Stop using "one-size-fits-all" tire pressures - a science based guide to the right tire pressure

[C-Mack]

i updated it.
here is a summary:
Made sure i picked the right Grenadier tires.
Re-did the calculations for larger tire volumes = lower tire pressures needed.

Also, redid some sidewall calculations to ensure that speed and lower pressure is compatible with side wall structures leading to an minimum speed floor for PSI.

made a point that these are minimums.

Perfect thanks for making those updates.

 

[HereinDaRockies]

Tire temp - is the off-road page’s wheel temperature a good proxy for tire temp ?

 

[parb]

i think you're asking for the highest tire temp you should be on the watch for?
I would try to keep it at 170F or lower, and lower my speed immediately if they go at 190F.

 

[HereinDaRockies]

i think you're asking for the highest tire temp you should be on the watch for?
I would try to keep it at 170F or lower, and lower my speed immediately if they go at 190F.

No i meant how to monitor tire temp.

The off-road screen that shows the tires’ psi, also shows temp. Is that temp a good measurement of tire temp ?

 

[parb]

TPMS temp is good but can be misleading. If you brake heavily it may show a false positive (eg heat from the brakes seep into the rim and heat up the tpms. Equally air is an insulator and since the tpms measures air it may take a while before it updates. But eventually it will be correct and show you the tire temperature if its consistently hot.

having said all of this i think TPMS is a decent indicator and i would try to keep the temps under 170. at 180f i would investigate. at 190 i would stop the car and let the tires cool down. an IR temp sensor on the sidewall would be more exact than a tpms.

at 200F and above is when i think sidewalls starts deteriorating for real and i would not want to be over 190F.

Overheating the tires and getting blowouts from tire deterioration due to heat should only be a concern mostly when driving at higher speeds. This is especially true underinflated at higher speeds (typically the speeds you may use on gravel roads and highways).

 

[Rok_Dr]

In my experience the tyre temp monitoring of the TPMS is fit for purpose.

I’ve been monitoring my temperatures, particularly on longer trips, for a while now. Provided the tyre pressures are correctly set for the loads carried, I’m seeing an approximate 20°C increase in tyre temperature over ambient air temperature. There will be some variation, for example tyres on the sunny side will have a higher temperature compared to the shady side.

Cheers
Steve

 

[NQ94]

Nice work, that is a comprehensive document.
I work with specialist off road truck and machinery tyre fitters regularly and they use similar information for tyre management.
With the off road quarry type truck fleets we measure tyre pressure and temperature religiously to the point our GPS based TPMS system transmits each trucks data back to the workshop office and sends texts for any overspeed, high tyre temperature, or rapid pressure change related issues. I am pretty sure the system can also geofence data to certain roads and corners. The company uses heavy off road high impact tyres for rock which have to be preordered and may only have one production run a year so tyre management is critical. In some tasks we have to reduce the pressure and lockdown the maximum speed to protect tyres on long loaded off road runs or extended downhill operations.
We tend to work to around that 94°C 200°F mark absolute maximum temperature for steel belted tyres before we park trucks up to cool tyres. Tyres are vulcanised starting around 130°C 270°F during production if a tyre is allowed to get near this temperature during operation from over flexing there is a good chance the vulcanising process may reverse and tyre separation or delaminiation may occur during operation.
The tyre fitters use a Ton-Mph (Tonne-kph) formula to predict tyre temperatures, pressures and road speed. It is calculated using tyre data from the manufactures and a fill in the box software from the tyre manufactures.

These calculations and recommendations take into account a number of factors and these can be applied to any tyre.
• Average tyre load
• Average speed
• Expected ambient air temperature
• Road temperature
• Observed or expected road surface type and condition

With over heated tyres we park in a safe location away from people, never approach the tyre from the side wall and let the tyre cool or if safe deflate it before removing it. There is a lot of energy in an inflated hot tyre and a zipper failure between the side wall and tread can injure or kill. For excessive over heating we have a tool we put on the ground and drive over to deliberately puncture the tyre for a quick deflation. For us if the tyre has been excessively hot and at around 70% recommended operating pressure for the task it is immediately scrapped. Every tyre should be dismounted from the rim and inspected internally if it has been overheated.