.


The two valves on the left are "Snap-In" rubber valves.  The two on the right are "Bolt-in" metal stems. By "Snap-In" we mean the valve is installed into the hole in the wheel by pulling on the threaded part of the brass until the small rubber ridge "snaps" through the hole.

The best way to know for sure is to look for a nut that "bolts" the stem to the wheel.  I would suggest a TR416 or similar as seen HERE from Auto Zone.  O'Riley's parts stores have a similar short stem.  You should be able to find similar in almost any auto parts store. These metal stems come in many lengths from less than an inch to 2" or longer (different lengths have different TR part numbers).  The hole in your passenger, trailer or light truck wheel is most likely 7/16"  Old VW wheels were 5/8" All 19.5 and 22.5 wheels should have come with a metal bolt in valves but those use the 5/8" rubber grommet/O-ring. Many metal stems sold at retail, come with two different rubber gaskets, one for each size hole. The gasket is just a snug fit and should just push into the wheel hole.

Note the nut has a torque spec of  25 - 45 INCH Pounds so do not over tighten the nut. I have found that a regular 9/16" wrench is just fine and you do not need a big ratchet wrench to tighten the nut.

Keep the stem short to lower the chance of the TPMS being knocked off if you get near a curb. There are some unique wheels that may require a bit longer stem to allow you to attach your TPM sensor. I suggest you have the sensors available when you install the bolt in stems to confirm sufficient clearance.

The main reason for metal stems when running TPMS is to prevent vibration of the stem which can fatigue the rubber stem.


While you are at the auto parts store be sure you have METAL valve caps. Plastic caps are IMO only good for keeping dirt and small birds out of the valve core area. Metal caps should have rubber "O" rings in them and can retain air if you are not running TPMS. Look in the thread end and you should see the gasket.

Each Fall, when I remove my TPMS for the Winter, I place metal caps on my stems. I will admit that one year I didn't do that and the valve core had a very slow leak but I ended up with a tire being damaged because it lost air over the 7 months between when I parked and when I was getting ready to go traveling.
  
I have a couple of posts that focuses on the valve cores. One on why they leak.

One detail is how to know how tight is enough for your valve cores. Over-tight can cause the small gasket to deform and even split and under-tight will result in a slow leak. After 40 years of installing valve cores I consider my fingers to be close to "calibration" but it would be better if you followed a specific procedure.

I did a test that may help. The spec for valve core torque is  1.5 to 5.0-inch pounds MAX  but I don't expect you to run out and buy a special inch-pound torque wrench as seen here.




To help you I devised this test. Using the test fixture I made when running my TPMS comparison I loosened a core till it leaked as seen here.

 Then using my torque wrench I tightened the core till the leak just stopped. I then continued to tighten the core till I reached about 1.5 Inch Pounds (this was 1/4 turn after the leak stopped) I then continued to tighten the core till I reached 5-inch pounds (This was 3/4 turn after the leak stopped)

  So I would suggest that you can simply tighten a core till the leak stops then rotate 1/2 turn more.

Here are sample core tools.
The one on the left is a "professional" tool but I have also used my home made core tool for many years. This is just an old scrap rubber valve stem with a cap that has the cut-out to fit a core.
I hope this helps you understand a bit more about valves and valve cores.


##RVT889

Friday, March 15, 2019

How much Reserve Load or "Headroom" is enough?

Following an RV forum discussion on How much extra load capacity or "Reserve Load" or "Head Room" is enough. Some folks had moved from LR-C to LR-D  others to LR-G but were concerned about running the tire sidewall pressure as it would be too hard on the trailer.

