Re: iX suspension mods

>Michael,

(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
> success.

> 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).

>Cheers,

>Filippo

Satch's response:

Yep.

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?

sc