Car actively trying to swap ends on track?

[cbaclawski]

Anybody got a pic of the c-beam?

I can at least get under the car and check that the existing bolts are tight if I know what I'm looking for...


Searching on google confused me more than I already was...

[Vette Guy]

IMG_5126.JPG


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[cbaclawski]

Originally Posted by Vette Guy

Attachment 9606


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Thanks, Hopefully I can get under there tomorrow...

[spork2367]

Originally Posted by cbaclawski

...and there aren't too many options in our size.

Rear tires available in 315/35R17

Hoosier A7
Hoosier R7
Mickey Thompson ET Street S/S
Mickey Thompson ET Street R
Toyo Proxes R888R
Toyo Proxes TQ
BFG G-Force R1
BFG G-Force R/S
Goodyear Eagle F1 GS-D3
Nitto NT555
Nitto NT555 G2
Nitto NT555R
Nitto NT05
Nitto NT05R
Nitto NT01
Nitto Motivo
Kumho Victoracer V700 (available but discontinued)



335/35R17

Michelin Pilot Sport PS2
Pirelli P Zero System

[cbaclawski]

Originally Posted by spork2367

Rear tires available in 315/35R17

Hoosier A7
Hoosier R7
Mickey Thompson ET Street S/S
Mickey Thompson ET Street R
Toyo Proxes R888R
Toyo Proxes TQ
BFG G-Force R1
BFG G-Force R/S
Goodyear Eagle F1 GS-D3
Nitto NT555
Nitto NT555 G2
Nitto NT555R
Nitto NT05
Nitto NT05R
Nitto NT01
Nitto Motivo
Kumho Victoracer V700 (available but discontinued)



335/35R17

Michelin Pilot Sport PS2
Pirelli P Zero System

This is a great list, thank you. I'm going to keep chasing suspension issues for now, but if that fails I'll def try another tire. If I do get it sorted, I'll need new tires even sooner than later anyway!

Thanks again

[ZWILD1]

I installed the Michelin PS2's so my son could do the HPDI at BG. Glad I spent the money. I rode with him on the touring laps which got pretty spirited. The car was stuck to the track really well. Not one twitch from the rear and the car has the power to kick it out. He really had me gripping as we went through the turns at BG. I was impressed with how well the car actually did staying planted. I was on top watching from the observation area when the 96 GS owner came up saying he was all over the place running on the Sumitomo tires. I think he was the only C4 that was not staying planted at the HPDI.

[Vette Guy]

Maybe a bad run of 315 Sumis? That did cross my mind...


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[cbaclawski]

Originally Posted by ZWILD1

I installed the Michelin PS2's so my son could do the HPDI at BG. Glad I spent the money. I rode with him on the touring laps which got pretty spirited. The car was stuck to the track really well. Not one twitch from the rear and the car has the power to kick it out. He really had me gripping as we went through the turns at BG. I was impressed with how well the car actually did staying planted. I was on top watching from the observation area when the 96 GS owner came up saying he was all over the place running on the Sumitomo tires. I think he was the only C4 that was not staying planted at the HPDI.

Originally Posted by Vette Guy

Maybe a bad run of 315 Sumis? That did cross my mind...


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Certainly could be. I haven't had a chance to get in to the suspension or the c-beam yet. Planning on thoroughly going over both and tweaking the new alignment a touch, then giving it one more shot with these tires. If that doesn't fix it, tires are the next logical step.

My track events are pretty booked up already until July(though I may be able to squeeze it in one day of a 2 day event in June). Once I get done going over it I'll post here if I find a smoking gun. Otherwise it might be a month or 2 before I get a chance to test it... Unless there is one of those SCCA "track night in America" events in the meantime (but not at Charlotte motor speedway - definitely not the place to test it!)

[Hib Halverson]

I'll be honest, because of time constraints this morning...I have a long list of honey-dos to address...I skimmed this thread.

