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

Is better tire wear AND better fuel Economy possible?

 We all see posts from people wanting better tire wear and better fuel economy. Here is some information from a friend "Dr. Joe"

Wear, traction and rolling resistance are interrelated (but adjustable) factors determined mostly by tread material properties fixed during the design stage of tire development. The rubber chemist's enduring dilemma has been that enhancing one tread attribute influences the other two – usually adversely. Marketing professionals tend to use the term “balance” rather than “tradeoffs” to describe these conflicting variables. Based on my reading of recent industry press releases, tire wear and traction seem to be playing “second fiddle” to rolling resistance in today’s push for “greener” tires – even though fuel efficiency has not been a top priority for US consumers. It is, however, well known that good tread wear resistance is important to motorists purchasing replacement tires. Contrarily, because of CAFE mandates, OEMs consider tread life subordinate to rolling friction in their procurement of new car tires. Unarguably, any decrease in wear out mileage increases the frequency of tire replacement and unwelcome scrap generation.
Tire traction, nonetheless, is important to safety conscious motorists; it is constrained by road conditions which control traction limits encountered by given tread compounds and patterns. These can be optimized for wet, dry or snow performance. While over 80% of tires in service in the US are rated at the UTQG traction level “A”, only 15% are rated at the highest level “AA”. Surprisingly, no real-world data exists indicating that tires with higher rated traction grades are less involved in highway accidents than lower rated ones – with snow tires an exception as they are not UTQG rated, For improved all-weather traction, so-called “rain tires” have been touted on-and- off over the decades, and promoted extensively by U. S. Rubber (now Uniroyal) beginning in 1965. Wet grip was achieved, then and now, by sacrificing tread wear. While this is an acceptable trade-off in Europe, US consumers have consistently rated long tire life more important than tire grip; and with relatively cheap fuel, rolling resistance tends to be a non-issue for individual tire buyers. The most common reasons reported by the influential Consumer Reports (2019) for selecting a particular replacement tire brand are price (44%), tread life (40%) and brand trust (31%). Similarly, the respected J. D. Power new car owner survey (2021) rates the top three tire satisfaction metrics as wear, ride and traction (in order of importance).

Regarding tread life, surveys of large numbers of scrapped consumer tires usually show that the majority are three to four years old when replaced. Since Americans drive between 11,000-12,000 miles per year on average (according to FHWA), this means that most passenger car tire wearout mileages occur between 33,000-48,000 miles. If light vehicle tire lifespans could be increased an additional year, demand for new tires would be reduced with lessened environmental impact. Also, tires become more fuel efficient as they wear. I wonder what an environmental and economic cost-benefit analysis of tire life extension might yield? Mainly due to existing and proposed government mandates, US consumers have been, or will be, forced to unwittingly accept reductions in tire life with increased costs in concert with lower rolling resistance. Then we encounter further demands placed on EV tires – which need improvements in tread wear, traction, and rolling resistance compared to their ICE powered counterparts. Additionally, the
California Energy Commission once again announced plans to implement a program to ensure that replacement tires sold in that state are as energy efficient as OE tires. This will only exacerbate the confounding situation facing consumers valuing tire life.
Ponder Michelin’s transitional development of the radial tire after WWII. Wearout mileages were doubled while rolling friction was reduced by 25% compared to existing cross-ply tires. Could the industry now develop tread compounds and/or tire constructions that at least make desirable improvements in both wear and rolling resistance without comprising grip? Unexpectedly, Bridgestone, Arlanxeo and Solvay have just announced material technology that claims to achieve just that; up to 30 percent better wear efficiency and six percent reductions in rolling
friction. Hopefully, this technology will be licensed to others if the claims are justified.

Joe Walter enjoys teaching Vehicle Dynamics and subjects related to tire materials and mechanics at The University of Akron. He previously served as Vice President and Director of Bridgestone Americas Research Center in Akron and President of its European Technical Center in Rome. Joe obtained graduate and undergraduate degrees in engineering from Virginia Tech a long time ago.

