tconn

I've been planning to upgrade my suspension. Rebuild the front struts and
upgrade to 300# springs.
On the rear I was thinking of installing the koni double adjustable coilovers
and leaving the stock torsion bars in place. Then I got to thinking that if I have to reindex the torsion bars to use the coilovers why not just put on larger
torsion bars? It would be about $300 cheaper to just upgrade the torsion bars.
So I guess what I'm asking is what is the benifit of coilovers on the rear?
Are they that much better than just useing torsion bars?

Sam Lin

From a different point of view, why the hell would you want torsion bars if you're going to coilovers?

Sam

Skip

The primary benefit of using coil-overs on the rear is they allow easy ride height adjustments and relatively easy spring rate changes. A side effect is that most coil-over capable shocks will normally be a better product. The benefit of double-adjustable is just that - you get to adjust both bump and rebound separately (in the case of Koni - other may vary.) Yet another advantage of running a coil-over without torsion bars is a dramatic reduction in unsprung and sprung weight. This directly contributes to crisper suspension movements.

There are a few other things to consider before getting coil-overs. Will you be competing the car in the appropriate class? Most clubs rule the coil-over as a major modification. This may move you up at least one class. Will you be using the torsion bars and the coil-overs? If so, the values of each are crudely summed but there is much to consider with respect to preload. Do you plan to remove the torsion bars? If so, it is recommended that you reinforce the lower bolt to handle that additional load AND also to replace the OE rubber spring plate bushings with either Polyurethene or Delrin to maintain structural integrity.

Ultimately, it is cheaper and easier to maintain torsion bars only and simply upgrade them. For strictly street-driven vehicles, the benefits of a coil-over are likely not observed.

joseph mitro

Skip - i would like to eventually remove my torsion bars altogether and go with the KLA coilovers which I already have installed. i've heard some comments about the rear suspension being less stable without torsion bars, like the rear end "wanders." any validity to this?

Skip

Dr. Mitro,

Yes, there is some validity to that. If you picture how the spring plate serves as a point of rotation, you may be able to see what would happen if the assembly were no longer "sprung." By this, the torsion bars actually add rigidity to the rear end by keeping all of the components taught and under load - preload, in fact. Without the torsion bars, the rotation point can become lazy and wander. This is why we recommend the addition of Poly or Delrin spring plate bushings to maintain some level of rigidity in the rotational areas. Some even go to the point of installing bearings there. However, this is a custom job at considerable expense. It's all a matter of perspective and what personally qualifies for "good enough."

joseph mitro

thanks for the help. with that info maybe i'll just keep the torsion bars. but then, i WAS planning on installing those delrin bushings anyways. do you think the rear end would be just as stable without the torsion bars if i DID have the bushings? and would the infamous "torsion bar reindex" job be very difficult without reinstalling torsion bars? i would guess it would actually be pretty easy if i didn't have to worry about all that reindexing.

Sam Lin

I disagree, there's no validity to the t-bar presence affecting whether the rear end "wanders." That's solely a function of the bushings, if you look at the t-bar geometry they do not provide lateral support at all. If the rear end wanders, it'll do it whether or not the t-bars are there, to the same degree, and will only be fixed with new bushings.

Sam

Skip

If you have t-bars and rubber bushings now, but then remove t-bars and use Delrin, then I'd say it's a wash. I think you'd like the end result. Remember, you'll need more spring now.

If you remove the t-bars you also remove the task of indexing. Never, ever again

Mongo

for the record 300lb springs on the street is stiff enough to shake a newborn out of a 9-month pregnant woman

Skip

Andy, that's confusing. Is the baby a boy or a girl?

Sam, I respect that opinion based on logic. However, the torsion bars put the whole assembly under tension through preload generated by the weight of the car on the springs (torsion bars in this case.) That adds to the rigidity of the assembly as a whole. It is reported from drivers of cars who have made this modification (removing t-bars but leaving OE rubber bushings) that without the upgraded bushings the rear seems to wander in transition. While you could logically deduce that the bushings are the only factor allowing the wander, it is in fact just hiding part of the problem. Either way, the fix is to install stiffer bushings.

tconn

I autoX the car will be running in Street Prep. I will also be running some
De events in the future. The torsion bars would be left in to meet rules.
I've wondered about the potential structual problems that might come up with using shock mounting points for load bearing applications. Would there be additional loading on the body causing chasis flex? What would this do over time? I've read where if you install a roll cage this would eliminate any flex.
I don't plan on installing a full cage anytime soon. If I'm reading to much into this let me know.

Skip , so really the benifit of adding coilovers would be easier adjustability of the rear suspension and the benifit of better shocks??

I've got to check the SCCA rules and see if coilovers would be allowed in SP
Class. The way I read the rules they would be allowed but maybe I'm being
to optomistic.

Sam did the smart camber work for you??

joseph mitro

hey i need all the business i can get . let's sell lots of stiff springs.

Skip

Tim, CSP does not allow coil-overs. You'd have to run SM2 or Mod.

You're right on with the coil-over benefits.

Many people run full coil-overs with no cage and have not experienced and structural problems. The biggest problem is the lower bolt. In order to run full coil-overs (without t-bars) you really need to use a stronger lower bolts. Unfortunately, the shock must use a 1/2" lower eye to use the Racer's Edge solution. Shocks such as the Koni Cup and the Bilstein Escort Cup cannot use the RE bolt without modification (spherical bearing installed to replace rubber bushing.)

tconn

Congrats Andy.
Would 300# springs with the struts set soft still drop a baby??

tconn

Skip , for autoX I would be running ASP but I guess that doesn't matter.
If I upgrade just the t-bars should I also upgrade the bushings to delrin?
Or is this over kill ?