Paul:
I can't help you directly but I can give you an example.
On my rally car I use a combination of 14" and 15 wheels
with different aspect ratios to get me the gearing that I need
for a specific rally (ie tight stages versus wide open, acceleration
versus top-speed).
First you have to establish a baseline, use one set of tires and
figure out acceleration in the various gears and your estimated
top speed. Then swap out to say a 10% smaller tire and you can
use some crude arithmetic to figure out your new top speed and
acceleration in each gear. For instance on a stage where I know
my top speed is 100mph, I'll use smaller tire/wheel combination,
than on a stage where I know my top speed is 125mph. You can use
the same logic for specific race tracks.
One point that has not been made is that the weight of each wheel/tire
combination makes a HUGH difference - especially on a low horsepower
car. I know when I am using 15" wheels with 7 ply rally tires - they
are heavy and do reduce you acceleration quite a bit (even on my
car with 250HP)
Personally on a light car like an MGB - 186-60 tires should be a good
compromise with weight/ratio/grip. You can get some pretty sticky
tires in that size (I use Yoko AVS - and they are pretty impressive)
gerry
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Date: Tue, 24 Feb 2004 10:21:32 -0800 (PST)
From: "Paul M." <rowman22001@yahoo.com>
Subject: Tire size vs. gearing
I need some help with how the overall tire diameter of
my tires will affect the overall gearing. The reason
I ask is because I have a dual purpose (vintage racing
and street driven) 1971 MGB that looks like it's going
to be significantly down on power from the front
runners.
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