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Thursday, September 14, 2017

Can I change from 275 to 295 size tires?

Read this post on an RV forum:

"I need 6 new tires for '04 Dutch Star 38' on a Spartan chassis. Michelin tire models and sizing has me totally confused. Current Michelin size is 275/80R22.5. Dealers claim this Michelin size is interchangeable to 295/75R22.5 from brands that don't offer the original size. They tell me there will be no ill effects on the drive line or instrumentation."

I was concerned with this possibly incorrect information. In this case the two sizes have the same load capacities so that was not my concern.

Some folks replied to the original question by suggesting he use THIS or similar web sites to learn about tire sizes. I did have a little problem of using such a "tire size" site as the information is aimed at car application and does not include special information regarding dual tire application. Also the resulting numbers may or may not match published industry standards.

I pointed out my concern about the Minimum Dual Spacing which is a published dimension in industry standards and has been covered previously in this blog.

Some folks reported that they have changes tire sizes and had no problems and implying that any change might be OK.

I provided this graphic to help people understand what this dimension is.

As you can see the wheel offset and even wheel thickness can have an affect on this spacing. I also pointed out this example.  275's have a MDS of 12.24 and 295's have a MDS of 13.19.
Let's assume that with your wheels and with the 275's you have a physical 1.00" clearance down at the bulge in the sidewall near the road. So if you don't change wheels and put wider 295's on the new clearance will be   1.00 - ( 13.19 - 12.24) or  1.00-0.95  or a final clearance of 0.05"which is clearly too small.

I hope that those considering changing tire size consider not only the load capacity, which is very important but also the dimensions.

Tuesday, September 5, 2017

Tire Terminology

Sometimes people use their own terms when asking a question. Some RV forums have people answering questions using incorrect terms which can mislead others who may be reading  the question or answer being offered. This is just a "Failure to communicate" which doesn't help anyone.

Here are some common terms with their correct definition or example of proper use.

Load Range - A letter code  E, F, G, H etc that established the inflation and max load capacity for a given tire size. (this replaces the old, out of date "ply rating")

GAWR  Gross Axle rating is the MAX design load capacity on an axle. You should never exceed that number

GVWR Gross Vehicle Weight rating is the MAX design weight of a vehicle. You should never exceed that number. Note that the GVWR may be lower than the mathematical sum of the Front GAWR plus the Rear GAWR

Tire Load capacity This is the number of pounds a tire can support at a specified inflation. The Load/Inflation tables establish the various steps in load capacity associated with a level of inflation. Sometimes people incorrectly use the term "Tire Weight" which is incorrect. A tire itself may weigh 45# but it may be able to support 2,800# when properly inflated according to the Load & Infl tables.

CIP  or Cold Inflation Pressure is the measured Psi in a tire when the tire has not been warmed from running or from being in direct sunlight for the previous 2 hours. Technically we are talking about the Cold Inflation Pressure whenever we are discussing tire "inflation pressure".

Hot Inflation Pressure. Sometimes we may want to discuss the pressure in a tire when it has been warmed from running or from being in Sunlight. If this is the case, the term "Hot Inflation Pressure" should be used to be sure all understand the condition of the tire being discussed. You should not be bleeding down the inflation of a hot tire except under special, specific conditions

TRA or Tire & Rim Association is the US group that published the Load /Infl tables for tires made for use in the USA. There are similar organizations with similar tables in Europe (ETRTO) and Asia (JATMA). The numbers of pounds (Kg) and the associated PSI(Kpa) are many times the same or slightly different. The difference is due to using SI or Metric dimensions and rounding and conversions between units. It is legal to sell tires in the US that were designed to ETRTO or JATMA standards but the tires must still have the symbol "DOT" and the individual tire serial code molded into the tire sidewall and must still be certified by the tire manufacturer to be capable of meeting all the appropriate DOT regulations.

DOT  U.S. Dept of Transportation. The regulatory agency that specified the performance requirements for tires intended for use on public roads.

"DOT Certified". This incorrect phrase is many times used by those that do not understand the regulatory process. The DOT does not certify any tire. It is the tire manufacturer that is responsible for "Certifying" that all tires they sell are capable of meeting the DOT Federal Regulations.

FMVSS Federal Motor Vehicle Safety Standards You can read Sub part B of these standards HERE.

Tandem axle. This is found on many trailers where each axle has one tire on each end of each axle. Here is a write-up on Tandem vs single axle trailers if you are not sure of the description.

Tire loads are ALWAYS based on the load on tires on a specific position ie RF, LR, RR or LR etc. Front tires are "Single". Rear tires on most Motorhomes mounted side by side are "Duals". The tables show load capacity for individual tires in "single" position or in "Dual" position. You need to pay attention as some companies publish their own tables and show Axle loads or axle end loads which can lead to confusion. Tires on one end of an axle do not "know" what the load is on the other end of the same axle is. RV companies however assume axle loads are perfectly balanced end to end at 50%/50%. This allows the RV company to select the smallest (lowest cost?) tires capable of supporting 50% of the published GAWR but if one end of an axle loads that tire to 55% or 60% of the GAWR we would be looking at a tire overload situation.

In trailer application with two or more axles they may be some load transfer between the axles such that the ends on the right side may share some of the side to side unbalance but I know of no case where all the side to side unbalance is shared equally between all the tires on one side of a trailer.


Wednesday, August 30, 2017

Why does a sidewall "blow out" when you run on low inflation?

The title for this post is essentially the exact question I was asked.
"Tireman9, can you explain why, when the tire pressure drops below a rating for a tire, that the sidewall of the tire blows out with great force? What pressure drop will cause this type of damage? When the tire blew it had enough force to damage the motorhome with the rapid escape of air that made a large bang when it blew."

My answer:
OK, let's see if i can cover the details of why and how a tire sidewall fails due to being run without proper inflation.

The mechanics are essentially the same, be it a textile (usually Polyester) tire as are most P, LT, and ST type tires, or for tires with steel body cord as most commercial grade LT tires and "TBR" Truck-Bus Radial" tires. These cords are referred to as the "body ply".

I think we all realize that tire sidewalls bend when loaded. This can be observed by simply looking at the bottom (near the road) vs. the rest of the tire sidewall. The amount of bending is essentially just a function of tire size, load and inflation. This bending includes some stretching of the outer surface of the tire and of the rubber surrounding the body ply. This stretching results in some heat being generated. You can test/experience this heat generation yourself with a simple test of holding a rubber band against your lip and stretching and releasing the rubber band rapidly. Your lip is sensitive enough to feel the temperature rise of the rubber band.

Now the rubber used in tire construction can tolerate some temperature rise. The heat generated can transfer to outside air at about the same rate it is being generated. This is what happens for hopefully tens of thousands of miles and hundreds of thousands of revolutions, i.e., sidewall flexes.

So what happens if there is a leak of inflation air? Or if the tire was not properly inflated in the first place? With lower air pressure the amount of bending increases and with an increase in bending we see more heat being generated. Increased heat generation means increased temperature of the rubber internal to the tire structure. Since rubber is a good insulator, heat transfer can be slower than heat dissipation to the outside air so the temperature can continue to rise ever faster.

