Motion ratios for E36's?

[NegativeCambre]

Yeah, rounding down to the nex 50ft/lbs/in, I still get the same value even with the new ratio--

Does anyone have motion ratio's for other BMW's, or even other cars for that matter? I'm trying to compile a somewhat extensive collection for my club.

Thanks,
Steve

[B.Watts]

Yeah, rounding down to the nex 50ft/lbs/in, I still get the same value even with the new ratio--

Now all you've gotta be worried about is whether your spring rates are what they actually say they are. I believe H&R and Eibach only build to a 5% tolerance...so a spring marker 1000 pounds could actually be 1050 and a spring marked 1050 could be less than 1000. That could be really confusing if you expect the spring to be stiffer and it's really 50 pounds lighter than what you had on it.

Though, because of that problem, I'm not sure if they space springs by 50 pound increments above a certain point. They may jump to 100 pound increments to prevent totally confusing someone while they are testing spring rates.

So, now you need a spring tester to find out what your spring rates really are. And then you can stick some needle bearings on and find out how that affects the spring rate...and on and on and on...

[NegativeCambre]

Now all you've gotta be worried about is whether your spring rates are what they actually say they are. I believe H&R and Eibach only build to a 5% tolerance...so a spring marker 1000 pounds could actually be 1050 and a spring marked 1050 could be less than 1000. That could be really confusing if you expect the spring to be stiffer and it's really 50 pounds lighter than what you had on it.

Though, because of that problem, I'm not sure if they space springs by 50 pound increments above a certain point. They may jump to 100 pound increments to prevent totally confusing someone while they are testing spring rates.

So, now you need a spring tester to find out what your spring rates really are. And then you can stick some needle bearings on and find out how that affects the spring rate...and on and on and on...

Yay! I figure for my autocross/track setup, rough spring rates are going to make less of a difference then my hit-and-miss driving. I'm either really on or really off right now, and until I gather consistency (read: experience, yos!), I'm not going to stress on the accuracy of the suspension. I'm running 550 all around right now, and I can't express how well it is working with solo2. Car handles brilliantly right now, and I'm very hesitant to start tearing it apart.

Steve

[B.Watts]

That demonstrates how much more roll resistance these cars need up front compared to the back...your rear wheel rates are less than 1/2 your front wheel rates

[Steve J.]

Time to think about moving roll centers

[NegativeCambre]

That demonstrates how much more roll resistance these cars need up front compared to the back...your rear wheel rates are less than 1/2 your front wheel rates

Yup--and camber. All the E36 Solo2 cars I know run lots of front camber.

Is there a 'rule of thumb' corner weight to wheel rate ratio for a track setup? I've heard that 70/40 is ideal for an autocross car. I wouldn't mind swapping springs for track days.

Steve

[thenobot]

That demonstrates how much more roll resistance these cars need up front compared to the back...your rear wheel rates are less than 1/2 your front wheel rates

Does this imply the need for a front swaybar?

Time to think about moving roll centers

How does one move a roll center?
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[B.Watts]

It seems you've brought an old thread back from the dead...

To answer your questions...yes, you definitely need a front bar on these cars. How big of a front bar depends on a lot of things, from your spring rates to your suspension geometry.

Moving roll centers is accomplished by changing your suspension geometry. You move your roll centers whenever you change ride height...the lower the height, the worse the roll center. Unfortunately, it gets worse much quicker in the front than the back, which is why the front generally requires a stiffer wheel rate than the rear to perform optimally. There are various ways of improving the roll center after lowering a car...it just depends how much $$ you want to spend and what sort of class rules you are building a car to.

[CAB IN BLACK M3]

Damn I learn more math equations from this site. This coming from a finance guy 1 + 1 = 2.5 right.

[FierySphere]

Damn I learn more math equations from this site. This coming from a finance guy 1 + 1 = 2.5 right.

2 + 2 = 5 (for large values of 2)
math joke...

[Steve J.]

