Suspension Bushing Question

[DavidNJ]

On the C5 Z06, ghoffman posted this:

The T1 camber plates are not always appropriate for all tracks. We never use them in the back because with them there is too much camber for most tracks, and only selectivly use them in the front. Especially with urethane or delrin bushings, less camber is needed since under load the changes are much less.

Now, C&D and some Internet reviewers have indicated that the C6 Z06 can be fidgety in a race track's bumpy turn. However, on the street, nothing but positive raves.

Could it be that under race track loads the bushings deflect to allow unfavorable bump steer? If so, would polyurethane bushings fix the problem? Or would they have too big a street penalty?

[jub jub]

Originally Posted by DavidNJ

On the C5 Z06, ghoffman posted this:

Now, C&D and some Internet reviewers have indicated that the C6 Z06 can be fidgety in a race track's bumpy turn. However, on the street, nothing but positive raves.

Could it be bushings that under race track loads the bushings deflect to allow unfavorable bump steer? If so, would polyurethane bushings fix the problem? Or would they have too big a street penalty?

Here's a bump. Maybe DJ or Subdriver can answer this for you.

[DJWorm]

The OEM bushings do allow too much deflexion on the track & for AutoX and do not last as long as they should under these conditions. If you are replacing them I recommend VB&P Poly-Graphite and do not recommend Poly-Ureathane, as it is too noisy.

The condition you describy as jerkyness or twitchyness can be attributed to many things

1. OEM or worn Bushings allow too much deflexion. Switch to Poly Graphite. Options for a dedicated race car are Delrin bushings or metal bushings (heim jointed/spherical or needle roller)

2. Alignment. Street alignments are sluggish and too slow on the track or AutoX, however an extreme AutoX alignment will make the car "want to turn" and "twitchy" on the street

3. Improper shock rebound will cause the rear tires to hop under hard cornering or acceleration. Use tunable at least DA adjustable shocks for track or AutoX.

4. Improper corner weight and/or Cross Corner Weight % Difference. Check Corner weights, corner weight car appropriately, make sure Corner Weight % Difference is within spec.

5. Rake: Make sure rake angle is within spec.

6. Tires. For street, make surei nflation pressures are correct, Runflats are NOT conduce for proper handling on the track and may seem unstable, "choppy" and maay have a quick and unforgiving "edge" as they approach their limits of traction.

7. Improper use of power and brakes. Driver induced suspension upset is frequently an untroubleshootable and overlooked factor.
Look ahead, anticipate and use smooth application of throttle and brakes. Keep head mobile and "on a swivel". Use A-Pillar scan to establish Turn In. Allow your hands to "follow" your eyes. DO NOT fixate while driving.

8. CG & RC are too high. Lower car.

9. Check Sppring Rate, Sway Bar Rates & Sway Bar pre load and correct to corner weights.

I suspect that C&D took the car off the show room floor and tried to track it. Their findings were probably a result of a poor street alignment, non compliant runflat tires. OEM bushings and shocks and most probably a driver that was somewhat unfamiliar with the car and added the "driver factor". Not an unexpected rexiew. Quite understandable. Had the car been set up for the track with a driver that was smooth and familiar with the car the review would have been much different.

[ghoffman]

David, you have run at LRP right? When I took my new C6Z there last month I thought it was pretty good, perhaps the magazines tested early models. Where it had some issues was exiting Big Bend where the inside front would shake under acceleration. Usually, the un-loaded wheel is the hardest thing for the springs and dampers to control, but, I am not sure how much was the bushings and how much was the shocks. Would stiffer bushings help, probably, but road noise would be increased. This was on the street tires, and race tires would certainly increase the cornering loads and I presume the problems would be more obvious. Overall, I thought it was excellent for a street car, and LRP has a rough surface. I know Moton has shocks coming out for it and it would be very interesting to see how they would be with no other changes.

[DavidNJ]

Were you really hauling or just driving fast? How did it compare to the C5Z? How did the brakes hold up?

C&D reported the problems when they were trying for times, about 2 seconds per lap off Chevy's test drivers.

[ghoffman]

The runflats would go away after a couple of laps, but yes, I was really hauling during that time. I have never had a HUD before but I saw 140+ into Big Bend, 120+ almost into the rev limiter down no-name and 1.17g's (when I looked) in West Bend. The brakes felt fine, worked reasonably well, but I had over 2mm of taper in the outside front pads when I got home. As far as compared to a C5Z, well, no disrespect to C5 owners (I had 2 of them) but it is way quicker in every way, no comparison. The motor is terriffic, I used 3rd for most of the track except at the bottom of diving turn I would grab 4th and actually motored by a couple of NASCAR trucks, and was pretty even with a beautifully prepared Mallet 383 CID C5Z on slicks. If it was allowed in T1 without restrictions, it would completely obsolete all of the C5s.

[DavidNJ]

Are the C6Z bushings are better than the C5 bushings?

[ghoffman]

Originally Posted by DavidNJ

Are the C6Z bushings are better than the C5 bushings?

I have no idea!