E30 M-tech springs

[noid]

My E30 came with the M-tech suspension option from the factory; Bilstein HD's from the factory (yellow mono tube, BMW stamped) and associated m-tech springs.

I had bought H&R OE sport springs and was surprised when I went to swap them that the M-tech springs were quite a bit thicker. Felt a bit weird swapping beefier springs for thinner springs

In the near future I plan to swap back to the M-tech springs as I found the OE sports are softer and I preferred the linear feel of the original springs versus the progressive nature of the H&R's.

That aside, I have been trying to do research on the M-tech springs, as they don't seem to come up in the ETK or places like real oem.

The front springs are stamped "BMW 11327422RBW 46 C" and marked with 4 hot pink dots.

The rears are marked 1132317 and are marked with 2 red dots.

Anyone have a way to look these part numbers up?

[e30sh]

From memory the H&R front springs have 6 turns. The factory sport spring has 7. For the same spring wire diameter, the spring with 6 turns will be stiffer than 7 so the 7 turn with a slightly larger wire diameter will still be softer.

I've read the H&R front rates are ~180 lbs/in and the factory sport are closer to ~120.

[noid]

Thickness should play a substantial role in spring rate, and considering these are not normal sport springs (these are derived from the S704 option), they may be of higher spring rate then the H&R's.

Messing around with this calculator:

https://www.thespringstore.com/spring-calculator/spring-rate-calculator.html

Even .1" difference makes a huge effect.

I'm ball parking the numbers on the calculator, but to put things into perspective, to make up a 0.05" difference in spring thickness you would need to reduce the spring count from 7 to between 4-5.

[e30sh]

That's a nice calculator. Mic your wire diameters and see what you have. Wire diameter does make a big difference.

If you just want a to see what going from 6 to 7 coils does, guesstimate and leave all the numbers the same except # of coils.

[noid]

That's a nice calculator. Mic your wire diameters and see what you have. Wire diameter does make a big difference.

If you just want a to see what going from 6 to 7 coils does, guesstimate and leave all the numbers the same except # of coils.

To make up for the difference in one coil, the spring would need to be ~0.02" thicker.

I have attached how small that really is.

[noid]

BMW Germany got back to me, front springs are 3686 newton at 140mm and rear springs are 5151 newton at 122.83mm.

F=Kx

K (spring rate) for the front is 26.32 n/mm or ~150 lb/in and rear is 41.94 n/mm or ~240 lb/in.

Too bad H&R springs doesn't provide their spring rates, its hard to know if whats floating around on the internet is correct. Considering the H&R's are progressive, it would be interesting to know if the initial spring rate is less than OEM.

[reelizmpro]

There's a spreadsheet somewhere that's pretty accurate.

[fporro]

Deffently add the M Tech option to list, here's one of many http://e30performance.info/viewtopic.php?t=1357

[jeffnhiscars]

I remember re tempering leaf springs so have to ask...can the nature of the temper effect the spring rate ?

[e30sh]

F=Kx

K (spring rate) for the front is 26.32 n/mm or ~150 in/lb and rear is 41.94 n/mm or ~240 in/lb.

That's a pretty soft spring. Compresses 150 inches for each pound. :)


Since you have that nice micrometer, take a measurement of the springs you have, plug them in the calc. and tell us what you find out.

Thanks

[noid]

I was able to pull a bunch of info together with the help of BMW Germany. Including spring rates for M3 springs, Evo 3 springs, post 09/87 Mtech springs, my S704 springs and rear springs.

I put it all together here for anyone who is interested:

http://www.rtsauto.com/e30-stock-spring-options-and-spring-rates/

[e30sh]

I was able to pull a bunch of info together with the help of BMW Germany. Including spring rates for M3 springs, Evo 3 springs, post 09/87 Mtech springs, my S704 springs and rear springs.

I put it all together here for anyone who is interested:

http://www.rtsauto.com/e30-stock-spr...-spring-rates/

Nice job, thanks for the trouble. Did you happen to measure the wire diameters?

Thanks

[noid]

I just bought new 31331130054 and 33539061134 springs.

Front thickness is 13mm.

Fronts are true 6 coil:

[noid]

HR OE sports, Mtech, S704 M sport suspension springs.