Tire temperature

[caymann]

I assume some of you are using the various Tire Pressure Monitoring systems out there such as Pressure Pro, Hawkshead, TST etc

Most times you probably only look at tire pressure or use the alarm for tire pressure.
Has there been an instance when you had looked at tire temperature instead because the temperature alarm kicked in?
Example: The pressure going on the road was (say)115psi but the temperature was at (say) 200F and hence you had to pull over.

[mythplaced]

On my TST the tire temp has never gone over 125....

[GaryKD]

Hi cayman,
Nope, only PSI does it for me.

[BryanL]

I watch the temps at most stops for fuel or breaks. One time I noticed a tire that was about 40F hotter than the others. It had a slow leak and needed repair. I caught it before blowout time which saved me a lot of grief and expense.

Tire materials start to degrade at about 180F and should run at no more than 120F to 140F. The sunny side in desert conditions may run 10F to 20F hotter than the shady side in my experience.

If your tires run much below 120F, they may be a bit overinflated. This is not necessarily a bad thing as the only downside in nominal conditions is a bit of extra center tread wear and that isn't usually an issue as most RV tires need replacement due to age rather than mileage.

You can only reliably measure PSI when the tires are at ambient temperatures (i.e. after sitting for a few hours without the sun on them). The general advice is that should be done every morning while traveling.

Temperature can easily be measured with an IR device and is a good way to detect problems early while en route. If a tire runs hotter than the others it is saying it needs air.

[caymann]

The reason i ask this is, Smartire website says...LINK

As a tire deflates, its rolling resistance increases and its operating temperature goes up. As its temperature increases, the air inside the tire expands so the tire appears to be operating at correct inflation. When measured using a non-temperature compensated gauge, a tire can be 30% under-inflated and still appear to be normal.

So TPMS system that rely only on pressure is not going to be enough.
If you have a Pressure and Temp readout, the above situation can be avoided.
Is this correct?

[BryanL]

re: "As a tire deflates, its rolling resistance increases and its operating temperature goes up." -- this is true, which is why you can use temperature as an indication of proper tire inflation. Think 'sidewall flexing' as being the main source of rolling resistance. Less air and the sidewall flexes more and that generates more heat.

If the tire has no leaks, there will be an equilibrium point where the temperature stabilizes.

If the tire leaks, it will get hotter and hotter until it fails (unless you stop first).

The relationship between temperature and pressure in a leaking tire can be a bit complicated. If the leak is fast, the drop in pressure will be the first symptom. If the leak is slow, then temperature rise will be the first indication.

[Cruzer]

That's one of the reasons I went with the SmarTire system. As the tire heats up the air expands and the pressure increases. A TPMS that does not monitor temperature won't be able to accuratelty tell if the pressure is correct. Eventually, if there's a leak, it'll get there and warn you but not for a while. The nice thing about the SmarTire is that it reports pressure, temperature, and pressure differential. It uses temperature compensated logic to determine ehat the true air pressure should be at the current temperature.

For instance, a 98 PSI cold tire that should be properly inflated to 100 PSI is underinflated by 2 PSI. You drive down the road and the tire heats up to 90 degrees. The SmarTire now shows 102 PSI as the tire pressure. Tioggling through the display shows 90 degrees as the temperature and -2 as the pressure differential. So that shows that you should have 104 PSI, not 102 PSI at that temperature. As the tire continues to heat, say to 115 degrees, the pressure will increase to maybe 112 PSI but the differential will still remain at -2. The low pressure warning are based on the pressure differential so you'll still have a -2 PSI reading on the display wheras other brands will think it's just fine and actually 12 PSI over, which is false. Warning usually go off at 10% pressure loss so a competitive system probably won't warn you until it sees 90 PSI, which is about a 22 PSI drop (or more as the tire heats up from low pressure) rather than the 10 PSI recommended warning level.

I've never had the high temperature alarm go off. The main use of the temperature sensing is to create the dynamic temperature compensated pressure tables that the system uses (as previouslty explained). It acn have value in that it would report if a brake was dragging or a wheel bearing was going out because that heat would be transferred to the wheel rim. Although, the odds of that happening are slim.

I do check the temperature differential when driving just to see where Im' at. If a certain tire is -2 PSI I know that I need to add 2 PSI to it one of these days. I can then check it with a gauge and add 2 more to whatever is in it regardless of what the temperature is. I no longer have to make sure it's a 60 degree day and the tire has been sitting, out of the sun, etc.

Every now and then I check the tire temps when driving because it does tell me a thing or two about my tires. If one tire is hotter than the other there's a reason for it. Chances are the pressure I'm running in that tire isn't adequate for the load I'm carrying and it's working harder and getting hotter than the rest. Coaches are not symetrically designed. Batteries re on one side, LP tank on the other, fridges not centered, etc. I may need to readjust my tire pressures or get a good 4 point scale reading to see where I'm at. It also will vary a bit depending on the crown of the road. Heavily crowned roads will create more heat on the right side. The right inner dual is always hotter than the outer dual for that same reason - roads just aren't that flat.