The strength of the rubber decreases with an increase in temperature which allows more bending. With slower heat transfer from the internal structure to the outer surface and increased heat generation as more air leaks out, I think you can see how it is possible to get to a point where there is something like a chain reaction or "runaway" temperature increase.

The above heat generation can also result in the polyester experiencing a rise in temperature with the associated loss of strength. You have seen the effect of high heat by holding a match near the end of a piece of Nylon or Polyester rope and see the textile melting. In the steel body ply tire the increased bending can result in a fatigue failure of a steel cord. You can test the fatigue with a steel paperclip. Simply bend the paper-clip a few times and it will break. In the case of a tire the number of bends to failure can easily be in the thousands.

So what you are seeing when the sidewall fails is the result of dozens, hundreds or thousands of miles of excess rapid flexing of sidewall rubber and sidewall cords. If the bending is great enough the materials that are being bent simply fail. An explosive loss of air can occur if/when the force of the remaining inflation exceeds the strength of the body cord. Since there is an almost infinite combination of load, inflation, bending and speed involved, it is impossible to give an exact answer as to when the sidewall will finally fail.

If we have a large tire we can have significant force involved even at relatively low pressure. 20 or 30 psi can easily generate over 30,000 pounds of force.


Tuesday, August 22, 2017

New GY Endurance only available in higher Load rating. What to do?

Hello Roger,
At the end of next season I plan to replace our GY Marathon tires after 5 seasons and about 20K miles and have been thinking of the new Endurance tire. However, the specs. are somewhat different between them and am not sure what to do.
Our Marathons are LR-D ST225/75R15.  I always run them at sidewall max. pressure 65 psi. The max. load rating is 2540 lbs and gives us about 30% reserve load capacity. The required rim width is 6-7”. The standard tires for our make and model of travel trailer are an unknown brand LR-C and the Marathons were an available option so we upgraded to them. No issues whatsoever with them. I do not know what the max. psi rating for our rims is without taking one off. They are 6-lug.

I like the idea of having a 225 wide tire vs 205 because I *think* it may provide better handling from lateral forces in curves. I have our TV & TT set up for better handling including shocks on the TT. It performs very well in twisty mountain roads at speeds up to 65 mph.

If we were to get the new Endurance tires in an ST225/75R15 width, it means going to LR-E tire which have a max. 80 psi rating. The load rating increases to 2830 lbs. Required rim width is still 6-7”. The increased reserve load capacity would be fine. I have no idea if our rims are rated for 80 psi and would have to remove a wheel. I believe in the practice of running the ST tires at the sidewall max. pressure to get max. reserve load capacity.

If we were to go with an Endurance tire in a 65 max. rating, it would mean going to a LR-D 205 wide tire and the max. load rating drops to 2150 lbs. I do not want to reduce the reserve load capacity that much and would rather not have to go to a skinnier tire.

What to do if going to Endurance tires? If our rims are only rated to 65 psi, could I simply reduce the LR-E pressure to 65 psi? Have not looked at load tables to see what this does. Or stay with LR-D and have skinnier tires and substantially less reserve load capacity? Are tires rated for and inflated to 80 psi going to result in better handling or perhaps an undesirable harsher ride for the trailer? Not sure why GY did not make the Endurance a direct one-to-one swap for Marathons. It looks like GY no longer offers the Marathon?

Comments would be greatly appreciated.
My reply:
Your 30% reserve load capacity is good. I wish other trailer owners had as much. You may not see any benefit in increasing the reserve load above the 30%. The reserve is based on actual scale readings, yes?
I would not go down to the ST205 @ 65 psi.
I see no problem with running the Endurance ST225 LR-E @ 65 until or unless you confirm higher rim psi rating. It may not be marked on the wheel and I doubt the wheels are "brand name". When you change tires you can look for anything that might ID the wheel such as part number. If the wheels are only 65, then 65 is OK.
Yes, in my posts on Interply Shear I have suggested increasing inflation, but your CIP should not exceed the rim rating (all ratings are for cold inflation pressure).

LR-E ST225's have same load capacity when inflated to 65 psi as do ST225 LR-D at 65 psi.
Hope this info helps. 

Tuesday, August 15, 2017

"Run Flat" vs "Blowout" protection

Saw a thread on run flat fixtures to be used on the front of an RV to provide some protection against losing control if a front tire were to fail. A lot of discussion and conjecture but not many facts. Before I start it's important to be sure we all are on the same page with these terms.

"Run Flat" capability in today's tire market is a reality for passenger car tires. Tires designed and so labeled can provide mobility at reduced speed for various number of miles even after a complete loss of air. Some advertise 50 miles at 50 mph. I know of no true run flat tires for LT, Truck or RV application.

"Blowout" is a generic term used by many to describe a tire failure. This term does not provide information to tire engineers on the condition or possible cause of the failure.

"Rapid Air Loss" or "RAL" is any sudden loss of all the air in a tire.

"Belt or Tread Separation" -- This is when the belt and or tread portion of a tire separates from the rest of the tire. The carcass or body of the tire many times will still hold air.

"Run Flat Device" -- This is some equipment that fits inside a tire. It may prevent the beads from De-seating from the rim or may limit the collapse of the tire after the loss of air.

"Steering Stabilizer" -- This is vehicle equipment that may lessen the "jerk' of the steering in the event of an RAL.

I do understand the concern of some about the loss of control of a large RV in the event of a front tire failure. Yes, I have seen some of the videos and they are spectacular, but a front tire failure does not have to mean you will have a crash.

Back in the early '70s I worked extensively on a new type of tire from Firestone, the LXX, which was intended to replace 10.00-20 and 11-22.5 size tires but used a 26.5 rim. I even spent a week in Texas at the test track intentionally puncturing front tires with a 2" diameter hole to test vehicle control. While the tire worked as designed, the cost of new wheels made the tire design not viable in the truck tire market.

Here is a picture in the Akron newspaper at the time showing the tire with my then boss Ed Henry.

The main challenge for vehicle control is to either limit the "drop" when a tire suffers an RAL or to limit the steering response which can send the vehicle into another traffic lane.

There are a number of systems on the market:

Tyron is designed to keep the tire on the wheel. It does not appear to lessen the collapse of the tire.

Rodguard inserts for 14" to 17" tires appears to partially support a flat tire.

Safe-T-Plus steering stabilizers take a different approach to vehicle control.

Hutchenson seems to focus on extreme situations, such as military applications.

I recall hearing about multi-piece inserts like this one from TAC but was not able to find current info for 22.5 RV size tires.

IMO the best approach to preventing a loss of vehicle control is three steps:

1. Use a TPMS and have it set to tightly monitor your inflation. Test your sensor to confirm it reports pressure loss at the level you expect. It may not be set correctly and a test can confirm.

2. Closely inspect your tires at least annually and if possible even have your tire dealer check for out-of-round or lateral wobble of the tread and bulges in the tire sidewall. These can be early warning of separations or other structural damage to a tire.

3. Study and review the safety videos on how to maintain vehicle control in the event of an RAL.
   Here is one from Michelin, and another, and yet another.


