I have been meaning to share this project with you fellow enthusiasts for a while, but didn't want to share anything before I could get some miles in and give a proper review of the setup.
After about a year of research, fabrication, and testing, I’ve finally finished a custom shock setup for my M3! This was quite a learning process to say the least. I am lucky enough to have access to some pretty neat tools, parts, and smart people in the suspension industry, which helped making this one-off setup possible.
Project goals
Overall, I wanted to improve the comfort, handling, and capacity to drive rough roads without bottoming out. It would also be nice to adjust the compression and rebound without removing the shocks or wheels, since that can be pretty cumbersome (looking at you, Koni rears).
Why not just buy something pre-built? Part of it was having access to the components, but I also wanted to turn it into a learning opportunity. To not only end up with a nice setup, but know how to get there and how to continually improve it!
For reference, my car previously had Dinan springs (175lb/in front, 475lb/in rear) with Koni shocks, and is stock other than some 245/275 tires on 18’s.
Rear shocks
For the rear, I used 2.0" monotube aluminum piggyback dampers with base valves. This reservoir positioning is convenient because I could avoid any modifications like drilling into the trunk or using any long hoses. The only thing is I had to convert the upper mount from the stock bushing to a clevis which required machining a mount.
The shock in place
The rebound adjuster
The Dinan springs (left) compared to Eibach's Extreme Travel 650lb springs (right).
Front struts
The fronts were a lot trickier since it's a strut and therefore a structural component that both pivots and rotates. I ended up using 2.0” monotube steel struts with a detachable piggyback. This was required so that the reservoir can be attached after installing the strut body into the knuckle. I did not have access to inverted strut body components at the time, so these are using a conventional architecture with a large shaft and oil flow through the bottom.
Initial install with 300lb/in springs.
After switching to 375lb/in springs.
Rebound adjuster
Setup
I went through a number of spring and damper iterations. Honestly, the first thing I tried was damn good and a huge improvement over stock. But there was still room for improvement. It was a bit soft when pushing hard, and the balance was a little off from a damping perspective. I experimented with the "flat ride" spring rates with and without rear swaybar, but it wasn't quite right for my preferences.
Halfway through, I hooked up a data acquisition system to monitor shock position and speeds to help speed up the process and know where in the travel it was operating. It is pretty eye opening, and shows that what you feel might not be what’s happening at all!
I finally settled on 375/650 spring rates, which puts it right around 2Hz front and rear. Ride height is 14” all around. Bump travel is maximized for my wheel/tire setup, and droop travel is only 1” less than stock. The dampers are matched accordingly and are pressure balanced at all speeds. I would say the tune is something between a street and track setup – firm but still compliant enough to handle anything from a bumpy mountain road to smooth high speed curves.
Driving impressions
It’s pretty amazing how much shocks can change a car. I’d say it’s the first or second thing anyone should do when modding their vehicle, right up there with wheels & tires. It completely changed the character of it!
The handling is so much sharper, and it can soak up anything I throw at it from bumps to pot holes to hard cornering. Seems like the faster it goes, the more planted and at home it feels. If I had to pick an area to improve, it would be that 2Hz is a little firm for city driving, as it tends to follow the undulations of the road. The 300/475 rates were definitely more compliant and would be a solid choice for a purely street driven car as well.
The next step will be making them electronically adjustable, which adds a ton of complexity but should be doable. That would be mostly for the learning, as I think these definitely do the job.
Anyway… I hope you guys enjoyed seeing something different! Also I should mention... as you can see I am using FOX shock components hence the sweet stickers, but these are not an official product of theirs.
Here are some really great resources I found during my research if anyone is interested:
After about a year of research, fabrication, and testing, I’ve finally finished a custom shock setup for my M3! This was quite a learning process to say the least. I am lucky enough to have access to some pretty neat tools, parts, and smart people in the suspension industry, which helped making this one-off setup possible.
Project goals
Overall, I wanted to improve the comfort, handling, and capacity to drive rough roads without bottoming out. It would also be nice to adjust the compression and rebound without removing the shocks or wheels, since that can be pretty cumbersome (looking at you, Koni rears).
Why not just buy something pre-built? Part of it was having access to the components, but I also wanted to turn it into a learning opportunity. To not only end up with a nice setup, but know how to get there and how to continually improve it!
For reference, my car previously had Dinan springs (175lb/in front, 475lb/in rear) with Koni shocks, and is stock other than some 245/275 tires on 18’s.
Rear shocks
For the rear, I used 2.0" monotube aluminum piggyback dampers with base valves. This reservoir positioning is convenient because I could avoid any modifications like drilling into the trunk or using any long hoses. The only thing is I had to convert the upper mount from the stock bushing to a clevis which required machining a mount.
The shock in place
The rebound adjuster
The Dinan springs (left) compared to Eibach's Extreme Travel 650lb springs (right).
Front struts
The fronts were a lot trickier since it's a strut and therefore a structural component that both pivots and rotates. I ended up using 2.0” monotube steel struts with a detachable piggyback. This was required so that the reservoir can be attached after installing the strut body into the knuckle. I did not have access to inverted strut body components at the time, so these are using a conventional architecture with a large shaft and oil flow through the bottom.
Initial install with 300lb/in springs.
After switching to 375lb/in springs.
Rebound adjuster
Setup
I went through a number of spring and damper iterations. Honestly, the first thing I tried was damn good and a huge improvement over stock. But there was still room for improvement. It was a bit soft when pushing hard, and the balance was a little off from a damping perspective. I experimented with the "flat ride" spring rates with and without rear swaybar, but it wasn't quite right for my preferences.
Halfway through, I hooked up a data acquisition system to monitor shock position and speeds to help speed up the process and know where in the travel it was operating. It is pretty eye opening, and shows that what you feel might not be what’s happening at all!
I finally settled on 375/650 spring rates, which puts it right around 2Hz front and rear. Ride height is 14” all around. Bump travel is maximized for my wheel/tire setup, and droop travel is only 1” less than stock. The dampers are matched accordingly and are pressure balanced at all speeds. I would say the tune is something between a street and track setup – firm but still compliant enough to handle anything from a bumpy mountain road to smooth high speed curves.
Driving impressions
It’s pretty amazing how much shocks can change a car. I’d say it’s the first or second thing anyone should do when modding their vehicle, right up there with wheels & tires. It completely changed the character of it!
The handling is so much sharper, and it can soak up anything I throw at it from bumps to pot holes to hard cornering. Seems like the faster it goes, the more planted and at home it feels. If I had to pick an area to improve, it would be that 2Hz is a little firm for city driving, as it tends to follow the undulations of the road. The 300/475 rates were definitely more compliant and would be a solid choice for a purely street driven car as well.
The next step will be making them electronically adjustable, which adds a ton of complexity but should be doable. That would be mostly for the learning, as I think these definitely do the job.
Anyway… I hope you guys enjoyed seeing something different! Also I should mention... as you can see I am using FOX shock components hence the sweet stickers, but these are not an official product of theirs.
Here are some really great resources I found during my research if anyone is interested:
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