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Mini/ Tyres setup

Discussion in 'Stock Car Extreme' started by Diego Balzarini, Aug 3, 2015.

  1. I've been trying to understand what tyre pressure would change in a Mini.
    I know that generally tyre pressure changes the temperature and contact patch but i was wondering if there's something else that would effect the car stability.
    Mini's dont have much to change in setup and some times they're tricky when braking.
    If tyres change the weight distribution could it be possible that they effect the braking too?

    ie : increasing front pressure tyre and softening the rear would move weight towards the rear and should help and oversteery car
    default setup for minis is 170 front and 240 rear.
    Am I completely wrong or there's some truth in my confused head?

    Thanks
     
  2. No, not weight distribution. Not significantly at least.

    In my view tyre pressure changes the contact patch, temperature and also wheel spring rate, which makes the car a bit more bouncy and responsive. I think they have an optimum pressure for maximum grip, but it is difficult to know which one.

    Maybe the stock rear pressure is high to induce oversteering in FWD cars, and it is possible to find more grip at the rear. In this case I would only drop the rear pressure a lot and see what happens. But let's wait someone more experienced to bring their two pence.
     
  3. Changed front pressure to 170 and rear 220 and it makes a huge difference already, especially in braking before slow corners.
    My idea was : more pressure in front less pitching during braking thus less weight moving to the front, even if not a lot
    Now i dont get a nervous rear that often anymore.

    Thanks
     
  4. Not disputing your results, just the explanation of results. The weight transfer is caused by the braking. The pitch is caused by the weight transfer, it doesn't cause the weight transfer. You can have infinitely stiff suspension and no pitch but you will still get the same weight transfer when you brake.

    You also say the default is 170 and your new setup uses 170, so you haven't incresed the front pressure but reduced the rear. I presume the default has high rear tyre pressure to lower rear grip and kill the usual understeer you get with FWD. By reducing the rear pressure you have probably increased the rear grip.
     
  5. Just to make things clearer, your problem is oversteer under combined braking and turning?
    Tyre pressure effects the cornering stiffnes and the contact patch (temperature is affected by the contact patch). In theory a higher pressure should increase the cornering stiffness and thereby reduce the slip angle on that axle. So higher pressure in the front and lower pressure in the rear would result in more oversteer. But if the pressure gets too high the contact patch decreases and you create an opposed effect that reduces cornering stiffness because the contact patch decreases. The base setup is quite oversteering so decreasing the tyre pressure in the rear could mitigate that opposed effect of a reduced contact patch and reduce oversteer.
    If nothing helps you could try to reduce the brake pressure and avoid trail braking.

    The tyre pressure does not effect weight shift to the front under braking.
     
  6. I made a mistake in the first post, default front pressure is 160, sorry:whistling:.
    I probably need to do more research about car setup.
    Thanks for the extra info. I'll try different brake pressure settings.
    I still need a lot of practice and car setup is not that easy to understand