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Friday, January 28, 2022

Your RV or car or truck Certification Sticker

This "sticker" has some critical safety information you should know. I don't expect you to memorize all the information but I strongly suggest you snap a picture of the sticker, keep it on your phone, and know where to find it. It has information that is critical when it comes time to knowing the proper tire inflation and when you are shopping for replacement tires.

First the basics. The Vehicle Certification label may be an embossed metal plate or a printed sheet or a sticker. Years ago (before about 2010) the label could be almost anywhere in or on your vehicle. I have hears stories of people finding them in the glove box, in the car trunk lid or on the side of the passenger door. The best I ever heard about was on the inside of an RV closet door that could only be seen if you were standing inside the closet with both the sliding doors closed. It seemed that some felt it was a game of Hide and Seek. Luckily this has changed. DOT now has specific requirements for the information on the label and the location of the label.

Motor Vehicles: Cars, trucks and Motorhomes with driver doors. The sticker must be on the door jam of the driver door. If there is no door as with many Class-A motorhomes the label must be near the driver left elbow and visible from the driver's seat.

Trailers; The label must be on the driver side, outside, toward the front of the trailer.

What information is on the Label:   Tire Size, Load Range, Grose Axle Weight Rating or GAWR and cold inflation of the tires. Many also have VIN along with other information.

Currently DOT requires the inflation be the minimum inflation needed to support the GAWR. As of 2017 RVIA added a requirement that tires be inflated to a level that included a margin of 10% so if your RV MFG certifies your RV to be in compliance the RVIA standards that would be the inflation shown on the label. If tire size or inflation is different for an axle the information must be shown for each axle.

Here are some examples of the sticker found on the Internet.

Us Federal Certification Label - Best Label Ideas 2019 

Some RVs have more than one label

2022 Keystone RV Premier 26RBPR | Camp Rite RV

Below is a label from an SUV

Tire And Loading Information (Tire Placard) | Tire Rack

Winnebago Serial Number | Identify Your Winnebago 


Friday, January 21, 2022

Question about LTX vs. Agilis line of Michelin tires

 Read a question on an Airstream forum:  

 I am replacing Michelin LT225/75R/16/MS2 tire on my 28 Serenity. I am confused ? I am told by the tire dealer that the Agilis CrossClimate has a rough ride. I also read that the LTX tire in not enough for towing. Can anybody help staighten me out ?? Thanks

Load capacity is not a function of the tire "line" but of the type (P or ST vs LT) and Load Range LR-C  LR-D vs LR-E or just XL.

Do not get confused by the "LTX" line as there are both P and LT "types" and there are different Load Range tires in the LTX Line but no ST type which might be what came OE on your RV. Check your placard / certification label.

You should know your actual scale weight of the RV when fully loaded from getting the numbers on a truck scale. Your RV also has a Certification Label (Out side on Driver side, toward the front) that tells you the GAWR.

What ever tire you are looking at it should be capable of supporting AT LEAST 110% of the GAWR with 115% being better, and of course your scale weights should be below the GAWR.

Reports of "Rough Ride" on the Agilis might be from SUV owners with sizes you are not going to run. I would be surprised is you can feel any "rough ride" with a properly balanced set of Michelin tires.

You might want to read my post for a bit more information. 



Friday, January 14, 2022

How old is too old

 I read a comment on an RV motorhome forum:

"I continue to read posts indicating that tires will calendar out, in 5 or 7 or even 10 years. After some searching I have yet to find a technical document regarding tire life expectancy. I'm not interested in sales brochures or salesmen guide lines. I'm looking for a document written by a subject matter expert in the tire manufacturing industry. IMO tire life is more a function of proper storage, inflation, maintenance, environment, and care. I believe a physical inspection by a tire professional is more reliable than an arbitrary date."

So I offered the following:
As an actual Tire design Engineer with 40+ years experience, I believe I can provide some information BUT if you are looking for an answer such as 62 Months 2 weeks and 5 days you are out of luck. It's just not that simple.

Maybe you can tell me, in hours, how long a gal of milk will stay "good". Since you know you can't answer that simple question why do you think the answer for a complex structure such as a tire age should be that simple. Do you think that all 27 basic components age at identical rates?

