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Friday, September 25, 2020

Weight Creep

 I have covered the importance of knowing your actual RV weight, as that has a direct impact on your tire loading which affects your tire life.

The idea of "4 Corner Weight" is that you get on scales that can measure the load on each end of each axle because very few RVs have an exact 50/50 end to end load split for every axle.

 Now I know that finding a location that can measure each tire position is not easy. Large RV gatherings such as FMCA Conventions and Escapees meet-ups sometimes have vendors offering that service. HERE is some information from another tire engineer on where and how individual weights can be measured. Others have learned that their state scales as in Oregon and I believe Washington state are left "on" and they can many times get the weight of each  end of each axle on the scale so they can calculate the actual loading.

This is my RV on a scale in Oregon. The red circle is the weight sign.

Some folks have contacted their state police and found them more than willing to provide the service. HERE is a work sheet you can use when you get the scale readings..

One other consideration for every RV owner, even those that have not yet learned their corner weights. This is WEIGHT CREEP. This slow increase in overall weight occurs as we travel and add small items to our RV. This might be another tool or book or nick-knack. Individually they only may be a pound or two but over time the total weight can become significant.

Now, I am not saying you have to search out a company to re-do your 4-corner weights every year but you can get a handle on your weight creep with a quick visit to a regular truck scale where you can learn your individual axle weight. With that new information you can compare the total for each individual axle of your 4-corner weight with the new truck scale weight. Hopefully you will not see any significant weight gain that would require you to get new corner weights BUT you will at least know the facts and know if the extra "stuff" is adding up to a significant weight gain which suggests that you put the RV on a "diet".


Friday, September 18, 2020

Don't get your shorts in a bunch about tire inflation. BUT you still should consult the inflation tables.

 I talked about this a number of years ago but it seems it's time to cover this again for those new to RV living.

I have covered what I felt is the "Best" inflation for tire life in my posts where we discuss "4 corner weights"  which means learning the actual load on each tire position by getting the RV on a set of individual tire scales. While large RV Conventions such as FMCA or Escapees events sometimes have those scales, many times they are not convenient. But you can find Truck Scales at many Interstate exits, where you can learn the actual load on each axle. Since we know that almost no RV has perfect 50/50 side to side load balance, learning the actual load on each end of each axle is a good idea. Some RVs have been found to be 1,000# out of balance.

If you can only find truck axle scales then I suggest the following rules of thumb until you learn your "4 corner weights".

- Class-A Motorhomes and large (28'plus) 5th wheel Trailers with slides and especially if they have a residential refrigerator, should assume they have 53% of the axle load on one end so should use that heavier number when consulting the tire Load & Inflation charts.

Class-C Motorhomes and trailers shorter than 28' with slides should assume a 52/48% side to side split, While Class-C without slide, Class-B and small single axle trailers can assume a 51/49% side to side load split.

Using the heavier end figure consult the published tire Load & Inflation tables to learn the minimum inflation pressure for the tires on that axle of your RV. This "minimum" inflation is the number you would consider for the morning of every travel day.To avoid chasing inflation changes due to changes in the weather, I suggest you add 10% to the number from the tables so you can simply monitor the inflation using your TPMS and as long as you never drop below the Minimum inflation needed to support your load.

I am also in favor of this plus 10% inflation margin so you don't find yourself chasing your tail every day by adding 1 or 2 psi when it gets cooler when you find yourself 1 or 2 psi low, or bleeding off 1 or 2 psi when the weather turns warmer. You can simply monitor the morning inflation number and as long as it stays near the +10% and does not drop to +0% or go above +20% you are good to go for that travel day.

With +10% margin it would be easier to discover you are low a few psi and simply wait till the next fuel stop, where there should be high pressure air available if you need to add air.

For those that don't know how to inflate a warm tire here are the steps:

1. Measure the pressure when the tire is at ambient temperature (not warm from driving or being in sunlight). Many consider this their "Morning Tire Pressure".
2. Note the number of psi you want to add to each tire to get to your goal inflation.
3. When you get to a fuel stop measure the warm pressure.
4. Add the number of psi from #2 to the warm pressure in #3 and add air till you get to at least this new warm pressure goal.

This "rule of thumb" will work for pressure changes of 5 psi or less. If you find you need to add 5 psi or more there may be something wrong,  i.e., a leak unless you have seen a long term decrease in pressure as the weather cools down. 

Don't get hyper about being 1 or 2 psi off. Remember, if you have a 10% cushion, you are good to go as long as you are within a few psi of your goal.


Friday, September 11, 2020

10% safety margin? Not Over-Inflation for more load capacity.

Originally Posted by Crasher View Post
Roger. When you refer to a 10% safety factor, is the tire any safer at 10% over it's rated load psi? If it is, why don't the manufacturers recommend a higher psi for the load? Or, is the 10% factor to cover the days when the ambient temp is lower which would lower the CIP eliminating the need to adjust the pressure? Whenever I have run tires above the load charts, the center of the tread will wear more than the outer sides. That tells me that the tire was not making optimum contact with the road for best wear and traction. Admittedly, it's a minor issue, but an inquisitive mind has to ask.

My +10% is on the set inflation and is NOT a "Safety Factor" in the normal sense. We know that tire inflation changes by about 2% for each 10°F change in temperature. The intent of this "Flex Range" of inflation is to avoid the need to mess with inflation on a daily basis.
Assume you needed 70 psi to support your heaviest ever expected load (this is why we say get on the scales when fully loaded to your heaviest). So assume you set your inflation to 70 psi and the Ambient temperature is 80F. What happens the next day if the ambient drops to 70F? Your tire pressure will have dropped by 2% to about 68psi which is below what is needed to support the measured heavy load. So you get out and increase your tire pressure back up to 70psi. A few days later it's 90F so tire pressure is now (90F - 70F = 20F so 2% per 10F = 4% increase of the 70 psi so now your tires are at about 73 psi cold so you drop your tire pressure.

See the problem? You are messing around with your tire pressure. almost every day.

However if you have a +10% "Flex Range" above your needed inflation, or in our example + 7 psi You can ignore the day to day pressure variation unless or until the temperature has dropped 50°F.

Tires can tolerate the increase in pressure with essentially no damage but low pressure can result in increased operating temperature which accelerates the "aging" of the belt rubber which can shorten tire life.

Also if you have to mess with your tires a lot, soon you will tire of the chore and stop monitoring and adjusting tire pressure which can lead to low inflation. This extra work can get old quickly and then you stop checking and setting your pressure. I Do Not Want That to happen.

RE center wear. That was an issue with bias tires but I do wonder what micrometer you are using to measure tire tread wear to 0.001" especially given that tire tread wear is normally in the .001" per 1,000 mile range and I doubt that your pressure remains constant over each thousand miles operation. Road surface (concrete vs asphalt) has a much bigger impact on tread wear. 


Friday, August 28, 2020

"Cold Inflation Pressure" and clarification of tire terms.

