Originally Posted by rldzhao
Thank you for your efforts. Glad to see someone on the forum who shares my passion
A couple comments. (more to come)
1) Great explanation on why most of the lowering spring kits are bad for handling
. When you drop the front by 1" and have very little of bump travel left, roll resistance will spike up even with slight compression.
When this occurs to the outer wheel during cornering, unpredictable high roll resistance means more weight transfer to the outer front wheel, which means more understeer...
2) I remember that Steve Dinan said that the OE suspension has 0.5" of travel before making bump stop contact. The bump stop is 2.375". Therefore, the total amount of compression travel (before considering the bump stop) is 2.875".
I also measured my OE front shock and there is precisely 5.75" of total travel
(bump and droop). Thus, per my measurements, the total front suspension travel (bump and droop) is divided 50/50, e.g. 2.875" for bump and 2.875" for rebound
. (give and take 0.25" due to variation in equipment, spring rate, etc.)
Further, let's assume that the stock bump stop will be compressed to about 1" at the limit (from 2.375" unloaded). This means that only 2.875"-1"=1.875" of effective bump travel is available for the M3.
(consider a kit that drops the front by 1" and you will see why this is a bad idea)
(note: I use bump/compression, rebound/droop interchangeably)
Thanks for the feedback and thanks for firming up the front suspension measurements - I haven't taken mine apart yet, so they're not as precise as yours.
We might differ a bit in our details - my measurements have the front damper further than half-way through its travel at static OEM ride height, while yours have it half-way. Other than that, our measurements are remarkably consistent.
It doesn't matter which numbers are the more precise; either way the conclusions are the same. The issue in the front is the limited compression travel and the problems it causes for suspension mods.
Edit: By the way, when I measured mine, I concluded that my front bump stops touch (lightly) on the top of the damper when the suspension is static. Steve D and I disagree, and it' s more likely he's right than I am.