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Old 03-25-2008, 06:41 PM   #1 (permalink)
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Tire pressure (of winter tires)

Why is it that the usual maximum pressure indicated on the sidewall of a winter tire is 35 psi while an all season tire is 44 psi? If it is safe to up the pressure of an all season tire to 50 psi, is there any major structural difference in a winter tire that would forbid upping the pressure as high as an all season tire? Is it simply that above 35 psi the tire might not perform as good as it should on snow/ice?

I would really like to up the pressure even higher on the TDI which I use solely for low speed city driving. Especially since every 0.3 bar increase in tire pressure leads to a 7% reduction in tire rolling resistance.

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Old 03-25-2008, 07:50 PM   #2 (permalink)
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This is just a guess, but the temperature differential is going to be greater in the winter after the tires warm up. My current tires don't specify whether the max psi is hot or cold, but I've seen tires that specify it as the cold pressure. I have observed on our Jeep with the fancy tire pressure monitor during cold winter trips (0 F ambiant) running 80mph that our 44psi rated tires will increase 7-8 psi before it plateaus. I've observed in the summer (100 F ambiant) during the same trip the pressure only increases 3-5psi. (Kind of off topic: One time after parking in the sun I actually managed to get the psi to go DOWN by driving 35-40mph for a few minutes; I'm guessing it was because of the wind.)

All that might go straigh out the window when you consider that all season tires are run in the winter too, so take what you will.
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Old 03-25-2008, 07:57 PM   #3 (permalink)
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I have been running 100 psi in my E-rated tires (sidewall pressure = 80 psi) in warm weather and cold. No "crowning" is visible and the wear seems even across the tread.
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Old 05-15-2008, 10:58 AM   #4 (permalink)
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OK, I'm at a lose as to what is a "safe" pressure to run tires at. My tires are rated for 32 or 35 PSI, and are the tires that I bought the car with. That is the "maximum" rating on the sidewall. What has been done to determine the "maximum" you can run safely at. I see a lot of guys running 50 PSI or even Big Dave at 100 PSI without a problem. What can I do to figure out what the "maximum" PSI is for my tires?

I do plan on getting new tires on my car, but I cannot push myself to throw out good tires that have at least another year of tread left on them. I'm easing into the Eccomodder car as it makes monitary sense to.
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Old 05-15-2008, 03:08 PM   #5 (permalink)
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My NON LEGAL ADVICE is try 37; and if that's good go 40 . . .

My experience is that when you become overinflated that car acts very bouncy, like super bounce jet ball bouncy, or is difficult to keep going straight.

Bear in mind that big Dave has E-load rated tires with a rated max of 80, he's only around 20% over .
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Old 05-15-2008, 03:39 PM   #6 (permalink)
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I ran my winter tires (35 psi max sidewall) at 45 all winter. I run my summer tires on my Matrix at 50 (51 max sidewall), and my Paseo is currently at 55 psi (44 max sidewall) and I'll be going to 60 once it is back on the road. I know that doesn't really answer your question, but if I have a tire blow out, you'll know. However, there are a handful of guys running at these pressures, and some running more that I know of without problems...
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Old 05-15-2008, 04:00 PM   #7 (permalink)
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My sidewall max pressure says 44psi, I am running 50 psi, with no problems yet ... I am also running Nitrogen in my tires to help curve the temperature variations since average mid day temp here is now closer to 90 degrees. The ride does rely more on your suspension now because the tire is much stiffer. But other than a slightly harder ride, which I already got use to I see no adverse effect.

In fact and as an aside, I also run 50 psi in my 4 runner now and recently had a blow out, as a result of debris, I saw no additional hazard to the extra PSI other than a bit more time to get over to the side before the tire went completely flat.
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Old 05-15-2008, 04:32 PM   #8 (permalink)
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I run 55 in 44 max sidewall tires and the only downside I've noticed other than some ride/noise changes is that traction on wet roads isn't as good. Fortunately the breakaway is progressive. Winter traction seemed fine.
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Old 05-15-2008, 04:36 PM   #9 (permalink)
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I'm not willing to exceed the maximum sidewall pressure. I just bought tires with a max psi of 44. Some low profile tires go even higher if you want, but with overinflating, the law of diminishing returns applies. If you're inflating a tire that explodes at 60 psi, they'll find puddles of you in three zip codes. I'm only half exaggerating.
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Old 05-15-2008, 04:59 PM   #10 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
Where did you find this?
In the sticky in general efficiency subforum, there is a link to a pdf titled zero inertia powertrain. Look in the rolling resistance section.

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