Early in this season, when I first got Kumho's, the Kumho technical
center suggested that to find good minimum inflation pressures for my
driving style and car was to start a bit high, in this case 40 rear 35 front
on my 93 MR2 and then look at the little arrows on the side walls right by
the edge of the tread after a run. If the tire is not rolling to the tips of
the arrows, then pressure can be decreased, if it is rolling past them, then
pressure needs to be increased. They indicated that running the tires with
sidewall rollover that goes past the tips of the arrows will cause
scalloping of the tires and possibly other problems. I initially found that
32 front 38 rear was a good minimum for my car, but that changes depending
on outside temps and the surface of the course.
This can also be done like the street tire guys do by simply putting
shoe polish or chalk on the side wall and checking for rollover. Just
because it is an R tire doesn't mean it is impervious to sidewall rollover.
The BFG's and Hoosiers have problems if they are underinflated as well. As
the surface changes and your driving improves, you may need to change tire
pressures to compensate. I'm not exactly an expert in the field of R tires
but common sense dictates that a tire rolling onto it's sidewall is not
getting as good of traction as one that is not. It also stands that
irregular wear patterns on a tire, while possibly being caused by a tire
defect, could also be caused by things like improper inflation pressures for
your Driving style, course surface, outside temperature and car type. All
these things must be considered to make a learned guess as to the proper
pressures to run to both give the car optimum traction, and keep the tire
from self destructing.
I'll get off the lecture stand now. I should probably actually get some work
done.
John Moore
1993 Toyota MR2 NA
> -----Original Message-----
> From: Paul Foster [SMTP:pfoster@gdi.net]
> Sent: Tuesday, October 05, 1999 1:39 PM
> To: Karl Rickert
> Cc: autox@autox.team.net
> Subject: Re: kumho crack
>
> Karl Rickert wrote:
> >
> > I run my tire pressures almost 10-12 lbs hign than what I do in my
> R-1's,
> > so I can't believe it's from underflation.
>
> I think you misunderstood. The sidewall cracks are due to
> underinflation, not the tread delamination.
>
> > I've never seen the sidewall crack thingie, but I'd think it might be
> due to
> > turning them around on the rim.
>
> If you mean running the outside on the inside, I don't do that. No, the
> sidewall crack thingie is _definitely_ caused by underinflation. If this
> is happening get thee to any inflatery.
>
> Paul Foster
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