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  1. #1
    Club Administrator
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    Default A Basic Guide to Tyre Pressures

    Thought this might help others...

    I've been looking for the correct pressure to run my new tyres at, and found rather a lot of not much. So I went hunting, and didn't find a lot more, until I stumbled across this, which is what I am using. Thought you folks might like to use it as well.

    The baseline method from Oscar Pereda of BF Goodrich. He suggests this as a good starting point if you have abolutely no guide as to what pressure to use in your tyres. This starting point should be regarded for road use only.

    (Vehicle Weight in pounds imperial/100) + 2 psi at heavier end + 2 psi all around if suspension and alignment are stock.

    Example:

    Stock 911, 3,000 lb.
    (3000/100) = 30 psi
    Add 2 psi all around = 32 psi
    Add 2 psi to heavy end = 34 psi at rear

    With modified suspension, the result would be 30 psi front, 32 psi rear.

    SO:

    Stock R33 GTR = 1530kg = 3366lb.

    3366/100 = 33.66
    Non standard suspension, so only adding 2psi to heavy end.
    36 psi front, 34 psi rear.


    NB: The next bit, compensating for driver weight, is not part of Oscar's calc. It what I have chosen to do, and I will let you know how it goes.

    But I'm a fat bastad, so that adds 240lb (let's be creative with the scales, eh?).

    Adding 2.4 and rounding down for the tyre's stated maximum pressure (40 psi) gives 36 at the rear and 38 at the front.

    PSI to Bar is 14.5038:1
    Pounds (lb) to kg is 2.2:1

    In all fairness, I should point out that my R33 GTR on 265/35/18 was running 34 front and 32 rear and that was superb. But me new tyres are bigger with a lower profile, so this is why I went looking.

  2. #2
    HJC Non Paid Member
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    Default

    Rotfl, try putting 38psi in your tyres if you don't want any grip. I've got 36psi in my rears for a laugh at the moment and the slightest prod of the throttle kicks the back into a slide. Not to mention it's back-breakingly bumpy as ****!

    32psi all round is what it says on the door shut and what feels better for grip, maybe 34psi just to help a tiny bit with turn in and a little less flex.

  3. #3
    HJC Non Paid Member
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    chris
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    Default

    Quick question on this,

    A stock aygo DRY weight is 790 kg and CURB weight is 890 kg
    what the difference?

  4. #4
    HJC Non Paid Member
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    Default

    Dry is without all the fluids and crap in it. Curb weight is with oil in the engine, full tank of fuel, coolant etc. so basically curb weight is the true weight, dry is just the weight when it's rolled off the assembly line.

    Your car is very light

  5. #5
    HJC Non Paid Member
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    Default

    Quote Originally Posted by Francis View Post
    Dry is without all the fluids and crap in it. Curb weight is with oil in the engine, full tank of fuel, coolant etc. so basically curb weight is the true weight, dry is just the weight when it's rolled off the assembly line.

    Your car is very light

    Ah ok thanks simple really.
    And its lighter than that now, its been stripped out completelly and has light alloys and bucket seats i think its curb weight is now round about 730 kg give or take a bit

  6. #6
    Club Administrator
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    Default

    Actually high psi is often used for fast road and track use - helps tyre wear for a start.

  7. #7
    HJC Non Paid Member
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    Default

    It's alright for drag racing lol, but **** for grip. I dunno about you but if I'm on a track ideally I'd like to stay ON it try putting 38psi in your back tyres!

  8. #8
    HJC Non Paid Member
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    Default

    i thought low pressure would be good for drag!!!!! lower pressure means more tyre on the track and more grip, higher pressure would mean less tyre on the track

  9. #9

    Default

    On our track day we where told to set our PSI to just under maximum for our tyre - reduces flex in the tyre wall when you are going sideways at 100mph!

    if you dont you risk tearing the rubber off the rim (nearly happened to one chap who smashed his alloy after taking a bend fast).

    on the road I just use stock pressures on the evo and find them fine.

  10. #10
    HJC Non Paid Member
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    Default

    Sideways at a 100mph isn't general trackday **** though. With my tyres at 26psi all round for a laugh, it's twitchy as ****! You also get less feedback through the wheel.

    Harder pressures for drag and sticking it on the dyno! Unless you're running drag tyres or something.

 

 

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