spring rate question. (coilovers)

[Jeff Alton]

What spring rate should I be shooting for on my 84 carrera. I got a deal on some coilovers that I could not refuse and am not sure what spring rates to go with. Car is used daily and sees about 10-12 track events a year aswell as 6 autocross. Weighs 2450lbs, Elephant swaybars, strut brace. monoballs, and polybronze bearings. Soon to be transplanted warmed over 3.6.

Thanks for your help.

Jeff

[Wil Ferch]

Jeff:

Long time with no response.....don't know if I could help but the torsion bars used as factory around these years was something like 19mm front and 24.1 or 25 mm rear. Equates to about 120 lb/in spring rates, as I recall from my posted charts...more correctly "wheel rates".

The coils you want to use....even assuming you want to duplicate these settings ( doubtful, I would guess)..would depend where on the suspension these mount. The altered leverage factor you get at various mounting points on the suspension arm, would end up with a different "wheel rate"..which is truly what you're after....not pure spring rate. I'm not sure if I explained this clearly enough.....

Wil

[Jeff Alton]

Wil, thanks, I do understand what you mean. I am looking for feedback on what people are using in their cars for rates. I phone one well known shop and they say 600/400. Then I phone SRP and they say 300/200. Getting a liitle confused. The car has 21/27 in it now but I was looking to replicate something like a 22/30 or 22/31 set up. I PM,ed Jack Olsen and he is running 600/400.

Thanks, Jeff

[Jack Olsen]

19/25mm torsion bars are the equivalent of coil springs with 110/140 pound spring rates. 23/31 torsion bars are like 250/332 pound springs. (At least, I think these numbers are right. I'm trying to find where I wrote them down.)

(My 400/600 springs are the equivalent of, well, really huge torsion bars.)

I would still suggest you sell the coil kit and keep your torsion bars. The pieces themselves are just a small part of what it's going to take to switch over to coils. You need to modify the chassis, especially in the rear. And unless you need more than a 23/31 torsion setup, there's not going to be any payoff for all the work.

[Jack Olsen]

Thanks to Wil Ferch, for this data:

Front Torsion Bars

18.8 mm = 110 lb/in
21 = 173
22 = 210
23 = 250
24 = 296
25 = 350

Rear Torsion Bars

23 mm = 100 lb/in
24 = 120
25 = 140
26 = 165
27 = 191
28 = 221
29 = 254
30 = 294
31 = 332
32 = 377
33 = 427

All the information is at this link.

[Jeff Alton]

The work is the fun part!! I am going to reinforce the rear shock mounts. and run with the rear 935 style spring plates and possibly the 935 style front a arms. I like the idea on being able to easily change the spring rates as well. I realize there is little benefit to going the coil over route, but I like being just a little different!! I want something a little bit different from the next guy I guess. This car may also end up as more of a track car and less of a street car in the future. I just like doing things that not everbody does. I know that may make me seem like a bit of a .... ummmmm.... dare I say fool, but it's my hobby.

Jeff

[dean]

Originally posted by catca
The work is the fun part!! I am going to reinforce the rear shock mounts. and run with the rear 935 style spring plates and possibly the 935 style front a arms. I like the idea on being able to easily change the spring rates as well. I realize there is little benefit to going the coil over route, but I like being just a little different!! I want something a little bit different from the next guy I guess. This car may also end up as more of a track car and less of a street car in the future. I just like doing things that not everbody does. I know that may make me seem like a bit of a .... ummmmm.... dare I say fool, but it's my hobby.

Jeff

Ditto

Dean