AHHHHHH!!!! Stop Already!!! I can't take anymore!!!
Dennis
----- Original Message -----
From: "Michael R. Clements" <mrclem@telocity.com>
To: "John J. Stimson-III" <john@idsfa.net>
Cc: <ba-autox@autox.team.net>
Sent: Wednesday, October 24, 2001 8:15 AM
Subject: RE: Classes and course speeds
> At that level of precision we should also consider inflation pressures and
car
> weight!
>
> Overall, if you use tire revs per mile, you will find that most tires are
a
> bit smaller than the measurements would indicate. The 185/60-14 should be
5.9
> feet in circumferance, yet 910 revs per mile implies 5.8 feet.
>
> As for another data point, when I switched the street tires to the
G-Forces on
> my Panoz, the difference was 2 mph at 60 mph. While both sets of tires had
the
> same "size", the G-Forces were about 3 % smaller. This actually made the
> speedo / odo more accurate, as previously they were reading slightly below
> actual values. Perhaps this is because the street tires have bigger tread
> blocks? Who knows. . .
>
> -----Original Message-----
> From: John J. Stimson-III [mailto:john@idsfa.net]
> Sent: Tuesday, October 23, 2001 23:36
> To: Michael R. Clements
> Cc: John J. Stimson-III; ba-autox@autox.team.net
> Subject: Re: Classes and course speeds
>
>
> According to the specs for the AVS Intermediate on Yokohama's web
> site, that tire makes 910 revolutions per mile in the 185/60-14 size
> and 913 revolutions per mile in the 195/50-15 size. Which yields 0.3%
> shorter gearing, not 4% longer.
>
> Among nominal size, measured circumference, and measured distance per
> revolution, the last is most accurate measure of how the tire affects
> your gearing. And of course, what you measured may be true for some model
> or combination of models of tires. But I don't think that it's
> typical. Most of the tires I've researched (by looking up
> manufacturers' specs) have all had roughly the
> same value for revolutions per mile in a given size.
>
> The 205/45-16 are bigger around, or at least cover more ground: the
> Yokohama A520 in that size is listed with 896 revolutions per mile.
> About 2% longer gearing.
>
> --
>
> john@idsfa.net John Stimson
> http://www.idsfa.net/~john/ HMC Physics '94
>
> On Tue, Oct 23, 2001 at 09:15:56PM -0700, Michael R. Clements wrote:
> > Well it's true that according to the math, they are very close:
> >
> > 195 mm + 381 mm = 576 mm
> > 356 mm + 222 mm = 578 mm
> >
> > Less than 1% as you say. But this is a case of theory vs. reality, as
you
> > suggest in your last sentence.
> >
> > Remember tire size numbers tend to vary slightly from one manufacturer
to
> > another. The numbers I have are from actual measurements of the wheel
> > circumferance of these cars using the stock tires. These were 5.74 feet
for
> > the 15" wheels, versus 5.53 feet for the 14" wheels.
> >
> > So if you do the math you expect both wheels to have the same
circumferance
> at
> > about 5.9 feet, but if you measure the actual circumferance they are
smaller
> > and different. And the difference of 5.53 versus 5.74 ends up being
about 4
> %.
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