It appears I messed up in my previous post on "Cold inflation and Set Pressure". I failed to properly define the terms I was using, so if you bear with me I will try and clear things up.
"Cold Inflation Pressure" This is the pressure number you see published in tire company "Load & Inflation" charts. It is also the pressure you see on the Certification Label sticker AKA Tire placard that vehicle manufacturers apply to all cars, trucks, and RVs. It appears that some folks have a little difficulty with the word "Cold". This does not mean the tire needs to be refrigerated or that inflation pressure needs to be "adjusted" by calculating the difference between some theoretical laboratory standard and the current air temperature. "COLD," for tires, simply means at Ambient air temperature and not warmed by either being driven on or being in sunlight for the previous two hours.
When I am discussing tire pressure I am always referring to the Cold inflation unless we are specifically discussing the pressure increase due to Sun exposure or due to being driven on and reported by the TPMS or if the driver checked the "Hot" pressure at a rest stop with their hand gauge.

Finally, the pressure number molded on the sidewall of tires is the cold inflation pressure required to support the load that is also molded into the tire sidewall. The load number is the maximum load capacity for the tire and so the cold inflation would be considered the minimum cold inflation required to support that load. The wording on tire sidewalls does vary a bit. If you look at a variety of tire types from different manufacturers you will see some variation in the wording and IMO this contributes to some of the confusion. One fact that many do not think about is that increasing the tire cold pressure above the number on the tire sidewall WILL NOT increase the load capacity number molded on the tire sidewall. It is also important for people to understand that tires can tolerate a significant increase in pressure due to operation under load or at speed. While I can't provide information on the specific design limits used by different tire companies, What I can say is that in my personal experience that many new tires are capable of tolerating inflation increase of upwards of 100% or more over the number molded on the tire sidewall so the idea that an undamaged tire will suddenly explode due to an increase in inflation due to operational heat is not justified.

Tire Pressure increases. In my post of March 3, 2014, I covered the science and math of pressure change due to temperature change. You can read that post HERE, or just accept the rule of thumb that pressure changes by about 2% for each change in tire temperature of 10°F.

While we are talking about pressure change You can review my post of July 8, 2011, where we pointed out that driving from Death Valley to Denver CO will only result in about + 2.5 psi but the change (drop) in Ambient temperature will probably decrease the pressure by more than that increase due to elevation. This is why we tend to ignore tire pressure due to changes in elevation.

Tire Load is important information. You know the GAWR or Gross Axle Weight Rating is on your certification label. The problem is that the actual load is almost never split side to side to give a 50/50 split. While many RVs may have a 48/52 % or similar, side to side split on an axle the actual scale readings have confirmed some RVs have as much as 1,000# unbalance. So without actual scale readings we could only guess which tire is loaded more.

A tire on one end of an axle has no idea about the load on the tire on the other end of the axle so simply dividing the axle load by two is not sufficiently accurate to be confident that you "know" the actual load on your tires. The other problem is that many people simply estimate the load on their tires. The reality is that a majority of RVs (10,000+) that have actually checked the tire loads have been found to have a tire or axle in overload. This data demonstrates the importance of learning the actual load on your tires. While learning the load on each tire position is not easy, at minimum RV owners need to confirm the load on each individual axle and this is easily done with a visit to a local Truck Stop. This needs to be done with the RV loaded with as much "Stuff" as you ever carry. With the axle loading known and until you can get individual tire position weights, I suggest you assume one end had 53% of the axle load.

My final point for this post is Reserve Load and this is where we get to the "Set Pressure".
First, we need to remember that Reserve Load is the load capacity of the tire at its cold inflation pressure that is in excess of the measured or calculated load of the RV on the tire. Some use the term Safety Factor but as an Engineer, this term is not really appropriate.

In general, it is suggested we have at least a 15% Reserve load. Most new cars come with 20% to 30% Reserve load and this is a major reason why we seldom see tire failures on cars. An exception was seen in the 90's when one vehicle MFG provided for less than 10% Reserve Load and a number of tire failures occurred and even made the TV News.

Many Motorhomes may have less than 10% Reserve load even if the inflation pressure and the loading shown on the Certification pressure are followed. IMO this is a major reason for the relatively high failure rate of tires in RV Motorhome application. RV Trailers have it worse. In addition to having 0% to 10% Reserve Load the suspension design contributes to high Interply Shear due to being dragged rather than steered around corners.

So what should an RV Motorhome owner do?
1. Learn your actual loads on your tires by getting on a scale for each tire position.
2. If you can't get individual axle end loads assume the heavy end has 53% of the axle load.
3. Use the tire Load & Inflation tables to learn the minimum cold inflation needed to support your actual (or 53%) load.
4. Consider applying a +15% to the load figure to give yourself a reasonable Reserve Load and consider that your Minimum Cold Inflation. You could also consider adding 10% to the load Table pressure if that is easier for you to calculate.
5. Consider adding 5% to the inflation in #4 and use that as your "Set Pressure. This gives you a cushion for day to day temperature variation which can change inflation pressure 2% to 5%
So what should an RV Trailer owner do?
Do #1, #2 & #3 above
#4 If you want to try and lower the Interply Shear I recommend you increase the inflation to the number on the tire sidewall and use that for your Set Pressure. If you have increased the tire Load Range from say a LR-D to LR-E you can use an inflation number the 65 PSI for LR-D and the 80 PSI used for LR-E tires and use that as your Set Pressure.
#5 Try and learn the wheel max pressure rating and do not exceed that number.


Friday, August 21, 2020

Tires are more than just Round & Black things

A question came up about the Max speed recommendation as published by Goodyear, Michelin, and Bridgestone for tires in RV use.
To help clarify:

Many times the "application" or use of an item results in it additional or different limitations or ratings.

 If I have a tire that is a 225/75R15 and inflate it to 35 psi, How much load can it carry?

If the intended use is on a passenger car 1,874#
If as a single on an LT it is rated for 1,445#
If as a dual on a LT 1,315#

If a Single on a trailer where having passengers in the trailer is actually prohibited 1,760#
and if in a dual application on a trailer 1,570#

Part of the decision process for a tire's capacity in each of these different applications includes such things as:

Will the vehicle carry passengers?  Is the "Reserve Load" of the tire in the application normally close to zero or maybe 10% or normally closer to 25%

An obvious example where the application affects the load capacity is well established in the use of "P" type tires on a truck, trailer or multi-use vehicle such as an SUV. In these applications the load capacity is reduced by Industry standards by dividing by 1.10 so the 1,874# capacity becomes 1,703#

For heavy truck there are published guidelines that allow an increase in load capacity if the max speed is significantly reduced.  As the speed is lowered the load capacity can be increased up to 16% with no increase in inflation.

Similar to above if the tire is made for a specific market a tire company my have more demanding requirements on the tire during the development process. An example might be it the tire was being made for a market where the speeds and Ambient temperature was both very high the tire might require a more robust construction. Another example might be providing a special tread rubber if the tire was to be used at extremely low temperatures where the tread rubber might even crack if a "High Speed" rated tire tread were used.

