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View Poll Results: Have you ruined a set of performance tires? | |||
Yes | 12 | 60.00% | |
No | 8 | 40.00% | |
Voters: 20. You may not vote on this poll |
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#16
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Based on this thread, I went out and changed my tire pressures to 40/36 today after completing my monthly oil change. Handling does feel better, and the higher tire pressures will actually improve my gas mileage slightly...
-Chike
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"Wise men talk because they have something to say; fools, because they have to say something." - Plato 2013 Cosmic Blue 5spd Evo X GSR 2006 Galaxy Gray 6MT RX-8 (sold) 2006 Steel Gray WRX TR (sold) 1996 Brilliant Red SVX L (sold) |
#17
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There are general rules for tire pressure for a specific application. A good tire shop will know. The general rules however, are just that: General. The only way to find the ideal pressure is to experiment. This isn't hard, but it's something most people won't find the time to do.
There are different pressures for different applications. For drag racing, lower pressures are sometimes better, but this isn't always true, especially on low-profile tires. For top speed, higher pressures are better. For best cornering, and tread life, moderate pressures are best. The tread life test can be done in two ways. The best way is to carefully monitor the tread over time to see which part wears out first. If it's the outside, the pressure is too low. If it's the inside, the pressure is too high. The other test is a footprint test. This is usually done with a special machine, but you can use carbon paper or thin sheets of Styrofoam, or even both simultaneously. You simply drive over the test material. This test just shows how much pressure each part of the tread exerts on the road surface. If you use carbon paper, the dark spots exert the most pressure. If you use Styrofoam, the most deformed parts exert the most pressure. If the pressure is to the outside, inflate the tires - and vice versa. (The texture of the surface you set the carbon paper on will affect the results.) The cornering traction test is done simply by measuring how well the car can corner. You can use an instrument to measure lateral G-forces, measure the fastest speed through a corner, measure the smallest radius you can achieve at a particular speed, or simply measure track times on an especially twisty course. Usually the ideal pressure for cornering traction will be very similar to the ideal tread wear pressure, but slightly higher. This is because when you corner, the weight shifts to one side of the car. Since a very large percentage of the traction is on that one side alone, the excessive pressure on the unladen side is trivial to the inadequate pressure on the loaded side, which makes up the majority of the traction. To combat this, the overall pressure is increased so the laden [important] side is at it's optimum. The consequence is that when driving straight, all the tires are overinflated. This is fine, if not good, for racing purposes, but for daily driving, it leads to poor tire wear patterns. Overinflation in general is preferable to underinflation. Economy will be better. The propensity for overheating and sidewall damage is reduced. Excessive wear in the center of the tread is less likely to cause hydroplaning than wear on the outside. Handling will be better. Tire balance will remain good, and wear should be relatively even about the circumference. Underinflation adversely affects all these things. In all cases, the ideal pressure vary between sizes of tires, the vehicle weight and weight distribution, the manufacturer and model of tire, and even between each tire on the car. For the rough numbers, call a few tire shops and ask. Quote:
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#18
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When I was looking for where to begin with my +1's I went to nasioc.com's tire forum and poked around - the autocross guys know their tire pressures well.
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Matt Locker Link 2015 BRZ Limited 6MT 92 Ebony LS-L ECUtune Stage2av1, Z32 MAF, 370cc injectors, TomsSVX intake, BontragerWorks 22mm RSB #003, HID Hi and Lo beams, OT endlink and bushing mods, PWR Aluminum radiator, Harvey's QC shift kit, 2.5" flowmaster 80 exhaust, 17" Michelin Pilot Sport A/S, Poly sway bar bushings, Slotted Bradi rotors, AFBeefcake powdercoated calipers, 97 grill, and a huge set of air horns. 300,000 miles and counting 92 Ebony LS-L. ecutune stage1v4, motorsport 1pc pulley. Garage Queen - sold to Dad in upstate NY 155,000 miles 19 Subaru Ascent Premium - -Hers !. 89 DL 4x4 little red wagon - a.k.a. The immortal suby. 275k R.I.P. |
#19
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Re: ???
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A very surface level explanation that isn't even 100% true just because of the very very complex dynamics (that I sure as hell don't understand) behind tire performance.
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Time for my very own long list of mods: 92 SVX LS-L - Ebony Pearl - 2002 WRX 5MT trans w/STi gearset (rebuilt & installed myself ) - BMW E46 HID retrofit - Kenwood Headunit - Phoenix Gold 75x4 RMS amp - Alpine Type R 6.5" front components - Alpine Type R 6x9 3way rear speakers - 18"x9" Rota G-Force wheels w/225/40ZR18 Toyo T1R's - Mychailo's custom springs - Urethane front & rear sway bar bushings - KC exhaust (2.5" dual magnaflow) - Escaine seat swap - Removed Spoiler I don't care if Subaru says it's STI...it will always be STi to me |
#20
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Re: Re: ???
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Just because the weight distribution is distributed 59 / 41 doesn't necessarily mean tire pressure should be balanced the same. The argument above for [relatively] higher front pressure is countered by the fact that low pressure in the rear tires can lead to stability problems, so the rear also should have plenty of air. Again, back to the "overinflation is better than underinflation" viewpoint. All four corners are better off that way. We could get into motorcycle tires if we wanted to get really complicated. I know their dynamics are far more complicated and varied between designs. My understanding is far less keen in that school - as is the understanding of their designers too sometimes. |
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