Section : Wheels and Tyres

Wire wheel tyre pressures

Posted By : Simon Coles, 01-Jan-2004, 08:20pm

• Wire wheel tyre pressures

  Posted By : David Styles, 02-Jan-2004, 10:05am

  Hi Simon...
  
  I've got a standard MKIII running 175/70's on wire wheels.
  (but spax adjustable's front and rear... set about midway)
  
  I used to run them at 26 - and the car was a bit skittish,..
  
  I took it to Jigsaw for 4 wheel alignment and camber angle malarkey,..
  
  and when it came back it was lovely.
  
  It was set to 23 all round. It may have been skittish due to 4 wheel alignment though....
  although now 26 seems way too high to me....
  
  So... 23 all round works for my car.
  
  PS. Took it on a trackday recently.. and other spitfire drivers were running 28 all round for the track...
  
  I stayed on my 23 rather than monkeying around, and it still felt nice.
  
  

  • Wire wheel tyre pressures

    Posted By : Nigel Gibbins, 02-Jan-2004, 11:23am

    If you asked each racer in the TSSC paddock what their tyre pressures were (and they answered honestly) you'd get everything from 18Psi to 28Psi and they are all using the same tyre for the same purpose.
    
    So I'm not surprised you are getting conflicting figures. You are trying to get as large a contact patch as you can - too high and you end up sitting on the middle of the tyre and too low you end up sitting on the rims. Neither is really any good.
    
    Either side of the optimum pressure you will lose grip, but you will lose more grip for being a pound under than you will lose for being a pound over - so if you are not sure you should err to a higher pressure.
    
    All tyres makes require different pressures/set ups and all tyre sizes require something different again (bigger the tyre the lower the pressure).
    
    And the real 'kick in the teeth' is - even when you have the pressures perfect - if it rains then you have to change them again. What fun....
    
    NiG
    http://www.niginthecar.net

    • Wire wheel tyre pressures

      Posted By : Van Hamlin, 02-Jan-2004, 01:18pm

      I have just tried to post this but it did not appear so I'll try and remember what I wrote....
      
      As a starting point I would use the standard tyre pressures. I would do this because when a car (such as a Sierra) is available with lots of different wheel/tyre sizes they all have almost the same pressure.
      
      Having said that, experiment a bit as a slightly lower pressure might work better for your car. The rear axle has quite a bit of camber, and the low profile tyres have much stiffer side walls than the standard ones. So the tyre is sitting on the road at an angle and the contact patch is reduced. Lowering the pressure by a couple of psi will make the tyre more floppy and you should get better contact.
      
      If you lower the pressure at the rear, do the same at the front by the same amount.
      
      I have a MkII GT6 with 175/65x14 Goodyear tyres and it handles great at standard 24 psi (no camber on Rotoflex rear axle though!).
      
      Regards
      Van