Lower Front Suspension

[jackthat]

Old School front suspension lowering was accomplished by cutting off a bit of the spring to the desired height. Why couldn't this be done on our e28's if we don't take off too much? I was thinking about lowering the front suspension about an inch with this method. What are your thoughts?
Rick

[Shawn D.]

There's no reason it couldn't be done, as a few of us have discussed before on the board. Make sure you loosen the control arm bushings and retighten them at the new height.

The problem is that when you do this, you're increasing the spring rate on the front only, thus increasing understeer.

[wkohler]

There's no reason it couldn't be done, as a few of us have discussed before on the board. Make sure you loosen the control arm bushings and retighten them at the new height.

The problem is that when you do this, you're increasing the spring rate on the front only, thus increasing understeer.

You also wouldn't be increasing the stiffness of the spring, so your spring deflection really wouldn't change, leading to a much higher force gradient compared with deflection. Pretty much what Shawn said, but aftermarket springs are plentiful and inexpensive, it seems somewhat of a waste to go through the trouble.

[wkohler]

Here's the equation for calculating spring rates:

Spring rate (K)=wire dia (d) to 4th power times Spring modulus 12.000.000 all divided by 8 times the number of active wraps(N)times Diameter of the coil(D) cubed.

[jackthat]

Yeah, well I'm a dumb ass. And also, I will be replacing my strut inserts soon and thought while I had them apart...
Also in my plans is a vegie oil conversion with an additional tank in the trunk, and additional weight.
I don't think I want the stiffer ride with the lowering springs. My race car rides like, well, a race car--a board on a rail. My 524 is a commuter, my old man sedan. I'm probably thinking backwards, but with the additional weight in the rear, cutting the front springs would even things? Dumb ass alert! If I knew anything, I wouldn't ask you bright guys. Thanks for your help. I'm liable to do something I'll regret.
Math, ouch.

[Shawn D.]

The problem is that when you do this, you're increasing the spring rate on the front only, thus increasing understeer.

You also wouldn't be increasing the stiffness of the spring, so your spring deflection really wouldn't change, leading to a much higher force gradient compared with deflection.

No, you are increasing the stiffness of the spring. "(A) higher force gradient compared with deflection" = increased spring rate. The rate won't be "much" higher, as the increase in stiffness is proportional to the number of coils removed.

[wkohler]

The problem is that when you do this, you're increasing the spring rate on the front only, thus increasing understeer.

You also wouldn't be increasing the stiffness of the spring, so your spring deflection really wouldn't change, leading to a much higher force gradient compared with deflection.

No, you are increasing the stiffness of the spring. "(A) higher force gradient compared with deflection" = increased spring rate. The rate won't be "much" higher, as the increase in stiffness is proportional to the number of coils removed.

Right. I should really write this stuff down when I think about it. I have it all figured out and I can't get it typed out the same.

[ISO_524td]

I cut 1.5coils, maybe a smidgen more, off of my 524td springs while the everything was installed on the car. I jacked up the front end, used a spring compressor on the strut assembly and cut off the coil using a metal cut-off wheel on a right angle grinder. Don't use a cutting torch to do this as this compromises the metal properties in the spring. Lastly, I rotated the spring perches to correctly seat the spring again before lowering the car off of the jack. Took about an hour to do and the results can be seen on my 524td yahoo album.

This lowered the car about an inch with only a slight increase in stiffness. The M21 engine is heavy and could actually use a bit more spring rate. I believe any possible increase in understeer was neutralized by the slight increase of negative camber. I'm going to do this on my other 524td as it makes the car look more level.

Chris H.

[jackthat]

Thanks gents, for the help. And thank you Chris for the particulars. That is my thought too, evening out the stance. I think I'll try it. I can always replace the springs if I no likey the results.
Rick