gt40 at mail.ev1.net
Fri Apr 21 12:03:12 EDT 2006
From: Brian J White <brian at bjwhite.net>
Date: Fri, 21 Apr 2006 08:24:22 -0700
>Rocky's blanket statement below depends on many factors. He's
>assuming that the larger wheel/smaller tire combo will be heavier
>than the 16". Which in a lot of cases is true, but what exactly
>"faster driving" mean. Yes, heavier wheels can affect handling
>acceleration, but we're talking Audi A4s here, not club racing
>Alfas. You would hardly feel the difference in a couple-three
>pounds per wheel in a heavy car like the A4. That being said,
>pound wheels are never a good idea.
>To me, I like the stiffness of the smaller sidewalls on a 17"
>on the A4. Slightly wider tread pattern does turn in a bit
>but also looks darn good compared with 16x7 wheels.
>And let's face it. The A4 isn't a track whore...it's a daily
And yet it does pretty well on the track, for a heavy,
underpowered 4-door sedan.
I race cars with the National Auto Sport Association, an on
occasion, I've taken my A4 TQMS on the track (Hallett Motor Racing
Circuit outside of Tulsa, and Motorsports Ranch outside of Fort
Worth, TX.) For as heavy as the car is, I was impressed with its
handling. Pull out 400 lbs and give it another 200HP and it would
make a fine track car.
As for a different sized wheel affecting handling, the effect will
be minor, based on the wheel & tire size alone. A larger effect
would come from using different brands or models of tire.
But, all things being equal, a tire with a shorter sidewall, will
give you crisper turn-in and more feedback through the steering
wheel (as the front tires loose grip, you can actually feel it
through the steering wheel.)
BUT -- the shorter sidewall tire may actually have less ultimate
grip, depending on the road surface. The tire's sidewalls act as
an undamped spring. Tires with a taller sidewall have a lower
effective spring rate in the sidewall than do tires with shorter
sidewalls. If you're cornering on a bumpy road, the tire with the
shorter sidewall will have more of a tendancy to skip over the
bumps, and as it's skipping, it's not generating as much lateral
On my race car, I'm 0.3 seconds faster at Hallett running a 50-
series tire compared to a 40-series tire simply because two
important corners are fairly rough. With the 40-series tire, I
have to go through the corner a good deal slower to control
understeer. The taller tire handles the bumps better and allows
for a faster cornering speed.
As in everything, it all comes down to compromises. On the
street, I'd run a taller sidewall because the tires are usually
cheaper, and they tend to protect the rim a little better from
curb-rash. Performance? Feh -- save that for the track where it
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