Miata Mailing List: December 1998, Message #125

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I agree with Jyri.  35 psi for street tires is not at all overinflated and
would be about the lowest pressure I would try on a track - I'd probably
start with 40psi in front and 35 in back and work around that.

R1's are a different beast. The right Miata pressure seems to be about
25psi-27psi, and BFG warned against trying much lower than this  - there
were stories of autoxers running 18-22.  The tire has a very stiff outer
sidewall, a less stiff inner sidewall and a tendency to grip more as
pressure is reduced - counterintuitive?

What was I runnign at LS2:
35/35 with RA1's 
36/34 with Kumho V700's

It would be risky for someone else to use these numbers because they have to
be put in the context of the rest of the cars setup, i.e:

Koni's, running on next to top  of 5 perches (stock ride height) full stiff
in back, one turn off full soft in front. 

1.0" -ive camber, 1/16" toe out at front. 2" -ive camber and zero toe at
back. 

Stock R springs. Stock wheels. 

1" front bar, stock (R model) rear bar.

This is a light-moderate understeer set up that I considered most safe for
me and the track. Its hard for me to screw up. I felt liek the car was
handling well while driving at 8/10's.

IMHO, the most critical part of a Miata set up is the rear toe, then the
rear tire pressure - but how criticial the tire pressure is depends on the
tire. 



Craig






> -----Original Message-----
> From:	Jyri J. Virkki [SMTP:jyri@virkki.com]
> Sent:	Sunday, November 29, 1998 1:21 AM
> To:	Multiple recipients of list
> Subject:	Re: Tyres (again)
> 
> Once upon a time John Freas wrote
> > 
> > 
> > I'm caught with the soft sidewall/high pressure situation.  My
> experience
> > has been that in order to get decent track/autocross performance out of
> > average street tires, they have to be over inflated.  That's not
> 
> Not sure what you mean by overinflated. If you mean higher than track
> tires, then more often than not, yes.
> 
> > necessarily the best for the tire, but it keeps them from folding over
> in
> > the corners.  Everyone thought that my cold pressure of 35 psi at LS2
> was
> > way too much, but it was the same as I ran on RAR at LS1 with very good
> > results.  I have marked the tread blocks and checked the wear after a
> few
> > runs and with that pressure, which comes up to around 40 hot, the wear
> 
> I don't think that is too much at all, for all-season tires (which I'm
> assuming RAR had) being used on the track. Also remember that having
> the pressures too low may cause them to overheat and thus increase
> more in pressure than if you had started higher cold.
> 
> The best thing to do is to check them cold and then hot (very quickly
> after a run) to see the pressure change, as you did. From 35 cold to
> 40 hot sounds like it was in the right ballpark.
> 
> Track tires are completely different beasts and the rules often
> change. R1s in particular reportedly need very, very low pressures
> (I've never had a set). In general they all seem to be happy with
> lower pressures than street tires. But for regular tires, too low is
> not where you want to go for track use.
> 
> 
> 
> -- 
> Jyri J. Virkki - Santa Cruz, CA - Linux: The Choice of a GNU Generation