Wednesday, August 9, 2017

New Goodyear Endurance pressure & temperature question

Saw this question on temperature and pressure increase on a new set of Goodyear Endurance tires.

"Took our first trip with the new Goodyear Endurance tires.
Trailer rode great, better than the old tires.
So, on this first outing I closely monitored the TPMS to see if there were any differences in the readings I had with the old tires.
Obviously, the first difference was the starting "cold" tire pressure. (65 psi vs the old 50 psi)
The first thing I noticed was how quickly the tire pressure increased once we got on the road.
87 degree day, 60-63 mph, tire pressure on sun load side got to 75psi (73 - 74 psi on shaded side). Tire temp got to 96 - 97 degrees (99 degrees on one tire briefly).
This compares to the average 5 - 8 psi increase I experienced on a typical trip with the old tires.
This brings me to my question.
Is a 10 - 12 psi increase in pressure considered acceptable? If so, what should I set the high pressure alert at on my TPMS?

My reply:
The temperature and pressure changes are reasonable for most 14" - 16" RV tires, especially trailer  applications, but I will focus on your question.

Not sure if your "test" is "scientifically" sound -- You were comparing two different tires (LR-C vs. LR-D) and a new tire vs. old used tire.

New tires will always run hotter than old tires.

With nominally dry air the pressure will increase by about 2% for each +10F. One other related item is that aftermarket external TPMS are not reporting the temperature of the hottest areas of the tire which is internal to the structure. Also while it may not seem reasonable, it has been demonstrated that the temperature of the air inside a tire is not uniform. It is also known that the metal body of valve stems and the metal body of the sensor will be cooled as it whips around in outside ambient air which will result in a lower reading.

In all probability your tire is actually 20 F to 30 F hotter than the TPMS is reporting, but this is within the expected design limits considered by tire engineers.

New tires do run hotter than old for a couple reasons. Extra stress as initial cross-link chemical bonds are broken as tire is "broken in." This takes about 100 miles. New tires have deeper tread depth, which will also make a tire run hotter, which means more pressure growth.  Your GYE have extra components (mass) in the tread. Read the sidewall and I believe you will see Nylon cap plies in the tread which were not in the old GYM tires. This is another contributor to more heat.

To your question on pressure increase setting for TPMS. As I covered in my blog post on TPMS settings I figure that +25% from baseline is a reasonable number, but obviously the pressure you select for your baseline may affect the top number.

Bottom line. Your numbers look normal and acceptable.


Tuesday, August 1, 2017

How I program my TPMS

As you know I am a strong supporter of having all RVs being equipped with Tire Pressure Monitor Systems. Since 2004 cars and many pickups with ratings less than 10,000# GVWR have come with TPMS installed by the factory.

RV companies have not been providing TPMS even as optional equipment from the factory, so we owners have had to make the purchase and install the warning systems ourselves. This means we need to ensure the warning levels are appropriate for our RV.

While I can't address how to program every different type or brand system, I can tell you how I have the system I purchased set up. I hope that after reading this post you can sit down with the information that is specific to your RV,  i.e., load on each tire position, tire size, Load Range and inflation info, and ensure your settings are appropriate for your personal situation. So I suggest you dig out the instructions that came with your TPMS and review your settings.

First off, some terms:

MOP - Minimum Operating Pressure - This is the minimum pressure that I think you should ever operate your tires. This pressure is found in the Load/Pressure tables and is the minimum pressure needed to support the actual measured tire load.

CIP - Cold Inflation Pressure. This is the pressure you would set your tires to before driving on them. The tire should not be warmed by either driving on them or having the tire in direct sunlight for the previous two hours. Some folks call this their "Set Pressure" or "Baseline Pressure". I suggest the CIP be set to MOP + 10%, or +10 psi, but not to exceed the pressure molded on the tire sidewall associated with its max load, as this tire pressure may be the intended max CIP for the wheel.

Tire Load - This is the actual measured load on the tires when the RV is at the heaviest you would ever expect to be. Ideally this has been learned by having individual scales under each tire position on your RV. If you can't get this number then at least get the RV on a truck scale such as a CAT scale at a truck stop and learn the actual load on each axle. We want to know each tire position or each axle, as loads are almost never completely evenly distributed. It is not unusual to have tire on an axle or on one end of an axle to have 500# to 1,000# more than another position. There are a number of posts in this blog on load and how to get the loads on each tire position. Note duals are considered one position. If you can't get individual axle ends measured then I suggest you use the measured axle load and assume one end has 53% of the axle load. This would provide at least a partial margin for error.

Hot Running Inflation - This is the pressure we see on a tire after it has been running down the road. I have previously covered the relation between Temperature and pressure in THIS post. Normally for properly inflated tires this will be 10% to 20% above your CIP.

When I bought my Class-C unit in 2008 the first "add-on" was a TPMS. At the time I was not really aware of the selection of TPMS available for the RV aftermarket but I found a system made by German electronics company Hella. It was an internal system but it was designed for passenger cars so I had some problems as my hot tire pressures occasionally exceeded the high pressure warning level programed by Hella. I learned to ignore the occasional high pressure warning levels. In 2009 I started to go to FMCA RV conventions and rallies where I discovered the aftermarket systems designed for the RV use. Based on features I felt important, I purchased a TireTraker TPMS.
When we bought our new 2016 Class-C coach, I needed a new TPMS and selected the TireTraker TT500 as I felt the features plus the lifetime guarantee made it the best option available for me.

Programing the TPMS:
This is usually a two-step process. First, you need to have the monitor/display "learn" which sensor is on which tire. For the TT500 it involves stepping through the monitor settings, identifying a position and installing a sensor at the appropriate position. Other brand TPMSs may have different setup steps or even may come pre-programed with each sensor marked by position. It's the next step that I think is also important to get right for your specific needs.

Setting the warning levels:
Before we start the actual process of setting the levels, it is important to know what the various levels should be. You also need to know which pressure warning levels you can set and which may need extra work if you can't set the levels yourself. Again I can't address every brand TPMS so you may need to re-read your manual or even contact the support people at your brand TPMS.

1. Low Pressure warning level. Some systems have a fixed % below your baseline pressure; others may allow you to set this level independent of the CIP. You need to know how to set this level or what the % below the baseline your system works on. My TT500 is pre-programed to warn at -15% from the "Baseline" or CIP.

2. High Pressure warning level. The TireTraker is pre-programed at "Baseline" + 25%.

3. High Temperature level. The TireTraker, as are many TPMS, is set to warn of high temperature at the 70 C to 75 C (158 F to 167 F) range. IMO it should be remembered that it is low pressure that generated high tire temperature. If you get a High Temp warning but the pressure is OK, then your sensor has detected high temp from metal components that transfer heat faster than rubber. This might indicate a bearing or brake problem which should be checked as soon as possible.

Here things get a bit complex:
We do not want to operate tires when under-inflated but if we set the CIP or Baseline pressure to just what is needed to support the load the TPMS will not warn till we are 15% underinflated. If our CIP is MOP + 10% (See definition of MOP above) we still could end up with an underinflated tire. So to meet my goal of never operating in an underinflated condition, I will need to set my TPMS "Baseline" pressure to MOP + 15%.

