12-07-2011, 06:00 PM | #1 |
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Different tire pressure with NON run-flat tires ?
Hello folks !
Just changed my summer tires for winter ones. Unfortunately, I had to settle for non-run flats (with an emergency kit in the trunk...). That's fine with me, comfort is great and I don't drive that much during winter. I just want to know if I should still pump the tires to 32 psi front, 35 psi rear ? They look (and feel) a bit "soft" and under-inflated... Maybe it's because of the tire's softer skeleton ? The tire footprint "looks" OK on the ground (eye-o-meter, about as good as my ass-o-meter for comfort...) Do you guys push up more psi with non run-flats ? |
12-07-2011, 06:14 PM | #2 |
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Should be the same...
Should be the same pressure for non-RFT and RFT. Profile should be the same too... since you're never really riding on the sidewalls of a RFT unless you lose air.
Also, watch the tread wear... If the outside wears sooner than the middle of the tread, they might be under inflated. If the middle wears sooner, maybe a tad over inflated. Mine always seem to wear a dad over-inflated... I like 'em that way I suppose. I'm running the 32/35 profile.
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12-08-2011, 12:05 AM | #3 |
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The 32/35 rating is only there for the staggered summer tires. Equal width tires do not require a staggered PSI setup. For example, the all season 309s recommend 32/32 because they're equally sized all around. I'd recommend keeping all four tires the same for the winter (but if you must bias towards the rear, I recommend just 1PSI in variation).
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12-08-2011, 05:24 PM | #4 |
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Thank you
Maybe it's because I came from the 245/275 staggered summer setup with high-performance RFTs, but 32/35 with non RFTs does feel a bit too soft. I'll try 35/38. Keep in mind, these are winter studded tires, so I do want maximum traction in difficult conditions (like Jeep off-roaders deflating tires before rocky passages |
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12-09-2011, 03:46 AM | #5 | |
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However, high tire pressure will decrease the size of your contact patch and increase the average shearing stress. Based on the tire data I saw in my FSAE days (and everything I have ever learned about vehicle dynamics) lower average shear stress in a tire results in higher coefficient of friction (important at high speeds). Higher tire pressure should increase cornering stiffness so your car should feel more responsive and at low slip angles it should perform better. However, passenger car tires are never designed to operate at "low" slip angles so these conditions probably don't exist during spirited driving. Front tire pressure also affects your steering effort... lower pressure should increase steering effort and higher tire pressure will certainly reduce it. Is this even noticeable on a passenger car? Doubtful. But I'm not a "driver". haha I think most people are aware that higher tire pressure reduces rolling resistance but is also reduced induced cornering drag on a tire. Tires are super complicated and not very well explained (the exact mechanisms of tire grip). I once attended a seminar about tires and the presenter claimed there are over 21,000 variables when designing a tire. RFT certainly add to the mix. I try to stick as close to the recommended tire pressure as possible... which by the way is interesting enough because my car is 32 / 32 and I have staggered setup Continentals 245 / 275's. |
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01-25-2012, 09:39 PM | #6 |
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I recently switched my wheels and tires out to staggered Non-RFTs and I noticed that the manual now explicitly identifies the specs being for RSC (Run-Flat) tires.
The specs have also changed to an even front/rear pressure for the staggered 19" setup, but is asymmetrical for the staggered 20" setup. What to you make of that? Last edited by renderfarmer; 01-25-2012 at 10:15 PM.. |
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01-26-2012, 12:05 AM | #7 | |
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