I just got a new TPMS from HawksHead (out of Canada) to replace the key fob one I had (don't remember the brand).  I really like this model as it has a display monitor that mounts to the handle bars and gives a constant readout.  It will also give you a realtime readout within 1 minute of turning it on, which was an issue I had with my previous TMPS.  During setup, I set the low and high pressure alerts at 20% (which would be 8 PSI) for a low alert of 32PSI and a high alert of 48PSI.

Anyway, I went for a few hundred mile ride on Saturday and both front and rear tires were at 39.5 PSI when cold (I usually try to keep them at 40 PSI).  Now I know the pressure will increase as the tire heats up, but what I can't find an answer to is how much should you expect to see the tire pressure rise.

During the ride, once the tires heated up, the front tire pressure rose to 44.5 PSI and pretty much stayed there.  The rear tire pressure rose to 50.5 PSI at it's peak.  I assume the rear tire gets hotter from more friction, but that is a rise of 10 PSI.  I should have checked the tire temps (from the TPMS), but didn't think about it - I will definately do that next time.

So, does anyone know what the expected increase in tire pressure should be as the tires heat up to operating temps??  And am I correct in assuming the rear tire should heat up more (and therefore see a larger increase in pressure) than the front tire??  And finally, should I be concermed about a 10 PSI rise in the rear tire, and if so, what would cause the additional friction/heat buildup?? 

Thanks for any light you can shed on this issue for me.

MaddMAx2u - 2012-02-22 11:12 AM I always laugh at the tire temp and pressure increase thoughts and questions. As Arkaineye stated aptly, there isn't anything you can do about it. And before you had the TPMS did you really care about, or concern yourself with tire temps and "hot" pressures? Of course not. You just rode and enjoyed. I have a TPMS which I use primarily for checking my pre-ride pressure. After that the info is just something "interesting" to view. Since I have the key chain model, after checking the initial pressure it stays in my glove box, so even the alarms for tire pressure loss are ineffective for me. I guess if you wanted to get all technical about it you would have to recognize that as your tire heats up, not only does the pressure rise, but since heat makes things expand, the actual volume inside the tire would expand also which would require more pressure (greater volume?) from the air inside to keep the same tire inflation? Hmmm. Way to much for me to think about!! Just sayin.

It's the heating of the air inside the tire that expands its volume, which means since it is in a constant (almost) sized tire volume, then the pressure rises as it can't go anywhere. Then, when it all cools, the pressure goes back to what it was in the cold tire.

MaddMAx2u - 2012-02-22 1:12 PM I always laugh at the tire temp and pressure increase thoughts and questions. As Arkaineye stated aptly, there isn't anything you can do about it. And before you had the TPMS did you really care about, or concern yourself with tire temps and "hot" pressures? Of course not. You just rode and enjoyed. I have a TPMS which I use primarily for checking my pre-ride pressure. After that the info is just something "interesting" to view. Since I have the key chain model, after checking the initial pressure it stays in my glove box, so even the alarms for tire pressure loss are ineffective for me. I guess if you wanted to get all technical about it you would have to recognize that as your tire heats up, not only does the pressure rise, but since heat makes things expand, the actual volume inside the tire would expand also which would require more pressure (greater volume?) from the air inside to keep the same tire inflation? Hmmm. Way to much for me to think about!! Just sayin.

You're right, this isn't something that I worried about before and it appears it isn't anything to be concerned about now.  My main reason for installing the TPMS is to get initial pre-ride PSI without laying in the driveway, and to monitor if the pressure drops too low while riding. Since I didn't know what if any range of high pressure I should be concerned with, I thought I would throw the question out to those more knowledgeable than myself.  I guess this only goes to prove that more information isn't always a good thing, especially if you don't know hoe to interpret it.

Thanks for the replies.