Looking for chassis setup help

[Daryl Lane]

Looking for some help - input on chassis setup - car is a 1979 BMW 3 series E21 - rear wheel drive.

Trying to figure out spring rates to be able to use the rear sway bar so we can fine tune the car more at events. Rear bar is a 19.5mm sliding adjustable piece which is the biggest one available for the car. The front bar is a 26mm piece and not adjustable it is also part of the front lower control arm, bad design, but is what it is.

With 325 pound springs in the rear and 425 springs up front car always pushed/plowed bad with rear bar disconnected. We connect the rear bar and the car became tail happy and would brake the rear loose.

Re valved the front inserts went to 550 pound springs up front and car responses to steering input great, same 325 rear springs and no rear bar. Car was very drive-able. Car would lift the inside front tire off the ground with this setup, 1/4" to 3/4" or so - seen in pictures.

Same front inserts and 550 springs changed rear springs to the 425s we had - rear is somewhat loose and unpredictable but still drive able. No way can the rear bar be connected. Car lifts the inside front tire very rarely with this setup.

Thinking of going back to 325 springs in the rear or maybe even 300 pound springs, the car was easier to drive and seemed faster even lifting the inside front as it did. To be able to use the rear bar I am thinking I need to go softer in the front also?

Looking for your thoughts and input, Thanks - Daryl

[Jake Stumph]

Does the car have LSD, or it open? big rear bar + open = bad. That said, in terms of balance, sounds like you need less rear spring rate, and more rear bar. The rear bar will help keep the front wheels planted and increase front grip while balancing out the softer rear spring.

[Sebastian Rios]

Same alignment settings for all of those spring combinations? A little toe goes a long way...

[Daryl Lane]

Car now has a rebuilt biffed LSD did some machining and it now has 4 clutches in it instead of 2.

Front suspension is fully adjustable, toe, chamber and caster - rear right now is what it is from factory non adjustable. Rear being semi trailing arms it has 2 to 3 degree chamber increases with compression of suspension and toe is about 2 to 2.5 degrees tow in. Maybe more semi trailing arm rear suspensions need toe to go straight under power.