Most tires fail for one of a couple reasons. You should have read THIS post if you searched on "why tires fail?" I have also covered this in detail in a number of posts on my blog "RV Tire Safety"  But we can cover the topic again.

Polymer Cross Link Density is the property that determines how flexible a piece of rubber is. If it is too flexible or elastic it will not hold its shape. If it is not flexible or elastic enough it will develop microscopic cracks. These cracks will grow with every revolution of a tire and also some will grow simply given enough time.

Heat and time will change the cross link density. The rate of change is not linear but doubles with each increase in temperature of 18°F. This means 4 times if it is 36°F hotter or 8 times if the rubber is 54°F hotter. This is why tires that are on RVs that spend most of their life in Southern Tier states like FL, GA, TX, AZ will fail earlier than tires that spend most of their time in ND, MI, NH, ID, OR. But a tire that spends it life in Phoenix will "die" in maybe 4 years an identical tire that spends it's entire life in Flagstaff may live to 8 years. But there are other factors that can have significant effect on tire life.
If we were to put a set of tires on a LT and another identical set on a 4 tire trailer, then load all 8 tires to identical load and inflate to identical level the tires on the trailer may have a life that is 25% to 50% shorter than the tires on the truck. This is due to Interply Shear which is the force in all radial tires at the belt edges that is trying to tear the tire apart from the inside (see "Interply Shear" if you want to see my posts on that topic.

This post is on a Class-C thread but I can guarantee that information published here will be incorrectly applied to information on a TT thread because people do not understand the significant different forces internal to a tire.

Michelin has published a guide on tire inspection which basically suggests at 5 years the tire be inspected inside and out annually and re-applied if no problems are discovered. BUT they still put a MAXIMUM life on the tire as unless you have "X-Ray" vision the structure can have cracks that are not visible on the tire surface, even not visible on the internal air chamber surface.


Friday, January 7, 2022

What's the best tire for my trailer?

 We have all probably seen this question on an RV forum or two. The problem is that many people have their personal choice but I doubt that any person has ever done any extensive controlled testing. If you think about it, why would anyone have a favorite brand but would be running a different brand unless forced?

As a tire design engineer I always depend on facts and data, and try and stay away from just an opinion. However since there is no way I can do a comparison of dozens of different brands in dozens of different sizes I do have to fall back on "opinion".  BUT if we think about tire performance and durability in general I think we can come up with some information that can guide us to a shorter list of potential choices.

All tires have a "Material List" molded on the sidewall. Based on this information plus a few generalities I think we can develop a plan.

Looking at your current tires you will see what materials are in your current tires. I suggest you write the information down so you can keep the information organized.

Lets talk about tire construction.                 Modern ST type radials will usually have one or possibly two ply or layers (we can use the terms interchangeably)  in the sidewall. The material used is usually Polyester. They will also have two ply of steel belts in the tread. Now this is the important detail. Some tires may also have one or two ply of Nylon or some other material in the tread in addition to the 2 ply of steel. This is the important part.

Radial tires have a high stress location at the edges of the belt. I have a number of posts on my RVTireSafety blog that focus on this force (Interply Shear) and location.  Here is the most important one

One way that tire companies can address the Interply Shear and end up with a tire that might perform better on the special tests like High Speed that tires need to tolerate if they are going to have a higher "Speed Symbol" marking is to add a ply of Nylon on top of the steel belts.

Now the problem you as a consumer face, is that not all tire companies report the materials in their advertising. But the good news is that the information molded on the tire sidewall must, by law, be accurate. So if the tire says it has Nylon ply it must have the Nylon. Now a performance improvement is not guaranteed but in general, it is likely that tires with Nylon ply above the steel belt edges can have lower Interply Shear forces which should perform better and possibly longer. So lacking any other data, I would use the Nylon as a plus for a tire if I were considering two different brand tires. 

You may need to talk with a tire dealer and possibly need to confirm yourself what the material list on a tire actually says.

Bottom line:

You can confirm which ST type tire you are considering has the Nylon cap ply and which does not. If they are different then it is possible that the tire with the Nylon might be a better choice. Please remember that this is not an absolute, as without actual performance data we can not be certain of the future performance. But this is something we can consider and this data is better than just a wild guess.