Tow vehicle tire wear and TT tire inflation

 A question from the owner of an Airstream. My answer would apply to other brands TV and TT.

"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 pressure for all models and all loads. So I got on the Airstream forum, contacted Airstream, and contacted Goodyear. Airstream offered no logic for there 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 40psi.
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 was very pleased with the numbers. I was 150 lbs under max payload for the car and well under the GVWR for the trailer of 6000. 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 can not detect any difference across the tread, from RF side to LF side or front tires vs back. However I can not 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 schedules. The car has 33,000 and was purchase in March.

I'm I too late to rotate them or just buy two new tires for the back and be sure rotate sooner."

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

Towing results in more drag so more tractive force is required which results in increased slip which means faster wear. Increase load on TV tires will also result in faster wear and 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 and can be behind Wet traction, Snow traction, steering response, noise and dry traction.

The rubber formulation is a compromise of various performance parameters and 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 UTQG wear rating number published by the tire company and 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 and a comparison of UTQG numbers between two different tire companies is not always reliable as 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 a SUV or car, can result in better over-all tire wear. My general recommendation for TV with 4 of the same tire, rotation schedule for non directional tires is to rotate using "forward-X" pattern at 1st oil change. Then rotate again at the 3rd oil change and again at 6th oil change and if still good at the 10th oil change. I suggest this sequence as tire wear rate slows down as they wear and the 1st and 2nd 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 TT 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 TT tire life and may end up with failures earlier than what other owners are reporting.

 

##RVT1022

Gage Accuracy, Rotation, Alignment, Fuel Economy

Went back and tried to review comments and questions. I know some have been answered in depth but some others maybe not enough to make the point clear so here are some short replies and thoughts.

May 15 Quampers asked about tire gauge accuracy.
Quampers, I currently travel with two digital gages that are accurate to 0.5 psi when compared to ISO certified pressure gauge in a tire testing lab. I can compare readings between these two gages and as long as they are within 1.0 psi or less of each other I can be pretty confident they are still giving me the correct pressure. I will have the gages checked on a two year cycle even if I find no change in their readings. These are the gages I will use to compare to others at my Tire Basics seminars. FMCA at Madison, WI Aug 11 and at Gypsy Journal Rally at Celina, Ohio Sept 27.

June 25 Tom asked about tire rotation and where to put the newer tires if you don't buy a complete set.
I have heard it said by others that if you don’t have a problem with irregular wear on your RV you don’t need to do an alignment or rotate tires. I guess that may be true as long as 1. The manufacturer of the coach bothered to do an alignment at the end of the assembly line and 2. You keep a close eye on the wear of your tires.
Now I can tell you that in my experience it appears that some manufacturers may be cutting corners when it comes to spending the time to set the alignment. After all your warranty is only good for a year and in that time most RV drivers will not get enough miles on their tires to see alignment problems. The second point is that even if you do complain the mfg will probably tell you it is your responsibility to ensure the coach or trailer is in align, even though there is no mention that as a new owner one of the first things you would need to do is to drive your new rig to a heavy duty alignment shop and do the work the manufacturer should have done in the first place.
When it comes to the question of where to place the new tires there are a couple of things you must consider. If your RV has dual tire position you need to be sure the Outside Circumference difference on a pair of tires in dual position is ¾” or less otherwise there will be more load transfer from one tire to the other than is advisable. Not Outside Diameter buy OC which is a more accurate measurement to get if you don’t have special tools. So for Tom it will depend on how many tires he needs to replace as to where they go.
When I recently rotated my tires because of miss alignment on fronts.
They looked like this in inner shoulder and this on outside shoulder













I measured all seven tires (including spare) then put the most worn tire as the new spare. It worked out that the still new original spare ended up on the front and I was able to match my duals to within ¼” for each pair.

Now if we are talking about a passenger car the two new tires should go on the rear to give you better wet traction and decrease the potential of a rotating skid and spin-out in an emergency. This is less of an issue for heavy RVs due to the weight cutting through the water better.
On multi axle trailers I would put the new tires on the front as this location is less likely to suffer a puncture and if you are going to lose a tire due to puncture I would rather lose the older tire. Hope this didn't confuse too many people. As you can see there are a number of things that need to be considered.


June 29 Bob asked about LRR or Low Rolling Resistance
LRR spec tires are designed to trade off a number of performance characteristics to improve fuel economy. Rolling Resistance is the force it takes to roll a tire under load. The more force the more energy needed to make the vehicle go down the road. I have not heard of LRR tires in RV sizes yet as most of this work is aimed at Hybrid cars getting 40 MPG or more.