There was also some confusion about the "Maximum" allowable inflation.  I said:
"The inflation on a tire sidewall is the MINIMUM inflation pressure needed to support the MAXIMUM load (also molded o the tire sidewall).
There is a sound scientific reason to run higher inflation when running tires on multi-axle trailers. It is called "Interply Shear". This force is what can result in belt/tread separations. I have covered this in detail along with references to technical papers on the topic.
IMO you need a minimum of 15% "head-room" of load capacity over the measured load of the heavier end of an axle. (CAT scale only gives the total on an axle and very few RVs have 50/50 load split. Some folks have discovered unbalance of 500 to 1,000#)
Most cars come with 20% to 40% tire load capacity headroom. I run 25% on my Class-C.
"
Which resulted in this reply:
"So if a given pressure (below the tires maximum) still provides the necessary headroom over the measured load, it's okay to run it, correct? Or am I not understanding something? "

This leads me to respond:
"I wish it were that simple but all radial tires have the Interply Shear force. It's a question of how much "tire life" is being "used up". The force results in microscopic cracks forming between the two steel belts at the outer edge. Once cracks form they do not repair themselves but can only grow.
No good tool or math model can turn Shear Force into Miles of tire life is "consumed" as there are just too many variables.
Finite Element models simply indicate that higher inflation can result in lower shear force every time you turn a corner or every time a tire completes a revolution. 

About the best you can do is to do a close visual inspection (Free Spin) to look for signs or out of round or side to side runout which are strong indicators of internal structural tears. I have a video and pictures of the autopsy I did on a tire where you can see the separations running across 50% to 70% of the tread width. This large separation might run a thousand miles or under certain circumstances might fail tomorrow.
Think of it like your Blood Pressure. Higher is worse. So the question is at what number can you expect to have a fatal attack?
If you consult your owner's manual you will see a suggestion that 3 to 5 years is the max expected life but obviously someone that runs at or above Max Load and above 65 mph and drives 4,000 mi a year is more likely to suffer a failure than someone that only drives 2,000 mi, never faster than 62 and at only 80% of tire load capacity.
Moving up one Load Range C>D or D>E can probably expect longer tire life if they also go from 50 to 65 or 65 to 80 psi. Going to LR-G in a Commercial grade all-steel tire should result in longer life even if you don't run 110psi.
Since load capacity is shown in the Load/Infl tables then I would suggest trying to get to 20 to 25% Reserve Load would be a good move. You still need to watch max speed and minimize sharp turns (as seen when backing) and of course, do a good free spin inspection once a year or once every 2,000 mi whichever comes first. Plus run a TPMS to confirm you never run lower pressure than your goal
."

I realize this is a long winded post but hopefully, you can think about the ideas and concepts we are discussing.  Easy questions do not always get simple answers, Especially when talking about a complex topic.

##RVT888

 

Friday, March 8, 2019

Are ST tires the "Best" tires made?

One fact that many choose to ignore, or just don't think about, is that very few RV have the axle load evenly split between axles on trailers or end to end on any one axle. Some owners have learned that there can be upwards of 500# to over 1,000# load unbalance.

It takes more work and effort to learn the reality of YOUR RV tire loading. I and others have covered the how and where to learn the loads on each individual tire (usually not on CAT or similar truck scales).

Regulations are written based on the assumption that RVs have close to perfect weight balance but few owners will make the effort to learn the actual tire loads. Also, those sacred regulations fail to tell the trailer owners that they can expect to need to replace ST tires at 3 to 5 years usage based on the tire DOT serial.  You will see numerous complaints about tire failures but most can be traced to overload/underinflation and over-speed or other external damage.  There is no "magic" rubber in tires with "ST" on the sidewall but many seem to want to believe there is.

As a tire engineer I have yet to have anyone explain why or how ST tires should be expected to perform better than any other tire of the same size on the road, yet that is what some would have you believe based on their insistence that simply because a tire company makes such an ST tire with greater capacity than their premium LT line.  Where is the tire company that makes an ST tire, that will offer a warranty on their ST tires comparable to what they offer on their premium P or LT tires?

Friday, March 1, 2019

Optimum, Appropriate, Required Inflation ?

I have seen people use a variety of words to describe the inflation numbers on Vehicle Tire Placards.  These numbers are arrived at by different methods for different vehicles.

For cars and Light Trucks (1/2 ton), Tire pressure is almost always arrived at based on on-vehicle testing and evaluation by the engineers of the vehicle manufacturer in conjunction with the tire company engineers. There will be a number of evaluations done using prototype vehicles and requests will be made to the tire company to adjust ride, handling, noise and a dozen other objective and subjective qualities of the tires. Eventually, the desired compromise is arrived at with one of the variables being the placard inflation.

