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      02-26-2011, 08:33 PM   #1
henslegw
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Drives: 2007 335i E90
Join Date: Jul 2009
Location: NOVA

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Setting Correct Tire Inflation for Winter Tires

I know this topic has been discussed in regards to changing wheel size or tire size, but I'm curious about a direct comparison of PSI between winter and summer tires of the same dimensions. (ie stock sizes)

I have a E90 335i with the staggard 18" setup (Front: 225/40/18 on 18x8, and the Rear: 255/35/18 on 18x8.5). I have Michelin PS2's on there now. For the winter I bought another set of OEM staggard 18" wheels and put Bridgestone Blizzak LM-25 tires on them. (same size:225/40/18 front & 255/35/18 rear)

My question is what PSI to inflate the Blizzaks? The placard on the door jam (for normal speeds) reads 32PSI Front & 36PSI Rear which I do run the Michelins at, but do I run the Blizzaks at that PSI too? Barring the usual temperature fluction issue, is the only factor "Load Index" since I kept the same size wheels & same tire sizes? It seems the Blizzaks could actually acheive the same load index at a lower PSI. Does the speed rating have any consideration? What if both these tires were "summer tires" (disregarding any winter tire myths) and the information about load/speed were the same below, does that have a different outcome in setting the PSI? (I'm thinking it shouldn't matter what season the tire is built for, but rather the specs like the load index are the critical factor)

Here are the specs on the tires:

Michelin PS2's
225/40/18 "88Y" Max Load 1235 lbs Max PSI 51
255/35/18 "90Y" Max Load 1323 lbs Max PSI 51


Bridgestone Blizzaks LM-25's
225/40/18 "92V" Max Load 1389 lbs. Max PSI 50
255/35/18 "94V" Max Load 1477 lbs. Max PSI 50