Re: Tire Question

[dmiller@iea.com (Doug Miller)]

>Hi Guys,
>
>Can anyone give me some advice as to what sizes of wheels/tires can fit on
>a 94 100 CSQ without adversely affecting power steering?  I've been told
>that putting say 225s could be detrimental to the car...is that true?  I
>was thinking that I'd be conservative and move from the 195/65-15 to the
>205/55-16, but I wouldn't mind experimenting with slightly sportier
>tires/wheels.
>
>As a side note, I have to say that I've never driven a sweeter 5-speed
>manual than the one in the 94 100CSQ I just bought; I fell in love with it
>immediately.  It was very different than the transmission in my 500TQ (of
>course, my 5000 had 3 times as many miles :).  I must admit I miss the
>rush of the turbo, though :).
>
>Thanks in advance for any advice you can give me!
>
>   -Mark.
>
>       ============================================================
>       | MARK BASSAM SALEM         EMail: msalem@cs.utah.edu      |
>       | Phone: (801) 898-8710     HTTP://www.cs.utah.edu/~msalem |
>       ============================================================

Mark,

I'm sure you'll get a lot of responses to your tire query, as it is a
fairly subjective area.  As for what will fit, I'd err on the cautious side
and try to go with close to factory dimensions for overall tire diameter
and width. Some of the mail order folks (Tire Rack notably) can give
various rim/aspect ratio/width ratios that keep you close.  From a speedo
accuracy and acceleration standpoint, this is a good strategy.  I've had
friends put bigger rubber on cars and tell me point blank they were
noticably slower (your tires are simply a lever from the axle to the
contact point - lengthen the lever and you reduce the engine's mechanical
advantage in accelerating the car).  Also, tires that "fit" under the
fender may be just fine until you are fully loaded one day and in a hurry
to bounce out of the Taco Bell driveway ($crunch!).

As for power steering stress, I'd be surprised if the added stress would
noticeably shorten the system's life, but wider tires will increase turning
effort, especially at a dead standstill (which you shouldn't do anyway)
causing added wear.

A wider tire will also change the shape of the contact patch from an oval
with its longer axis in the direction of travel more toward an oval with
its longer axis at right angles to the direction of travel. This will cause
added steering inputs from bumps, cracks, uneven pavement, etc and may
reduce your satisfaction with your Q's rock steady high speed stability.

I don't know what your goal is for the tire upgrade. Appearance, quieter
tires, dry cornering, wet cornering, and ride quality are just a few of the
often divergent impacts of tire changes.  If you are looking for more dry
grip for instance, I'd suggest you focus on finding a stock sized tire with
a gummy rubber compound and more solid rubber tread blocks than the ones
you have (the more and smaller tread blocks, the more tread squirm and
subsequent heat buildup).

In sum, I have seen a lot of people excited about a wider tire upgrade that
improved transient response and cornering, who later wished they hadn't
done it. After a few thousand miles of tar strip thumps and previously
quiet interior trim pieces that now buzz and rattle, they've had it.  As a
former Product Planner for both GM (Vette, Lotus, Fiero) and Lexus, I can
say that the factories put a great deal of research into choosing the size
tires that end up on the car.  Staying close to their choices can often be
a smart move unless your goal is so important you are willing to give up
daily drivability.

As for your 5 speed, I am extremely jealous.  My Quattro was unavailable
with a manual (97 A6 Wagon), and I would have loved that choice. Can't have
everything, I guess..

Doug Miller
dmiller@iea.com