RE: 16" Rims on 4kq's

[Mark Nelson <mnelson@brls.com>]

Think about this for a moment on the older Porsche 911 for example.  The
911 used the same trailing arm suspension setup up through '89 (C4 only)
and then '92 (or was it '94, I can't quite remember) when they changed
to the A-arm setup on the rest of the 911's.  Anyway, the point being
that through out those years, the same basic suspension was used on the
911/Carrera, 930 Turbo, 934, 935, etc.  The spring rates were obviously
different, but the tire size range was ENORMOUS (i.e.. anywhere from a
15" rim to a 20").  When they would go to a larger tire and wheel on
these different cars, they always_helped_the_handling_and_traction on
the car.

The 930 Turbo makes an excellent example.  Anyone who has driven one
will tell you that the car is absolutely one of the most terrifying cars
to drive at times, because of the trailing arm suspension setup.  The
930 Turbo has the bad characteristic of squatting the back end of the
car down under hard acceleration, then going around the corner for
instance, if you let up to abruptly, get ready to pucker up, because the
ass-end of the car is going to come around REAL fast.  To address this
issue, wider Z-rated tires and rims were added by owners, which improved
handling and traction of the car drastically (still didn't cure the
problem though).  Switching to these wider tires and rims, caused there
to be a necessity for a wheel spacer, to compensate for the offset
differences.  At no time have I ever seen this upset the handling of the
car.  *Minor* offset adjustments are not going to affect the strength of
the ball joints or the wheel bearings.  Obviously something like a low
rider with tires sticking half way out the fender wells, are going to
causes serious drivetrain problems.  If anything, with wider tires, you
are going to get a MUCH quicker response and better feel from the car.

If you're experiencing wheel bumps or poor traction over rough surfaces,
it is quite obvious that the suspension setup on the car is wrong,
especially if you have changed the ride height on the car.  You have to
compensate with different spring rates, possibly different strut
inserts, and sway bars.  When you change the suspension and tire/wheel
size dramatically, you have to make compensations somewhere.  If you are
running that 205 series tire on your 16...you are actually
running_a_smaller_diameter tire than was on your 14's.  The math won't
lie.  Remember as well, that you don't have as much sidewall as your 14,
which that in itself significantly changes the handling and feel of the
car...much stiffer ride, but better road feel and handling.

Another example is the Touring Car classes around the world.  If wider
and taller tires are a bad thing, then why do they run 19" diameter
wheels with extra wide tires and rubber band side walls.  These cars run
essentially the stock suspension design.  If switching to a larger and
wider tire is a bad thing, then WHY do road racing classes do it??

I've been around all kinds of racing long enough to know how these
changes affect the handling of a car, and how changing something as
relatively simple, such as the tire size or compound, may in some cases
require retuning the suspension.  Just so it is clear, changing the
suspension setup on a car, is NOT a bad thing.  You're looking to
improve the car, and if you have to deviate from the stock settings, the
world is not going to come to an end, regardless of what Audi originally
engineered the car to do.

cya!

-mark nelson
mailto:markn@brls.com

'90 s2 (building for scca pro rally)
'85 4ktq (10vt transplant in the works)

> ----------
> From: 	PAT MARTIN[SMTP:MARDKINS@classic.msn.com]
> Sent: 	Thursday, September 04, 1997 8:51 PM
> To: 	Mark Nelson
> Cc: 	quattro
> Subject: 	RE: 16" Rims on 4kq's
> 
> I disagree with the wider tires =better handling automatically.
> Unless you 
> are going to engineer a suspension around your tires they will
> probably make 
> it handle worst.  Even when I went from the stock 14" wheels and tires
> to the 
> 16's the suspension is not up to the task.  I can feel the wheel
> bounce over 
> bumps at higher speeds. This is with a "performance" suspension. I am
> not an 
> engineer but I wonder if there is a point on a car where the wider
> tires start 
> to decrease traction due to the weight being spread by more surface
> which 
> would equal less psi.  He is also right about the geometry's.  If you
> push the 
> center of the wheel out you are going to change the geometry's of the 
> suspension. Now why that is bad I do not know but it does open up some
> 
> questions like where do you set the alignment and what does that do to
> things 
> like bearings and ball joints.  
> Pat Martin
> 864000csq  2 1/2 cat back, H&R-Boge,advanced and loving it.  Drilled
> and 
> stopping it.  Koenig Cobra 16x7 with AVS Intermediates, turbo coming
> soon, 
> K&N.
> 95 subaru legacy 
> Bothell, Wa
>  
>