Tires are much more complex than many people suspect. Ideally, an owner would be more informed and knowledgeable about tires and their limits and capabilities when making a purchase. They are much more than just "Round Black" things that almost no one "wants" to buy.

Friday, August 14, 2020

Does your tire dealer know what they are doing?

Just got this message from a reader.

"I just replaced 6 235/80R 22.5 XRV Michelin tires on my 2013 Monaco Monarch Class A Motor home. The dealer installed, balancing bead bags and new valve stems. I have good access to all valve stems now and have an after market TPMS. A couple of the rears were below the 95 Pound alarm point when cold and I decided to add air. When I removed the TPMS sensors, the valve stem seats leaked on three of six tires. I replaced the faulty valve stem inserts, completed pressure checks and all is well. I heard from one of my friends that the bead bags are causing the valve stem seat to fail and I understand there are redesigned valve stem seats that solves this issue. Can you comment?"

I responded:
The dealer that installed the "balance" stuff should have also installed the special valve stem/core air filters. Powder from beads can get into both the core and the TPM sensor and make them malfunction.

Bolt-in valve stems have a rubber insert on the air chamber side and a large metal washer on the outside. There is a torque spec on the bolt in valves. This blog post, covers valve stems of different types and has the torque spec for the bolt in nuts.
By "stem inserts" do you mean the valve core? Every valve stem I have ever seen comes with a new core. The only reason for them to leak is some "stuff" got into the new core and most likely was from the balance stuff.

This makes me wonder if the dealer was just interested in selling you the balance beads but didn't want to kill the sale with an increased cost for the valve air filters.  OR He didn't know that filters were needed when you put "stuff" inside a tire.

Also did the dealer give you a written tire warrantee that covered the use of the balance stuff? 


Friday, August 7, 2020

Another question on "Cold Inflation" vs your "Set Pressure"

Got this question from a reader of an RV Forum:

Thank you for all of your informed comments regarding proper tire care. I need one clarification. I have always considered the cold psi on the side of my 22.5 RV tires to be the minimum to carry the maximum rated load, but have assumed that psi was also the maximum COLD psi the tire should see. From your recent post, am I to understand that unless the tire states that it is the maximum cold pressure, I can exceed it by 5-10 psi?
Thank you for your time, Doug

My Answer:

The wording on tire sidewall IMO was written by lawyers, not engineers or users. Info on the sidewall is the inflation needed to support the Max load.  The difficulty is that few understand that the pressure changes with temperature and the only meaningful pressure, measurement is when the tie is "cold". This still confuses some because some want to apply Chemistry Lab practice of adjusting to theoretical 72.5°F when what "cold" really means for tires is at "Ambient Temperature" and does not include any pressure build-up"   In real life terms this means "Not warmed by being driven on or in direct sunlight for the previous 2 hours"
Now we need to address what is meant by "Cold Inflation" vs the psi to set your tires to or what I like to call your "Set pressure".
I like to suggest the "Set Pressure" for motorhomes to be the minimum needed to support the maximum load on the tires PLUS 10% inflation. 
RV trailers are different because of their Interply Shear problem.

For RV Trailers,  I would like to see a minimum of +15% load capacity over the measured heaviest loaded tire, with +20% to +25% Reserve Load capacity being better. Sadly most RV trailers come with tires that provide +0% to +10% load capacity vs GAWR
NOTE: I am not even addressing the tendency for most RV owners to overload their tires.
So for trailers I try and simplify:
- To lower, but not eliminate the Interply Shear problem I suggest the "Set Pressure" when the tires are "Cold" to be the pressure on the tire sidewall. BUT I still want trailer owners to confirm they have at least 15% "Reserve Load" over their measured scale reading.


Friday, July 31, 2020

Can't "Balance" your tires? Bad ride?

Can't remember the number of times I have seen someone post about the "bad ride" they had in their Motorhome and that they took the vehicle to their RV dealer but was told they could not "Balance" the tires or that they were balanced and the ride was 'What it is".

The ride can be affected by a number of different contributing factors.

1. One or more tires may be out of balance
2. The tire may not be properly mounted to the wheel
3. The wheel could be out of round
4. The brake drum/rotor may be out of balance
5. The wheel may not be mounted to the hub correctly
6. The tire may be out of round
7. The tire may have internal structural "uniformity" problems.

Many times people jump to the conclusion that the tire must be "Out Of Balance" and they want to ignore all the other possibilities.

Back in Nov 2011 I covered a number of possible contributing factors when I answered the question of Do You Need To Balance Your Tires? Obviously, those that just focus on "balance" did not review this blog post.
In that old post, I said it was possible to balance a cinder block. You might consider reviewing this post as it has some good pictures of the other conditions that can give poor ride.

I have used this comment a few times in my RV Tire Seminars but I bet few believed me. Well here is the proof.
This first shot is of my "Bubble" Balancer and my test cinder block. Yes, the balancer is old ( from the 70's) but I have balanced hundreds of tires.

Even those used on my Camaro race car

where high speed (125+) would quickly show up if the tire was out of balance.

Now first I confirm the balancer is adjusted to a near-zero level of out of balance itself. We can see the bubble is very near to perfect balance with it right at the center point.

Next, I loaded the cinder block onto the balancer. I chose to not try and pile standard wheel weights on the block, so just grabbed some hand wrenches. After some moving these "balance weights" around I ended up with a

very acceptable level of balance.

I do hope this clears up some of the confusion on Ride vs Tire Balance. 


Friday, July 24, 2020

One tire fails. What about it's "mate"?

Had a question from a friend about replacing both tires when one failed on the same side of the RV. 

 In Motorhomes with "Dual" tires (side by side) in the rear and you do not get the early warning from TPMS of air loss, you need to seriously consider replacing the "un-failed tire" because when it's "mate" failed the un-failed tire was overloaded by 100% for some unknown number of miles. 
You can always take the un-failed tire to a dealer, for that brand of tire, and have it inspected inside & out, and if ruled OK, in writing, by the dealer, you could keep the tire as a spare.
However, if it ran some unknown number of miles at 100% overload, I would not even trust it as a spare. 

 Now in the case of a multi-axle RV trailer (tandem axle) and one tire failed and again you were not running a TPMS to get an advanced warning, we need to consider what happened to the load on that side of the trailer. Wouldn't all the load from that end of the axle with the failed tire transfer to the un-failed tire on that side of the trailer? This transfer would be transferred through the springs and the link between the axles. The load supported by the "failed" tire doesn't simply evaporate, does it? It has to be taken up by the un-failed tire on that side of the trailer.

So again that tire should be removed, inspected, and replaced as with the Motorhome example. It might be OK to keep as an emergency spare but only used with great caution and only if inspected and judged OK by a dealer of that brand of tire.

