The thing I worry about with short tires (like a 24.4" tire) is that I will
have to go to 3rd gear on some courses. With the 245's I have bounced off
the rev limiter a couple times in 2nd, but I haven't had to go to 3rd and
lose precious time during the shift. Otherwise, I'm all for getting as much
low end torque as I can out of my GSX.
Ian
92 GSX: Philly Region ESP, now retired to commuter duties
97 GSX: Philly Region Street Modified #87
> -----Original Message-----
> From: owner-autox@autox.team.net [mailto:owner-autox@autox.team.net]On
> Behalf Of Bradley Lamont
> Sent: Sunday, May 28, 2000 4:09 PM
> To: autox@autox.team.net
> Subject: thrust calculations based on tire size
>
>
> Hey all -
>
> I am debating what tires to purchase for my Eclipse. Currently, I have
> 245/45R17 Kuhmos on the car. I was planning on just getting the same
> tires, but I decided to compare the acceleration provided by the g-Force
> tires since they are offered in a smaller size of 235/40R17.
>
> What I found is that the smaller tire offered by BFG offers a pretty
> significant advantage in acceleration of about 5%. This would seem to be
> enough to justify getting the g-Forces.
>
> So here are my calculations:
>
> Notes:
> (1) using dyno measured torque at wheels
> peak torque = 190 ft-lbs @ 3000 RPMs
> (2) using 1st gear
> torque @ wheels = peak torque * 1st gear ratio * final ratio
> = 190 * 3.083 * 3.8
> = 2226 ft-lbs
> (3) disregarding tire deformation since it should be similar on both tires
>
> Kuhmos (245/45R17):
>
> diameter = ((width * series) * 2) / 25.4 mm/in) + wheel size
> = ((245 * .45 * 2) / 25.4) + 17
> = 25.68 in
> radius = dia / 2
> = 12.84 in
> = 1.07 ft
> thrust = torque / radius
> = 2226 / 1.07
> = 2080 lbs
>
> BFG g-Force (235/40R17):
>
> diameter = 24.40 in
> radius = 1.017 ft
> thrust = 2189 lbs
>
> Thrust difference = (2080 - 2189) / 2080 = 5.2 %
>
> So are my calculations correct?
>
> Brad
> -------------------------------------------------------------------------
> Bradley Lamont
> email: lamont@xnet.com
> http://www.xnet.com/~lamont
>
>
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