Tire Pressure Theory

[1993CivicVX]

Originally Posted by RoadWarrior

IMO sidewall pressure is maximum recommended cold pressure for tires to survive being driven at 110% of rated speed for 4 hours straight on a 40C day on a harsh road. So you can push it a bit if you intend driving at the speed limit and your temperatures aren't so extreme.

On word of warning though, tires do stretch a bit when you go overpressure on them, it happens gradually though. So you'll put 50 psi in a 35 psi tire and it will be only 45 a couple of days later... then you top it up to 50 again... then maybe it's 47 next time... eventually it will hold 50psi fairly constantly, BUT the tire is now stretched and may not run right at standard pressures again. Also there is potential that you are nearing the elastic limit of the tire and that trying for 60 might cause it to burst catastrophically.

Soooooo... sidewall pressure is the safe cold pressure under all conditions, but messing with that makes you responsible for evaluating conditions.

When I stopped by a tire shop I mentioned in another thread, the guy said you don't have to worry about tire bursting until 160 or 170PSI -- Tom and Ray said it won't burst until something like 200PSI. The other thing the tire shop guy's partner said was that the max sidewall PSI number on tires is NOT the PSI for the tire, but rather information pertaining to something else involved in mounting the tires, and that the actual Max sidewall pressure for the tire is less than whatever the number is on the side of the tire. She said usually it's around 30-32PSI! I have no idea if these people know what they are talking about, but they spoke as if they knew very well, for what that's worth. Nevertheless, I so far do not feel riding at 55PSI has any averse effects except maybe worse traction in wet conditions, but that may have just been an isolated incident of slipping on wet leaves and nothing to do with overinflated tires. The tire shop guy said my tires were in good shape and would replace just one tire with a new one (indicating the tires were not worn enough to justify replacing both) and they have about 10,000 miles or so of ~50+ PSI.

[JanGeo]

Wait a second - the tire print says "maximum cold inflation pressure 44 psi" (or words to that effect). Now they wouldn't say inflation and cold if it was not ment to indicate while operating on the vehicle just like the maximum load weight (at the max pressure).

[1993CivicVX]

Originally Posted by JanGeo

Wait a second - the tire print says "maximum cold inflation pressure 44 psi" (or words to that effect). Now they wouldn't say inflation and cold if it was not ment to indicate while operating on the vehicle just like the maximum load weight (at the max pressure).

I have no idea, just passing along what the tire folk were saying.

[GasSavers_RoadWarrior]

well I'd imagine they're right about them taking 100 or so PSI... because they have to take 30-40ish plus survive knocks. I don't know what the hell they were on about for the max sidewall pressure though.

by the way, was on a long summer highway trip once, pulled off for food, checked the tire pressures, read 50 psi, when they were inflated to 36 psi cold, nearly went and let pressure out..doh!.. after we had eaten .. checked them again and they were down to 40..

[GasSavers_Ryland]

My car owners manual, and my motorcycle manual both recommend increasing the tire pressure for any kind of high speed, or extended distance travel, a 4-5psi increase seems to be most common.
I have never had any issue at all with running 50psi, dead even tire wear, awesome traction in snow and rain, I replaced a pair last fall after running over a bunch of hard ware that was on the road poking a 3 holes, two nail holes and a good quarter inch hole thru my tire at 50psi, plugged it and added some sealant and drove another 2,000 miles with it again at 50psi before getting the tire replaced.

[GasSavers_Otto]

Every time you hit a bump or pothole, the tire pressure spikes. Overinflation may bring the tire somewhat closer to its bursting pressure, but if that were really a problem, we'd surely have heard about that here.

That said, tires can burst from overheating, in extreme cases. Hard braking makes heat that is transferred to the tires. Surely more a problem for jet aircraft and racing cars than economy cars.

[fowljesse]

The only problem I ever had with this is when my girlfriend gave me a Mazda 323 when I lived in Hawai'i. The car was in okay shape, and ran great. I have no idea how old the tires were, but within weeks of overinflating the tires to less than sidewall max, 3 of them seperated (I mean the tread form the rest). You may ask why I didn't deflate them to norm... I wanted to replace them, anyway, and did experiments with different pressure.

[VetteOwner]

Originally Posted by Otto

Every time you hit a bump or pothole, the tire pressure spikes. Overinflation may bring the tire somewhat closer to its bursting pressure, but if that were really a problem, we'd surely have heard about that here.

That said, tires can burst from overheating, in extreme cases. Hard braking makes heat that is transferred to the tires. Surely more a problem for jet aircraft and racing cars than economy cars.

lol well yes i can pertain to that, you know you have a dragging brake when your able to get a 3rd degre burn from just touching the metal hubcap....

but yes, tires are the things that absorb most of the bumps in the roads, the shocks just keep the tires on the ground and to keep the car from boucing up and down after a bump.

now if you think about it for about 12 micro seconds if thje tires are stiffer than factory now, then the energy absorbtion is now beign doen by the ball joints and cv axels and whatnot, which isnt what their designed to do and COULD wear out prematurely if the car has cappy ball joints, etc. but yes usualyl factory specs are low to make the ride seem comfy so id bump em up a bit but not too crazy