This is one of the things people do not think of when considering running TPMS. If you get advance warning of air loss in one tire in a "Dual" or "Tandem" location you not only might save the cost of the punctured tire if it was caught soon enough to be repaired but you might even have saved enough by not losing the 2nd tire not to mention avoiding the $Thousands of possible damage to the RV.


Friday, July 17, 2020

Shield your tires from exhaust heat

Some folks are noticing the inner dual on one side seems to always run hotter than the outer dual or the inner on the other side of their coach.
IMO it is the radiant heat from your exhaust system that is causing your tire to always run a bit hotter.

Remember that the "aging rate" of tires doubles with each increase of 18°. This means you are potentially cutting the life in half.

I suggest you take a look underneath your coach. You do not need to wrap your exhaust. This can cause problems and may shorten the life of your exhaust system. A simple metal shield can shield the tires from the IR heat.

Here is what GM installed on my C4500 for my Class-C. Simple sheet metal with a bottom lip to provide some stiffness and to prevent cuts I guess. Just some galvanized 16 to 20 Ga steel can do the job. I bet if you check with a Home heating shop that does ductwork they can cut and bend a piece for not much $.  My shields were welded (1" every foot or so) and show no signs of failing after 17,000 miles. Could also drill and use some heavy metal screws too.

Friday, July 10, 2020

Why doesn't Bridgestone, Michelin, Hankook, or Continental make ST type tires?

I was asked by a fellow RV owner if I could recommend a tire for their trailer.

We have asked why the major tire companies other than Goodyear (Bridgestone, Michelin, Hankook, and Continental) don't carry ST tires, but they didn’t really provide a direct answer.  Just sort of danced around it.  I have been reaching out and trying to find an ST provider, but have not had any luck so far.  

My reply:  In My Opinion,

None of the "major" tire companies are interested in the RV trailer market (ST type tires) because of the documented poor level of weight and inflation management. Goodyear tire company pushed for the introduction of Special Trailer tires back in the late 60's & early 70's at a time when 20' single axle trailers pulled with bumper hitches were the norm. a 1/2 ton truck was rarely an option for average family use vehicles. ST tires were offered with increased load capacity i.e. lower cost to the RV company and to compensate for this the 65 mph max speed and reduced tread depth was presented as required and sufficient to allow the bias tires of the day to run to wear out in maybe 10 to 15,000 miles. Many times P-type passenger tires were applied to these smaller RV Trailers but a -10% load capacity adjustment to the P-Type load capacity was required.

The 1974 National 55 mph speed limit kept operating speeds down so tire failures were still at a lower level but with the introduction of steel-belted radials to the tire marked coupled with the growth of trailers to 35'+ and tire mileage theoretically increased to the 30 or 40,000-mile range the tires no longer wore out but started to fail at an unacceptably high rate.

The annual tire market in the US is 200 Million a year for Passenger type tires and about 37 Million LT type. Annual sales of all types RV is very volatile and ranges from 160,000 to 500,000 a year for all types, from Class-A down to teardrop,  Some industry information suggests only 20% of the RV market are "conventional RV Trailers so that would translate to a market of 400,000 tires in the best years  When looking at the tire market I think we can see little incentive for a company to go to the effort and expense of developing tires for a market that is only 0.5% of the P- and LT-type tire market. Especially considering the high level of warranty claims and problems due to the extremely poor maintenance record seen from RV owners.

BUT   back to the original question. The only ST tire that I was able to look at a section of recently was a Goodyear Endurance. It looked like it might perform better than some other ST tires I have looked at.  BUT  the only performance data I have is just the reports on various RV Forums where customers seem happy with the Endurance.

Sorry to say that your choice is relatively limited if you have to stay with St type tires. While Maxxis and Cooper have supporters you might be better off switching to LT type as long as you make the required adjustments for load capacity by increasing physical size and or Load Range. If you follow my blog you should have already see THIS post of the topic of lT vs St type tires..

Friday, July 3, 2020

Valve Stems and TPMS Part 2

As a follow up to last week's post of why I recommend people NOT use rubber valve stems with their external TPMS sensors I decided to show some of the "guts" of valve stems.

Standard "rubber snap-in" stems like the TR413. If you look down the hole you can see the end of the brass part of the stem. More on this later.

These have been used for decades on hundreds of millions of tires. These can be installed by hand using a "puller" that stretches the rubber which makes the diameter of the stem small enough to "snap into place in the wheel hole.

Once installed the wheel "pinches" the rubber part of the stem to seal the air in. The arrows show the location of the wheel relative to the metal part of the stem.  Note the part of the valve stem that goes into the air chamber was cur off before I took this picture.

You can see that the brass stops before it gets past the edge of the wheel. This makes installation easier.

Next, we have the "High Pressure" stems such as the HP-500.

 Here you can see the brass part extends almost to the bottom of the valve and into the air chamber.

When the rubber is buffed off you can see that the brass part extends through the wheel hole (location shown with the arrows.)

Now when we look at a "bolt-in" stem, like this TR416s
we see the location of the wheel hole at the arrows. We can also see the much larger brass body (nickel-plated in this piece) that goes inside the air chamber and expands to a broad base. This type of stem needs to be installed through the wheel hole with the rubber grommet sealing the air. An external washer is used and the nut is to be tightened to specification to prevent air loss.

I am also including pages from the US Tire & Rim Association yearbook which publishes the "interchange and fitment" specs so all tire companies and valve manufacturers know what dimensions are required. This is the book where all the Load & inflation tables come from and might be considered the Tire Engineer's "Bible" and is used by tire engineers around the world when they are making tires that are intended to be used in the US.

Here we find the details of valve stem designs as specified by TRA.

Finally to show the attention to detail here is the spec for the little pin that sticks out of the valve stem. Not meeting this specification could be the reason your TPMS does not register your tire pressure. (Yes I have run into that problem)

 I just wanted to try and give you a little understanding of the attention to detail tire engineers go-to when designing tires and when trying to understand the "why" for a tire to lose air.


Wednesday, June 24, 2020

Valve stems and TPM Sensors

I read the ongoing discussion on what valve stem to use with an external TPMS sensor.

A standard 65 psi max, rubber valve stem is very flexible as seen here.

 Some people think the 80 psi max, "High Pressure"

 HP 600 rubber valve stem is Ok to use with external TPMS sensors but you can see the HP-600 is still flexible.

 Here is proof that an HP rubber stem can fail when a TPM sensor is installed.

IMO staying with any "snap-in" type stem is false economy given the metal bolt-in stems only cost $3 to $4 each. Not all tire stores will have the metal valve stems so check first. if they don't you can get stems at AutoZone, O'Riley's, Advance Auto Parts or NAPA or most any auto parts store or even on Amazon.
They are easy to install too. Don't let the service center tell you installing metal stems is a lot of work.  Watch and you will see.


