Is there a critical do-not-exceed tire temperature?

5

RV Tire Safety

with RV tire expert Roger Marble

Question:
Hi Roger,
I just read your article on sidewall strength and “blowouts.” You mentioned that if the temperature rises too high the sidewall cords may melt. I have a 2017 Winnebago Grand Tour with a built-in TPMS system with pressure and temperature sensors. Most RVers know (or should know) to keep their tires at the proper inflation level. The one thing I haven’t seen addressed is tire/air pressure temperature.

As I drive down the road I can watch the pressure rise with a corresponding temperature increase. Is there a critical temperature to watch out for exclusive of tire pressure? If so, I’m sure it would be different for each make/model and tire size. Do manufacturers publish any specific data for their tires (i.e., a critical do not exceed temperature)? Thanks for all you do to keep us in the loop. —Ken

Answer:
Ken,
If you check out the posts on my blog you will find numerous articles on tire temperature and pressure.

Regarding critical temperature: For short term (minutes or seconds), I would consider structural temperatures in the 205 F – 230 F to be critical. Size, brand or design – doesn’t make much difference. The problem is there is no way to measure the temperature as the  hottest location is at the edges of the radial belts. In racing, like at Indy, we use a needle probe and stick this into the tire about 1/4″ to 3/8″ deep.

External surface temperatures are much cooler because of external air moving over the surface. With rubber being such a good insulator, the heat does not travel to the surface fast enough (minutes) relative to the ability of the temperature to rise (seconds) at the critical location we see it, so it’s possible to have internal rubber failure before the surface temperature gets to a critical point.

I think you can understand that the rubber can get softer with an increase in temperature. As it gets softer, it stretches more, and as it stretches more it gets hotter, etc. Up to about 210 F, this increased softness can be managed with construction and thickness design changes, but each of those changes can result in some other property getting worse. Also, that 210 F point changes with time and temperature history.

Tire design is a balancing act and a series of trade-offs. One thing that happens with a loss of strength and increased bending is the potential for tearing of the rubber at the molecular level, which can result ultimately with the tearing to grow to the width of the belts, which in turn results in a belt separation.

BUT the key thing to understand is that temperature damage is cumulative and the chemical reaction that occurs can eventually result in a loss of elasticity at higher temperatures so the rubber tears, which leads to a separation. The rate of these changes can itself change over time and the rate is also affected by the temperature.

Even for a single rubber compound, there is no exact temperature for it to “fail.” The physical properties of rubber changes with temperature, but here there is no exact point at which the strength goes from 100% to zero.

A TPMS gives an approximate temperature of the air inside a tire, which is also lower than the critical temperature. Most TPMSs have a high-temperature warning set to 158 F, and if you see that reading then you do not have enough pressure for the load you have or are driving too fast. This does not mean you can lower pressure till you see a reading of 158 as you are still doing damage and “consuming” the finite life of the rubber in a tire.

Read my blog, learn the actual load (when the RV is its heaviest) for each tire position (4 corner weights), consult the tables, learn the MINIMUM inflation pressure, add a +10% inflation margin to learn your “cold set pressure” for each axle based on the heaviest axle end, and adjust your TPMS low pressure level to never be lower than the minimum. Then go and enjoy your RV.

 

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

 ##RVT903

 

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ken kausner
1 year ago

Hi Roger
I read all your articles and appreciate your practical advise and training backed with engineering and racing background.
My question is that I do not see much emphasis on lug nut torqueing. I had the misfortune of losing a tire from my 33 foot 2017 Crusader fifth wheel, duel axle RV. We were travelling south on route 95 in Florida on a clear Saturday afternoon. We traveled close to a mile after losing the tire, but I felt no vibration and did not actually realize it was gone, except for someone yelling from their car window at 65 mph. Fortunately no one was injured and had great assistance from the local sheriffs department and road service who was able to replace the 5 damaged lugs. I realize wheel nut torque should be checked and I was thinking about that 2 hours prior, but rationalized that my dealer just checked the brakes and bearings packing 800 miles ago. Your comments please.

Roger Marble
1 year ago
Reply to  ken kausner

Ken, If you check your owner manual you will find info on checking lug nut torque. While not all Rv trailers have identical numbers most say to re-check torque at 100 miles after wheel service. Others say check torque before each trip. I definitely would agree that after a wheel has been off the RV the lug nut torque should be checked every 100 miles till you have two checks with no lug needing any additional tightening. IMO a dealer should have reminded you of the need to check nut torque after the service.

Roger Marble
1 year ago
Reply to  ken kausner

I now have a blog post in the works for publication in a couple of weeks. If you keep your eye on my blog http://www.RVTireSafety.net you will see the info. RVTravel .com will also post when the Lug Nut torque post is available.

Wolfe
1 year ago

I set my TPMS limits by history… my tires normal rise 8psi and max out around 110F on hot days. I SET 10psi above spec cold pressure and 120F. Baking in the sun parked can heat the sensors close to the 120, but the senders cool once rolling again.

Roger Marble
1 year ago
Reply to  Wolfe

Your plan sounds reasonable. You might check out my TPMS setting suggestion on my Blog http://www.rvtiresafety.net/2017/08/how-i-program-my-tpms.html