For most cars, the inflation is significantly higher than the normal expected GVWR. Many cars have reserve load 0f +20% to over + 30% of the normal vehicle loading. You will note that the tire placard for passenger vehicles do not show GAWR or GVWR.
Lightweight trucks (1/2 ton) will normally be treated more like a car but as you move the heavier vehicles Federal requirements kick in and by the time you get to HD 3/4 ton and certainly 1-ton units the GAWR & GVWR ratings become a higher priority.

RVs have different DOT requirements and also different Tire Placard requirements. Most RVs have the inflation specified based on just one criterion, that is load capacity.

DOT requires that the inflation specified to provide the load capacity of the tires when inflated to the specified level, be able to support half the GAWR.
RVIA in 2017 upped their requirement to requires to be capable of supporting 110% of the GAWR (IMO this is better but not enough).


So the bottom line is that for most RVs the inflation is basically the level needed to support 100 to 110% of the GAWR. But many RVs are not loaded to that level which means you can lower the inflation to achieve better ride as long as you don't end up with overloaded tires.

DOT doesn't trust the average driver to know the actual weight of the RV. They have done studies and discover that a significant portion of the population thinks they are OK but actually have tires in overload. So the DOT doesn't publish alternative inflation guidelines and RV companies follow what the government does.

It's just that simple.

##RVT886

Friday, February 22, 2019

"China Bomb" tires

I continue to see people talking about 'China Bomb" tires. As an engineer, this makes me a bit sad that so many people appear to have such a poor understanding of the difference between "causation" and "correlation".

While it is true that a majority of the tires on RV trailers that fail were made in Asia, and for many folks that meant "China".

But I would ask if 90+% of the tires applied to RV trailers were made in "China" why are you apparently surprised to learn that 90+% of the tires that fail in RV trailer use were made in "China"?

In an effort to make the difference between "causation" and "correlation" a bit easier to understand I  have sometimes offered the following example.

If you check with people in prison you will probably find that 90+% have eaten McDonald's fries. So, therefore, it could be concluded that eating those fries can be considered something like a "gateway drug" to breaking the law and ending up in prison. I think we can see that that conclusion is not sound or reasonable but clearly the numbers are similar to what we see in the RV community.

Yes tires in RV Trailer have shorter life than in other applications but  major reasons for the higher rate is clearly a combination of the documented very high percentage of RV Trailers with tires in overload/under-inflation as well the clearly identified impact on belt separations due to Interply Shear due to the suspension design of multi-axle RV trailers.

##RVT885

Friday, February 15, 2019

Small Single axle travel trailer tire inflation

I have received questions on tire inflation from folks with small single axle travel trailers, boat trailers, and utility trailers. There is some confusion, which I understand, so let's see if I can clarify my recommendations for inflations.

One common bit of information would be to learn the actual load on each tire position when the vehicle is loaded to the heaviest you ever expect it to be.
- For each axle identify the heaviest end and use that load when consulting tire load & Inflation tables.

Motorhomes  and Trucks
These vehicles would use the heaviest axle end load when consulting the Load & Inflation tables.

- The inflation needed to carry or exceed the measured load would be your MINIMUM inflation.
- I suggest you select inflation that will provide at least 15% "Reserve Load" for your Cold Inflation Pressure. Some find it easier to go with a +10% inflation over the inflation in the tables.
- Just be sure you have some Reserve Load capacity.
- I see no problem with running higher inflation as shown on the "Vehicle Certification Lable"

Trailers with a single axle
- There can follow the same guidelines as seen for Motorhomes.

Trailers with two or three axles
- Run the inflation molded on the tire sidewall that is associated with the tire "Maximum Load" capacity. many RVs show that inflation on their label, but it is still a good idea to ensure you have a reserve load capacity. SOme RV companies provide almost no load margin so it is up to you to make the appropriate adjustments. Running the tire sidewall inflation will give a lower Interply Shear force which, as you know, is a primary cause of belt separations on these RVs and are why tire life is about half what it is of comparable tires and loads on Motorhomes.
- Select the heaviest load as measured on all four or six tire positions and confirm that the tire load capacity at the sidewall inflation provided at least a 15% Reserve load.

