From: Satch Carlson <satch_at_alaska.net>
Date: Sun, 13 Oct 1996 15:37:12 -0800
Subject: 325 iX understeer corrections (Satch)
Re: iX suspension mods
(Filippo Morelli replied)
> Any thoughts on what this will do to a car (325iX) with a tendency to
> tramline? I've been trying to solve this for a while with limited
> Filippo's reply:
>Tramline I suppose is understeer in a big way. First time I've heard >that term, but I'll have to remember it.
>Sounds like you need to drop a line to someone like Satch who has
>probably done many nasty things to 325iX's at this point, or witnessed
>such. He may have some advice. Being AWD, it's different enough from >the stuff I've played with that I wouldn't want to guess the approach! >(I'd be doing a stress bar and an adjustable rear sway bar).
Actually, physics is physics, except with some cars, which seem to defy
the laws of God and Schnitz von Bimmerhead. Anyway: the iX (as I
understand it---there are a lot more knowledgeable gurus out there than
Yr Hmbl Etc) uses the Ferguson Formula 4WD system. That's (sort of) the
good news; it means what you have is a torque bias of 67% (rear) to 33%
(front). Briefly, that means under MOST conditions the car behaves like
a phenomenal rear-drive cruiser, the front pulling only enough to get
you through corners without going tail-happy like our less fortunate
Bimmer Brethren. The ultimate tarmac rally car.
The trade-off for this stability at most speeds is that the car tends to
plow like a hungry shoat in Very Intersting Situations.
Our approach on the Alaska Rally Team (mostly through modifications to
Steve Norman's iX, the Red Dog, because he can afford it) has been to
get the car to pivot around the inside front wheel in a trail-braking
approach to a corner (different driving schools use different terms:
basically, you want to start the turn before you're completely off the
brakes. This wonderful area of TRANSITION is what separates smooth fast
drivers from the also-rans).
The turn-in can be effected through several means. With the Red Dog, we
had Steve Dinan install your basic Big Mothah anti-roll bar in the back
(well, the car was there already, after all, getting a 2.7 Dinan engine
transplant), along with Bilsteins all around. Dinan also changed the
springs, but it was a mistake in our case, because on marathon rallies,
especially one like the Rally of the Lost Patrol, you need all the
ground clearance you can get.
Of course you have the tower-to-tower strut, because you won't get
anywhere trying to set up the suspension on a flexible flyer.
Anyway, one thing you'll notice even after you get the car to turn in is
that as you apply power, you experience the joys of weight transfer; all
the mass you've happily placed on the front wheels so they could do
their job in braking and steering has now gone to the back wheels, which
are dumbly trying to push the car; at this point, of course, the fronts,
being relieved of that downforce, are happy to relinquish their little
task of steering. . .
All these phenomena occur in other cars, of course, but they are not so
easily demonstrated. A good torquey open-wheeled car, like the
turbo-Renaults they used in Yurrup a few years ago, is an exemplar: In a
turn, with the suspension laoded, you can actually watch the difference
in steering and pushing as you play with the throttle (coming to your
senses somewhat shy of the Armco, one presumes).
With a pant-load of cash, you can revalve your Bilsteins (the approach
we will take when we rebuild the Bad Dog); in short, on braking, the
mass will shift quite readily to the front tires, but on acceleration,
the return dampening will keep the front end down. This is the sort of
experimentation best carried out on the race track, as a 5000-mile rally
doesn't usually give you lots of opportunities to change things.
Gordon Haines in Colorado(ghaines_at_epol.com) puts out a newsletter
devoted to the iX; you MUST sign up for the iXChange! But most of its
members are rather kinder to their rides than I am, so there is not as
much development in these cars. . .
And now a question to our Yurropean amigos (and amigoettes): Since over
there one can lay hands on a 5-series iX, should it not be possible to
lay one's mitts as well on, oh, I don't know, maybe the BRAKE ASSEMBLIES
AND SPINDLES?! Gee, if they would fit the E30, we could have an iX with
BRAKES for once! And FIVE BOLT WHEELS! And---
Well, I can dream, can't I?
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