2 + 2 * 2 = 6

[CAB IN BLACK M3]

HA HA.....You guys are great...provide me much humor ...when its 10:45 at night and I am still at the office......This forum provides a nice diversion.

[warptkid]

According to the image above, is the following true for determining an accurate Motion Ratio?

ds/dw = L1/L2

[Stuntman]

The front is approx .94 for spring and damper.
The rear is approx 1.05 for the damper, approx .65 for the spring.

Those are approximate because this all changes as you change camber, ride height and other things.

The front is not 1 to 1 because of KPI (kingpin inclination).It has nothing to do with the fact that the wheel is kicked out a little from the strut. If KPI is zero (the line from the outer control arm pivot to the upper strut mount pivot when viewed from the front) then you will get 1 to 1. If it has an angle, it will be less than 1.

Hope this helps,
Barry

Great information!

So:

Front Motion Ratio - .94
Rear Motion Ratio - .67

To calculate Front wheel rates: SR*(.88)
To calculate Rear wheel rates: SR*(.44)


Tourenwagen - Is the rear motion ratio for the damper truly 1.05 to 1? I don't understand how it can be >1 when the damper is inboard. So a 'coilover' in the rear using the stock damper locations would have a motion ratio of 1.05 ?

Sorry for bringing this thread back from the dead, their's great information on here that hasn't been talked about in a while...

[blackparis]

Great information!


Tourenwagen - Is the rear motion ratio for the damper truly 1.05 to 1? I don't understand how it can be >1 when the damper is inboard. So a 'coilover' in the rear using the stock damper locations would have a motion ratio of 1.05 ?

Sorry for bringing this thread back from the dead, their's great information on here that hasn't been talked about in a while...

I believe 1.05 sounds right, The damper is mounted inboard, but the Trailing arm movement axis is across the car, not down the center.. and the Damper is mounted behind the center of the CV axle = Motion Ratio >1 However I am a noob, and Only looked at it for 5 minutes... when I bought the car a week ago....

Maybe someone else can draw a picture?

[mazur]

Steve - It's beneficial if all you want to know is what your wheel rates are so that you can have a better understanding of what changing your actual spring rates does to your car's balance. That seems to be all Kos wants.

Kos-motate - According to Gustave's E30 site, the rear motion ratio for the spring is .67. I don't know the info for the damper.

Here's a good question.

On my previous car, an E36 M3, I had 550# springs in the rear which would equate to a wheel rate of 242#. On my E30 I have 750# springs which equates to a wheel rate of 502#.

Now, why, when I would try to push down on the rear of my car, would the M3 not budge the tiniest bit, but my E30 compresses considerably? What else could have been adding to the stiffness in the rear? It can't be the shocks' compression because both cars had/have Koni singles.

[sstecker]

Here's a good question.

On my previous car, an E36 M3, I had 550# springs in the rear which would equate to a wheel rate of 242#. On my E30 I have 750# springs which equates to a wheel rate of 502#.

Now, why, when I would try to push down on the rear of my car, would the M3 not budge the tiniest bit, but my E30 compresses considerably? What else could have been adding to the stiffness in the rear? It can't be the shocks' compression because both cars had/have Koni singles.

valving is probably different between the 2 shocks - and have adjustable setting in different position for each cars setup. different sway bar rates?

[BMWParkingOnly]

Here's a good question.

On my previous car, an E36 M3, I had 550# springs in the rear which would equate to a wheel rate of 242#. On my E30 I have 750# springs which equates to a wheel rate of 502#.

Now, why, when I would try to push down on the rear of my car, would the M3 not budge the tiniest bit, but my E30 compresses considerably? What else could have been adding to the stiffness in the rear? It can't be the shocks' compression because both cars had/have Koni singles.

The effective wheel rate is the motion ratio ^2. This, the e30 and e36 have a VERY similar calculation (although not identical) and it appears you used the effective wheel rate to calculate the e36, and only the motion ratio to calculate the e30. Using 0.44 * Spring rate, your rear effective wheel rate on your e30 was 330lbs, not 502 as you had stated. Still stiffer than the e36, but not as dramatic as you thought from above.

