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RV Tire Safety: All about tow vehicle tire wear and TT tire inflation

By Roger Marble
Below is a question from the owner of an Airstream. My answer below that would apply to other brands of tow vehicles and travel trailers.

After driving my new trailer home from the dealer, a 316-mile drive, I was alarmed at how badly things got shaken up. I noticed that Airstream recommends one tire pressure for all models and all loads. So I got on the Airstream forum, contacted Airstream, and contacted Goodyear. Airstream offered no logic for their 80 psi recommendation, even though I penetrated fairly deep into the organization. “80 psi is on the placard and that’s our answer.” Goodyear referred me to the chart we all know, but also discussed my concerns for the ride and my expected travels with my trailer. We concluded 40 psi.

I tow my trailer with a Mercedes GLE450. I have a 600 lb. equalizer hitch.

I follow Mercedes’ tire inflation recommendations – going from 36 psi front and back for normal load, to 39 front and 50 back at full load. I ran the rig fully loaded over a CAT scale and for the life of me can’t find the numbers – but I remember I was very pleased with them. I was 150 lbs. under max payload for the car and well under the GVWR for the trailer of 6000 lbs. The equalizer put all the weight back on the front wheels, confirming my wheel well to ground measurements.

I have now put 11,000 miles on the rig since March. I compared tread depth using an improvised depth gauge. I cannot detect any difference across the tread, from RF side to LF side or front tires vs. back. However, I cannot claim great resolution.

I’m happy with the wear on the tires. I’m thrilled that things remain in place even when driving unmaintained roads. So take that for what it is worth.

I do have a question for the group. The rear tires of my Mercedes are very close to the wear bars, while the front tires show very little wear. I’m disappointed that the dealer did not catch this during the “A” and ‘B” services. Rotating or even inspecting the tires is not included in either service schedule. The car has 33,000 miles and was purchased in March.

Am I too late to rotate them? Or just buy two new tires for the back and be sure to rotate sooner?

My response:

The rear axle tread-wear on the tow vehicle (TV), especially with the OE spec tires, is almost always going to be lower than the same vehicle if not towing. OE tires tend to not deliver the same wear mileage as replacement tires.

Towing results in more drag, so more “tractive” (power exerted in pulling) force is required, which results in increased slip, which means faster wear. Increased load on TV tires will also result in faster wear. Finally, since fuel economy is a requirement for the car company to meet federal standards, that is one feature that tends to be lower on the tire design “want” list. It can be behind wet traction, snow traction, steering response, noise and dry traction.

The rubber formulation is a compromise of various performance parameters. Tire design engineers have to select the compromise that meets the goals as established by the car company. If tread wear is important to the car owner, then you can look up the Uniform Tire Quality Grade (UTQG) wear rating number published by the tire company. Select your replacement design to have a higher wear rating, while remembering that you will be giving up on one or more of the other performance goals that are not identified in the UTQG list. You can learn more about UTQG HERE.

When looking at UTQG numbers for different designs or “lines” of tires, people need to remember that the ratings are not absolute. Also remember a comparison of UTQG numbers between two different tire companies is not always reliable. Different companies use slightly different statistical models when developing the UTQG numbers. I have even heard of companies putting lower numbers on a line for marketing purposes. BUT this comparison is better than nothing or simply shopping on price.

Tire rotation, especially when towing with an SUV or car, can result in better overall tire wear. My general recommendation for a tow vehicle with 4 of the same tires, rotation schedule for non-directional tires, is to rotate using “forward-X” pattern at first oil change. Then rotate again at the third oil change, and again at sixth oil change and, if still good, at the tenth oil change. I suggest this sequence as tire wear rate slows down as they wear and the first and second rotation are most important for minimizing irregular and rapid wear – which are more likely in tires with deeper tread depth.

Here is some information on tire rotation from Tire Rack

Concerning the travel trailer tire inflation

The inflation specified on the certification sticker, by regulation, must be sufficient to support 110% of the GAWR for the tires selected by the trailer company. When you run lower inflation than what the tables say is required to support 110% of the actual scale measured weights, you are shortening the TT tire life and may end up with failures earlier than what other owners are reporting.

 

Read more from Roger Marble on his blog at RVtiresafety.net or on RVtravel.com.

 ##RVT1022

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Kip
1 month ago

We should not just arbitrarily decide how much air we want in our tires.

I’ve been told by various tire dealers that SP TRAILER tires should be run at the “Maximum PSI” Shown on the side of the tire. If there is a manufacturers document available showing reduced PSI for reduced weight, that can be used. The construction of SPT tires is different from truck or Car tires.

Reduction of PSI is inviting real problems, especially if a blown trailer tire results in a wreck, resulting from owner’s neglect.