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[Nhe261]

E90 335i, sport suspension, changed the tire to Michelin super sports non-RTF tires, front 225 40 R18, 92Y EL, rear 255 35 R18, 94Y EL, what's the right pressure should I use?
I have 38 psi front, 41 psi rear, is it OK?
Thanks.

[flip4335]

Originally Posted by Nhe261

E90 335i, sport suspension, changed the tire to Michelin super sports non-RTF tires, front 225 40 R18, 92Y EL, rear 255 35 R18, 94Y EL, what's the right pressure should I use?
I have 38 psi front, 41 psi rear, is it OK?
Thanks.

Under normal conditions (light load, you're all alone) of daily driving, the door jamb on my ride indicates 32psi Front/38psi Rear, regardless of type of tire (rft or non-rft).

There is a yellow sticker that recommends higher pressure for heavier loads (passengers, cargo) or for speeds up to and beyond 100mph:

39psi Front/45psi Rear

I am usually somewhere in between as a happy medium:

35psi Front/41psi Rear, or
36psi Front/42psi Rear

This allows for tire pressure inflation in hot weather.

If you will notice, there is always a six pound difference in tire pressure between the fronts and the rears, probably because when you accelerate, most of the weight is transferred to the rear wheels, so they need to have more air to accommodate the load. Just sayin'

[Nhe261]

Originally Posted by flip4335

Under normal conditions (light load, you're all alone) of daily driving, the door jamb on my ride indicates 32psi Front/38psi Rear, regardless of type of tire (rft or non-rft).

There is a yellow sticker that recommends higher pressure for heavier loads (passengers, cargo) or for speeds up to and beyond 100mph:

39psi Front/45psi Rear

I am usually somewhere in between as a happy medium:

35psi Front/41psi Rear, or
36psi Front/42psi Rear

This allows for tire pressure inflation in hot weather.

If you will notice, there is always a six pound difference in tire pressure between the fronts and the rears, probably because when you accelerate, most of the weight is transferred to the rear wheels, so they need to have more air to accommodate the load. Just sayin'

I did 45 rear but too firm I think.

[jadatis]

Is not it XL instead of EL , or what does EL stand for?


but you can calculate the needed pressure with spreadsheet I made.
In this older spreadsheet I still use the pretty save officially used formula and system, that European ETRTO uses , and since 2006 also American TRA for Standardload/P-tire and XL/reinforced/Extraload.
Needed tire pressure is all to give a sertain deflection of the tire , wich is save for it, so the tire dont get damaged by driving with the actual maximum speed and camber-angle( alighnment tires like this on the axle /-\ instead of this|-|)

https://skydrive.live.com/?cid=a526e...E092E6DC%21235

But for the tires you have with low Aspect Ratio ( AR = the 40 in your tires), you first have to substract 20% of the maximum load, before filling in , because they are to high maximum load given on the sidewall.
That is the reason why verry high pressure advices are given after 2000.
We are not supposed to know this, but now you do.

If you cant work it out, let me do it, then give here the needed details, and I will make the calculations, and give an image of the calculator in that post.

[VMRWheels]

Originally Posted by Nhe261

I did 45 rear but too firm I think.

45 front and rear is high for most driving situations. Take flip4335's advice on the pressure. It won't matter whether it's an RFT or a non-RFT.