My situation and solution:
As measured by RVSEF (RV Safety & Education Foundation):
My front tires are loaded LF 1,900#   RF 2,100#   and
Rear Duals  LR 3,550#   RR  3,850#
Tires are LT225/75R16 LR-E

Based on Load & Inflation tables for my size tires, my MOP for my front tires on my Class-C is 60 psi based on the 2,100 load and also happens to be 60 psi based on my read dual load of 3,850.

I add 10 psi to 60psi and get 70 psi for my CIP.

If I want my TPMS to warn me before I get to my MOP, I need to set the "Baseline" pressure on my TPMS to MOP + 15%, which for 60 psi is 9 psi. So in my case my "Baseline" for the TPMS and my CIP are within 1 psi of each other. I don't worry about trying to measure or set my tire pressures closer than +/- 1 psi. I would say that if you are within +/- 2 psi when setting your CIP you are in good shape.

We need to be careful when discussing safety margins or pressure changes as people with Load Range C, D and E tires will have different calculations than the folks with LR-G & H tires where 15% might be 18 psi.

The High Pressure warning level for TireTraker is Baseline +25%, so with a Baseline of 69 to 70 psi, that equates to 87 psi. On a recent trip to Indianapolis in the heat of the day I noted my tire pressure had gone up about 15%, so my settings worked out for me.


Tuesday, July 25, 2017

New trailer sat for 5 years. Does it need new tires before a long trip?

Got this question:

"Good Afternoon Roger;  I have kind of a critical need for your expertise.  I've been a "Hardtopper" since 1970, and have always made every attempt to take good care of my travel trailers.  My latest and last, is a 2013 Flagstaff with of course dual axles.  I brought it home new after trading with a dealer, on August 31st, 2012.  Then the fun started !!  The tires are covered and are on wood planks, never having touched ground.  Rather than being able to realize a life-long dream of just once getting out of this horrible Winter climate, say to Florida for a season's stay, I was hit with the need for surgery and lengthy PT.  Each year since, I have been stricken with yet another number of surgery's for different reasons, and this past December fell on the ice at my home, breaking 3 ribs, thus cancelling once again, any hopes and dreams.  Now, after all that drama, I wonder if you might offer some "practical" advice on my tires.  I am a long ways from a rich man, barely getting by on my Social Security, so I'd really hate to have to replace the tires sitting unused as they have been after five years BUT, I would defer to your advisory.  I have read posts on and others have posted any number of articles in the past on tires, so I am a bit apprehensive, and sure to heck would appreciate your input.  Many Thanks in advance,  Grant M."

My reply:

"Sorry to hear about your situation, Grant. Your tires may be 2012 or even 2011 vintage (you can check the last 4 numbers of the DOT serial to confirm) but either way that's pretty old. How often did you check the air pressure? It should have been every month.  While they are covered and on boards, which is good, they were still under load without ever moving, which is bad, especially if they ever lost more than 5 to 10 psi.
If they are Radials there is a chance the steel belts may have lost some adhesion to the rubber due to moisture never being driven out of the tires with the warmth of being run down the road.
I would suggest you sell the tires to someone who has a utility trailer that only travels locally. If they have very little wear, you should get a reasonable price for them. You didn't say where you live but if you are thinking of travel from "North" to Florida I would recommend against the trip with a trailer that has just been sitting for 5 years. As a minimum you need to have bearings and brakes checked and yes, I am afraid new tires. You are just pushing the odds of having problems on the road that would be much more expensive to fix on the trip than confirming they are all OK before the trip.
Here are some of my posts on tire AGE from my RV Tire blog you might want to review."

Good luck.


Friday, July 21, 2017

When should you replace your tires?

Saw the following question on an RV forum from a motorhome owner.
"Does anyone ever just replace their front tires after 7 years? It seems that a tire failure on the front is much worse than the back. If the tires have a lot of tread and no sign of cracking, why replace the back ones?"

One reply correctly said, "There's more to consider than age. Were they properly inflated? Did you bang into curbs to damage the sidewalls? There are many failures due to improper operating conditions. Not just age."

I would first ask if you know the "life experience" of the tires:

Did the RV have a previous owner?
While they may claim they always checked inflation, can we be 100% certain?
Did you purchase the tires direct from a major tire company and know the complete use history?
Have you confirmed your load on all the tires from day one?
Did you ever discover one of your tires 20 or 30 psi low one time?

There are many things to consider, but if you are confident the tires have always been properly inflated for the actual load the following should help.

"Blowouts" (look at the picture at the top of my page), or more properly Run Low Sidewall Flex failures, happen because of running on low inflation. This can be avoided with the use of TPMS.

Belt separations, which are much less common on commercial grade tires, may occur after the rubber at the belt edges degrades due to cumulative damage from heat.

UV does not affect the internal structure of tires and external cracking is only one symptom of exposure to sunlight. I consider external cracking like having a person run a temperature. Having a temperature is just a symptom of some other illness, usually an infection. You can be seriously ill but not be running a temperature. Think of heart disease or cancer as two things that can kill you but don't cause you to run a temperature.

The suggestion on when to replace tires is only based on probability, as it is impossible to know just how much damage has been done to the components of a tire. The general suggestion is to have tires closely examined by a tire expert at 5 years and each year after that. Tires should be replaced at 10 years no matter what is visible on the surface of a tire.

I wrote a blog post on a suggested inspection and "step replacement" concept. A version of this suggestion could result in your keeping newer tires on the front, which in theory should improve your chances of not having a belt separation on the front. Of course also running TPMS will improve your chances of not having a Run Low Flex Failure too.


Thursday, July 13, 2017

How are RV tires developed?

 By Roger Marble

If a tire is being designed for a specific vehicle manufacturer such as Ford, Chevy, Toyota, or BMW, there will be a number of tires submitted by competing tire companies all trying to deliver the best overall compromise in performance characteristics. Please note that all original equipment ("OE") vehicle manufacturers have slightly different requirements but all make similar requests for performance improvements in many areas. In the future I will use the term "OE" to include these car and pickup manufacturers.

Compromise: Now is a good time to talk about some of the various trade-offs the engineer is faced with when trying to meet conflicting goals and customer wants. I am sure we would all like an RV that has all the interior space and amenities of a 40’ diesel pusher but gets 25 mpg and can be driven down crowded city streets without knocking off our mirrors. Oh yes, it should also cost under $30k. Well, Bunkie, that just ain’t gonna happen in real life.

The same goes for a tire that handles like an Indy tire, is as quiet as the proverbial mouse, has great off-road traction, is good for 100k miles, and costs $25. One thing few people realize is that most if not all performance characteristics are a compromise. For example, if you improve wet traction you probably hurt fuel economy unless you use a special type of rubber that costs double per pound and is more difficult to process. If you improve handling you might hurt ride and noise. When you improve noise you can significantly increase the cost of making the molds used in manufacturing. The cost of a tire mold can be as low as $10,000 and can approach $100,000 each. Depending on the production volume needs, a tire manufacturer could need 30 or more molds. The list of trade-offs goes on and on.