In reading it fast, apparently the OP has been over the car or had a service shop go over the car and the suspension and brakes are in excellent working order, with the exception of checking the torque beam bolts at the trans and axle. As others have suggested, installing torque beam plates at the time you check those bolts is a good idea.

If any of my assumptions are incorrect, then the suspension, brakes, torque beam bolts and powertrain mounts need to be inspected in their entirety and serviced/replaced as necessary.

Ok, now a few comments...

On suspension condition...if you're going to regularly going to track the car, the suspension needs to be better than just "good" condition. All suspension and chassis parts need to be in excellent condition or new. Ball joints, front tie rod ends, bushings, stab. bar links, trailing arms, rear tie rods and etc need to be at least in "very good" condition if not new.

Ditch the Sumitomo tires. They are crap. I don't care what anyone else, here, says. For track use Sumitomos are at the bottom of the list of tires I'd consider for tracking. You need some tires suitable for track activities. The tires need to be predictable at the limit, ie: their breakaway is such that the driver has some good feedback as he/she approaches the tire's limit, they need to have excellent grip and they need to have good steering feel. Someone else posted a list of tires. I'd be looking at some of the brands on that list.

The alignment you have, now, is not inappropriate for track use. The car is going to be way tight and you'll burn though a set of front tires in no time. Ah, well, considering the Sumitomos, maybe that's not so bad. A good street track alignment is half a degree negative camber all the way around, as much front caster as you can get with that negative camber, zero toe up front and a 16th to a 32nd toe-in per side in the rear. A track-only alignment needs to be more aggressive in negative camber both front and rear.

All ZR-1s suffer from drop- or trail-throttle oversteer to some extent, so you need to be like a Porsche guy: don't lift abruptly at corner entrance or that sucker is going to rotate faster than you can say "in the fence". That said, in this case, it sounds like the car's normal trail-throttle oversteer is being amplified by some aspect of the car's set-up or condition of suspension parts. Again, inspect everything and service/replace as necessary and give the Sumitomos to someone who you don't like.

If you're really serious about tracking, you may want to update SRC to the 92-95 config with the late shocks and the late controller because the late system can change bypass valve position much faster. Even better would be a set of late SRC shocks with Bilstein "Moraca" valving, if you can find a set. That valving included some changes to address the ZR-1s tendency towards trail-throttle oversteer. The idea is to better control the car's weight transfer during the transition from accel to dccel.

You said this car has been prepared by someone else for "road course duty". Can you post the spring codes and the stabilizer bar sizes? Also, what kind of stabilizer bar links does the car have? Lastly, does it have base or Z51 lower front control arms?

Coilovers are likely not the solution in this instance. While they do offer a lot of adjustment and can enable a lower ride height, the downside is, in a track environment, you have to know how to use all that adjustment and the whole set-up needs to be more stiff because of the ride travel you loose when you go from composite leaf springs to coil overs. What I'd do is try to get the car sorted with the production-based suspension and then, later, once you can lap the car competitively with the plastic springs, then covert to coilovers if you feel the need. I would not look at a coilover conversion as a quick fix.

Hope you get the car sorted so it's quicker on the track.

[cbaclawski]

Originally Posted by Hib Halverson

I'll be honest, because of time constraints this morning...I have a long list of honey-dos to address...I skimmed this thread.

In reading it fast, apparently the OP has been over the car or had a service shop go over the car and the suspension and brakes are in excellent working order, with the exception of checking the torque beam bolts at the trans and axle. As others have suggested, installing torque beam plates at the time you check those bolts is a good idea.

If any of my assumptions are incorrect, then the suspension, brakes, torque beam bolts and powertrain mounts need to be inspected in their entirety and serviced/replaced as necessary.

Ok, now a few comments...

On suspension condition...if you're going to regularly going to track the car, the suspension needs to be better than just "good" condition. All suspension and chassis parts need to be in excellent condition or new. Ball joints, front tie rod ends, bushings, stab. bar links, trailing arms, rear tie rods and etc need to be at least in "very good" condition if not new.

