Some Tire Temp Info
I have some familiarity -- if not, alas, expertise -- with many of the sub-topics discussed in this thread. I think I can provide some useful resources for anyone really interested in learning more, though.
[Note: I don't know how many posts I have to have here to be allowed to post links. And I only post here every few years, so it could be awhile. If you want to follow any of the things that seem similar to links, well, I bet you can figure it out.]
1) LDR Workshop Article:
Tom Austin, IBA Chief Technical Advisor, has this "Tire Pressure Monitoring" article (date of publication unknown) on the web:
dubba dubba dubba dot ironbutt.com/ibmagazine/IBMag4-p76-83.pdf
This is an eight-page PDF file, and contains a wealth of information, and I think those who are serious about gathering information on this topic should read it.
On the second page is a nice chart that gives examples of "The Effect of Temperature on Tire Pressure."
Mr. Austin also has this to say, early on:
"During summertime weather, the air temperature inside the rear tire of a motorcycle running at freeway speeds may be 150°F or higher. If the tire pres- sure was set to 40 psi after the bike had been parked overnight at 60°F, the tire pressure would rise to 49.5 psi when the tire temperature increases to 150°F. On a heavy touring bike, like a Honda Gold Wing, the rear tire temperature can easily reach 180°F at freeway speeds on a hot (90-100°F) summer day. A tire set at 40 psi in the cool of the morning would increase to 52.6 psi. It’s difficult to find published specifications on the maxi- mum “safe” tire temperature, but, based on the warning levels used on two different TPMS brands, 176-194°F is as hot has you would want to run."
2) Tire Warmers:
You may want to look at some tire warmers, to gain additional information in a roundabout way.
For instance, if you go to ...
dubba dubba dubba dot motodracing.com/pro-series-single-temp-tire-warmers
... you will see that it can be set as high as 185°F. Of course, as a result of conduction losses, the air inside the tire may not actually get to the same temp, but it will be very close.
In any event, this should give you an idea that tires can handle much more heat -- and hence pressure -- than you might think after glancing at the max (cold!) PSI figures on the side of a tire.
3) Motorcycle Ads:
Take a look at this video, for instance, by Husqvarna of its 701 SUPERMOTO (from 2015):
dubba dubba dubba dot youtube.com/watch?v=tGh_OHlpg3Q
At 0:54, the graphic shows 84.2°C as the TYRE-TEMP. That's 184°F for us non-metric folk. At least in the video, the tire does not explode.
Note that motorcycle tires will undergo a much more dramatic change, in terms of the temp of the air inside, than car or truck tires. This is because, well, I'm not an engineer, but I'd postulate that we're dealing with an awful lot of additional flex going on here, what with the leaning over, the cornering forces, the generally greater power-to-weight resulting in big-time acceleration flex in the rear, big-time braking flex in the front, and that sort of thing.
This is pretty easy to verify lately, as a lot of cars these days have individual-tire pressure readouts on the dash. I haven't had an actual Beemer since owning an R850R from '97-'00, so I don't know whether your readouts show actual pressure. Me, I've added a Doran 360M TPMS to one bike, and a FOBO TPMS to another, and I can see that the pressures go way up after a spirited ride. Not like the Husky supermoto, but up. In contrast, the readouts on my two-year-old car go up at most 2 or 3 PSI during a drive.
4) Easy Calc:
If you want to figure out a cold-to-another-cold PSI setting ... ah, that's an awkward sentence.
What I mean to say is something like this. You've just come out of your motel room in Death Valley, very early in the morning, and it's say, 60°F. But you figure most of your riding that day will be at, say, 90°F, and you want to set your (cold) tire pressures for, say, 40 PSI ... right now, at 60°F, but pretending that it's 90°F. How do you do that?
Well, you make use of Gay-Lussac's (part of the underpinnings of the ideal gas law). What you need to do is add the ambient atmospheric pressure to that 40 PSI gauge pressure, convert those 60°F and 90°F temps to an absolute scale, i.e., Rankine or Kelvin, note the ratio of the absolute temp difference, apply that ratio to the sum of that 40 PSI plus atmospheric pressure figure, and then, from that result, subtract atmospheric pressure, to give you your desired gauge pressure.
Thus, in this particular example, if you're filling your cold tire while it's 60°F out, and you want to fill it 40 PSI as if it were 90°F out, you would pump it up such that your gauge reads 37.0 PSI. That is, if you just went back to bed, and woke up three hours later, when it's now 90°F outside, and put your gauge on the tire, it would read 40 PSI (because the air in the tire had heated up to 90°F while you were napping).
If anyone's interested in this sort of calculation, I have a page on my web site, on which you can just enter the parameters in question, and some JavaScript will do the math:
dubba dubba dubba dot billanddot.com/tire-pressure-vs-temp-calc.html
That's all I got. I hope someone found something here helpful, or at least interesting.
Cheers,
Bill P.
