Upper pressure limit for Marathons

[mamestra]

Since I've already had one blowout of a Marathon tire I have been paranoid about the pressure in the tires (I'll replace them when in Phoenix early next month). While I start with 80 lbs cold my tire pressure alarm went off when I reached 97 lbs when it increased to 98 I let some air out. What is the maximum safe "high pressure" for this tire?
Thanks
Michael

[DQDick]

Generally tire pressure will increase 20-25% as they heat up. Letting the air out isn't the answer if they go over that because the increase in pressure is based on an increase in the temperature of the tire. The only solution for a tire that has gained too much pressure is to stop and let the tire cool down. Once the tire gets over 160 degrees you are starting to do damage to the tire that can't be reversed. If it's not under inflated to start with, not exceptionally hot outside or the trailer isn't overloaded then you have a tire with an endemic problem that makes it unsafe to drive.

[Hooker]

The manual that came with my tires says NEVER let air out of a hot tire.

[Irlpguy]

I am curious to know what the ambient temperature was when you set the pressure to 80lbs. Did all tires increase in pressure or only one tire. If they all increased then I would consider what weight is on the unit, or perhaps a significant increase in the ambient temp, or even perhaps road conditions.

Did the tires feel unusually warm to the touch when you stopped to let air out of them, if so were they all warm or only one. If they are not hotter to the touch than your TV tires then I am not sure I would be worrying about that increase. When I check my tires I always feel the tire, the hub and the rim to see if there is anything unusually warm/hot.

As was mentioned by Hooker, do not let air out of hot tires, or you are likely to find them under inflated when they cool. If this is showing on only one tire, then as Dick says it could be an indicator of things to come with that tire.

[DQDick]

I use an infrared thermometer to check the tires and bearings whenever I stop or I would also check the temp if I get an alarm on the tire pressure monitor. Infrared thermometers are cheap and provide even more peace of mind.

[ols1932]

First things first: If you are pressurizing the tires to the "Cold" pressure as stated on the sidewall, then never, I repeat, never let air out because the tire has heated up to something in the range of which you mentioned.
My tires run in the mid to high 90's when it is a really hot day but I've never seen them any hotter. I believe that the make of tire has a lot to do with how hot the tire may get, providing you are not traveling too heavily overloaded. Sometimes I think we can get very paranoid about some of these things and void the happiness and joy of traveling.

Orv

[1retired06]

Official answer is as reflected on the side of the tire, 80PSI cold. I have always defined cold as 6-8 hours of the rig parked. I dont have the equipment Dick has, so that is my shadetree logic. As stated on previous threads, the consensus is that the Marathons overheat despite maintainig proper PSI because of overloading; the tires cannot take the weight of the heavier rigs.

[mamestra]

Thank you for your answers, I certainly won't do that again, my tire pressure in the tire that I removed some air from is 79lb at a temp of 65 this morning. On the day in question the morning temperature was about 43 degrees and by the time we reached Rockport Texas the outside temperature was in the mid80's. My rig is a 3750FL so it is a heavy rig, I'm not over weight as I now am carrying less than I did with my smaller Sunnybrook and my numbers we fine with it's less carrying capacity. Thanks again.
Michael

[DQDick]

Since it's just the one tire, I would keep a close eye on that one and try and monitor the temperature. You could have belt separation beginning to go on there and that's what's causing the excess heat. If it were me and I was going to replace them anyway after one more trip I'd change that one out for the spare.

[Irlpguy]

mamestra, here is a really great website for just about everything you might want to know about tires.

http://www.tirerack.com/tires/tirete....jsp?techid=73

Ambient air temperature increase/decrease has the least effect on pressure according to this article.
The load on the tire, road conditions and the tires condition are the greatest factors in a tire over heating, causing the pressure to increase. It is likely prudent to keep a close eye on that tire, or as suggested change it out for the spare. I think I would change out that tire.

Good luck and safe travels.

[Art-n-Marge]

I am with Irlp on this one. If only one tire is experiencing this problem then it might be more overloaded than the others (only the scales will reveal this). Another thing I suspect is that tires may rot at different rates or just not be as good out of the factory as another for many reasons and maybe this tire is the weakest since one can't see the interior of it.

As others have suggested treat it like you treat the others, and make adjustments as necessary.

The safe high pressure for this tire is the maximum cold pressure stamped on the tire which is 80psi. The engineers that designed the tires were supposed to determine that this maximum is the best for it to account for loading (keep under its maximum), speed (ST tires have a speed limit), road conditions and temperatures. This is why one should never deflate a hot tire and ONLY check pressure for a cold tire.

For me I ONLY check tire pressure in the morning after the tire has sat overnight. 6 to 8 hours is a decent gauge, but I prefer 12 or more hours, to be sure. I wish I had a TPMS (pressure and temp) but my fear that having too much information might drive me nuts. I hope I just use it to correlate what I am supposed to know. A bad tire will go bad and the TPMS should help me anticipate the actuality, maybe.

[mamestra]

This one tire was only a couple of lbs above the others, and it was on the sunny side, not sure if that makes a difference. All of my tires were in the mid 90's, this tire was higher and since it was in the exact position that I had my blow out I was probably more concerned than I should have been. I certainly will monitor the pressure, I guess my best bet is to pull over if my alarm goes off, since I rarely travel above 55 I'm not sure what I can do to reduce this problem, as I don't think speed or weight has much to do with it.
Thanks for all the information I did look at the site Iripguy and it certain contains lots of information, thanks for the tip.
Michael