spitfires
[Top] [All Lists]

Re: Brake pedal shudder - tyre psi

To: "Mitchell, Doug (D.B.)" <dmitchel@ford.com>
Subject: Re: Brake pedal shudder - tyre psi
From: James Carruthers <j.carruthers@rave.ac.uk>
Date: Thu, 29 Aug 2002 14:59:20 +0100
Hi Doug,


> 
> Assuming that the shudder to which you refer is a pulsating
> brake pedal, I would suggest that you have the front brake
> rotors checked for runout. (Trueness). This is usually an
> indication of a warped rotor.

Can I check this trueness roughly myself? Is this something I am likley to
have "made untrue" myself when I was fitting my Spax. It was a rather rough
operation at times.

> How much higher tyre pressure are you talking about? On my
> '73, I try to keep close to the original spec. I feel the
> ride is much too hard if you go too far over the recommended
> pressures. I generally keep mine at 22-23 front and 26-28
> rear.

Well, I did some tests at various psi both front and back, and on my new
tyres, I keep them at 30-32psi all round. The steering is so much lighter,
you just wouldnt believe it was the same car!

Regards the difference (22/26) - this was originally to compensate for the
likley to oversteer with the rotoflex spring on earlier cars - I think -
possibly - whatever - it was to reduce the likleyhood of you ending up in
the middle of a roundabout. Depends on if you like to get the tail out on
roundabouts, but at 30/30 - I can't do it unless I really really try... In
fact, its pretty much impossible if you dont want to do it. Although maybe I
havent tried hard enough, Im yet to light up the tyres with this new set...
<mental note, for the way home tonight>

Depends on how you drive your car I guess, but if you increase the psi all
round from the 22/26 base then I guess you keep the understeer
characteristics.

I didnt find that increasing the pressure to 30-32 psi made much difference
concerning ride hardness - not compared to the steering ease. I also tried
up to 36 - I could detect a slightly more firm ride, but I quickly changed
the pressure as the car was a bit too skitish for my liking.





James

///  spitfires@autox.team.net mailing list
///  or try  http://www.team.net/cgi-bin/majorcool
///  Archives at http://www.team.net/archive


<Prev in Thread] Current Thread [Next in Thread>