The competition for a tire application might start three or more years before scheduled start of delivery with two to five tire manufacturers competing for the contract, knowing that only one or two will end up being selected to actually provide tires. The costs associated with building and testing special prototype tires can run in the hundreds of thousands of dollars and are absorbed by the tire company. The only way a tire company can afford this type of activity is by landing a contract for a few hundred thousand tires so the costs can be spread out.

Unlike “OE,” an RV manufacturer may only need a couple thousand tires, so a custom tire designed for a specific RV would be cost prohibitive. Since the RV manufacturer won’t be trying to get custom tires, it doesn’t have staff engineers working on developing specifications for such tires. The RV company will in all likelihood either take what comes already on the cut-away chassis or the bare chassis for Class-C or A vehicles, and in the case of trailers, may buy the tire with the lowest cost that can meet tire size requirements and expected delivery schedule.

For RV applications the one thing that is in the control of the manufacturer is “Reserve Load.” This is the difference between the load placed on each tire with the RV normally loaded and the load capability of the tires at specified inflation.


Tuesday, July 4, 2017

"Care and feeding" of your valve stems

I suggest that if you are looking for long "bent" metal stems you ONLY get them installed by a Truck Tire store. Preferably not just a "dealer," as anyone can sell tires, but a "company store" that is owned by a tire company or a store that is part of a large chain, as they are more likely to have a selection and actual training on proper installation of long truck valve stems. The shop should have the proper tool for bending the long brass stems without cracking them, if bending is needed.

With long stems it is also important to remember to not just press the air chuck or pressure gauge onto the end when adding air or checking pressure as you can generate a lot of force on the joint between valve and wheel. Always support the stem or hose extension with your other hand even if the stem or hose has a hard mounting, as you can loosen the mounting point too.

There are specifications for torque of the metal nut for bolt-in valve stems. (25 to 45 inch pounds) This is especially critical on your car or truck if it came from the factory with an internal Tire Pressure Monitoring System (TPMS). Many of the internal TPMS are made of aluminum for light weight and as such have very low torque specs. It is easy to break the aluminum nut or, even worse, the stem itself – which could cost you $50 to $100 to replace.

"Tire Review", a trade magazine for tire dealers, had an article on TPMS sensors and they point out the following:

"What is the torque value required for the nut?
Typical torque values for the base nuts on a TPMS valve stem range from as low as 35 in.-lbs. of torque to as much as 80 in.-lbs. of torque. That’s quite a range. This doesn’t mean that any torque value within this range is acceptable. It means that the torque specifications for the base nut on one vehicle might re­quire 44 in.-lbs., another might re­quire exactly 62 in.-lbs., yet another might specify exactly 71 in.-lbs., and so on. Don’t guess. Look up the torque specifications for the vehicle you’re servicing to make sure you use the correct torque.

Why should the nut be replaced every time a sensor is serviced?
The nut is made of a softer metal than the stem, so it will be damaged – not the sensor – if it’s over-tightened. The material of choice is typically aluminum. If the nut is over-tightened, it will develop hairline cracks."

NOTE: Those specs are INCH-Pound, not your normal Foot-Pounds. Here is a picture of my TPMS Inch-pound Torque Wrench.

Standard "metal bolt-in valves" also have specs for the nuts and those valves are usually brass or plated with nickle or chrome. I am not aware of any stainless steel valve stems for regular automotive use. There are some aluminum bolt-in stems too, but those are expensive lightweight units made for race car application which would not normally be sold without being identified as such.

Even valve core have a spec (2 to 5 in-lb) as there is a tiny gasket that can be distorted and even broken if you over-tighten the core. There are some special tools. But rather than buy some special tools I suggest you tighten core till air stops, add no more than 1/4 turn more, then confirm no air leak by testing with soapy water. When no bubble forms the core is tight enough. I then attach the metal valve cap to ensure no air is leaking. There have been a few cases of slow leak through the valve core that ended up as a tire failure as no metal cap was used. The cap is primarily intended to keep dirt out of the core area but is also a "backup" on preventing air lost past the core.

Whenever "messing" with your valve it's always a good idea to confirm there are no leaks with a quick spray of soapy water.


Tuesday, June 27, 2017

Change your own tire ?

For my Class-C  I have a bottle jack with a rating greater than GAWR of rear axle. Since I would only jack one side that gives me plenty of lifting power. It's also easier to jack while laying on the ground.😥

Harbor freight has good deals.
An important item is a large flat plate to support the jack if not on concrete.
Maybe 12" x 12" 1/4" thick steel plate or 2" wood but you might still need a 6"x6" 1/4 steel so you don't split the wood.  Check with local shop offering welding or tow hitch install as they many times have scrap pieces available.

If jacking, be sure to set brake and block the tires front & back so the RV can't roll.

Whenever I change an outer dual I run a couple lug nuts on the inner (hand tight is good enough) as soon as I remove the outer, just to keep one wheel under the coach in case something slips with the jack.
If changing the inner dual I temporarily use the outer tire as safety backup.

IF YOU RUN 19.5 or 22.5 tires
I strongly suggest you get a service truck and let them wrestle the 150#+ tire and wheel around.

Also it is important to remember if you have lost more than 20% of your air in any tire it is considered flat and if you drove any distance on it you may have damaged the body and it could explode when re-inflated.  Inform the tech and let them inspect and re-inflate or replace. This could result in injury or worse.

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Should you "plug" your tire?

This is an oldie but goody.  I was just asked about plugging tires.

 This is a very important post. Improper repair can lead to a false sense of security and even to a tire failure which can cause damage or even injury. Please read this entire post.

I recently read a statement that could be misleading as it is not supported by any of the major tire manufacturers or the National Highway Traffic Safety Administration.

The writer said that “plugging a tire can work well.” This is just as true as making a statement that you can play Russian roulette and survive or you can beat the odds in Vegas or you can survive jumping out of a plane without a parachute.

Guidelines for proper repair of a tire for highway use are available from a number of sources.

Your well-being may depend on following these guidelines from NHTSA.
“The proper repair of a punctured tire requires a plug for the hole and a patch for the area inside the tire that surrounds the puncture hole. Punctures through the tread can be repaired if they are not too large, but punctures to the sidewall should not be repaired. Tires must be removed from the rim to be properly inspected before being plugged and patched.”

If you don’t trust NHTSA, How about Goodyear?
“It is crucial to know when it is okay to have a tire repaired and when a tire should be replaced. If a tire loses its air pressure, it must be removed from the wheel for a complete internal inspection to be sure it is not damaged. Tires that are run even a short distance while flat are often damaged beyond repair.
Most punctures, nail holes, or cuts up to 1/4 inch can be repaired by trained technicians as long as the damage is confined to the tread. DO NOT repair any sidewall puncture. Most tire repairs should be handled by trained professionals.”

If you don’t like Goodyear, maybe Michelin?
“There is a good chance that your tire can be repaired if:
1. The tire has not been driven on when flat
2. The damage is only on the tread section of your tire
3. The puncture is less than ¼"
However, you need to have an authorized tire retailer or technician remove the tire from the wheel and inspect the tire from the inside. This inspection is absolutely necessary because internal damage is not visible while the tire is mounted.
The proper way to have a tire repaired is to patch the tire from the inside and fill the puncture hole. If someone offers you a plug repair, refuse! Plug repairs do not involve taking the tire off the wheel for a proper inspection. A plug is simply inserted into the punctured area. Plug repairs are not reliable and can lead to tire failure. Insist on a full inspection and patch and fill repair on the inside of the tire.“

OK, not Michelin, then maybe Bridgestone Firestone?