Friday, June 19, 2020

Another post & question of "Trailer tires vs Truck tires"

Original post and question on a 5th wheel RV forum I follow.
"Searched this forum (no, didn't search travel trailer forum) for any info on using LT (truck) tires instead of "trailer" tires on a 5th wheel.
Nope, didn't find anything - So,
Any problems with using a 6 or 10 ply LT tires on my '99' trailer instead of the replacement tires for trailers?"

He gave the dry weight and stated GVWR but no actual scale readings. He also did not provide information on his current size or type or Load Range of his tires. He did provide info heard around various campfires. In the forum, there were a number of replies. A few OK and sadly a number just plain incorrect.

In the'60's RV trailers were mostly smaller single axle and towed behind a car or 1/2 ton P/U. RV companies wanted less expensive tires. Speed limits and actual travel speeds were lower so Goodyear came up with "Special Trailer" tires with a 65 mph max speed as part of the load formula specification. This speed reduction and decreased tread depth theoretically offset the increased load capacity when compared to the same dimension LT type tires.

In 2002 after the Ford Explorer fiasco, new tougher standards for tires were implemented by DOT. RV companies fought to keep the old test requirements for ST type, the same as they were in 1968, while P-type and LT-type had to meet new, tougher standards for the 21st Century.

In 2017 China was accused of "dumping" cheap tires of all types into the US market. Trade restrictions by FTC (not tire safety standards) identified speed-rated tires as not having to pay the import duty. Almost overnight almost all ST type tires became speed rated. The SAE test for speed rating is stated as a "passenger car tire test" but was applied to ST type. It only requires tires to run for 30 minutes at the stated speed and to not come apart.

Back to the OP. "Dry weight" and GVWR are of no value when selecting tires. GAWR is almost useless as it is well documented that a majority of RVs have tires and /or axle in overload when actual loading is measured on scales.. The only weight number that really means anything is the actual scale reading for each tire, as RV weight is almost never exactly split 50/50 axle to axle or side to side. Some big RVs have been found to be 1,000# or more out of balance.

Reserve load is the extra load capacity above the actual load. Cars and P/U have reserve load in the 20% to 40% range while RVs have 0% to maybe 10%. That is a MAJOR reason for the difference in durability. There is also the shear forces seen in trailers that can be 24% higher than an identically loaded tire on a motor vehicle. This is a function of suspension dynamics. Tire Interply Shear was a complete unknown back in the 60's and not as well known or understood even in the 80's. You see the large tread distortion due to lateral loading when backing into a parking spot when the tire bends sideways. You never see this bending on a motor vehicle. The shear is always there in every curve or turns not just when backing into a parking spot. Even the normal sway observed when a trailer is towed down the highway is generating high Interply Shear. You can lower, but not eliminate the Interply Shear by increasing your Reserve Load.

So how do you improve your Reserve Load? An increase in load capacity would be a good approach. For most trailers, there are a number of options. Increased Load Range is one as long as you confirm wheel limits on load & inflation. Changing to larger tires. Even changing to larger diameter wheels might increase load capacity. I have seen some that increase all three specs, with reports of eliminating all tire failures other than road hazard or valve-related issues that can occur on any size, brand, or type tire.

If or when you replace tires the new tires should ALWAYS at a minimum have equa load capacity.

I have covered the above in numerous posts on my blog if you care to learn the facts from an actual tire design engineer.

Or you can listen to the guy in the camping space next door or the salesman at "Billy Jo Bob's Cheap Tire and Bait Emporium".


Sunday, June 14, 2020

New updated post with videos on how tires are made.

The original was posted July 2019 but there are new and better videos available so I updated all the links.

Friday, June 12, 2020

Tire "Flat Spotting" when parked

Another post from an RV forum
"I'm no tire engineer but I always thought of a "flat spot" as an area ground off from a long skid. The old bias ply tires of years ago would "deform" or become "out of round" (especially in cold weather) but a few miles of rotation would flex it back into shape. But that's all just semantics."

Well I am a Tire Engineer and the correct terms are "Flat Spot" for an out of round condition. and "Brake Flat Spot" for having an area of the tread worn off due to locking up the brakes so the tire is dragged along the road and does not rotate. When I was racing I would sometimes lock-up the brakes to avoid a spinning car. This would give a strong vibration and we would have to change the tire at the next pit stop.

You can develop "Flat Spot" from long term parking. The degree or level or amount of this type of flat spotting depends on time, temperature load, inflation pressure, rubber chemistry and tire construction.
You can decrease this flat spotting with:
Lower Load  or Higher inflation or not parking when the tire is still hot or keeping the tire out of direct sunlight
The owner has no control over the rubber chemistry or tire construction.

FYI In general tires with Nylon cap ply (seen in tires with higher speed rating) tend to develop and hold the flat spot longer, but I would not reject tire purchase because of the Nylon cap ply as that might give you more life of the tire.

You can see and probably measure the amount of flat spotting from either brake lock or long term parking if you check with a "Free Spin" inspection as seen in the video in THIS blog post. 


Friday, June 5, 2020

Tire Advertising claims ???

Read this on an RV forum.

"I am using Carlisle Radial Trail HD Trailer Tire, not at all but I think it is a good tire for my trailer. these tires have an added protection against the heat with built-in weathering and ozone protection. And with the summer months getting into their absolute hottest parts, this feature could be a nice addition to have in my trailer tires. Additionally, these tires have interconnected tread blocks that I find encouraging. See, this interconnected tread blocks ensure the tread will last for a longer time and that’s something I find it very intriguing."

I have nothing against Carlisle.  I do find the ability of Copywriters to make features common to almost all tires sound unique and special. I do question the ability of anti-ozone waxes and oils to provide any "protection against heat" and I consider that claim a serious stretch. I would love to see any test data that supported that claim.

Be a smart shopper and don't fall for slick promotional claims. Ask to see the data and results from direct comparison tests. You will many times just get the sound of crickets.

Friday, May 29, 2020

Are your "Nuts" tight enough? Part 2

This topic of how to ensure your Lug Nuts are tight enough, but no too tight,  is a two-parter and this is Part 2.

The first part, if you missed it, covered the Science and Engineering behind the basics as I am expecting that there will be a number of people who will say something along the lines of "Roger, You are all wet. I've done it THIS way for years and never had a problem".

You are certainly welcome to ignore my advice and continue with the methods you have used for years. My target audience is those who are still new to the RV life and do not have years of automotive or mechanical background or training, and those that want to ensure they do not end up with a wheel coming off their RV or breaking a wheel stud.

OK let's jump in.

I am confident that no one wants a wheel of their car, RV, trailer, or dolly to come off while traveling down the road as seen in THIS video. Or maybe even worst to cause someone personal injury as seen HERE. (The man suffered a fractured skull and chest injuries). So what do we all need to do to prevent a wheel coming off one of our vehicles? It's easy. Just make sure all your lugs nuts are properly tightened and neither the wheel or nuts or studs have been previously damaged. Sounds simple enough but how do we do that?

