Mongo

For this next car I plan to convert the front struts to a coilover type with the Paragon Products Ride Height Kit. They offer many types of springs with it. I also plan to do KLA Industries rear coilovers too. I'd like to keep the rear torsion bars in there and avoid any major headache with those things. KLA's springs on their coilovers rate at 100 lb. Would this be too stiff for the rear if I were to leave the torsion bars and run with a low spring rate?

As for the front? To stabilize the front a little more and to get exceptional handling, what spring rate would be reccommended for this? Paragon sells them from 200lb-300. (their site is down right now unfortunately) I want to be sure I don't have too stiff of a ride and that the handling will be sharp at an autocross track here.

In case some of you wonder what sway bars I'll be buying soon, they will be M030 sways. Will these be an issue too??? I did some searching on previous posts and some of them weren't specific enough to answering the questions I have, which is why I'm posting this...

Andy

joseph mitro

Here is my setup:
FRONT: paragon ARHK with 275# springs, and 27mm sway bar. front ride height set at 25 1/4" from ground to top of fender arch; koni yellows

REAR: KLA coilovers - 140# springs, 9" in length (IIRC), 19mm adjustable M030 sway bar. Ride height at 25 1/4" from ground to wheel arch

I have the 16x7 and 8 D90 wheels with standard size tires. In my autocross last week the car felt pretty neutral with the front shocks set at half stiff and the rear shocks set at 1/4 stiff. The rear sway bar is on the softest setting. This setup is definitely comfortable enough for street use (although "comfort" is a very subjective term - my wife thinks it's a little stiff). I usually set the front shocks at full soft for street use. In the future I actually intend on installing the 30mm front sway bar to give me more leeway for adjustment in the back.

In my opinion, this setup will give you a well-handling car which is comfortable enough for street use but sporty enough and adjustable enough for autocrossing.

FYI - you can buy any spring rate you want with paragon. from 200# up to 1000# - they just have to special order anything they don't stock. I have the hypercoil springs 10" in lenght (IIRC)

Mongo

thanks, joseph for the tip You think 250 in the front with 100 in the back would be too unstable? BTW, I forgot to mention I will be using Boge shock inserts for the front since I have rebuildable front struts...Koni would set me out of my price range since I'll be using the rest for a paintjob and school come April.

Andy

joseph mitro

nah, I think it would work out just fine. i'm no suspension expert by any means, just telling you my experience. jason at paragon products will be very helpful for you.

also, i think alignment will be important at making the car feel stable. mine is a stock alignment, but i'm considering adding a little negative camber.

mochman

I have 400 frt po did it it is a coilover conv kit. I'm going to go to 250 frt and 350 rear with no torsion bars and see how it works.

joseph mitro

I'm guessing that combination would give you a lot of tailhappy oversteer character. Stiff in the rear means more oversteer, especially with a 951. I would decrease your rear spring rate to keep the car more neutral

RedlineMan

Hey Joe;

One thing you are apparently not aware of is leverage losses in the rear. A 375lb spring will give you about 180-190 effective rate.

The "original" 400/350 he had would be a VERY nice setup, albeit perhaps a bit stiff for street use. May not be within the damping range of the shocks either.

You open up all kinds of crazy things when you start throwing disparate parts at suspensions like these hybrid coilover systems. OK for dinking around on the street or farting around at autocrosses, but you need to do some serious homework to make something that will REALLY work to your advantage at the track.

Manning

I've read in a few different places coil springs are between 56 and 65% effective when used on the rear while fronts coils are between 85 and 90% effective. The 350 rear springs combined with the 250 fronts should then be either nearly equal wheel rates or a little front biased.

joseph mitro

John - you're right, I've never heard the term leverage losses, so enlighten me. All I can speak from is my own experience. Certainly track racing is different than autocrossing, but I would argue that autocrossing requires just as much homework to get a competitive suspension setup as racing. It's all about trial and error.

Now farting around on the street might be a different story.....

RedlineMan

Hey;

If the shock were mounted directly at the axle point, and was completely vertical, it would be a straight ratio of 1-to-1. In this instance, there is no leverage working against the spring, and the wheel rate would equal the spring rate.

Since the shock does not mount at the axle point, but up the line ways relative to the pivot (bushing), it is then a fulcrum and subjected to simple leverage losses. You would also have to factor in the angle of inclination of the shock to be completely accurate, as this will also create leverage working against the spring. It is relatively trivial, however.

Incidentally, you have no losses in the T-bar either because it is AT the pivot, right? The only way to change its rate is to change its diameter, or the length of the trailing arm, eh?

So, you have roughly a 52-56% loss in rear spring rate. You also have a small loss in the front, as the strut does tip in a bit. This is again relatively trivial for most purposes.

As for application, autocrossing and track driving are very different. For chasing cones, you do not need to worry so much about spring and damping rates so much as you simply need chassis balance that is suitable for your needs. Since you see little to no steady state cornering, such things as damping rates and valving have little effect.

Auto-x is cut-&-thrust, toss-&-catch. Running 60-100 mph around a long sweeping bend is a whole other ball game!