Quote:
Originally Posted by Snertz
Honest question, I wasn't aware of the outer limits as to what spacers can be run before steering is significantly affected.
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That's not an easy question- it depends on the car, usage etc. I don't know the 1M numbers, but a guestimate would be up to maybe a 6mm/ 1/4" spacer for street use. For competition cars things get more complicated...
As a generalization, a smaller scrub radius is desirable for tight, low speed corners, such as autocross, while a larger scub radius is good for higher speed and steering feedback.
By adding a spacer to the 1M you're moving it towards more scrub radius, but realize that's not true for most cars. Porsche, for example, runs a negative scrub radius on its newer cars, so it you add a 6mm spacer to a 996 you go from negative 7mm scrub down to just negative 1mm scrub. As you might imagine things start to get wonky around 0 scrub, as the forces to the steering wheel get reversed as you cross zero scrub radius. This changes all kinds of things- the direction the steering wheel will jerk when ABS kicks in, etc, and really ideally needs a different setup and alignment.
For this reason you'd notice the effect of moving the 1M's wheel inboard quite quickly- off the top of my head I think I'd try to stay within ~3mm of stock moving in that direction unless I was doing a competition/ autocross setup. Outboard is less sensitive, but you're still dealing with small numbers, so adding 6mm to the spacer would certainly be noticeable if you were looking for it, as it might be doubling the scrub radius. The wheel will jerk side to side harder under ABS, the wheel will kick harder over bumpy pavement in cornering, and steering effort (and feedback) will generally increase.
For street use for the best feel I'd really try to stick close to stock- it's one of the more sensitive number in the suspension. I guarantee you BMW engineers agonized over a 2mm difference in scrub and this is what they came up with. Seems a shame to chuck that hard work without a good reason when you can "do it right" with lighter, wider wheels.