Geoffrey

One project I've been thinking about but never had the time was to stiffen the suspension side members and steering rack. To be honest, I really don't know what that 18" wheel TSB brace really does. As far as I can tell, it doesn't really do anything substantial since it is "floating" on the steering rack mounts. So, what I've decided to do is to triangulate the suspension side members in the front, and triangulate the steering rack in the rear. The suspension side members have 3 holes drilled and tapped already and they are about even with the control arm forward pivot point so I'm going to use these. On a C2 the brake booster is bolted to the left side set of holes.

I bought some 1" .050" wall 4130 chromolly tubing and .080" 4130 chromolly steet steel. Since it is stronger than mild steel, it will allow me to use thinner lighter tubing. I made a 2" wide plate to go where the steering rack brace is and will return to the original shorter bolts. I made a 2" wide plate for the front of the chassis against the rear of the trunk floor. I cut templates for plates on the side members and cut them out. I welded a short piece of tubing from the front center plate to the plate bolting to the suspension side members. I still need to add a gusset in the front between the two tubes.

I have to wait until Monday to have some tubing bent to finish the project. I will add a second tube from the side members to the steering rack plate. This requires two shallow bends. I'll slot the tubing and slide the plate through the slot and weld both sides. This will keep the rack from moving in any direction and tie it into the side members.

In the trunk, I'll add another tube to be bolted to the front suspension mounting point. In the center, I'll put two threaded inserts where the piece from the underside of the car can bolt to. This should triangulate all of the suspension components together.

So, here is a picture of the first component.

CWay27

No picture Geoffrey.

Geoffrey

try pressing F5, Rennlist lately doesn't seem to refresh the pages correctly. I have no issue seeing the picture.

Tom W

I had to reload the page to see it ...

mjshira

really cool.

Are these 'known' improvements? or are these ideas you're trying out?

Geoffrey

I have seen a very simple form of bracing on several of the factory supported race cars (Alex Job RSR for instance). The GT3 platform, although different, has some additional bracing on the subframe supporting the side members. As I mentioned, I don't understand the function of that steering rack brace and have been thinking about it for a few years. At one point I was going to try to move my shock position sensor to the suspension side member to see if I could measure any deflection, but never did that test.

Geoffrey

I finished tacking up the first piece tonight. The project went much easier than I thought it would. I was able to borrow a "joint jigger" to properly fishmouth the rear bar where it meets the side pieces and that made things fit much nicer. The hardest part was lying on my back trying to tack the pieces together using my TIG welder. I slotted the rear bar completely in the front and back, slid the flat plate that connects to the steering rack through the bar and welded the back side flush and ground down the weld. Right now it is just tacked together and I simply ran out of time to finish weld it. I also want to put a small gusset between the two bars and that should finish it off and I can send it off to the powder coater. The entire part weighs 2.8 lbs. Now that is what I call a steering rack brace.

amr89c4

Geoffrey,

WOW! That is a really cool idea. I have to ask a stupid question; how much do you think the brace will arrest rack movement? If I recall correctly the rack is mounted in rubber. Does the rack mount move that much?

Geoffrey

I have not tested to see how much deflection there is in the front suspension. I was going to move one of my front supsension position sensors to the subframe side member to measure the deflection, but I never got around to it. I've been slowly improving the front end of the car since I originally built the car, and this is the last piece. With this bracing, I don't expect there to be any movement of the subframe at all. I think the rack moves back and forth a fair amount in the rubber mounts and I'm going to make solid bushings for the rack.

I am thinking about designing a new upright and machining it from a solid piece of aluminum. I will also change the front suspension to a double 'A' arm setup like the GT1 and replace the lower control arm with a custom piece. I'm just starting to think about this and am looking at a kinematics software package to help work the geometry out.

ThomasC2

That's the ****!! Make a batch and sell :-)

amr89c4

I am really impressed with the idea and then it hit, I have a C4. I don't think I have all that glorious space to mount the bracket.

D666S

Geoffrey?, have you tried that double 'A' arm suspension?
David

Geoffrey

Not yet.

demonfish

i have just realised, how much easier it must be to work underneath a white car, as opposed to a black one!

its a nice bit of kit - may knock something similar up myself if i keep the car.

chaoscreature

Another post brought this thread back alive.

Geoffrey,
Was there any increase in NVH with the addition of the new brace you made? This brace not only connects the steering rack to the subframe but also creates a solid link between the subframe and the unibody. I thought of the same thing when I made the brace for my 95 but assumed the factory solution was probably sufficient. Please post your driving impressions.