Ditch the Sumitomo tires. They are crap. I don't care what anyone else, here, says. For track use Sumitomos are at the bottom of the list of tires I'd consider for tracking. You need some tires suitable for track activities. The tires need to be predictable at the limit, ie: their breakaway is such that the driver has some good feedback as he/she approaches the tire's limit, they need to have excellent grip and they need to have good steering feel. Someone else posted a list of tires. I'd be looking at some of the brands on that list.

The alignment you have, now, is not inappropriate for track use. The car is going to be way tight and you'll burn though a set of front tires in no time. Ah, well, considering the Sumitomos, maybe that's not so bad. A good street track alignment is half a degree negative camber all the way around, as much front caster as you can get with that negative camber, zero toe up front and a 16th to a 32nd toe-in per side in the rear. A track-only alignment needs to be more aggressive in negative camber both front and rear.

All ZR-1s suffer from drop- or trail-throttle oversteer to some extent, so you need to be like a Porsche guy: don't lift abruptly at corner entrance or that sucker is going to rotate faster than you can say "in the fence". That said, in this case, it sounds like the car's normal trail-throttle oversteer is being amplified by some aspect of the car's set-up or condition of suspension parts. Again, inspect everything and service/replace as necessary and give the Sumitomos to someone who you don't like.

If you're really serious about tracking, you may want to update SRC to the 92-95 config with the late shocks and the late controller because the late system can change bypass valve position much faster. Even better would be a set of late SRC shocks with Bilstein "Moraca" valving, if you can find a set. That valving included some changes to address the ZR-1s tendency towards trail-throttle oversteer. The idea is to better control the car's weight transfer during the transition from accel to dccel.

You said this car has been prepared by someone else for "road course duty". Can you post the spring codes and the stabilizer bar sizes? Also, what kind of stabilizer bar links does the car have? Lastly, does it have base or Z51 lower front control arms?

Coilovers are likely not the solution in this instance. While they do offer a lot of adjustment and can enable a lower ride height, the downside is, in a track environment, you have to know how to use all that adjustment and the whole set-up needs to be more stiff because of the ride travel you loose when you go from composite leaf springs to coil overs. What I'd do is try to get the car sorted with the production-based suspension and then, later, once you can lap the car competitively with the plastic springs, then covert to coilovers if you feel the need. I would not look at a coilover conversion as a quick fix.

Hope you get the car sorted so it's quicker on the track.

Wow, Thank you!

I tried to give alignment specs to the quickie lube shop where the car was, but they didn't have the equipment to do anything other than "factory" I figured since it was there getting a tire replaced anyway, just let them do it. Even if for no other reason than to see the before #'s and potentially rule that in or out as the issue. I'll have it done correctly soon, but haven't had time yet.

I don't know the spring codes or stabilizer bar sizes, but I'd assume they are whatever came stock in 1990. Being a ZR1 I'd expect it to have the z51 lower front control arms. Again though, I'm not 100% sure. Was this an option on ZR1's or did they all come with the z51?

The car has been inspected by my local race shop (which is admittedly more of a BMW racing shop), and also shipped to Marc Haibeck for a thorough once over. Both were told of my intentions with the car and gave the suspension a clean bill of health. The beam bolts may well have been checked, but seem easy enough for me to double check just in case.

My plan is, time permitting, go over everything you mentioned myself just to be sure. I have both a 4 post lift and a set of quickjacks, so access shouldn't be a problem.


Hopefully I can get the car controllable on the sumi's, wear them out quickly, then go to a better tire. If I can get it decent on the existing tires, it'd probably be great on better tires.


If after everything is done, and it's still uncontrollable, I'll swap the tires proactively. If that doesn't work, I'll just put street pads back on it and reinstall the factory seats and enjoy it for what it is on the road...(I really hope it doesn't come to that)


Thanks again for your interest and help!