Re: wider rear track handling discussion.......

["Scott F. Williams" <sfwilliams@worldnet.att.net>]

Chris Coracini wrote:

> ok, i've gotten lots of mail about this.  so far, two people have
> responded that they have 15mm spacers on the rears, both claim to not
> notice any difference at all and one guy has gone 80,000 km on them with
> no problems (these are spacers behind the wheel, not the stub axle...).
> the rest responded saying that it will adversely affect handling, namely
> the car will understeer/push more.

Yeah, I can guarantee that this will happen. Widening the rear track makes that
end more stable or less prone to rolling. There will be a resultant increase in
traction and this bias will promote understeer. If anything, you'd want to
increase the track up *front*. I think folks do this to front wheel drive cars
so that they look like "faster/racier" rear wheel drive cars. Now, to my eye it
just makes them look like dumbasses who don't know their asses from their
elbows, but...

> i'll grant that as being true, i'm sure this is known to people that race
> their cars.  i'm having a hard time seeing why being FWD that it would matter
> that much, most of the traction comes from the front wheels, the rears just
> follow.

Well, actually, the traction "comes" just as much from both ends. However, the
amount traction at the front end is much more critical for us. The front end is
loaded more not only because it must support the weight of the front mounted
engine and transmission but because it must also brake, turn, and accellerate.
Often times two of these chores are done at the same time. In other words if
one end of the car is going to lose traction, it'll probably be the front end.

> if it understeers more, that being the case, could the understeer be
> compensated for?  i really don't see why not...  installing a larger
> rear bar?

Gross understeer in our VWs can be "cured" by running a larger rear bar as well
as a big front bar. What the rear bar does is make the rear end work harder at
controlling body roll. Reducing the work load on the front end promotes
traction up there and the car handles more neutrally. So, how does a bigger
front bar accomplish this, right? It would seem that this would effectively
negate anything that the rear does.

Well, it does. -after a point. When our Veedubs roll, the front end changes
it's geometry such that it loses traction. The camber of the wheels turns
positive versus negative.

Positive camber looks like this when you look at the wheels from the front:
\     / On the other hand, negative camber looks like this: /     \

Notice that in the first "diagram" the track (distance between the tires) is
effectively made smaller and that with the negative camber, the track is made
larger. So, what does this have to do with a fat front anti-roll bar? Well, a
bigger bar up front will better control the tendency to go to positive camber
and "voila" you get more traction up front. A popular bar combination for
autocrossing is 28mm rear and 22mm front. For the street I like the 25mm rear
and a 19mm (stock Scirocco 16v?) front. For rallying, I don't run any bars at
all to retain suspension independence.

> i still don't see why it would make a big difference.  i'm sure it will,
> but it should be very subtle...

Actually, it makes all the difference. Well, that is in concert with proper
selection of springs, tires, shocks/struts, etc...

> i've read an article about something else, though, that no one has
> mentioned.  it's "cross weight" (i think that's what it's called).  in other
> words, you have the weight
> distribution front/rear, and side/side, but also diagonally across the
> car (front left to right rear/front right to left rear).

Yah, ideally your front/rear weight bias would be exactly 50/50. -as would be
your side to side and diagnol weights. This is with a driver "installed", of
course. No car is absolutely perfect in this regard, but many come much closer
than others.

> apparently this affects the handling too, and maybe this is the reason
> widening the
> rear track does that....

Um, yes, it affects the handling but no, widening the rear track has nothing to
do with it.

> right now i'm still debating it.  why wouldn't increasing the rear track
> AND adding a stiffer rear roll bar balance each other out?

Ehh... umm... er... You know what? I know that it won't really balance the car
correctly, but... I can't explain why not. I'm at a loss and I'll definitely
ask some folks who can educate us both. Please stand by!

> i hope i'm not coming off as a jerk, i'm just naturally inquisitive....
> thanks for
> all the input on this!

You're coming off like someone who actually wants to learn something. This is a
beautiful thing because now I'm going to get schooled, too. -more news after
this commercial break...
--
Scott F. Williams
NJ Scirocco nut
Hotrod Rabbit GTI
SCCA ProRally driver


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