[BiturboS4] Wheel time

[S Stiles]

Sport compact car tried to quantify this, and I think they came up with
something like 1:2. They also, IIRC, showed that the bigger wheel+tire
setups typically ran quicker lap times.

In my experience, I've found that the lighter the car, the bigger a deal
this is. For instance, I went up ~5lbs from stock on my Miata and it was
like I'd thrown a 100lb bag of cement in the trunk. Accel & Braking were
both affected significantly.

Now, on my S4Avant, I went with a setup that was 7lbs lighter than stock
(17" ABT Z4s, stock size & offset), and felt very little difference. There
appears to be a very subtle increase in steering feel, but the car is so
beefy to begin with (1600lbs heavier than my miata) that it blunts the
effect.

Net: my take on this is that the S4 is heavy enough that +/- 5-10lbs is
probably such a small difference as to not be noticeable. Ideally, I
wouldn't *increase* wheel+tire weight. It also turns out that it's really
expensive to stay at/near stock weight at 18".

Another data point: the e46M3 (another beefy car) stock wheels are just as
heavy as our S4 wheels, as are their optional forged 19" wheels. Given the
increased focus on handling on the part of the M3, I'd think they would have
gone with a lighter wheel if it would have provided significant benefit.

Scott.

>From: "California Fields" <cfields72 at hotmail.com>
>To: biturbos4 at audifans.com
>Subject: RE: [BiturboS4] Wheel time
>Date: Wed, 12 Mar 2003 21:21:45 -0800
>
>[ Converted text/html to text/plain ]
>
>Do you guys know if that whole phrase, "Reducing unsprung mass by 1 pound
>is
>equivalent to reducing 5 (or 10) pounds of weight in the car," is really
>true?
>I mean, I'm sure we've all heard it tossed around but has anyone ever shown
>*definitively* (i.e. by experiment or by equations) that this is true? I
>could
>have sworn I read somewhere that this weight savings is an exaggeration and
>that really the ratio is like 1:2 instead of 1:5 or 1:10.  I'm curious how
>much the unsprung weight actually affects the acceleration and other
>performance aspects of the car...especially since many of us have (or plan)
>to
>spend a lot of money towards getting light wheels and tires.  If 1 pound
>unsprung = 1 pound "sprung", then spending $2,500 on tires/wheels to save
>50
>pounds doesn't seem worth it to me.
>
>Carter.
>
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