Severe wheel hop issue

[sahlman]

@Joe Dozzo @GT@50 is correct above. That made up rear suspension with inboard rear brakes needs an upper link to the ~upper balljoint going forward to control the large caster wind up of a high HP car. The little wider a-arm at the bottom is not remotely enough. Don't know what is there to control the independent diff wind up but that probably needs help too though should be easier to control in this independent configuration.

Don't think new coil-overs will help this wheel hop a lot, but should be more for when this issue is fixed.

Static toe should be inward not out. And should not be changing much (bumpsteer) with travel, but should be inward in bump.

Good luck. That is a straight-line car...Detroit Speed or otherwise solid axle four link with a track bar will put the big power down. Think along these lines to fix this issue. A high speed camera from the frame toward center facing out toward the wheel end can tell you alot

 

[GT@50]

@Joe Dozzo @GT@50 is correct above. That made up rear suspension with inboard rear brakes needs an upper link to the ~upper balljoint going forward to control the large caster wind up of a high HP car. The little wider a-arm at the bottom is not remotely enough. Don't know what is there to control the independent diff wind up but that probably needs help too though should be easier to control in this independent configuration.

Don't think new coil-overs will help this wheel hop a lot, but should be more for when this issue is fixed.

Static toe should be inward not out. And should not be changing much (bumpsteer) with travel, but should be inward in bump.

Good luck. That is a straight-line car...Detroit Speed or otherwise solid axle four link with a track bar will put the big power down. Think along these lines to fix this issue. A high speed camera from the frame toward center facing out toward the wheel end can tell you alot

Toe in? My thoughts are that as the tires are trying to move forward they'll start to toe in, so starting with a hair toe out, acceleration would bring them to 0. ? I'm no expert but appreciate conversation.
Are you sure it's wheel hop and not driveline vibe because of U joint angle?
If memory serves correct, 7* max combined angles for a 2 joint shaft is ideal, -3.5* on one joint, +3.5* on the other to cancel them out. That'd be ideal anyways. I get a lot of cars in with whacked angles and no issues.

 

[sahlman]

Toe in? My thoughts are that as the tires are trying to move forward they'll start to toe in, so starting with a hair toe out, acceleration would bring them to 0. ? I'm no expert but appreciate conversation.
Are you sure it's wheel hop and not driveline vibe because of U joint angle?
If memory serves correct, 7* max combined angles for a 2 joint shaft is ideal, -3.5* on one joint, +3.5* on the other to cancel them out. That'd be ideal anyways. I get a lot of cars in with whacked angles and no issues.

Without doing detailed analysis of that suspension the toe change is unclear...toe should not remotely be noticeable. And toe out or zero toe at the rear is unstable for cornering.

He said wheel hop. But most likely both wheel hop and driveline vibration as the caster is changing and wheel center moving forward. And guessing he is spinning the tires hard at zero speed so he is not experiencing this there, but rather at 35 mph when the tires are able to hook up and highlights the suspension and driveline issues.

Your vehicles with no issues...solid axle? 4-link with a trackbar?

 

[2112]

Not going to help Joe, but I rigged a solid axle with 2 stout Lower contral arms, a torque arm and Watts link and eliminated all wheel hop.

 

[Joe Dozzo]

2112, I am ALMOST there....

 

[w.a.nelson]

This thread demonstrates what is so great about this forum.

Kudos to contributors!

Good luck Joe.

 

[PeteK]

Scott, if I can bend your ear for a moment: several guys who race and do suspension work on Porsche old air cooled 911's, strongly recommend zero toe on the rear and front, maybe even slight negative toe on the rear. I have my 1973 911 set at zero toe on both ends now, but I have to be very attentive to the steering, constantly making small corrections, to keep it from diverging from straight ahead. It feels like the rear is less stable than the front. Zero to slight negative toe goes against what I learned over the years about suspension set up. But these old 911's are odd critters.

Do you have any experience setting up old 911's and what you think works best?

Thanks in advance.

 

[Joe Dozzo]

RESOLVED!

Much to my great surprise, I was able to completely eliminate my wheel hop issue with some pretty simple shock adjustments - took some trial and error but no new parts. Still have the 500lb springs (vs recommended 350's) but I can live with those.

Many thanks for all those who offered advice and suggestions!

 

[twobjshelbys]

Thanks for letting us know the resolution!

 

[sahlman]

Scott, if I can bend your ear for a moment: several guys who race and do suspension work on Porsche old air cooled 911's, strongly recommend zero toe on the rear and front, maybe even slight negative toe on the rear. I have my 1973 911 set at zero toe on both ends now, but I have to be very attentive to the steering, constantly making small corrections, to keep it from diverging from straight ahead. It feels like the rear is less stable than the front. Zero to slight negative toe goes against what I learned over the years about suspension set up. But these old 911's are odd critters.

Do you have any experience setting up old 911's and what you think works best?

Thanks in advance.

Yep a lot of guys think toe out at the front is especially better because it is very darty. This is even more the case at the back. These toes actually have less grip ( by a little), are unstable and the car won't follow your hands. I had to prove to my IMSA GS guys toe out at the front was not a good idea. They did run reasonable toe in at the back. Bumpsteer- your front will toe out in bump and rear will toe in.

The rear engine 911 make this even worse because of the huge rear weight bias. So Just run the Porsche recommended OEM toes front and rear at whatever ride height you have chosen. The car will be more intuitive and have better grip.

 

[sahlman]

RESOLVED!

Much to my great surprise, I was able to completely eliminate my wheel hop issue with some pretty simple shock adjustments - took some trial and error but no new parts. Still have the 500lb springs (vs recommended 350's) but I can live with those.

Many thanks for all those who offered advice and suggestions!

That is surprising, but I didn't know the concern in detail, so not the level of wheel hop I have experienced. 500's are stiff springs it seems. Tire wear may affect this coming back, but glad you have it resolved. Are you spinning the tires on a launch?

 

[Joe Dozzo]

Depends how hard I launch... Dumping the clutch at ~2500 rpm definitely spins the tires.

 

[sahlman]

Depends how hard I launch... Dumping the clutch at ~2500 rpm definitely spins the tires.

Understood. I am guessing hard to make a fast launch on an unprepped surface.

 

[nota4re]

Joe - I'm glad you got everything resolved! The recommendations/advice you're getting from Sahlman should have a weight factor of 100 attached to it. He lives and breaths this stuff... and is a very recognized expert in suspension design.