“Tread punctures or penetrations left unrepaired may cause irreversible tire damage. An improper repair can damage the tire and will void the warranty.
Combination patch/stem repair. Steel cord damage must be repaired immediately to prevent rusting of the steel. Using plugs or patches alone on any type of tire is not a safe repair.“

Here is an example of a tire with three plugs and the owner also used a sealant that goes through the valve, all in an effort to save a couple of bucks.

Here you can see the cracks through the interior rubber of the tire from driving hundreds of miles on an under-inflated tire.

This tire had a piece of wire sticking into the air chamber. You can see where it was wearing through the interior.

None of these “repaired” tires were dismounted as instructed by tire manufacturers but each had a cheap, improper plug repair made by someone that thought they knew something about tires. I will leave it up to you to judge the quality of the suggestion that a plug is acceptable repair and "can work well".

As you can tell this topic is a “Hot Button” for me as I have seen entirely too many improper repairs done by the uninformed in the name of saving a couple of bucks.


Monday, June 19, 2017

Another example of learning correct tire inflation

Originally Posted by Ron View Post
Tireman9 and others....I just ran my coach over to the local Cat Scales at a truck stop nearby. As I stated earlier they do not make things easy and a 6" curb on each side of the scales prevented me from putting each side on separately so that I could get a close four corner figure. I settled on the two axle approach. All tanks were full, (water tank was actually just over 2/3, it fills very slowly and I got bored). Front axle came in at 11,400 lbs, rear axle was 16,560 lbs. My front axle is rated at 13,300 lbs and the rear is 21,000 lbs with a GVW of 34,300 lbs. 295-75R-22.5 tires. I have looked at the tables but would like to see what you folks come up with for approx. front/rear inflation? Thanks, Ron
Ron, you didn't say the brand tires. To my knowledge all major brands except Michelin have the same info for load & inflation and Michelin is same on maybe 95% and those that differ may only differ by 5 psi or so.

Since you only have total for an axle and do not know the heavy side we estimate one side at 53% -- So Front would be 6,042 and rear 8777 (4,389 per tire).

Most 295/75R22.5 LR-G need 110 to support 6,175 F (single) and 80 psi to support 4,540 in Dual.

Since I recommend a +10% of air for a good margin, that would suggest 121 psi front and 88 for the rear. BUT a LR-G is only rated for 110 psi so you need LR-H on the front. Also need to confirm the front wheels are rated for 120 psi and since even H are only rated for 120 that makes the recommended Front inflation 120 psi.

Clearly the estimate of 53% is causing the problem so it increases the need for you to learn the actual side to side load on the tires by going somewhere other than CAT truck stop scale.

It is CAT policy to not do one side weights and that is why they are making it harder to only get one side on the scale.

I suggest RVSEF

Check this site for scales

SmartWeigh is another option

I checked around home and found a local building supply that had a scale that would give me 4 weights for $10. Only about 3 mi off I76 just East of Akron OH.


Monday, June 12, 2017

"Dry Rot" is a misnomer regarding tires

Read this on an RV trailer forum, but most of the info applies to all types of tires.

"My understanding is that there seems to be a belief or a known orthodoxy that despite external appearances, the inside could rot out and that tires that appear all fine and dandy on the outside, after that long are not on the inside?

I believe the only "proof of concept" is common anecdotal experience:

People have owned tires that appear fine that are "old yet all seems fine", and they experience unanticipated tread separation and such....several anecdotes to the point of it being a "common wisdom" best I can tell.

Beyond that, I have not seen a "more objective" verification of my mind, after the death of such an "old yet otherwise in good shape and used properly" tire, an autopsy of that tire could show evidence of this "rotting from the inside"....I am not sure anyone has posted details about what that would look like (beside unexplained otherwise tread separation)?

Absence of such "more objective review", I am very very inclined to accept the common wisdom or orthodoxy on this matter until clearly proven otherwise as the cost of being wrong is potentially massive comparatively!!!!!!!!! Many many posts on this site have expressed huge regret about pushing past such "widely accepted advice"

My response to the above:
I did "tire autopsies" for decades before retiring. I have even posted pictures on my blog and have over 30 posts that have "Failure" as a label. Best advice I can give is to read and review the information on my blog. Listen to the only two (to my knowledge) actual tire engineers on RV forums: myself and CapriRacer.

"Dry Rot" is a misnomer. Rubber is a long chain polymer. The chemistry is such that the polymeric chains break down over time. The rate the chains break is related to heat and other energy (UV) input. Nothing is actually "drying out" or "rotting" in the common understanding of the word. Sidewall cracking (dry rot) is just a symptom that suggests the internal rubber compounds have probably lost some of their elasticity, which increases the potential for cracking, which may lead to separation.

There is no single answer to why some people have longer tire life than others except for the fact that some operate their tires at higher temperatures (load, speed and inflation plus ambient temperature) than other people.

Any tire can fail with a Low Inflation sidewall flex failure or "Blowout". Radial tires in trailer application are exposed to significantly higher Interply Shear forces due to suspension design that the tires on the tow vehicle - See my post on Interply Shear.

While operating a tire can help the "Anti-Oxidants" or AO's migrate to the surface, simply driving the tire is not IMO an efficient or effective thing to do, especially when we consider that cleaning of the tire sidewall, which will remove the AO's, can result in more harm that any driving around can prevent.

How many of you have bothered to make load and inflation adjustments necessary for driving your ST type tires any faster than 65mph?

Do you even know the actual loads on your trailer tires?

How many do an annual "free spin" inspection of your trailer tires?

How many are running TPMS (tire pressure monitoring systems) so you get warned when you drop down to the minimum inflation needed to support the measured tire load?

If you feel that checking your pressure with a hand gauge is sufficient, do you make that check every 10 to 15 minutes of operation? If you have a tire leaking air you can destroy it in just a few miles, so the fact you checked the air 4 hours prior to the failure is of no importance.

Sorry for the rant but the FACTS are out there. It takes a little effort to drastically reduce the potential for premature tire failure. There is no magic snake oil spray that will make your tires last 20 years. There are steps that you can take to get 5+ years of life in trailer application and 7+ in motorhome and tow vehicle application.


Monday, June 5, 2017

"Only" drove 750 miles with companion dual tire low on air

Originally Posted by Charlie View Post
What should I do? I had checked tire pressure the day before and only drove about 750 miles when the right rear inside duel blew resulting in damage to the MH and the tow. Only the side wall blew and the tire stayed on the rim. This is the first time in over 25 years of RVing that I have ever had tire trouble. I only had about 14,000 miles on these tires that are less than 2 years old. I bought the best tires they recommended. I will not say the brand but it begins with M.
I had pressure set at 120 psi and they were filled when the tires were cold and had not been driven for over a month, Should I be concerned about the other tires?

