That's what my door jam sticker says. Why is it supposed to be so much higher than the fronts? I thought a 50/50 weight balance should mandate even pressures front to back.
Enforcer
That's what my door jam sticker says. Why is it supposed to be so much higher than the fronts? I thought a 50/50 weight balance should mandate even pressures front to back.
Messaggero
The idea with this higher rear figure is to make sure that the car will always understeer, which is really redundant as our rear tires are wider then our fronts anyway. I believe it is a CYA move by the BMW Brass in case you are ever in an accident and try to sue them. I run 32 PSI all around, with 38 PSI all around as my hot temperature on the track.
-Brettski
Big Earner
Brett nailed it on the head. Overload the front with grip and it will understeer.
I run 38 hot front and 36 hot rear for autox.
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Big Earner
I used to run 39.5 rear and 38 front on the zhp. I had perfectly even tire wear as well. the 135 is the same way, with a bmw suggested 3-4 psi increase in rear over front.
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04 330i ZHP (sold)
David
Messaggero
Edit: shoulda figured I'd get ninja'd by the track rats!
Y'know, I scratched my head about this topic & dove into the world of tire sizes, load indicies, & vehicle weights & ended up with a shrug & "I guess the BMW engineers had a reason, probably mostly because the rear is a bigger tire".
Longer version: I'm sure the final recommended tire sizes & pressures were chosen with balancing performance (exciting, neutral sports car handling) & predictability (less exciting, for-the-masses understeer tendencies) in mind. More grip in the rear (or less up front) induces understeer at the limit of traction; a wider tire with higher PSI has more traction available (to a point). So wider & more inflated rear tires will hold on more than the narrower, less inflated fronts will at a given cornering load.
To reduce understeer / increase oversteer, drop rear PSI / increase front, decrease rear tire width / increase front. That's why you'll find a great many enthusiasts swapping the stock staggered wheels for a square setup.
And that's my (grossly oversimplified) $0.02.
Last edited by Crickett; 01-30-2013 at 01:28 PM. Reason: ninja'd
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Running 36/38 F/R
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Enforcer
Good info here...
http://www.zhpmafia.com/forums/showt...=tire+pressure
In that thread, we learned that our recommended pressures varied. The door jam on my 05 indicated 46 in the rear.
I run 33 all around on most of my cars, including the zhp when I owned it.
Campieri
35 all around is my choice.
Hot is 38-40 on the track depending on tire selection. Dunlop Star specs don't like 40..but RE11 do... at least on my car..
Messaggero
I'm running 38/39. I've experimented with 36/40, 35/40, 35/38 etc. found this to be the best for my car.
Yep same here.Originally Posted by danewilson77
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