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      10-21-2012, 09:42 PM   #16
RPM90
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Drives: 335i Msport w/sport AT
Join Date: Mar 2006
Location: Chicago

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Quote:
Originally Posted by Koer View Post
I damaged my runflats setting them at 30 psi because any imperfection on the pavement would impact directly on the wall support of the tire. 30 is definitely too low for a runflat, but i run my pilot sport plus at 29 front and 31 rear COLD! Remember that at highway speeds the heat inflates the tires up to 2 or 3 psi. Great handling, great steering feel and 7 series ride quality!
If you're running 29 front and 31 rear COLD pressures, then you are running with UNDER-inflated tires, and your going to get greater wear, and more importantly you have less grip.

Remember, COLD tire pressures already take into account that the tire will heat up and psi will rise. How much psi will rise depends on certain factors, like ambient temps, how fast you're moving, and your cold tire pressure.
That's why tire pressure is set to the recommended psi when COLD not hot.
Again, the hot psi depends on various factors and thus it's not used as the base starting point.

If you run with under inflated cold temps, you may very well end up with HIGHER hot/running temps, because an under inflated tire doesn't have the proper psi to maintain the needed sidewall stiffness. So, as you're driving the tires heat up. The low pressure puts more tread in contact with the road surface increasing friction and heat, more than with proper PSI. Also, the lower psi soft sidewall will flex MORE and that will generate even more heat and higher psi. This added flexing is what leads to premature sidewall wear and greater potential for sidewall failure/blow out, along with the greater tread wear from the added friction and hotter running temps.

A 335i with non staggered 18's should be running 32psi front and 38psi rear.
You're 3psi too low at the front and 7psi too low at the rear!
Also, I don't know where you live, but ambient temps can swing a good bit from early morning to afternoon during the fall and spring seasons.
If you set your tires to 29frt and 31rr in the afternoon and it was let's say 70F, then in the morning if the temp is 50F, now your cold tire pressures will be 27frt and 29rr, even lower than where they should be.
Static, non moving, tire pressure can change by an average of 1F for every 10F degrees.

Yes, the ride may be comfy, because the sidewalls are soft, but your tires won't last as long, and your MPG is suffering, and worse you're compromising traction/grip resulting in worse handling and braking.
I don't know how your car can have "great" steering feel and handling with such low psi mussy sidewalls.