help from suspension gurus

jmz · jmz's Garage

I will be adding new front struts to my car soon to accomodate the 3.5" spacing of turbo calipers...i know more needs to be done to make them fit.

question, if I am going w/ the bistein rsr type front strut what are the pros and cons in going with coil over springs instead of torsion bars. I was talking to Ollies machine shop at some point about raising the spindle on bilstein struts and he was adamant that going w/ coil overs was the only way to go.

Randy W · Randy W's Garage

Pros: Bigger springs available, Improved stability in corners
Cons: Puts load into parts of the car it was never designed for

I think you will want to reinforce your tub and maybe put a cage in if going to coil overs. I would consult a reputable shop who has done this for advice.

jluetjen · jluetjen's Garage

Anyone who tells you that "Coil Springs are the only way to go" is trying to sell you -- coil springs. As long as the springs hold the car up, don't settle and provide the desired rate -- they're fine. It doesn't matter if they are T-Bars or coil springs.

From a packaging perspective or for tunability, there are different benefits to both T-Bars and Coils. Most of these benefits are really only going to be meaningful to someone who is building a 10/10ths race car.

jmz · jmz's Garage

john, I agree with you. Here is the dilema, New bilstein rsr struts w/ raised spindle and hd re-valved insert = $1,400.00 New bilstein rsr struts w/ raised spindle and a set of springs...same price + about 100.00 for springs. I am fine w/ t-bars but is there any drawback to going w/ springs.

Randy Webb · 04-02-2003, 09:16 AM

2 other benefits -- front can be made lighter with coils & the 935 style kits; also you could get progressive coil springs but there is no way to make a T bar progressive.

Does that matter to you? Are you racing?

Big drawback to coils is the cost.

jmz · jmz's Garage

Randy, not really planning on racing. the car will never be a pure street car though. uses will be track days auto-x and weekend drives. i need to change from m-calipers to something bigger...decided to go w/ turbo brakes and be done with it. this leads me to new struts and my thinking is raised spindles make a lot of sense. after buying inserts, struts and raising the spindle I would be very close to the price of new rsr struts w/ raised spindle. anyway the price i got for struts and springs wasn't that much more. i am not sure how much strengthening has to be done to the shock tower...maybe that is the cost prohibitive part. my gut tells me that making such a change isn't that simple or cost effective otherwise everyone would be doing it.

Randy W · Randy W's Garage

If the impetus for the change is better front brakes, why not use C2 front brakes and have the calipers modified for your early car - much cheaper than going the turbo route and maybe a better brake too. I do not think raised spindles are necessary for the purposes you mention. Torsion bars are fine for most of us and they are progressive springs.

Jack Olsen · 04-02-2003, 10:05 AM

A downside to coils in front: reduced clearance for wider wheels/tires.

RallyJon · 04-02-2003, 10:26 AM

From your posts, it sounds like you're in the same situation I'm in. I did a lot of research and decided that RSR Bilsteins were a pretty bad value for what they are. I looked at a lot of options and settled on Leda struts and shocks. They have many high end options, but I ordered the basic model which will end up costing about $1600 total, for all four corners.

They use a donor Koni or Bilstein strut just for the stub axle, so you get the 3.5" brake mounting. The struts are slightly shorter than stock to begin with, plus they'll put the stub axle at any height you want--just like RSRs.

The best part is they're adjustable, so you're not locked in to what I've seen called "punishing" RSR damping levels. You can get them with or without spring perches for coilovers. I'm using them with torsion bars.

No testimonial yet--they'll be here in about three weeks. But I've used Leda coilovers on another car and they performed quite well.

Just wanted to give you another option to consider.

Jon

jluetjen · jluetjen's Garage

Progress springs sounds like a neat idea, especially if you buy into the myth that "Stiffer is better". But the reality is much more subtle then most people appreciate. Some things to consider if you are going down that path...

1) What is your wheel rate? Many cars have regressive wheel rates because of geometric constraints of the suspension.

2) How much wheel travel are you currently using?

3) As the car rolls through its range of motion in a corner, how do the wheel rates at the front relate to the wheel rates at the rear.

Without taking these issues under consideration I could very easily picture someone taking a car with minor understeer in a constant corner (like 911's are often prone to do) and turn it into something that could understeer in mild corners, oversteer in moderate corners and seriously understeer under hard cornering. Try figuring that out!

(BTW - F1 and CART cars will almost always use progressive wheel rates, but they have so much downforce (2X the cars weight) that they constitute a decidedly different situation from a 911.)