Car actively trying to swap ends on track? - Page 5 - ZR-1 Net Registry Forums

WARP TEN · 05-29-2019

Quote:

Originally Posted by Vette Guy

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

Quote:

Originally Posted by Hib Halverson

.......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.............

Have to concur with both. Not sure there has ever been a good run of Sumis. I had a couple of sets of Sumis, one I bought because they were cheap ('93) and one because they were on the car when I bought it ('95). They got hard fast, seemed to have little traction and on my '95 I had a wheel vibration that I could not eliminate by balancing until I finally got to a great tire place in Bowling Green (S&R Tire on Lover's Lane) with an excellent tech and a Hunter Road Force machine in 2014. He had to spin all the tires on the wheel rims to get them even close and one tire he said he could not balance properly because it was so far out of manufacturer's specification. He eliminated about 95% of the vibration though which was a help. I switched to Michelin Pilot Sports shortly thereafter. Great tires even if a little bit wider in the rear. --Bob

cbaclawski · 05-30-2019

Ok, While I still haven't had a chance to inspect the suspension/c-beam (real life, other projects...) It seems pretty clear that the Sumitomo's, even if not the main problem, certainly aren't helping anything.

So here is my dumb question:

Since the car really only struggles for rear grip and the front seems great, how bad of an idea would it be to replace only the rears? One of the fronts is 100% brand new, and the other is 90%(they'll even out after 2 track sessions, the driver side wears much faster)

Maybe I'm just being cheap, but I run 4 track cars, and the expenses really add up. If possible, I'd like to spend as little as I can replacing essentially new tires on a car that only gets 2-3 track days a year....

Curt

RussMcB · 05-30-2019

Wait until you've had a chance to find the real culprit, then go back to the track with your four Sumitomo's and see if you found and fixed the problem.

I'm thinking (without really knowing) that the Sumitomo's may be lousy tires, but they are unlikely to be the real problem, and you should still be able to have some fun with them before replacing them. I mean, they can't be so bad and unpredictable that they try to kill you every corner, right? :-)

I'm a low budget racer, too, so I certainly understand using up what you have before spending money to replace it.

cbaclawski · 05-30-2019

Quote:

Originally Posted by RussMcB

Wait until you've had a chance to find the real culprit, then go back to the track with your four Sumitomo's and see if you found and fixed the problem.

I'm thinking (without really knowing) that the Sumitomo's may be lousy tires, but they are unlikely to be the real problem, and you should still be able to have some fun with them before replacing them. I mean, they can't be so bad and unpredictable that they try to kill you every corner, right? :-)

I'm a low budget racer, too, so I certainly understand using up what you have before spending money to replace it.

That was kind of my plan, get the car running straight, burn out these tires(which only takes a couple days @ CMP), then replace the tires and start pushing it. With all the negativity towards the sumitomo's, and the possibility that they could be a real part of the problem, I was starting to waver...

Thanks

cbaclawski · 05-30-2019

I finally got the back wheels off and inspected every suspension joint and lubed the bushings. Everything seemed in order. It felt really good on the street, but it's hard to simulate track conditions on the street, in the dark.

I'm still planning on getting it up on the 4 post to tweak the alignment and inspect the c-beam, but feel like maybe between the somewhat better alignment and the lubricated joints, I'm making progress.

I'll be thrilled if I can get this right. There was a guy at the SCCA Time trial I attended last weekend in a heavily modified non-zr1 c4(don't know year, but def. pre '91) turning some really fast laps. I didn't get a chance to talk to him so I don't know exactly what his set up was, but I'd put money on it that properly configured my car has more potential than whatever he was running. (though for all I know I suppose it could have had a pro-charged lsx, giant brakes, etc... but I doubt it)

32valvesftw · 05-31-2019

You need to try different tires and see what happens. The single biggest improvement to the handling of my car was getting rid of the BFG tires on and going with Nittos, now that the Nittos have a few years on them they are getting less grippy. How old are the Sumis did you check the date code? Maybe squirt some tire compound in them for a few laps and see what happens.

cbaclawski · 05-31-2019

Quote:

Originally Posted by 32valvesftw

You need to try different tires and see what happens. The single biggest improvement to the handling of my car was getting rid of the BFG tires on and going with Nittos, now that the Nittos have a few years on them they are getting less grippy. How old are the Sumis did you check the date code? Maybe squirt some tire compound in them for a few laps and see what happens.

I haven't checked the date code(which I will do), but they were purchased new from Tire rack < 1yr ago.

Tire Compound? That sounds interesting, what is it and what does it do?

When I had the tires off last night, I inspected them and they didn't feel hardened, though I'm not sure how much you can tell just by feeling them cold...