While Dr. Joe's article is aimed at the passenger and light truck vehicle market you can be assured that as new technologies are developed in one sector of tire design the features and advantages soon spread to other product lines. 

##RVT1010

Question on tread scrubbing on trailer tires.

Got this question:
"I have a question regarding interply shear or scrubbing common on double or triple axle fifth wheels. I have a double axle and try to avoid sharp turns and U-turns as much as possible, but I see visible signs of scrubbing on the tread of my tires. It looks like flat spots on the edge of the tires. After a turn, I can go back and see the rubber I've scrubbed and left on the road. It's frustrating. I have the axles aligned and tires balanced once a year and have individual wheels weighed occasionally. I try to keep side-to-side and front-to-back weights within a couple hundred pounds. I currently carry 85%-90% of load capacity, or about 3300-3400 lbs per tire.

"My question is: Would going to the next load range up (from G to H) or going to a harder compound tire reduce this problem? I currently use Goodyear G614RST tires, size LT235/85R16. I've heard in the past that Michelin uses a harder compound in their tires, which makes for a little stiffer ride, but might this overcome some of the effects of scrubbing? I feel I could get a lot more miles out of my RV tires if I could reduce the flat spots or sculpting caused by unavoidable scrubbing."

My answer:
Axle alignment or wheel balance isn't the problem. There is a sketch in this post on interply shear that shows why the tire tread scrubs. The center of tire rotation is not pointed to the center of the turn radius so the tires are always being dragged around every turn. It is just worse on tight turns.

Lowering the percentage of max load capacity is a good idea. Don't forget that it is the air pressure that determines the load capacity not the Load Range (G to H). You will gain nothing from a Load Range change if you do not also increase the air pressure. You do need to confirm the wheel max psi capacity which, for some wheels, is not easy to do as some wheel manufacturers do not have high pressure ratings easily available.

Regarding tread compound: Sometimes it isn't just the hardness of the rubber but also the tread pattern that can affect scrubbing wear.

In general, the tread scrub is a function of dragging a trailer around.

Send your questions to me, Roger, at Tireman9 (at) gmail.com


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##RVT783

How old is too old?

Been following an RV forum thread on tire age and have been trying to explain why there is no strict guideline for exactly when a tire should be replaced. I summed up my position...


The general guidelines for motorhomes is to have the tire inspected starting at about 5 years and to replace at 10 years no matter what the inspection indicates. Due to the Interply Shear effects on belt durability, trailer tires need to be closely inspected after a couple of years and it appears that 5 years may be the max life for most applications.

I do understand that people would like a nice clear precise answer but the problem is that with load, speed and temperatures all having an impact on the life of a tire it is impossible to give a precise time of when to replace a tire.

In today's society no company can give a specific answer to the question as they would be sued if a tire failed before the "end of life" time and they would be sued if the tire lasted past the "end of life" time. We are talking about probability.

You have a sticker on your RV telling you the inflation to use based on an estimate of how much "stuff" you will be carrying. Federal Regulations say the tire load capacity at the specified inflation must be able to support the load rating of the axle. This assumes an exact 50/50 side-to-side load split all the time. It also assumes you do not put more or less load in your RV than what would result in each axle being exactly at GAWR. Many have learned of the importance of getting the actual load on each tire.

Maybe it would help if we thought about tread depth instead of age.

Exactly how much tread can be worn off before a tire becomes "unsafe'. Most states say 2/32" for passenger car tires but does that mean the tire with 3/32" tread will always perform equally to a tire with 10/32"?  Of course not. As the tread wears the wet traction capability goes down. Do you always wait till each tire gets to 2/32" before replacing it? If not, why not?

Conversely the dry traction can go up as tread depth goes down, so there is a trade-off. I dare say that if you live is an area with lots of rain or even snow, you probably change tires before they are that worn. However, if you live in the dry Southwest you may be tempted to run less than 2/32" tread as you have seldom if ever have wet traction problems.

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