BMW E82/E90 Coilover Ride Height and Spring Preload Fix Trick
BMW OEM part improves ride quality, maximizes available suspension travel for KW, Bilstein and TC Kline (Koni) coilover struts.
The BMW E82 1-Series (2007-2013) and E90 3-Series (2006-2013) represent modern high-performance bargains, with the turbocharged 135i and 335i models being plentiful, inexpensive, and having massive aftermarket support. However, while modifying the engines for power is extremely simple, upgrading and effectively tuning the suspension is quite a bit more complicated.
This is especially true of the very tire-limited 135i, which has a shorter wheelbase and requires widebody fenders to comfortably accommodate anything wider than 255 section-width rubber under it. With such a limited amount of tire grip available, careful suspension tuning is paramount to achieving adequate ride, handling and limit performance, especially with tuned cars easily producing over 400 WHP.
Unfortunately, many of the prominent aftermarket suspension tuners and manufacturers of adjustable coilover systems, like KW, Bilstein and TC Kline, among others, have come up short for the platform, taking ideologies from previous BMW chassis, like the E46, and calling it good enough. While spring rates, sway bar sizing and bushing design are the subject of a future episode, for now let’s focus on a more immediate issue: spring preload and ride height.
Simply put, with an adjustable “coilover” front suspension, ideally, the spring will be minimally compressed at full droop (i.e. when the car is on jack stands and the wheels are off the ground). If the coilover spring perch is wound up too high the spring will always be under too much spring preload, which is exactly what it sounds like. The “ideal” amount of spring preload is usually just a few millimeters, which will prevent the spring from making any noise or rattling while at full droop, or when going over bumps at speed.
However, with KW, Bilstein, TC Kline and many other European brand coilovers, there is no provision to set the vehicle ride height by adjusting the length of the shock body. Instead, the ride height is determined only by the stiffness of the springs, and the willingness of the driver to compress that spring further to lift the car. This not only reduces available suspension travel, but compromises the ride quality and handling by creating excess spring preload.
Other coilover suspensions, like Ohlins Road & Track for the BMW 1M and M3, correctly allow for the strut length to be adjusted, dictating the ride height. This allows for the spring perch to serve as a means of simply adjusting spring preload, or being moved up or down to accommodate different spring lengths.
Fortunately, there is a fix for BMW coilover setups that do not offer independent ride height and spring preload adjustment, but it does come with some caveats.
Project 135i rolls on TC Kline single-adjustable coilovers, which do not have independent ride height adjustment. However, as I have now swapped in softer springs for street use, the front end has been lowered even further, which looks cool, but is not practical for driving around Los Angeles. To correct this, the body of the car needs to be lifted, while allowing the spring perch to be wound down to allow for near-neutral spring preload and full suspension travel.
BMW part number 31306779671 is an OEM part directly from BMW that allows the front end to be lifted 20mm (0.8”), by sitting between the strut top and the strut tower (body) of the car. It is intended for “rough road” driving and to prevent bottoming out or scraping the underside of the car. And, while BMW did not intend this for aftermarket suspensions, it works perfectly for our application, however, there are a few caveats to make it work.
First, flip the ride height spacer over and knock out the factory alignment dowel, which limits front negative camber adjustment. A punch and a hammer will make quick work of this.
Pro tip: this install requires six (6) new M8x1.25 nuts for assembly. Thread them onto the studs before you knock out the alignment pin to prevent the studs from popping out from the impact of the hammer.
If you have an OE-type suspension, like lowering springs with stock top hats, simply bolt the ride height spacers on and reinstall into the car. However, if you have adjustable camber plates it’s a bit more complicated as the studs that mount the spacer into the chassis are 180° opposed from the studs coming out of the coilover’s camber plate. Put simply, this will mis-align the camber plate, unfavorably altering the vehicle’s alignment and reduce overall adjustment range of the plate.
For the Vorshlag camber plates on Project 135i, the remedy is an old school BMW handling trick: flip the camber plates from side to side. By using the driver’s side camber plate on the passenger side and then rotating it 180° (front-facing to back-facing), and vice versa, the ride height spacer can now be installed, and the camber plates are oriented in the correct fashion once assembled, maintaining both the full range of adjustment and the vehicle alignment settings. On the E82 and E90 chassis there is ample clearance within the strut tower to do this safely. Newer BMW platforms with more complicated strut tower designs may be less forgiving.
With the 20mm body lift in place, the daily driver-friendly 280 lb-in, 8” Swift coilover springs can now be wound down to the ideal near-neutral spring preload, allowing for maximum suspension travel while retaining adequate front ride height. Praise be the OEM BMW parts bin.
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