When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
C7 Z06 alignment question-Granatelli Toe links and DSC Sport specs
Hello,
I bought a DSC Controller V3 from Katech last July. I also had a local shop perform a track/street alignment to DSC specs. I have Granatelli rear toe links and had the shop set the rear toe to +1.5mm on each side. Normally DSC recommend -.5mm on each side. The car feels very darty and unstable in the rear especially under acceleration.
Also on my local track (autobahn country club), there is a hump where the north and south track connect and I hit it about 120mph. The car feels very squirrley in the rear going over the hump.
I've read that the Granatelli toe links don't change any geometry, so why would DSC recommend a different toe setting with the toe links? Also could too much rear toe in be causing my handling issue?
My alignment specs are:
Camber
LF-2.2 RF-2.0
LR-1.7 RR -1.5
Caster
LF+7 RF+7
LR+.8 RR +.9
Toe
LF-.5mm RF-.5mm
LR+1.5mm RR+1.5mm
I have AMT Camber plates and that is as close as the shop could get the alignment without spending a lot of time messing with shims.
Overall the car feels good except for the handling issue in the rear.
I have the same setup as you. You need to shim the uca's to get the caster correct on the rear. If you don't do that you are wasting your time. You'd be better off putting the stock camber plates back on and adjusting the caster correctly.
I have the same setup as you. You need to shim the uca's to get the caster correct on the rear. If you don't do that you are wasting your time. You'd be better off putting the stock camber plates back on and adjusting the caster correctly.
I thought the rear castor should be +.75 mine isn't close enough? Or am I misunderstanding you.
I thought the rear castor should be +.75 mine isn't close enough? Or am I misunderstanding you.
Sorry I must have looked at it wrong. Your specs look good. One thing I found is that if the front wheels aren't straight when you get on the brakes the rear end will move around like it has a mind of it's own. I was having the same issue at VIR and started concentrating on having the wheels straight when I really hit the brakes hard and that made a world of difference. You can always play with the rear toe a bit but it should be really close like it is.
OP, how do you know you have the toe settings you asked for? Did the shop that did the alignment have a machine that showed toe in mm's or inches Vs degrees? The +1.5mm toe in recommended with the Granatelli Toe Links is a lot of toe in. About .17 degrees toe in at each wheel which is a lot compared to normal GM specs which are 0 degrees total toe plus or minus 0.2 degrees. Total toe with +0.17 degrees at each wheel is +0.34.
Here is a chart that I developed using the Tangent Function to show toe in degrees at each wheel based on inches or mm measurements.
If you truly have that much total toe the back end should be fairly stable on smooth pavement but may hope around a fair amount on bumpy pavement where one of the wheels loses contact with the ground briefly and the other tire steers the car. I run about .2 degrees total toe in on my car with the Granatelli links.
The shop that did the alignment is a reputable shop in the area. They do performance work, and have a very nicely equipped shop with a dyno. They also have a hunter tire machine, and road force balancer. They did an excellent job mounting and balancing a set of cup2's on my Forgeline wheels. They have an alignment rack and I think a hunter alignment machine but I don't know for sure. They also had the rear caster tools and knew about setting it on the C7's.
The rear of the car seems to dart around but besides that the car feels better overall. I ran six 30 minute sessions at the Autobahn full track a couple weeks ago, and the new cup2 tires seemed to be wearing evenly. Before the alignment, on the original set of MPSS, the outside edges of the front tires were wearing heavily, and the car felt like it was sliding around the track.
The rear feels the worst in tour under acceleration. It feels better in track mode, but I still feel it under acceleration. I also feel it going over the hump at the track where the suspension is unweighted. I almost get air over it and the rear end feels really loose until it gets some weight on it again. This wasn't happening before the alignment.
Do you remember where the toe, in the rear, was before the alignment? You might want to try a little less toe in. If it's better then that's good. If it's worse then go back with a little more.
Last edited by badhabit_wb; 06-15-2019 at 05:40 PM.
It was my 2017 Z06 that DSC used to develop the different specs with the Granatelli toe links. The links moved the geometry of the toe link and we verified this by measuring how the toe curve changed as the suspension moved compared to the stock suspension. I wouldn't expect too much rear toe to make the car darty under accelleration, usually that is a rear caster issue.
I will add that sometimes issues with the back of the car are actually caused by the front. Last time I was at VIR with Mike Levitas (owner of DSC Sport) I was complaining that the back of my GS was moving around in the back under heavy braking. He thought it was an issue with the front and I tried arguing with him but he insisted that I remove the front wheels and turn each front toe link in one flat. We did that and the next session it was like magic the issue was gone.
Do you remember where the toe, in the rear, was before the alignment? You might want to try a little less toe in. If it's better then that's good. If it's worse then go back with a little more.
No, the shop didn't record the initial settings. I think they would have if they didn't have to put the camber plates and toe rods in on the two post lift first.
I don't know much about how alignments are done, is toe the last thing that's set? If changing the toe doesn't affect anything else maybe I try turning the links in a half turn and seeing how it feels.
You could do that. Whatever you do be sure to do it in small increments. It would still be better if you could measure the change. I use the Tenhulzen string setup and it works great for setting toe. It was around 500 but you could rig something up to measure to for a lot less than that. There are how to guides that would help you get set up.
Just an update. The shop that did the alignment rechecked everything and nothing moved. I have amt camber plates so nothing should have moved. They reduced the rear castor from +.8 to 0 and took out a little rear toe. I'm not sure how much off hand but I have it written down somewhere. That made a huge improvement! The car handles great now!
Just an update. The shop that did the alignment rechecked everything and nothing moved. I have amt camber plates so nothing should have moved. They reduced the rear castor from +.8 to 0 and took out a little rear toe. I'm not sure how much off hand but I have it written down somewhere. That made a huge improvement! The car handles great now!
It is my understanding that Jim Mero recommends rear castor to be 0.....
06-13-2019, 10:33 AM
C7 Z06 alignment question-Granatelli Toe links and DSC Sport specs