Should you be concerned? It depends. Why did the tire fail? If the failure was a sidewall flex failure (sometimes called a "zipper") from running low then there was most likely an active leak, i.e. puncture or leaking valve core would be on the top of my list. In this case the other tires are no more likely to fail next week than they were last week with one exception to be covered in a moment.

If you take the failed tire to a heavy truck tire dealer for the brand involved they should be able to confirm the mode of failure.

Since you were not running a TPMS (tire pressure monitoring system), all we know is that probably sometime between checking the tire pressure and 750 miles later (2 days?) one tire had lost most/all of its air. We also know that the outer dual was run with possibly 100% overload so it probably sustained internal structural damage that shortened its life (months or years). Since we do not know how many miles at what % overload, it is impossible to predict -- so the suggested best practice is to replace the companion dual.

One thing we can do is to use this as a learning experience. With a TPMS a driver would get early warning and many times can stop before a tire is damaged and, by extension, avoid damage to the RV and even not damage the mate in a set of duals. A single warning in the life of a TPMS (years) could save much more than the cost of the system.

Now as to the other possible reason for a tire to lose air. It is possible for a piece of grit to get into the valve core and allow air to leak. I suggest you review the posts on "Valves" (list to the left) and you can see an actual example of a leaking tire and the grit that caused it. So, as I have pointed out in the past, the very act of checking air pressure can sometimes result in a leak and potentially a failed tire.


Monday, May 29, 2017

Is your TPMS warning psi set correctly?

Originally Posted by Dan O. View Post
"The 'Safety Steer' is definitely a good bit of insurance. I also run the tire monitor system on all six MH tires and the four race trailer tires. I run 110 pounds in the coach tires and did pick up a nail in a steer tire one day. At 80 pounds the tire alarm went off (handling felt the same) and I saw 40 degrees more temperature in the low tire. Point is, some other warning signs are sometimes there before you experience an actual blowout."

I suggest you change the warning psi level. Many TPMS come with a single warning after a loss of 20% from the cold inflation. We all know that when running, tire inflation can increase 10 to 20 % from the CIP (cold inflation pressure). I would suggest that if your CIP is 110 then the warning should be no lower than 100.

Some TPMS provide early warning and alert when the hot pressure has dropped faster than normal so you can gain seconds to minutes advance warning if the TPMS provides "rapid air loss" warning or some other warning based on the hot pressure.

For example
Based on weight my small Class-C needs at least 65 to support the measured load. I use 75 as my CIP and my warning level is 65. My normal hot pressure is 80 to 85. If I pick up a nail I would get a warning if a tire looses more than 3 psi in a couple minutes so I might get a warning at 77 to 82 psi, which is well above the minimum needed by the tires for the actual load.

If a tire loses 20% of the air needed to carry the load it is officially "flat" for warranty purposes so there is a potential that the driving as Dan did with the tire down at 88 was damaging the tire structure which could shorten its life by months or years.

According to the U.S. Tire & Rim Association the warning signal from your TPMS should go off if inflation ever drops to below the level needed to support the actual load on any tire.


Monday, May 22, 2017

Goodyear Endurance ST tire info

I have been in touch with Goodyear and while there are still some technical details that need to be clarified, I have permission from GY to post the info sheet and the Load & inflation chart. (Click on each image for a much larger view.)

Monday, May 15, 2017

Another example of pressure and TPMS setting calculations

David said:

"I am a newbie. Just 5 weeks with my 2017 Newmar Bay Star 3113. I need some help understanding just what would be the correct or appropriate tire pressure on my coach. When loaded with my wife, dog and self, partial food and clothing, tools, chairs, BBQ ladders, 2/3 water, full gas and propane and misc stuff I got the following from the CAT scales: Front axle - 7,300. Rear axle - 13,260.

Here is my dilemma: The dealer delivered the coach with about 85 lbs. per wheel cold, but when I use the Michelin tire pressure chart for my 235/80R 22.5 XRE tires they should be just 75 lbs! I am concerned that they will be "underinflated" and could build up excess heat. Should I keep the 85 lbs. or lower the pressures

My reply:
David, Welcome to RV fun.

For all things tires (except buying) I obviously suggest you check my blog. I don't expect folks to remember everything but if you spend a few minutes checking it out you will learn how to use the "Label List" on the left to find a post of the topic of interest. There is also a search box in upper left.  Now to your specific question.

1. We want to know the heaviest load on your tires and since few RVs are perfectly balanced side to side for weight we ideally want to know the "4 corner weight" to learn the heavier end for each axle. Lacking knowing that number, IMO, we can do a rough calculation by using 53% of the axle scale weight for the RV when it was fully loaded (the expected heaviest it will ever be).

2. 53% of your front would be 3,870# and rear would be 7,030# or 3,515 on each dual.

3. Looking at the Michelin load tables we find for your size at 85 psi can support 3,975 for single (front position) and 80 psi supports 7,050# for two tires in dual position.  Yes, we always round up.

4. Based on the above, your MINIMUM inflation would be 85/80. This is the number I would use for the low pressure warning numbers on your TPMS.

5. I recommend adding 10% and again, rounding up, that means 93/88 psi for your Cold Inflation Pressure or CIP. In your case, given the close numbers for the front load, I would be comfortable using 90 psi all around, as a single number is easier to remember. This 10% gives you a nice cushion so you do not have to chase your tire pressure around whenever the temperature rises or falls. You could even get down to 85 psi before needing to "top off" the tire pressure again.

6  All tires on an axle should be inflated to the same level for improved handling and response in an emergency situation.

7. I would set the TPMS High Pressure warning to 110 to 115 psi and your high temperature warning level to 160 F.

8 Remember CIP means when tires are at ambient temperature and have not been in direct sunlight or driven on for at least two hours.

Finally, in your case, you are close to some numbers when we round so if your RV is more balanced than my suggested 47/53% you may be able to lower my suggested inflations by 5 psi, but only when you confirm your heavier end is less than 53% of the total.


Monday, May 8, 2017

Why do some tires "explode"

OK, let's see if I can cover the details of why and how a tire sidewall fails due to being run without proper inflation.

The mechanics are essentially the same, be it a textile (usually Polyester) tire, as are most P, LT, and ST type tires, or for tires with steel body cord, as most commercial grade LT tires and "TBR" "Truck-Bus Radial" tires. These cords are referred to as the "body ply."

I think we all realize that tire sidewalls bend when loaded. This can be observed by simply looking at the bottom (near the road) vs. the rest of the tire sidewall. The amount of bending is essentially just a function of tire size, load and inflation. This bending includes some stretching of the outer surface of the tire and of the rubber surrounding the body ply. This stretching results in some heat being generated. You can test/experience this heat generation yourself with a simple test of holding a rubber band against your lip and stretching and releasing the rubber band. Your lip is sensitive enough to feel the temperature rise of the rubber band.

Now the rubber used in tire construction can tolerate some temperature rise. The heat generated can transfer to outside air at about the same rate it is being generated. This is what happens for hopefully tens of thousands of miles and hundreds of thousands of revolutions, i.e., sidewall flexes.