32valvesftw · 05-31-2019

Tire compound is a chemical used to soften tires and improve their grip.
A couple of examples below. The kart racing guys use this as do some stock cars (but not legally)

https://www.speedwaymotors.com/Track...oaAg3qEALw_wcB

https://www.ombwarehouse.com/9863-ft...4aAmEzEALw_wcB

cbaclawski · 05-31-2019

Quote:

Originally Posted by 32valvesftw

Tire compound is a chemical used to soften tires and improve their grip.
A couple of examples below. The kart racing guys use this as do some stock cars (but not legally)

https://www.speedwaymotors.com/Track...oaAg3qEALw_wcB

https://www.ombwarehouse.com/9863-ft...4aAmEzEALw_wcB

Any experience with it? How long does it last? I'm intrigued!

cbaclawski · 06-01-2019

C-Beam bolts are good and tight...

I gave them all everything I've got with a long torque wrench, could only budge one of them, and even then less than 1/4 turn. I'm not a small dude either (6'2" 275lb who once benched 225lb 32 times on a burnout set)

Tomorrow I'm going to tweak the alignment a bit to give it some rear toe in and a touch of negative camber.

Then I need to get it back on track, I think there is a SCCA Track night coming up in between events I've already committed to in other cars... Fingers Crossed!

05-30-2019	#42
cbaclawski Join Date: Feb 2017 Location: waxhaw, nc Posts: 93	Re: Car actively trying to swap ends on track? Ok, While I still haven't had a chance to inspect the suspension/c-beam (real life, other projects...) It seems pretty clear that the Sumitomo's, even if not the main problem, certainly aren't helping anything. So here is my dumb question: Since the car really only struggles for rear grip and the front seems great, how bad of an idea would it be to replace only the rears? One of the fronts is 100% brand new, and the other is 90%(they'll even out after 2 track sessions, the driver side wears much faster) Maybe I'm just being cheap, but I run 4 track cars, and the expenses really add up. If possible, I'd like to spend as little as I can replacing essentially new tires on a car that only gets 2-3 track days a year.... Curt

05-30-2019	#43
RussMcB Join Date: Jan 2015 Location: Marietta, GA USA Posts: 1,160	Re: Car actively trying to swap ends on track? Wait until you've had a chance to find the real culprit, then go back to the track with your four Sumitomo's and see if you found and fixed the problem. I'm thinking (without really knowing) that the Sumitomo's may be lousy tires, but they are unlikely to be the real problem, and you should still be able to have some fun with them before replacing them. I mean, they can't be so bad and unpredictable that they try to kill you every corner, right? :-) I'm a low budget racer, too, so I certainly understand using up what you have before spending money to replace it.

05-30-2019	#45
cbaclawski Join Date: Feb 2017 Location: waxhaw, nc Posts: 93	Re: Car actively trying to swap ends on track? I finally got the back wheels off and inspected every suspension joint and lubed the bushings. Everything seemed in order. It felt really good on the street, but it's hard to simulate track conditions on the street, in the dark. I'm still planning on getting it up on the 4 post to tweak the alignment and inspect the c-beam, but feel like maybe between the somewhat better alignment and the lubricated joints, I'm making progress. I'll be thrilled if I can get this right. There was a guy at the SCCA Time trial I attended last weekend in a heavily modified non-zr1 c4(don't know year, but def. pre '91) turning some really fast laps. I didn't get a chance to talk to him so I don't know exactly what his set up was, but I'd put money on it that properly configured my car has more potential than whatever he was running. (though for all I know I suppose it could have had a pro-charged lsx, giant brakes, etc... but I doubt it)

05-31-2019	#46
32valvesftw Join Date: Jun 2015 Location: Texas Posts: 530	Re: Car actively trying to swap ends on track? You need to try different tires and see what happens. The single biggest improvement to the handling of my car was getting rid of the BFG tires on and going with Nittos, now that the Nittos have a few years on them they are getting less grippy. How old are the Sumis did you check the date code? Maybe squirt some tire compound in them for a few laps and see what happens.

05-31-2019	#48
32valvesftw Join Date: Jun 2015 Location: Texas Posts: 530	Re: Car actively trying to swap ends on track? Tire compound is a chemical used to soften tires and improve their grip. A couple of examples below. The kart racing guys use this as do some stock cars (but not legally) https://www.speedwaymotors.com/Track...oaAg3qEALw_wcB https://www.ombwarehouse.com/9863-ft...4aAmEzEALw_wcB

06-01-2019	#50
cbaclawski Join Date: Feb 2017 Location: waxhaw, nc Posts: 93	Re: Car actively trying to swap ends on track? C-Beam bolts are good and tight... I gave them all everything I've got with a long torque wrench, could only budge one of them, and even then less than 1/4 turn. I'm not a small dude either (6'2" 275lb who once benched 225lb 32 times on a burnout set) Tomorrow I'm going to tweak the alignment a bit to give it some rear toe in and a touch of negative camber. Then I need to get it back on track, I think there is a SCCA Track night coming up in between events I've already committed to in other cars... Fingers Crossed!