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E30 Stock Spring options and Spring rates

July 5, 2017
By

These are from technical specification drawings for stock E30 springs straight from BMW Germany. The spring forces and lengths were from BMW Germany, while I calculated the spring rates to accurately compare the springs per inch of travel.

Only looking at spring force does not allow you to compare springs because it only signifies the force when fully compressed. Because of different ride heights, the total force to compress is not that important (unless you want to know at what force you would completely bottom out the spring), for road feel and understanding how stiff a spring is relative to another, we need to measure the amount of force it takes to move each spring an inch (spring rate).

Below the way this was done was by using F = Kx, or Force = spring constant*distance, where the spring constant K is our spring rate.

 

Front Springs

S704 M sport suspension package (pre 09/87) 31331132742 with Pink dots:

Spring force = 3514 – 3686 Newton at Ln length 140 mm

Spring rate at upper level: 26.328 N/mm or 150.336 lb per inch

 

M-tech suspension package (09/87+) 31331130054:

Spring force = 3426 – 3614 Newton at Ln length 126.5 mm

Spring rate at upper level: 28.569 N/mm or 163.133 lb per inch

 

E30 M3 springs 31331130046:

Spring force = 3117-3283 Newton at Ln length 126.5 mm

Spring rate at upper level: 25.952 N/mm or 148.189 lb per inch

 

E30 M3 Evo 3 springs 31332226781:

Spring force = 2970-3130 Newton at Ln length 116.5 mm

Spring rate at upper level: 26.875 N/mm or 153.46 lb per inch

 

Overall heights in order (S704 not available, albeit overall longest of the 4):

31332226781 (E30 M3 Evo 3)> Ln: 116.5 mm / Overall: 305.7 mm
31331130054 (Mtech) > Ln: 126.5 mm / Overall: 313 mm
31331130046> (E30 M3) Ln: 126.5 mm / Overall: 318 mm

 

Spring Rates in order:

31331130046> (E30 M3) > 148.189 lb per inch
31331132742 (S704 M package) > 150.336 lb per inch
31332226781 (E30 M3 Evo 3)> 153.46 lb per inch
31331130054 (Mtech) > 163.133 lb per inch

 

Rear Springs

S704 M sport suspension package (pre 09/87) 1132317 (sold as pair 33539061085) with red dots:

Spring force = 5038 – 5151 Newton at Ln length 122.83 mm

Spring rate at upper level: 41.936 N/mm or 239.460 lb per inch

 

M-tech suspension package (09/87+) 33539061134:

Spring force = 4739 – 4885 Newton at Ln length 115.7 mm for springs with red dots

Spring rate at upper level: 42.22 N/mm or 241.082 lb per inch

Spring force = 5032 – 5177 Newton at Ln length 115.7 mm for springs with white dots

Spring rate at upper level: 44.745 N/mm or 255.50 lb per inch

 

E30 M3 springs 33539061510:

Spring force = 5165 – 5365 Newton at Ln length 122.80 mm

Spring rate at upper level: 43.688 N/mm or 249.464 lb per inch

 

Spring rates in order:

33539061085 (S704 M package) > 239.460 lb per inch
33539061134 (Mtech) > 241.082 lb per inch (red dots)
33539061510 (E30 M3) > 249.464 lb per inch
33539061134 (Mtech) >  255.50 lb per inch (White dots)

Overall height lowest to highest (specific overall height unavailable, extrapolated by Ln value):

33539061134 (Mtech)
33539061510 (E30 M3)
33539061085 (S704 M package)

One Response to E30 Stock Spring options and Spring rates

  1. Teutonic on July 12, 2017 at 6:01 pm

    Thanks for posting this useful info. I had the M-Tech suspension on my 318is and still have the springs on the shelf. The Mtech rear spring free height (white dots) is 9 inches.

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