So what happens if there is a leak of inflation air, or if the tire was not properly inflated in the first place? With lower air pressure the amount of bending increases and with an increase in bending we see more heat being generated. Increased heat generation means increased temperature of the rubber internal to the tire structure. Since rubber is a good insulator, heat transfer can be slower than heat dissipation to the outside air, so the temperature can continue to rise ever faster.

The strength of the rubber decreases with an increase in temperature, which allows more bending. With slower heat transfer from the internal structure to the outer surface and increased heat generation as more air leaks out, I think you can see how it is possible to get to a point where there is something like a chain reaction or "runaway" temperature increase.

The above heat generation can also result in the polyester experiencing a rise in temperature with the associated loss of strength. You have seen the effect of high heat by holding a match near the end of a piece of Nylon or Polyester and see the textile melting. In the steel body ply tire the increased bending can result in a fatigue failure of a steel cord. You can test the fatigue with a steel paperclip. Simply bend the paper-clip a few times and it will break. In the case of a tire, the number of bends to failure can easily be in the thousands.

I will cover the "explosion" in an upcoming post.


Monday, May 1, 2017

How tires are built -- now and in the past

First video is of  overall process of manufacturing a tire.

Next is how tires (in this video from the 1930's) were made.

Then how larger farm tires were and in some cases still are made.
Bias tires in U.S. in '60s and in third world countries today.

State of the art tire assembly machine. This would be what you would see today for passenger and LT. The process is similar for truck (RV) tires being made today with just a little less automation by top tier tire company.

And I bet some just thought rubber was squirted into a mold.

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Monday, April 24, 2017

How fast can an ST tire run?

Monday, April 17, 2017

Question of running year old tires or Running less than max psi

Question from Chris

Hi Roger,

I came across your website by way of referral from a member on a Keystone RV forum.  I have a concern regarding upgraded tires and wheels for a Keystone trailer I own.  

As most manufacturers continue to cut costs in value models, wheels and tires seem to be ground zero in their savings.  So, to help mitigate tire failure on my coach, I've upgraded my china bomb OEM 14" tires sized ST205/75R14 LR-C to ST225/75R15  LR ? and purchased new wheels to accommodate the new rubber.  My wheels are Sendel wheels that support 2540 lbs of load each. 

I purchased Carlisle Radial HD tires in LRD from Discount Tire.  Unfortunately, they received LRE tires in instead of the LRD tires.  The Discount Tire salesman quickly resolved the error and within 2 days, had LRD in stock.  I returned to the store to have them balanced and mounted on the wheels. The stock they received in had DOT date code of 1516. He told me that was the newest in all his warehouses. I didn't want year old tires so I rejected the sale.  

Then, I ordered the same tires from  Same story, the DOT date code was 1616 and 2016.  Rejected that sale.  Finally, I ordered them from  They arrived today.  Again, tires are around 1 year old and I'm sending them back.

My first attempt at ordering tires from Discount Tire resulted in LRE tires. They were much newer around Nov 2016. I think my quest for load rated D tires from Carlisle in size 225/75/15 is futile.

So now, I'm considering purchasing the LRE tires as I think the local stock is much more fresh than I can ever find with LRD. The only limit I have is my wheel capacity at 2540 lbs. If the LRE tire max inflation pressure is 80 lbs supporting 2830 lbs, will it compromise the tire if I inflate only to 65 lbs (in order to stay within the specs of the wheel)? The OEM tires were LRC on 14 inch wheels supporting only 1760 lbs at 50 lbs. Weight is not a concern as I will never come close to max weight limits with my trailer on either LRD or LRE tire. 

Another thing that worries me is the stiffness in the LRE rubber. Comparing the Carlisle LRD to the OEM Trailer Kings is night and day. The tire is just so much more beefy. Don't really want to rip apart the trailer because it's rolling on unforgiving rubber. 

Any opinions and recommendations is greatly appreciated.

Thanks in advance.

Chris M.
Concerned RV owner

My answer:

OK you have a couple different issues.

You need to know that tires are made in batches. For relatively small markets it's possible that a company may only make an item once a year or even less frequently. While tire age is of concern when the tires are on the ground and exposed to sunlight and heat, it's less of an issue when in the factory warehouse.

One way to let your mind rest a bit is to ask when the warranty clock starts ticking. Some companies clearly state on day of application or first retail sale. Others say the warranty is based on DOT serial. If it's based on date of sale and clearly stated as such in the literature, I would be less concerned and just be sure that the sales receipt has the date and DOT serial of each tire identified and keep both warranty and receipt in a safe place.

Now, since you have taken the step of going from the ST205/75R14 LRC to ST225/75R15 LRD, you have increased the load capacity from 1760 @ 50psi to  2540 @ 65 psi. You have increased the reserve load capacity by over 50%, which should deliver very reliable service. While I do not have any data to go on, I think that when inflated to the same psi the LR-D and LR-E would have similar stiffness. It's the air that supports the load and it's the air that provides the majority of the tire stiffness.

For your application I would think there would be no problems with running LR-E tires at the wheel limit of 65psi.

So, bottom line, I think you can go with the year-old LR-D tires or run the LR-E at 65.

Monday, April 10, 2017

Why isn't my TPMS accurate?

Comment on an RV forum
"I just bought a new TST 507  TPMS (tire pressure monitoring system) and  I gotta say they could improve the documentation.
Definitely confusing as setting up is a bit complex. At one point you are told to press a button and wait for the second beep (not the first!) before setting the pressures or whatever.
But once that's over, it works as advertised. It does seem to take a while, once turned on, for all the sensor readings to be displayed. After that it just cycles through them every 5 s, and beeps when one is over or under.
Not sure how accurate the psi readings are. Will have to get out my pressure gauge and compare."
My reply

TPMS are primarily designed to WARN of a loss in pressure and are not intended to be your primary source of accurate pressure measurement. In my experience ALL TPMS will have one or more sensors reading a psi or two different than a hand-held digital gauge. For that matter even hand-held gauges are seldom accurate to +/- 1.0 PSI based on the calibration checks I offer at my tire seminars.

IMO best practice is to set your tire pressure as close as possible to the desired CIP (cold inflation pressure) using your personal, master digital hand gauge and then install the TPMS sensors. Wait about 5 min for pressures and readings to stabilize, then do a pressure check on the monitor. You will note slight variation, but all should be within the specified range (some spec +/- 2%  some spec +/- 2 psi) You will find that after a few days use you will get comfortable with the pressure readings showing some variation from each other. With a little experience you will get comfortable and know the range of normal variation.

What I do...
Each morning when I get up, I first turn on the TPMS monitor and go get my coffee. By the time I am done with the 1st cup - about 10 min - all the sensors have sent in a reading. I step through each tire on the system and based on experience, I know if the tires are ready to go as far as being properly inflated. Yes, the numbers vary, but as long as they all are in a range of a couple psi from what I got when I last set the tire pressure all is good.

With the above practice I am getting the "cool tire" pressure reading which is the only reading of importance. With my +10% over the minimum inflation needed for my Motorhome, I don't have to worry about a daily +/- 2 to 4 psi variation. However, if I have a few days in a row with the display pressures consistently showing a few psi lower than my CIP goal I know it's time to plan on a stop at the truck stop for a shot of high pressure air.