First, you need to know how tight the nuts are supposed to be. This information should be in your Owner's Manual 

You can check out this YouTube How to Tighten "Nuts" - The Right Way. Note: I covered the sequence for setting or checking the torque depending on how many lugs you have on your vehicle in THIS blog post. One important point to consider. If you had service on your brakes or tires and someone else tightened the lug nuts how do you know they did the job correctly? Many of us have heard about or experienced an over tight lug nut so I recommend you set the torque your self as seen in the video. Then when you are doing the recommended "Torque Check" at 50, 100, and 150 miles you will know that you don't have a nut that is significantly over tight. Note if your owner's manual has different mileage for torque check follow your owner manual. If you find a nut that turns after the 2nd check keep an eye on it in the 3rd check and if still turning you need service as something is wrong.

Let's review the tools you will need and seen in the video.
Remember this info is aimed at owners of RVs with tires smaller than 19.5"So if you are in a Class-A you can read to understand what is happening to your "baby" when you call the service truck.

Torque wrench, 6 point socket of the correct size for your nuts, 2' "Breaker bar", 12" long 1/2" drive extension to allow you to get to your dual wheel nuts. Note Trailer owners may not need this tool.
You will probably not need to use these tools too often so top quality (expensive) is not needed so in those cases I head for Harbor Freight for low-cost tools.
Check these links:
1/2" Drive Torque Wrench. Harbor Freight    or  Lowes

1/2" drive extension     Harbor Freight   or Lowes

6 point "Impact" rated socket I recommend you not use a "12 point" socket as they are more likely to spin off or round off your nuts. You do not need to buy a set. You might want to confirm the size by borrowing a socked from a friend or fellow RV owner. Example 13/16"  Lowes
Note it might be better to go to Lowes or similar as you do not need a set, but be sure to get the correct size not something close enough or you can damage the lug nuts. Here is a 3/4" socket from Lowes.

Now how do you get the tight nut off? a 2' long Breaker Bar will make the job easier. This is what I use. and I can easily generate 200 Ft-Lb

OK so with all the tools you may need collected, How do you set your clicker torque wrench to the spec for your vehicle,
Here is a YouTube to help those who have never used a Torque Wrench.

Hope this helps and if these couple of posts help a few RV owners avoid problems we will be happy.


Friday, May 22, 2020

Lug nut Torque? Why is it important and why measure the force? Part 1

Here are some YouTube videos on the topic of Torque". What it is and how do we measure the force. As an engineer, I sometimes just assume that everyone understands some basic Engineering terms but I am wrong to make that assumption. You don't have to remember all the details. I am just hoping that when we are done with this topic you will accept our recommendations on how to set and how to check the torque of your lug nuts.

Important info. It is impossible for me to know the size lug nut or specification for every vehicle but you, the owner should know this important spec and it should be in your owner's manual. If you can't find it, find a dealer of your brand RV or check the on-line forums for other owners of your exact make and model and ask what the specs are. These numbers are critical for the safe operation of your vehicle. I can only talk in generalities in this blog.

One thing to remember is that for Class-C and Class-B RV motorhomes and for RV trailers as with your car or pick-up with 14" to 16" steel wheels, the torque spec is probably between 75 Ft-Lb and 85 Ft-Lb, while 19.5 tires run about 135-145  and 22.5 tires run 450-500 Ft-Lbs. So you folks with large wheels will have to depend on the service truck to tighten your lug nuts. It is possible to get a hand torque wrench with 1/2" drive sockets that will get you to the 150# to 200# range, but it is probably safer for you to leave the larger wheels and lug nuts for the service tech that has the proper tools. I will address the tools you need next week.

Here is a video that explains what torque is?

Friction is the next topic.

For proper torque of our lug nuts, the stud and nut need to be clean, rust-free, no damaged threads, and no oil lubrication unless specifically specified in your owner's manual. If you have had problems with a stud or nut, such as a nut coming off, or broken stud, or the wheel being partially loose or the threads have been cross threaded or the nut was significantly over-tightened, both the stud and nut should be replaced. Over-tightening can get the stud into the "yield" load range which can lead to incorrect tightening and even to stud failure.

This video shows why nuts come apart
"Transverse vibration" is what happens with a wheel is fastened to a hub. This is why we need to check torque to be sure the assembly is retaining it's clamping load after we start driving.

Tensile strength is covered in THIS video.

HERE we learn about SHEAR

Ok, enough "Engineer speak". This stuff is what we engineers learn and use when designing joint and developing specifications for studs and lug nuts. There is no test in my blog on this topic, but if you are going to argue with an engineer, then you will need a solid understanding of these forces.

Now the next step is for you to do a little research
A. Find your owner's manual and look up the specifications for each of your vehicles.
B. Make a note of the torque spec and lug nut size where it is easy to find. A permanent marker on your door jam might be a convenient location.

Ok here is a short video on using s "Clicker" type torque wrench.
We will cover this tool and some others next week.

Stay Safe

You can check out this "entertaining" YouTube from a guy in Australia on How to Tighten "Nuts" - The Right Way

Friday, May 15, 2020

Was your "Blowout" caused by parking at Quartzsite two years ago?

This is a bit of a continuation on the topic of "tire Dressing" from last week's post.
I do wonder how many that complain of sidewall cracking or less than desirable tire durability makes the effort to protect their tires from the heat and UV degradation from direct sun exposure.
While there might be some benefit and shielding from applying such as "Dressing" or "Shine" or other "stuff" to the tire sidewall for UV shielding. No dressing will protect a tire from the accelerated aging process due to being "baked" by the sun's heat.

There is no standard SPF for tire dressings as there is for sun-tan lotion, It would not be that difficult to measure the level of UV shielding by measuring the UV going through some clear plastic sheeting and then applying the tire dressing to the sheeting and measuring the level of reduction if any in UV rays.

In many cases, the rubbing of the tire sidewall when applying a dressing can remove the special anti-oxidants and UV protection provided by the chemicals the tire companies use in all tires.
All rubber, natural or synthetic, loses strength and gets stiff over time. The rate of degradation is also temperature-dependent with the rate effectively doubling with each increase of 18° F. As I have shown in my blog on the use of tire covers sunlight can easily accelerate the rubber degradation by 4 times with 8 times not unreasonable in Southern states. This loss of strength and flexibility can eventually lead to a belt separation, which many sometimes call a "blowout". Maybe that unexplained "blowout" in June was brought about by the eight months of direct sun exposure in Quartzsite, AZ, over the last two winters.

I have confirmed, with temperature measurements, the significant temperature drop with the use of white vinyl covers on Class-B, Class-C and RV Trailer sizes, and the use of a flat mesh "Tire Shades" on Class-A motorhomes. I would recommend against the use of black or dark color solid vinyl covers as they would act more like an oven by both transferring the sun's heat to the tire and preventing cooling air circulation around the tire.


Friday, May 8, 2020

Tire "Dressing" and "do not use covers"! Where's the test data?

