v8killer

Changing springs to 400lb front and 500lb rear. At this point do I delete the torsion bars are leave them? What will be the difference if I go either way?

caster951

The consensus will be to delete the torsion bars, I sent you everything that you will need to do just that!

333pg333

Are you asking if after adding 500lb rear springs if you should remove the torsion bars? Sure as hell you should or get some replacement ones with very little rate. Otherwise you will have an extremely out of balance car. The advantage of t bar delete would be weight and the ability to swap out coils more easily. If you aren't going to swap out coils then some might say that you are weakening that area also by removing them....

eniac

delete the torsion bars. There is nothing more you need to do other then simply take them out and put everything back together without the bars.

vt951

Search for "motion ratio". I think you will find that you won't have enough rear spring rate if you remove the torsion bars. The effective (wheel) spring rate at the rear is much lower than the front.

333pg333

The wheel ratio of 400lb front and 500lb rear would be approx 340lb/in front and 300lb/in rear. That would probably fall into the ok category.

Bri Bro

At the spring rate you are going to, its sounds like it life is mainly for the track. I would delete the Tbar to allow quick changes to the ride height and spring rates.

Effective spring rate front is 0.94
Effective spring rate rear is 0.42

So
400 * 0.94 = 376
500 * 0.42 = 210

For a back to front ratio of 0.56

I try to be around 0.6 to 0.7. I would bump the rear spring up to 550. It is really a matter of how you like the car to handle. And the shocks need to be valved for these spring rates.

333pg333

Yep that's right Brian. I was basing my number off the motion ratio only which is about .65 but forgot that this should be squared which brings it back to .42 in which case I'd agree that the rears should be bumped up a bit.

ArthurPE

1986 951
so if I go 200 front (oem is 126 correct) effective is ~190 (200 x 0.94)
and if I want a ratio of 0.65 R ~ 190/0.65 ~ 290 for the rear effective rate

I want to leave the TB's, so using: TB rate + (coil rate * 0.65) = effective rate
oem TB rate = 175
effective rate/rear = 290
solving for coil rate = (290 - 175)/0.65 ~ 180 lbs...

so ~ 250/250 on a coil over kit with TB's should be 235/340 effective? ratio ~ 0.69?

does this sound OK for a street set-up?

I'm thinking about the Paragon 1 Koni Cup kit

v8killer

So would a 600lb rear springs be a good choice if I want the car to have a tendency to understeer?

I hope this does not sound like a moronic question but is there is any chance the 500lb coilovers would have synergistic effect with the OEM torsion bars to put me at a desirable spring rate? Sorry never had a car with torsion bars.

964-C2

I thought it was 0,55-0,6 on a 944 (?).

333pg333

No, Brian is correct. It's .42 effective.

DanaT

Just out of curiosity, where are you get the formulas for the spring rate and motion ratio? I haven't seen this and would be interested in reading up on this.

Thanks
-Dana

Bri Bro

235/340 effective? ratio ~ 0.69? The ratio is rear to front so this would yield 1.44.

I would go 250 front an add 100 lb coils in the rear. I have heard that anything over 100 lb rear coil over requires that you re index the Tbar. You could also change the Tbar to 28 or 29 mm.

550 to 600 should give you a slight understeer with good handling. I would pull the Tbar, just makes changing the setup so much easier and I don't know of any advantage of running both the Tbar and coil overs.

Nice write up from the BMW side. My original link is broken, so it got moved somewhere.

http://www.e30m3project.com/e30m3per...e/eff_rate.htm
Sway away had a nice tech write up but it appears to have been replaced by a calculator spreadsheet. Might contact them and see if they have the original write up.
http://swayaway.com/TechRoom.php
http://swayaway.com/calculators/diag...gArmModel.html

ArthurPE

so the front spring rate is > than the rear?
oem is F/R ~125/175 correct?

wouldn't 100 coils ~ 175 + 0.65 x 100 ~ 240 effective? ~ 1:1 ratio?

my BMW's all have lower in the front, e46 ~F/R 225/400 or so

M030 sways are on the 'want' list