Eric, there are three factors to consider here. Rolling radius, aerodynamic
drag, and rotating weight.
Aero drag is not a factor since the car is fully bodied.
The changes is rolling radius, have fairly obvious effects, in that a larger
tire will turn more slowly, and thus your top speed in each gear will be
higher. Also the car's ride height will change by some amount. All of this
leading to acceleration being slower, but top speeds higher. The difference in
rolling radii from current tires to the new ones will help you determine how
much different the acceleration will be.
Finally, rotating weight, this works exactly like your engine's flywheel. The
lighter weight produces snappier, quicker changes in speeds but less momentum,
heavier weight is more fluid, and higher momentum. Lighter rotating weight
also lessens unsprung weight and will aid suspension compliance. The heavier
the wheel/tire the slower it will change rpm (and the more energy must be put
into that change). All in all less rotating weight is good.
So, have a look at the combo you are considering and decide if they are heavier
or lighter and how much is the rolling radius different. Bear in mind that a
15" setup is not necessarily heavier/slower than a 14". All of this is also
ignoring the 'it didn't work for the other guy so why would it work for you?'
argument that has already been mentioned. That argument is not necessarily
valid, as driving styles, setup, and many other factors differ and what works
for one doesn't always work for another.
Good Luck
--
James Nazarian Jr
71 MGB roadster
71 MGBGT-V8 in need of bodywork
01 Impreza 2.5RS
A complex system that does not work is invariably found to have
evolved from a simpler system that worked just fine.
On Mon, May 07, 2001 at 08:53:19AM +0000, Eric profoundly declared:
> THE ARGUMENT is that I should NOT put 15 inch rims on my car as I will
> have to alter diff ratios to get the speed/performance I would get from
> the 14 inch rims (extra money and no guarantees). There were other
> elements thrown in there... but they became just a wall of sound after a
> while. Yes, I know the physics behind turning the wider diameter wheel
> with the same force, etc., and my 'real' racer mates have 13 inch
> wheels!
>
> Eric
> '68MGB MkII
> Adelaide, South Australia
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