Threaded Body Coil-Overs

With 2.5" Race Springs

Adjustable perch and spring installed on strut housing

 

Modified strut housing. It isn't even really necessary to remove the stock spring perch. I removed it because I'll never reinstall the stock suspension.

 

Here is a threaded spring perch.

 

Threaded spring perches allow ride height fine-tuning and the use of 2.5" ID springs which come in a wide variety of free lengths and rates. E28's love lots of spring rate due to high weight and a high center of gravity. The high spring rate cuts down on dive under braking and body roll while cornering. The disadvantage of such spring rates is ride harshness if you care about such a thing.

 Car

 Spring Rate (In/Lbs)

 535i

155

 535is

175 

 M5

195 

These rates are approximate and based on information from a variety of sources so don't bet your car on the numbers above. Most aftermarket springs run in the low to mid 200 range. I am currently using 500 in/lb fronts and 400 in/lb rears. Ouch! My kidneys. When combined with the largest sway bars I could find, I got a car with little body roll or dive.

Spring free length is critical. Too short and either the car will sit too low or you run the risk of coil bind if the perches are too high. Too long a spring might cause coil bind because the perch can only be adjusted so low before rubbing the tire. The alternative is to weld a ring to the strut housing below the original perch for the threaded tube to sit on and using a lower mounting point on the rear shock. Then wheel offset must be looked at to avoid rubbing the inside of the tire on the spring.

I got my threaded adjusters and springs from Jay Morris at Ground Control. He has gone to great lengths to ensure my satisfaction, so give his outfit some serious thought if you are considering going this route.

I've heard that the 2.5" springs can be used with the stock upper strut bearings with a special upper perch, but that is not ideal. An adjustable camber/caster plate should be used.

Shock and strut selection presents another problem. See my shocks/struts page for details.

Ed

Back to the E28 page

Team DFL home