For those interested in the science behind Interply Shear you might read this post.



Friday, February 8, 2019

Tire ramps or "blocks": Many can damage your tire

Last year I was at a large RV event

 and noticed many Class-B    RV were using various blocks or






ramps in an effort to get the RV level.
Here are a few examples.






None of the above are what I would consider acceptable. They all are too narrow or the tire is not properly centered.
 


The ENTIRE tread contact patch should be supported. On the left above you can see the contact patch and the size board I use.   
Too narrow or with part of the tread hanging off one side can put extra stress on the belt edge and result in the initiation of microscopic cracks that could grow into a Belt Separation.

If you have some of the plastic supports you first need to confirm they are wider than your tire. You also need to pay attention and be centered side to side and fore /aft on the support.

Friday, February 1, 2019

What size tire is it?


That seems to be an early response whenever you ask a question about tires. Whether you ask about price, load capacity, or inflation, the first response may be “What size is it?”  The answer you give should not be “It’s a 22.5”  or  “it’s a 225-R-15”. These are just partial answers and indicate to many that you don’t really understand much about your tires.
 The reason you need to provide the complete tire size information is simply because there are so many possible replies and starting to narrow down the possibilities by properly identifying the size is just the first step in learning the details so the person that is offering the help can provide the correct answer you seek and not just a wild guess. Knowing your tire size can be confusing and sometimes it seems as though we tire engineers and government agencies have conspired to make things difficult. What is needed is to remember there are three basic features that must be established first. Tire type, tire physical dimensions, and tire strength.
This article covers a number of different type tires. Please do not skip over any part as the knowledge provided here builds on previously covered information.
Let’s start off with TYPE. This is usually a function of the application. For most tires, there is a letter code as the first part of a “Complete” identification of a tire. For most tires sold in the US, the code for tire type is either a “P” for Passenger, “LT” for Light Truck, “ST” for Special Trailer, or no letter for commercial or heavy duty. Tire engineers sometimes call these commercial sizes “TBR”, short for Truck Bus Radial. If you are reading this article, most likely you have a Recreational Vehicle or RV of some sort so the use and application of tires on the various type of RV will be our focus. There are of course many other type tires. OTR for Off the Road or AG for agricultural or AT for All-Terrain or M for Motorcycle and others, but we will not cover those and will focus on the type, size and strength tires used in various RV application.
First, we will cover “P” type tires. Most of us own or have owned some form of a passenger car that came with P-type tires. Older and smaller trailers may also come with "P" type tires mounted by the manufacturer. When our car required replacement tires, we seldom needed to think much about the proper size nomenclature, as it was the responsibility of the tire dealer to confirm the appropriate type and size tire that was needed.  Our car tires would probably be identified as a P195/75R15 94S or similar combination of letters and numbers. The P, as you now know indicates Passenger car application. 195 is the width in mm.  Not the tread width but the maximum width. 75 is a ratio of the tire width to the tire height from the wheel to the tread. “R” stands for radial. Since there are very few non-radial “D” or “Diagonal” construction tires, we don’t need to go down the road of old tire construction. The "15" is the wheel size. Finally, there is the “Service Description” which is a combination of “Load Index” number, 94 in our example and finally, the “S” is the Speed Symbol. In the US, the speed symbol is really just an indication of the level of handling capability or steering response with increased handling potential as we move from Q to R, then S followed by T, U, H, V, W, Y and finally Z. Unlike Europe where by law you are required to replace tires with the same speed symbol, we have the option of changing the rating but should expect the steering response to get slower if we go to a lower symbol. The final bit of information concerning the use of P-type tires in RV application, the load capacity of a P-type tire must be reduced by dividing by 1.10 per tire industry design standards.
