In performing some recent work on my car I came across some potentially useful information so I figured I'd post here as an FYI in hopes that it may help others in the future.
It's been common knowledge for a long time that Bilstein inserts for BMW E30s are notorious for inducing a lot of contact with the bump stop even at very reasonable (i.e. not super low) ride heights. I recently installed a fresh set of B8s on my S54 swapped 1991 318is without trimming the bumpstops. The shocks were purchased in late 2023 from Rockauto. The spring setup is Ground Control coilover sleeves, Ground Control street camber plates, and 225lb front and 450lb rear spring rates. I hadn't fully dialed in ride heights before tearing the car back apart, but the car was sitting at a very reasonable height upon initial install, much higher than most people seem to go for. With this setup I actually thought the ride was quite good even over bumpy Michigan roads. I noticed that over potholes where the suspension first extended into rebound before compressing, the ride was surprisingly comfortable. However, the front suspension felt harsh over abrupt raised bumps in the road, which lead me to believe that I was riding on the bump stops.
My goal was to trim the bump stops enough to eliminate the harshness during normal driving but keep enough of the bump stop so that during hard corning the bump stop is engaged and contributing to the overall spring rate. Many people overlook this, but it is a key component in suspension setup, and many sporty OE suspensions are tuned like this from the factory. Mcpherson strut cars have little to no negative camber gain as the suspension compresses from ride height, so it is often advantageous to prevent excessive roll to maintain the optimal tire contact patch. This is commonly done with stiff springs and anti roll bars, but those sacrifice ride quality so I'm trying to avoid going too extreme on those. I selected spring rates to target natural front and rear suspension frequencies similar to OE high performance vehicles such as the 911 GT3, Mustang GT350, Camaro ZL1, etc. I may adjust my spring rates to hit my target frequencies once I get a final corner weights on the vehicle.
I had pulled an old set of B8s out of the car, age unknown, before installing the new shocks. I pulled them apart to access the bump stop only to find that the original bump stops were completely disintegrated. I took several measurements of these old B8s and the new B8s on the car. Then I removed the new B8s and pulled them apart to access the bump stops and take some measurements.
Here's what I found:
-Old B8 total front shock travel sans bump stop: 168mm
-Front wheel travel distance (on vehicle) from ride height to full droop: 87mm
-Front shock travel distance from ride height to full droop: ~82mm. Calculated using 87mm wheel travel multiplied by .94 motion ratio found here E30 Effective Wheel Rates - Page 2 (e30sport.net)
-New B8 total front shock travel sans bump stop: 165mm (shock appears slightly redesigned)
-New B8 front bump stop overall length: 85mm
Using these measurements, you can calculate how far off the bump stop you are at ride height. Simply take the overall shock travel and subtract off the bump stop length and the distance between ride height and full droop. In this case that would be 165 - 85 - 82 = -2. This tells me that at ride height I am compressing the bump stop by 2mm. I plan to trim 15-25mm off the bump stops, still trying to work out exactly how much I want to do. I'll report back with my findings.
It's been common knowledge for a long time that Bilstein inserts for BMW E30s are notorious for inducing a lot of contact with the bump stop even at very reasonable (i.e. not super low) ride heights. I recently installed a fresh set of B8s on my S54 swapped 1991 318is without trimming the bumpstops. The shocks were purchased in late 2023 from Rockauto. The spring setup is Ground Control coilover sleeves, Ground Control street camber plates, and 225lb front and 450lb rear spring rates. I hadn't fully dialed in ride heights before tearing the car back apart, but the car was sitting at a very reasonable height upon initial install, much higher than most people seem to go for. With this setup I actually thought the ride was quite good even over bumpy Michigan roads. I noticed that over potholes where the suspension first extended into rebound before compressing, the ride was surprisingly comfortable. However, the front suspension felt harsh over abrupt raised bumps in the road, which lead me to believe that I was riding on the bump stops.
My goal was to trim the bump stops enough to eliminate the harshness during normal driving but keep enough of the bump stop so that during hard corning the bump stop is engaged and contributing to the overall spring rate. Many people overlook this, but it is a key component in suspension setup, and many sporty OE suspensions are tuned like this from the factory. Mcpherson strut cars have little to no negative camber gain as the suspension compresses from ride height, so it is often advantageous to prevent excessive roll to maintain the optimal tire contact patch. This is commonly done with stiff springs and anti roll bars, but those sacrifice ride quality so I'm trying to avoid going too extreme on those. I selected spring rates to target natural front and rear suspension frequencies similar to OE high performance vehicles such as the 911 GT3, Mustang GT350, Camaro ZL1, etc. I may adjust my spring rates to hit my target frequencies once I get a final corner weights on the vehicle.
I had pulled an old set of B8s out of the car, age unknown, before installing the new shocks. I pulled them apart to access the bump stop only to find that the original bump stops were completely disintegrated. I took several measurements of these old B8s and the new B8s on the car. Then I removed the new B8s and pulled them apart to access the bump stops and take some measurements.
Here's what I found:
-Old B8 total front shock travel sans bump stop: 168mm
-Front wheel travel distance (on vehicle) from ride height to full droop: 87mm
-Front shock travel distance from ride height to full droop: ~82mm. Calculated using 87mm wheel travel multiplied by .94 motion ratio found here E30 Effective Wheel Rates - Page 2 (e30sport.net)
-New B8 total front shock travel sans bump stop: 165mm (shock appears slightly redesigned)
-New B8 front bump stop overall length: 85mm
Using these measurements, you can calculate how far off the bump stop you are at ride height. Simply take the overall shock travel and subtract off the bump stop length and the distance between ride height and full droop. In this case that would be 165 - 85 - 82 = -2. This tells me that at ride height I am compressing the bump stop by 2mm. I plan to trim 15-25mm off the bump stops, still trying to work out exactly how much I want to do. I'll report back with my findings.
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