Been following a long thread on an RV Forum on the topic of "Tire Dressing" aka tire treatment or "Tire Shine".
The good news is that most posters knew to not use any product that contains Petroleum Distillate. Too bad some RV dealers don't follow the guidelines on this. I have seen a number of display coaches almost dripping with some slippery fluid. Might be Brake Fluid or even motor oil as the tires were shiny and I could scrape the coating off, leaving a "slimy" substance on my finger.

I saw a number of different products mentioned and many suggestions that a product called 303 was a good UV protectant.

I saw no one provide any actual direct comparison test data for any product that would support the claim of protection against UV damage. With a little work getting through the maze of retailers selling "303" I finally made contact with their customer service. I asked "Can you provide any test data on 303 vs other tire protection products. Also info on if 303 application removes any of the wax or oil or anti-ozone chemicals built into tires." The answer was that they would ask their chemists. This seems strange that a company making claims on the performance of their product would not have comparison data available that would back up and support the claim. Please note, I am not saying that 303 does not offer some "protection" against UV damage to tires. I am concerned that the actual application as seen on YouTube may be removing the special waxes and anti-ozinate chemicals tire companies put in our tires.

If I receive actual test data that compares 303 against other products that make similar claims I will post on this blog.

What was most concerning were a couple of posts where the writers claimed
"I got tired of reading all the opinions on tire dressing so went to the source, Michelin. They stated that washing tires with mild soap is the only thing they support on their tires, no dressing no covers, no nothing. You don't see shiny tires at a truck stop and these are the people who put on the miles."
Another said "Goodyear RV tire guide says. Just keep them clean, no dressings, no covers, zip. You can use the same stuff you wash your RV with perhaps use a medium brush on stubborn spots."

I responded:   Interesting comment on "no covers". Wonder what Goodyear RV guide you are looking at? 
I found in THIS Goodyear RV Tire Guide and under storage the advice to store tires "in sunless area" and "Don't store tires where they are subjected to direct sunlight or extreme temperatures".
Based on the above, how does telling us to not use tire covers make sense?
I have confirmed with actual test data that covering tires can reduce the tire temperature by about 40° F which could extent tire life by many months, depending on how long you protect them from artificial heat aging.

I checked and found just the opposite on the shielding from the Sun. In fact I even contacted an Engineer at Michelin and he said "Our position regarding tire dressing and protection has not changed. It is still recommended that tires are cleaned with a mild detergent and water, and they are protected from direct sunlight when the vehicle is parked for extended periods of time. This is usually accomplished with the use of some type of cover. "

So I don't know where the "no cover" info from either Goodyear or Michelin comes from and if you read my blog you know that this tire design engineer is a strong proponent of using White vinyl on Class-B & C tires and the flat mesh of any color on Class-A.

I have nothing against 303. I am wondering why, for the price they don't have any actual direct comparison performance data on UV protection.

PS. If you don't want to protect your tires from the heat aging due to sun exposure please don't ask me to explain why you don't get longer life from your tires. Also next time you run into someone selling an brand  "Tire Dressing" ask to see the test data and see what happens.

Friday, May 1, 2020

Is Moisture in tires a bad thing. Why with RVs?

The question of Nitrogen being used to inflate a tire has been covered in a few of my blog posts and on some other posts on the internet. It is often mentioned that the Nitrogen used to inflate tires is "dry" and so that is considered a positive but I don't recall anyone getting too specific on why "dry" is better than "wet". Before we get into that part of the discussion I want to be sure that everyone understands that any "gas" you buy in a high-pressure tank aka cylinder, will be "dry" as the process of separating the gas and compressing it removes the moisture. So if you were to buy a cylinder of CO2 or Argon or Helium etc the gas would be "dry.
I did a post in May 2012 as one of my early posts on How to get dry air for your tires by making your own air "dryer" for less than $20 for an almost endless supply any time you need it.
There are some companies that sell small cylinders of various gasses but you would also need to have a pressure regulator and a source of high pressure (1,000 to 2,000 psi) gas to refill your tank.

But back to the original question of why do we want to keep moisture out of our tires and why would getting "dry" or at least "dryer" air for our RV tires be advisable. By "Dryer" I am referring to the wet air you can get out of the "free" air at some gas stations where they might not maintain their air compressor or air dryer.

In the past when RV trailers came on Bias or tube-type tires we didn't worry too much about dry air primarily because the tube did a pretty good job of keeping high-pressure moisture out of the tire carcass plus those bias tires did not have steel belts and were probably just Nylon or Rayon cord.

The modern radials we use today are almost all "Steel Belted Radials". So the question is what happens when you "mix" steel and water?  The steel can rust over time. Now in most tires on your car or TV you may drive it almost every day. The driving generates heat and this heat is highest at the belt edge which would be the most susceptible to moisture. This heat tends to drive the moisture out of the tire rubber. However, if you let the tire sit for days or weeks moisture in the air can migrate into the tire structure. Moist inflation air can be driven into the tire structure and over time this moisture can attack the ends of the steel belts and form iron oxide. Rubber doesn't stick very well to the rusty steel so tears can initiate at the molecular level. Once cracks or tears are initiated in a tire they can only grow and if allowed to grow long enough or big enough you can end up with a separation in the tire structure.
Keeping moisture out of the rubber structure is why we also recommend you not park with your tires on wet sand or dirt and the moisture can migrate into the structure if exposed to water for weeks at a time.
Please don't jump to conclusions and say "Ya but I drive in the rain" or "Occasionally it rains and my tires get wet".  I am not talking about a few hours of exposure or even a few days. If you drive and heat up the tires it will drive the excess moisture out of the tire. It is weeks or even months of parking in a wet situation that we want to avoid.
Not inflating your tires with wet air (if you get water drops spitting out of the air hose it is way too wet to use except in an emergency) is what we would like to do. If you remove your valve core and what looks like fog or steam or water droplets spits out you have too much water in your tires and this is under high pressure all the time so this can affect the life of your tires.

Many after market tire sealants are water based so using that stuff can hurt your tires.

So that is why inflating your tires with dry or at least drier air is a good practice.


Friday, April 24, 2020

Contain tire Blowout?

Every few months someone posts a question on one of the numerous RV Forums I monitor, asking if it is possible to prevent the damage done to the RV when a tire fails and has a belt separation or comes apart from a sidewall Run Low Flex failure.

 I have previously written on the idea of trying to "contain" tire failure on my blog but for those that missed the information here is a summary and links for more details.

In the tire industry, we have test drums surrounded by steel grating which weighs 6 to 10# per square foot so don't forget you would need a substantial structure to support a 200# - 500# "shield over each tire position. This extra weight would also significantly decrease the amount of "stuff" you can pack into your RV.
 IMO having worked around tire test labs, an effective "shield" on an RV is unlikely to work. I feel that prevention is a much better approach.

To better understand the problem I suggest you review the following.