As to what adds to the rear stiffness, it is mostly dampers unless your ride height is so low that you're into the bump stops? And perhaps the lever arm from the bumper to the rear wheel is different on the e30 thus providing you more ease of compression at the bumper?

[brilliantrot]

Additionally what are you running for trailing arm bushings? The lower the friction in the bushing the lower the wheel rates as the friction in stock bushings is considerable. On my 914 when I went to bearings in the back, I had to rethink spring rates big time.

[jmitro]

It seems you've brought an old thread back from the dead...

To answer your questions...yes, you definitely need a front bar on these cars. How big of a front bar depends on a lot of things, from your spring rates to your suspension geometry.

Moving roll centers is accomplished by changing your suspension geometry. You move your roll centers whenever you change ride height...the lower the height, the worse the roll center. Unfortunately, it gets worse much quicker in the front than the back, which is why the front generally requires a stiffer wheel rate than the rear to perform optimally. There are various ways of improving the roll center after lowering a car...it just depends how much $$ you want to spend and what sort of class rules you are building a car to.

Bringing it back from the dead again.

I converted to rear coilovers, previously was using 800lb F and 950lb R springs. Now keeping the 800lb F springs, I'll have 450 lb R springs in the coilover location, for wheel rates of 707F and 496R. (car weighs about 2450lbs empty)

The car was quite neutral last yr with the spring rates, but now I'm adding roll center-correcting front control arms, as well as bump steer adjustable tie rods. Will these two changes impact the spring rates or affect the car's overall handling? I know I'll be able to get more negative camber in front, but don't anticipate changing the front spring rate.

[=BA=]

If your front roll centre comes up you will probably have to lower the front springrate or less bar, otherwise you will have a chance it understeers a bit I would think.

Interested in what these roll centre correction control arms are btw? Tubular ones as on the Watts car?

[jmitro]

no, not tubular. standard E36 control arms with spherical bearings pressed in, then using an extra long bolt with a spacer on the knuckle, sold by Bimmerworld

[delcbr]

I want to get my rear shocks revalved to suit new spring rates of 400lb” should they revalve it for 400lb” or 400x0.44=176lb”

[jdehaan]

This thread has been very intriguing to a newbie with a race car that I want to improve the handling on. I've just spent an hour googling how to use Wheel Rates to calculate an ideal spring rate. I've followed a few pages of various threads on this forum only to feel like the other variables that aren't easily calculated make it a futile effort. Is that true, or is there in fact a way to use the information being discussed here to make a useful calculation on spring rates? Is there a good source that can easily explain this to a non-engineer?

[CoMZ302]

This thread has been very intriguing to a newbie with a race car that I want to improve the handling on. I've just spent an hour googling how to use Wheel Rates to calculate an ideal spring rate. I've followed a few pages of various threads on this forum only to feel like the other variables that aren't easily calculated make it a futile effort. Is that true, or is there in fact a way to use the information being discussed here to make a useful calculation on spring rates? Is there a good source that can easily explain this to a non-engineer?

Google "Ride Frequency" then decide what's right - for you. Dual purpose car? Track only? Aero? Rear coilover conversion?

There are fast guys running 500lb front springs with huge bars, and fast guys running 1100lb front springs.

Just getting the spring rates where you like them is only one piece of a very large puzzle. If you focus on the end goal (the stopwatch vs drivability) you'll see springs as a part of the overall package.

- - - Updated - - -

I want to get my rear shocks revalved to suit new spring rates of 400lb” should they revalve it for 400lb” or 400x0.44=176lb”

Call them. 400lbs of rear spring on a stock E36 is almost stock. I doubt there's any revalving necessary.

As far as your math, no that's all wrong. The rear shock does not have the same motion ratio as the rear spring anyway.