to keep it simple, tire sitting in the sun doesn't increase pressure significantly to even talk about it. more of a myth than anything. tire blowing up in transition do because they are pinch...not because of excessive pressure

pump them to 95...you should be good to go

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Jonathan Caron / Professional Coach / ironman champions / age group world champions
Jonnyo Coaching
Instargram

92.3 psi.

So, why not do an experiment. Pump up your tires and then come back a couple of hours later and see where they are. I doubt you will lose more than a couple of PSI (which is probably within the accuracy of your meter anyway). As to sunshine blowing up your tires, ain't goin to happen. If there is something wrong with your setup (i.e., bad rim tape, part of innertube caught in tire bead, etc.) a little pressure change could trigger a blowout while you are swimming -- but if you have that problem, there is a good chance that you would have had a blowout out on the road anyway as you go over bumps, etc. that stress the system as much or more than the few PSI that would be caused by having your tires in the sun. Maybe we need to have a PV = nRT expert chime in, but starting @ 90 psi, you should not get anywhere near your tire's rated maximum pressure from sitting in the morning sun (maybe from sitting in a closed parked car sitting in the sun, but not out in the open).

You hardly need an expert when V, n, and R are constant. Besides, what's the difference between sitting in the sun on a rack and sitting in the sun while you ride? 20mph of convective airflow. Do you think the safety margin on the tires is so low that without that 20mph of airflow the tire could develop a pressure high enough to rupture? Do you think that DOT (or whoever certifies tires for consumer safety) would allow such a design limit? Uh....no.

Nevertheless, for reference, "ideally" you gain about 0.18 psi per degF (change from temperature at time of inflation). That's assuming no leakage, and no change in tire volume, neither of which are true. So, if you inflated your tires indoors at home at 68F or so....then let it sit outside in the sun in Phoenix, and somehow the tire heated to 168F (for a 100F deltaT), the tire might gain, at most, 18psi. The reality is that your tire will never get that hot, and less than 5psi is much more realistic.

So, to summarize everything above:

Pump your tires to 90psi.
In the two hours sitting in the sun, they *may gain ~1psi.
In that same time, your latex tubes *may leak ~1psi.
Start ride at 90psi.

Don't over think it. ;)

for the technonerds like me.... below is a good link with the maths and a chart at the end.

I think more of an issue would be heat affecting the tyre strength, personally I have had the glued on tread come loose on a Vittoria in sunlight, but that may be a fluke.


http://flocycling.blogspot.co.uk/...re-pressure-and.html

Also the popular myth that your tyres will explode in an airplane is pretty much rubbish, worst case your going to add 1 atmosphere (14.7psi) to a tyre in a pure vacum, so in real terms a couple of PSI.

 I think you are talking about a <5psi affect in both directions. Probably within the error or your pumps gauge in the first place (especislly taking into account any air loss when disconnecting, etc.).

I was actually expecting worse losses from latex. Had them for nearly a week now. i ride at just under 100 psi and 3 days later, they were still near 75 psi. No sealant.

I have always worried about pressure loss not gain. Also, and perhaps I am wrong, but I always feel higher tire pressure climbs better; so, I want a bit higher pressure for the climb at the beginning. Any studies on tire pressure for climbing?

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David
* Ironman for Life! (Blog) * IM Everyday Hero Video * Daggett Shuler Law *
Disclaimer: I have personal and professional relationships with many athletes, vendors, and organizations in the triathlon world.

It won't be hot enough at that time in the morning for the tubes to really increase pressure significantly. You can always test it out in the days prior to the race once you get to Chatt. I'll say pump them to 92-93 psi.

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