Next, we will cover "ST" or Special Trailer tires. This is a special type tire, unique to the US market. It was developed and introduced in the late ’60s for exclusive use on trailers. In fact, it is against safety regulations to use ST type tires on vehicles designed to carry passengers. In this category, we might find an ST205/75R15 101K LR-C  For these tires the ST205/75R15 101K is similar in meaning to what we saw in the Passenger type tires. The primary difference is that the Speed symbol K, L, or R is lower for these applications than for passenger type vehicle. The K stands for up to 68 mph. Because the ST type tires are expected to carry higher loads at higher inflation levels the trade-off is the restriction to be operated at lower speeds. The load formula used by tires engineers when designing ST type tires is based on a stated upper operating speed of 65 mph. While today highway speeds can be significantly higher than 65 we should remember that when St tires were introduced we had a nationwide Speed Limit of 55 mph so a tire design limit of 65 mph was not unreasonable. You should be aware that in 2002 both P and LT type tires had the test and durability requirements significantly updated and improved but ST tires only need to pass the same tests as in 1970.  In ST type tires, the abbreviation of LR for Load Range is introduced. You can think of the Load Range as a replacement for Ply Rating. This is really an indication of the strength of a tire to hold the inflation pressure, not the ability of a tire to support additional load It is important to remember it is the inflation pressure and not the tire construction that supports the load. This is why we have Load and Inflation tables not Load and tire construction tables.
 For RV application you will see that Load Range starts at C (old 6 ply rating) and moves through D, E, F, and G. Basically the Load range identifies the highest level of cold inflation to be used starting at 50 psi and moving up to 100 psi or even higher as identified on the sidewall of your tires. Unlike Speed Symbol you should never consider moving to a lower Load Range than selected by the RV manufacturer. The Load Range along with the original size, inflation level, and type tire is shown on the RV Certification Label that the RV company applied to your RV.
The next type tire is “LT” or Light Truck. These will be found on both Class-B and Class-C and possibly a few small Class-A RVs. Since these RVs are larger and heavier, they will normally come in larger physical size and stronger Load Range. For example, a popular tire for Class-C motorhome might be an LT225/75R16  115/112 LR-E.  The double number 115/112 is the different Load Index for single (front) application and dual (rear) application where two tires are mounted side by side. The Load Range (ply rating) has the same meaning as it does for ST type tires. As with the ST type tires, you should not consider moving to a lower Load Range than selected by the RV manufacturer. The LR along with the original size and type tire and minimum inflation is shown on the RV Certification Label.
Finally, we move to TBR tires as seen on most Class-A RVs. Generally, these are considered Commercial type tires and not consumer level tires. If you have and need this type of tires it is expected that you have a deeper level of knowledge about tires. Most of these tires come on 19.5 or 22.5 size wheels. They do not have a letter preceding the size description and may be something like 255/70R22.5  139/134 LR-G
These tires seldom come with a Speed Symbol but if you review the Data Books from the major companies that make most of the TBR tires you will see that they specify 75 mph as the maximum operating speed level. The double Load Index numbers 139/134 relate to the single and dual application and the Load Range letters continue to identify the normal upper level of cold inflation pressure.
There is a lot more information on tires available in tire Data Books and Industry Standards organizations. You do need to be careful about the source of the information you are relying on. Some sources, as in tire industry publications, can normally be relied upon as accurate but even there the information may not be aimed at the specific and sometimes unique needs of the RV community. There are many forums on the internet with hundreds of self-appointed “experts”. We need to be careful as just having used or sold tires for decades does not mean that all the information from that person can be relied upon all the time.
If you have questions about tires for your RV, it may be best to review some of the other posts on this blog.

