Quote:
Originally Posted by boro92
Firstly, the above alignment is achieved all on stock xDrive ride height (I am on stock springs). The only suspension modifications to the car are Vorslag camber plates and Bilstein B8 shocks. The latter is important. Bilstien B8 shocks are shortened shock bodies with also reduced shock stroke. I run these on stock springs for a couple reasons. The obvious one is firmer bump travel and a significant boost in rebound. There is simply much improved body control with these shocks. The less obvious reason is reduced suspension droop. Suspension droop is a big factor in tuning how the car handles. Droop is defined as how much the wheel can extend downwards beyond the stock ride height. IE: Notice when you jack up the car, the wheel has a lot of downward travel? This is droop. Droop determines how grip is maintained on both front and rear axles to a degree. Consider this: When you accellerate, the rear end squats. But also, the front end lifts. In extreme situations, reduced droop will reduce front end rise under accelleration, which as you can imagine, will affect how the front tires grip in these situations. But what's more is that if the front end rises less during hard accellerations, this also means weight transfer happens more quickly between front to rear - it simply takes less time for the rear end to squat and load up the rear tires. In a dynamic driving situation, one can load up whichever end of the car more quickly to manage weight balance - which is a great advantage on the track. What's more, reduced droop also helped me pick up the inside rear tire during cornering. Yes, you read that right. A BMW is picking up the inside rear tire during cornering. What's this mean? It means a lot of weight is transfered to the nose of the car, helping generate more mechanical grip (to a degree - and in very specific situations, which is beyond the scope of this post. But hear me out), and ultimately helping the car rotate on corner entry.
|
I'm interested in your outlook on suspension droop. I made a thread a while ago, and people basically told me I was an idiot for worrying about droop. I'm not sure that pursuing limited droop on the front axle is the best way of going about things. With our xDrive suspensions, we're already limited in total travel, and our suspension is shifted up a bit too, so in comparison to a RWD car, we've got roughly the same bump travel, but less droop.
With the B8's, you're limiting the droop travel even further. When your on the throttle then, you're taking grip away from the front, and I would think that it would result in late corner understeer just as you're getting on the power. Its fairly easy to drive around corner entry understeer (trail braking), but if your car wants to push wide on corner exit, that means you've got to wait longer to add throttle.
Wouldn't a more effective way to speed weight transfer be to increase overall spring rate? Maybe run a longer, stiffer bumpstop in the rear? Decreased front rebound and rear compression damping and increased front compression and rear rebound?
Quote:
Originally Posted by boro92
The best thing to do here to really make the car a precision machine is to insert some full aluminum subframe bushings in the back. Turner, RE and Bimmerworld make these.
|
I'm interested in these, mostly just from a durability standpoint--I don't want to ever have to replace those suckers once I've done them the first time. I worry a bit about the chassis attachment points though. The E46 cars have cracking problems, I'd hate to encounter something similar on our vehicles. I also haven't heard from anyone who is running them, it seems like only race teams are using them.