I built a five bar rear suspension similar to the C4 model. I used the longest toe control rods I could fit and set them for the minimal amount of toe-in on compression as possible. By measurement I get about 0.8 degrees of toe in from a normal resting position to full compression. which on 25 in diameter tire gives about 0.175" of toe change from ride height to full compression.

Unfortunately this seems to be far too much. When I hit a bump, the resultant toe steer is so strong it really pushes the rear of the car around. A bump on the right side pushes the rear left and vice versa. It is scary actually and I can't leave it like this. There is limited room to decrease the toe change a little more, but everything I have read, (and that is a lot - so much for self study!) says toe-in on compression is a desirable thing. And I think if I set the toe control rod closer to parallel at rest, I risk going to toe-in at partial compression to toe-out at full compression. So I really don't know where to go at this point and I don't really like driving it the way it is.

Here is a shot of mine.


Here are shots of a couple of others that really take the toe change to opposite ends of the extremes.

This one would have a LOT of toe-in on compression


And this one would have toe-out on compression


Maybe somebody here knows how much toe change a stock C4 suspension produces? I checked the C4 forums and there does not seem to be too much hard technical discussion over there. Any ideas?

 

You're on the right track. I plan on going with a five link also but for toe control I'm going to use a link that is parallel with the lower strut rod.

Try a search on TwinTurbos thread becuase he said there was an issue with earlier C4 suspension and roll center.

Good luck!

 

I always find these treads interesting, and hope to try this one day. I notice in the above pics, the strut rods are not parallel with the haft shafts. Could this cause driving problems by the different components being at different angles throughout the travel range?

 

Looking at your picture, it looks like that upper rod is now carrying the load that the halfshafts previously did. If that's the case, did you modify the halfshaft spindle that goes into the diff to free-float? I've never done it, but there's a retainer inside the diff that locks it in place - it needs to come off. If it's still locked in and not slipping in & out, the suspension will bind, especially with the new rod you installed bending the trailling arm to a large amount of tow-in & the halfshaft is traveling on it's own arch with no relation to the two strut rods. Also, does the new upper rod line up with the lower?

 

Zimo - With a 5 link supension the T-arm is replaced with two links that have flexible links at each end. The T-arm no longer controls toe the links replacing the forward part of the T-arm are use just to control froe and aft movement.

The upper drive shaft is still the upper link. The new link you see added is to the rear and attaches to the back of the old T-arm/spindle mount and is used to control toe. Done this way there is no binding.





Other comments - Since the toe link is longer proper placement is critical. If the toe link is were made the same length as the upper or drive shfat link it could be placed in parallel with either and properly track giving no toe change. With the longer link it can't be parallel because the the other links will tilt the spindle in or out sooner. To copy the C4 design the pivot would have to be in the exact same place in relation to the u-joint and lower strut rod bracket because this is where the control takes place.

 

bingo!



Not sure I follow you here. The toe control needs to have a downward angle all through its available range of motion hitting horizontal at maximum compression - ideally. If it were parallel with my halfshafts I would have massive toe out, the exact problem I am trying to solve. What you are describing sounds more like the guldstrand style 5 link which uses parallel control rods to eliminate any toe change at all.

I wish I could find some good pictures of a C4 rear suspension. Anyone?

 

You need to plot the toe curve, then you can determine what to do with the toe rods. Making them longer is not always better. Sometimes longer is just too long.

The toe rod needs to follow the same arc as the spindle, any deviation will cause toe change.

Height is very important.more important in fact than length. When I was building my rack and pinion I found a couple of inches in lenth was about the same as a couple .010" in height.

It is very important that you have understeer on bump, aka roll steer. If you have any oversteer you will be very very sorry! more understeer is safer, oversteer is unsafe.

In the front you want toe out on bump, in the rear you want toe in on bump.

here is a chart use it to determine the correct length and location;



Here is what I was getting for bump steer, This wasn't good enough, I eventually got it better.