1. Read this post.

2. This post shows the kind of forces we are talking about.

3. Check out the safety cage around this tire test machine.

4. Buy, program and test a TPMS

5. Every 2,000 miles or annually (whichever comes first) do a "Free Spin" inspection of trailer tires.

Prevention is much better than and less expensive than trying to protect your wheel wells.

Friday, April 17, 2020

Tire industry magazine announces expansion of SAILUN brand

Modern Tire Dealer, a trade publication posted this information on Sailun brand tires.

  I do know that there are many RVs running this brand in 16" and 22.5" sizes and thought this information might be of interest. 

Sailun Will Expand Passenger, Truck Tire Plants

Posted on March 11, 2020

Sailun Group Co. Ltd. has started major expansions at its production facilities located in Dongying and Shenyang, China.
“The project expansion will focus on plans to equip these additional production lines with the latest cutting-edge manufacturing and testing equipment, as well as increasing IT capabilities to meet domestic and global customer needs,” according to Sailun officials, who add that intelligent manufacturing and the application of big data will be the focus of the both expansions.
“Each facility will be equipped with the world's most advanced production equipment and fully automated tire logistics lines, aimed at effectively enhancing the level of automation, information, and intelligence of core equipment and enhanced AI in the tire manufacturing process.”
The Sailun Dongying plant expansion is a major strategic project for the Sailun Group.
After completion of the final stage, the factory expansion will allow Sailun to reach an annual production capacity of 27 million passenger tires.
The Sailun Shenyang plant expansion will focus on increasing radial commercial truck tire capacity and is also a strategic initiative for Sailun in 2020. Once complete, the plant will have an annual production capacity of more than five million truck tires.

Friday, April 10, 2020

Things to do while not traveling.

Ya it's really a pain to not be able to enjoy our RVs.

But There are a couple of "Projects" that may make life a bit better down the road.

Tire Inspection

Recording your DOT Serial

Testing your TPMS

Reading to increase your general tire knowledge.

First is Tire Inspection. Here we are focusing on possible separations. This is a bit easier for Trailers but also it may be more important for them because of higher separation rate. First off you need to be safe. This means ensuring the trailer or Motorhome can not move. It may be best to hook up the trailer to the TV and set the brakes. Motorhomes can use the parking brake and put the unit in gear. For either type of RV you should block the tires that are on the ground so the unit does not move.  Not everyone will be able to do these steps, but if you can, here is what I suggest.
Jack up one end of one axle (motorhomes this means one end of the front) You then want to place a reference bar or pointer or stick near the tire, then rotate the tire watching the space between the reference pointer and the tire. Do this for the side of the tread and center of the tread. If you can see the relative movement of more than 1/4" you have a suspect tire. Mark the location where the tire is moving outward. you might snap a picture where you can also read the words on the sidewall at the location of interest for future reference. You might even consider a 10 second video that shows suspect movement.  I cover the general visual inspection and have a youtube VIDEO in THIS post.  I have a series of posts with more details on tire inspection HERE.
While Trailer owners can do this for each of their tires Motorhomes are probably limited to just "spinning" the front tire and even then need a HD jack.  Remember if unsure or do not have a solid surface to work on, or the proper tools, you may not want to do this rotating inspection.

If you have a suspect location you should contact your tire dealer. If you have a video you can show them that. Since they can see the tire close up if necessary they are in the best position to confirm there is a problem or to say all is OK.

DOT serial. If you haven't recorded your full DOT serial numbers and kept that information with other important papers, this "downtime" might be a good opportunity when you have a nice weather day. Having this information might save you some time in the future if you hear there is a recall on your tire brand and size. Recalls are based on the DOT sericl and tires will be replaced for free if covered by a recall.

Testing your TPMS.  I bet almost none of you have tested your TPMS. This should be done at least once a year. Some nice afternoon when you have nice weather with your traveling companion in the driver seat. AND when you have access to air of high enough pressure to top-off your tires. Go to each tire and unscrew the external sensor and have the person in the driver seat let you know that they can see and hear the warning for each tire position.  you don't even have to completely remove the sensor. Just unscrew enough to hear air leaking out. As soon as the monitor in the cab sounds you can screw the sensor back in to stop the air leak. Once you know that every sensor works you then need to go around and add back in the 5 psi or so that leaked out.
Doing this will also confirm you have your low pressure warning level set properly as the warning should go off as soon as you lose about 5 psi. I cover how I suggest you set your warning levels in THIS post.

Finally, with all the time on your hands, you might consider simply reading through all the posts on my RVTireSafety blog. I don't expect you to remember everything but I believe that if you have reviewed the entire blog you will then know where you can go to get an answer to just about any question you might have on tires, tire pressure, valves, TPMS, weight and inflation.

Be sure to sign up for the weekly RV Travel Newsletter, published continuously every Saturday since 2001. NOTE By subscribing to RVTravel you will get info on the newest post on RV Tire Safety too
click here.

Friday, April 3, 2020

Side to Side Motorhome weight balance

Got this question and thought that others may have similar problem.

Hi I have followed your postings on this forum and I own 2017 Newmar Ventana 4002. I am trying to understand and resolve an issue with my coach where I have a 1000 lb difference in weight on the front axle side to side. I have had the coach weighed on all 4 corners 3 times and get the same results. My understanding and I think it may have been in one of your post that the difference should never been more than 500 lbs side to side.

I am having a conversation with Newmar about this and pushing them for answers why as I am well under the GAVR and well under the GVWR. I have unloaded and moved the contents in the basement and inside the coach around hoping to make a difference and the reality is I don't have much to move.

I am looking for any studies or evidence that I can show Newmar that this is not safe if indeed my information is correct that side to side should not be more than 500 lbs. I am hoping you might know of something I can get my hands on or someone I can talk to.

Thank you for taking the time to read this PM.

Sincerely,  Newmar owner.

My reply:

You may have misunderstood the side to side weight comments.

It is suggested that people get "4 corner" weights rather than just axle weights, as it is known that some coaches are unbalanced side to side.
We do this because if you only get axle weights and simply divide by 2 and assume your side to side weights are even, you could end up with an overloaded or underinflated tire IF the sides are not close to even.
Not sure where the 500# figure comes from other than looking at the load increments in the tables for each 5 psi. You will see that with some large tires the load capacity can increase by a few hundred pounds with an increase of 5 psi.

I do not remember ever seeing a "should" not be more than 500# different statement

You have confirmed that your coach is not balanced side to side and it appears you have made a good effort to get more balanced but have not been able to because of the design / layout of your coach.

With that in mind, and knowing the load on the "heavy end", you need to consult the Load/Inflation tables and use the heavy end weight to learn your MINIMUM inflation for all the tires on that axle. I still recommend you add 10% to the table inflation number as long as you do not exceed the max inflation rating for the wheels. This 10% helps avoid TPM low-pressure warnings due to an occasional drop in Ambient air temperature 

I trust you have confirmed with your RV Mfg that the wheels are capable of supporting the heavy end load.
I hope this clarifies what you need to do and answers the "Why" we suggest you get the weights on each end of each axle.