Friday, January 25, 2019

Can TPMS provide advance warning of a Belt/Tread Separation?

Read the following on a forum for one brand of trailers where they were discussing the advantages of having a TPMS:
Someone said "How do you know if you have picked up a nail, which is leaking air, since your last walk around? A TPMS is like a fuel gauge. You could always dip your fuel tanks at every stop too."  Another reader replied "Great point; I might add, if there is something happening to the tire like tread separation which could lead to a blowout the temp likely would be going up and the alarm would sound and show temp compared to other tires.... I have read here on the Forum and other Forum's several incidents where a blown tire has caused extensive damage. Same if you picked up a nail or something where a "slow leak" might become a fast leak after your back driving on the highway... Like insurance...but, maybe not worth it to some folks."
I then replied:

As a tire engineer, I am sorry to inform you that having a belt separation will probably not generate enough heat to set the TPMS warning off.

TPMS stands for Tire Pressure Monitor System. It does not and for all intents and purposes can not provide advance warning of a tire failure due to belt/tread separation.

Air leaks can cause failures in a few miles as seen in my blog post on Blowout a real-life experience on an Airstream, to after a few hours depending on how fast the leak is. Some TPM offer warning if the pressure drops by just a couple psi in a couple of minutes or less. Some will not warn till you drop 15% to 25% below the cold inflation pressure which means you first have to lose the pressure you gained from normal driving.

I know of no consumer-level device that can advise of a belt separation as separation can take thousands of miles to grow large enough to result in the tire coming apart.

I have posted on this blog on how to do a thorough tire inspection to discover if you have a separation. Even a video and pictures of a tire belt separation before the tire came apart.  I covered the "Why" of tire failures in THIS post. Did you read and understand that information?

Friday, January 18, 2019

Another question on having a spare

Was reading another RV Forum thread on spare tires. The questions about cost and difficulty in actually doing the change came up. One person said a spare for his Ford Transit van (Class-B?) would cost $400.
I offered the following.

A little shopping around and you should save a lot. New steel Ford transit wheels are available for $70 on eBay. Probably $25 at a local junkyard. Remember Class B and C RVs are basically just large pick-up chassis and there are thousands of those in junkyards. Also, a steel wheel is fine for a spare.  Used tires usually go for $25 to $50. A spare only needs to be good for 50 to a couple hundred miles so again a few phone calls to local tire dealers and you should be able to find an acceptable spare, especially for Class-B or Class-C. Class-A owners will need to check with HD truck repair shop.

You need to be a bit creative and not simply go to your RV dealer and ask for a new tire & wheel. Very few RV dealers are in the business of selling tires & wheels and if they are, they probably only have new tires.

What I am suggesting is that if you have to buy a tire from the service truck, on the side of the road, the price will probably be 125% to 200% of a sale price.  If you have a Class B or Class C most people should be able to do the change themselves with a little planning and preparation.
Planning and maybe even practice on a nice sunny afternoon would be a good time to confirm you have all the tools and supplies (like a solid platform to place under the bottle jack if you are on dirt)
 
 Class-A can save time (hours or days) and maybe $hundreds and space by being able to provide just a tire that fits their RV. HD Service Trucks are equipped to change and inflate a tire on the side of the road. If you have different size front and rear I suggest you have a spare for the rear as they suffer a higher percentage of punctures than the front.

##RVT880

Friday, January 11, 2019

Did you really read your Owner's manual?

Ya, I know that if you are like me you were given a stack of Owner's manuals with your new RV.

 I doubt that many have ever read every page of the 6" to 8" stack of papers.

However, I would suggest that you at least check the section of the basic manual that covers "Tire Safety".

I was recently involved in some litigation on tires and quickly learned that the folks who were complaining about their tires may have claimed to have read the manual, but for some reason didn't understand the information or felt the information didn't apply to them or just didn't care as it was obvious that they had failed to follow the tire maintenance and safety instructions when it came to RV weight or tire inflation.

A review of the table of contents will find section titles such as "Tire Safety" or "Weighing your RV".

I have to wonder why so many seem to feel that instructions such as "Before using your RV, you should inspect all the tires for proper inflation, uneven wear on the tread, cracks, foreign
objects, or other signs of wear or damage. Don’t .forget to inspect your spare tire!"
  do not apply to them.

I read questions on tires on the many RV forums I follow, and almost every week someone is saying  things such as " I have looked everywhere for tire inflation information but can't find out about my tires" 
 or "What size tire can I run" or similar questions. In reality, they have the information in their personal files.

I have found that copies of many Owner's Manuals are available for free on-line so even if you lost your manuals or didn't get them when you purchased a pre-owned RV, you should be able to find them online.

While I might be able to nit-pick at some of the details in the information, in general, I believe that if people read and followed the instructions, the percentage of people who have tire problems could be reduced significantly.

It really doesn't take a lot of time or effort to read and review the information on tires, proper inflation and correct loading of your RV. It also doesn't take much time to actually follow the instructions. If there is some part you don't understand I along with others would be more than happy to help out our fellow RV owners.

Certainly making a little effort to educate yourself will take less time than it would take to change out a tire after it had failed and also MUCH less expensive too.