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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Suspension Setup with Coilovers



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      09-12-2018, 06:50 PM   #1
Turbo Seabass
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Suspension Setup with Coilovers

Hi, sort of new to this but I have a 2007 335i with Bilstein Pro Street S coil overs sitting at 22.75" measured from bottom of wheel to fender arch, on the left side, and 22.6" on the right side. I found that the M3 Comp Package sits around 23.6" (600mm) up front and 23" (584mm) in the rear.

1. Does the increased rake negatively affect handling considering the front is lowered by an additional 0.6" when accounting for a ~0.3" drop all around (compared to an M3 zcp)? I'd think I should keep the drop level with the factory height, but don't know the acceptable amount of additional drop in the front.

2. How much higher should the left side coil overs be in order to balance the car with my weight in the drivers seat (150 lbs)

Any help is appreciated!
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      09-13-2018, 08:03 AM   #2
bbnks2
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Quote:
Originally Posted by Turbo Seabass View Post
Hi, sort of new to this but I have a 2007 335i with Bilstein Pro Street S coil overs sitting at 22.75" measured from bottom of wheel to fender arch, on the left side, and 22.6" on the right side. I found that the M3 Comp Package sits around 23.6" (600mm) up front and 23" (584mm) in the rear.

1. Does the increased rake negatively affect handling considering the front is lowered by an additional 0.6" when accounting for a ~0.3" drop all around (compared to an M3 zcp)? I'd think I should keep the drop level with the factory height, but don't know the acceptable amount of additional drop in the front.
2. How much higher should the left side coil overs be in order to balance the car with my weight in the drivers seat (150 lbs)

Any help is appreciated!
1. It's hard to say whether or not more rake will negatively affect handling. That depends on a lot of factors. I think the main reason you see more lowering up front with aftermarket springs is to get a more "flush" look. Another possibility is that it could be done to combat the affects of the staggered factory wheel setup which generates under-steer. Lowering the front should help reduce under-steer. Although, if you drive the car on track, you'll find you also need a bit more static camber to offset the camber curve penalty that lowering comes with.

The car already has about 1/4" rake from the factory despite the front fenders having a larger visual wheel gap. Personally, I don't see more rake than that as really being beneficial on a car that doesn't have proper aero. Adding rake to a car without aero can actually result in more air leakage under the car in the rear without a sealed diffuser in place. This would increase rear lift (make it unstable at high speeds) and offset any gains you made in aero by lowering the front end. A lot of BMWs I see at the track have a pretty neutral rake and they sit pretty close to factory height. Put a proper wing and diffuser on the car and you'll need to add more rake (and/or change springs) to prevent the car from going into positive rake (due to down-force) while on the straight-aways. In factory form, the car is probably not going to be producing too much rear down-force. So, rake would not be needed for this reason. It would only really be needed for the reasons mentioned above, to correct a visual thing (wheel gap), or, to mitigate a handling problem (address the factory wheel setup which produces understeer). All this being said, <1" of rake is not all that excessive and you probably won't even notice any difference until you get to advance level of HPDE.


2. You can't really try to blindly compensate for driver weight like this. You really need to get the car corner balanced. Ride height differences don't always correlate to weight differences. Putting the car on scales is the only way to know if what you're doing is helping or hurting the cars balance.

Last edited by bbnks2; 09-13-2018 at 09:12 AM..
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