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Thread: Tire Pressure 330ci

                  
   
  1. #16
    For track days I have a basic cold setting that I modify once the tires are hot. I go for HOT pressures on the track. Cold to hot on the track can be a good bit of pressure and be very different front and rear.

    At FATT sessions autocrossers tend to have WAY to high starting pressures that makes life fun. The track generates much higher pressure gains.

    As for the quesiton about 50+ psi hot on a street tire, no problem. The tire is rated for a maximum COLD pressure (on most performance passenger car tires I run, that is 44 psi) that will go a good bit higher in high speed summer driving.

    In autocross I set the pressures cold to what I want, then bleed each run to keep the same pressure. I get 2 - 3 psi gain first run (normal day) and then 1 - 2 psi for a couple of runs, then pretty much no change.

    I disagree about the value of a pyrometer. Yes the tires cool down fairly quickly but not THAT quickly. But you do need a person to read tire temps as you roll into the pits, not after you slowly drive back to your paddock, unstrap, take off your helmet, climb out, THEN take temps.

    And if you are serious, come in off a hot lap and have someone take temps, then go back out. No cool down lap.

    As for price, OG had a basic pyrometer at about $100. Not too expensive, even better with a couple of people going in together.

    A pyrometer is very important when you start to set camber when you upgrade the suspension.

    With a pyrometer you shoot for even temps across the tread. With stock suspension you will likely see higher outside edge temps, but go for an even gradient across the tread. Center hot, lower pressure. Edges hot increase pressure.
    Terry Carraway
    02 Topaz E46 M3 SMG
    00 Dakar M Roadster
    95 Alpine E36 M3 LTW
    SCCA Spec Racer Ford Red/White

  2. #17
    Barry--
    If you ran/run the same tire pressure scheme in your M3 (asyou ran in the 330i) that explains (to me, anyway) why you were so slow and tentative in the turns at the Shenandoah circuit last weekend. Just as at an autocross, the front tires absolutely need the extra pressure up front to stiffen the tires' sidewalls in order to provide some responsiveness at turn in. And, in my experience driving lots of different BMWs at the track and in autocrosses, 42psi rear is excessive (by at least 6psi)--it might be an appropriate figure for a hi-power rear-engined car like a 930 turbo where the driver likes to power oversteer, but in a BMW, maybe not the best way to go...

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