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Hello guys
This weekend, I did my first hpde on Hoosier r6 slicks. Typically I have run pilot sport cups as to not push the car too hard, but opt'd to try really stepping up the track times.

The morning was foggy and damp, so my first two sessions were very easy on the car. Proper warm up lap and a couple 6/10 intensity level laps, followed by 2 cool down laps. No issues.
Afternoon cleared up and it got hot out. Track was sticky and perfect, so I decided to let her rip. I did the warm up lap and 5 hard laps. On my last lap, after some fairly intense braking, I started developing a wobble in the steering wheel when I was 65mph or faster.
Did the cool down laps and continue to drive around for another 20 min to really cool everything. Parked it. After an hour, went back on the track and the wobble was horrible. Steering wheel shakes fairly violently over 70mph. The rear view mirror looks like it's going thru an earthquake.

I came back into the pits, swapped my front tires to my stock wheels. The vibrations after 70mph was still there but not as bad.

I'm leading to believe my rotors may have been warped?
Wheels bearings felt solid still.
Everything looks right underneath so I'm really not sure wtf happened???

Any suggestions or opinions as to what may be the culprit here?
Any help would really be appreciated.
Thanks guys!
Aj

phipp85

Was there a bunch of build up on the tires? You also could have spun tires on the rim and caused some nasty vibrations.

One time I had vibrations similar to what you are describing. Long story short it was just a combination of the tire rotating on the rim, build up on the tread, and tire turds stuck to the inside of the wheel. I had them balanced at the track and the vibrations went away......... until the tire rotated some more.

Unless you run fairly aggressive amounts of camber you're gonna get some build up on the inside of the tires.

SouthernSon

You have some bad problems somewhere. Closing in on 10K hard track miles in same C5Z with 710's, A6's, R6's and a bunch of others without any wobble. Have replaced plenty of tie rod ends, wheel bearings and several dozen rotors but no wobble ever of any concern. You need to check all ball joints, A-arm nuts, steering connections, corded and/or tire tread separations, etc.....

2002rich

Sounds like you lost your weights

StKnoWhere

Warped rotors are normally felt when braking. If its happening at a range of speed, probably wheel balance.

FuriousDonuts

Probably worth checking your wheel hubs. It's a whole different ball game when you make the transition from street tires to DOTs. If you're running hard, you're putting a lot more stress on the hubs. Most racers have to change them out every season.

Next time the car is in the air, grab the wheels at 12 and 6 o'clock position and give them a pull forwards and backwards. If you feel it move, imagine what it's doing when 3,000+ lbs are going around a corner at 80 mph.

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Thank you guys for the input. I'll respond to some of the suggested issues:

Could possibly be a spun tire on the rim, didn't even think about that. That would def knock off the weights.
Wheel weights are taped over with gorilla black tape. They are all intact so no issues there.
I did check the hubs. Grabbed at 12/6 and tried to wiggle. It's solid. No movement at all.
I also did check all tie rods, control arm bolts etc, everything was tight.

This is why I'm confused. I don't think it's the rim/tire bc I swapped to my stock set in front and the wobble was still there. It's got to be something in the car.

Dropping at the shop today, see what they can figure out. Rear tires are getting swapped as well so that will eleviate any tire/wheel related cause.

I was reading on another thread that rotors can wrap and come out of line. The runout would be minor and not an issue at low speed but one you start rotating them at 70mph? The runout is soo bad you can feel it thru the steering wheel and the front end. To me this makes sense since I was hot on the brakes. I'll see what turns out this afternoon.

Thank you again guys, appreciate the input.

naschmitz

My guess is uneven pad deposits on the rotor:

From: http://www.essexparts.com/learning-c.../swapping_pads

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pads and rotors are brand new last yr. they maybe have 3-4k EASY miles on them.

I will note, the rotors are cross drilled and slotted from a manufacturer selling them on ebay. I used the same set on my last Z06 and tracked that one 3 or 4 times without any issues. Granted, this time i am on slicks so the car was run harder then previously...

RDnomorecobra

you sure a rotor is not cracked?

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^^^pretty sure. looked them over REALLY well.

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Got the car back from the shop, all is ok now. It seems i may have rotated the tires on the rim, thus knocking off the balance. They said the fronts were fine (since i swapped wheels anyhow) but the rears were way off. I had the tires dismounted and put my drag radials back on. Took her for a rip and shes solid as usual.

I've never rotated a tire on a rim before while on the track. Is this common? Or was i really pushing it that hard?

Anyhow, thank you all for the comments, do appreciate it.
Aj

0Randy@DRM

Pretty common actually. Tell Blake not to use any lube when mounting. Yes he will have to work harder. I dipped my finger in their lube bucket one day to see what they are using. My best guess it's the sperm of some mythical creature.

You can mark the tire where the valve stem is and see if it moves around with a quick glace.

Randy

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Yea, the guys at Samaritan did use a fair amount. There was a lot of remnants of the lube on the sidewall. I never thougtht anything of it tho. But Rob re-balanced the fronts, mounted my Drags on the rear and all is good now. I checked hubs, nuts and bolts on the entire front suspension, everything is tight.

either way, i am happy now.

BTW Randy... we miss you back home!
aj

5280Racer

It very common thats why they invented bead locks and other methods or retaining the tire on the wheel. Drag racers use bead locks or screws to hold the tires.. in Road racing like my Finspeed wheels they are often knurled on the bead so the rotation of the tire on the rim is stopped. Very easy way to see if its still happening. get a paint marker and mark your tires and wheels as they sit then run a session come bad and see if the lines are shifted.

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Yea, i knew they did that for drag racing. Never figured for HPDE.
Yes, i will have the tires re-mounted/balanced for the next event. Its in sept so i have some time. I don't road course as often as i'd like to. Prolly a good thing...

VatorMan

Glad you figured it out. We typically put chalk marks on our wheels/tires so we can see how much they spin on the rim. Even dry, you'd be surprised how much they spin. I've been threatening to get a bubble balancer for my trailer.

0Randy@DRM

AJ,
It's a good idea to check out all of that stuff anyways!!!

Rumor is I will be back in MN next week Hanging out with the in laws in MPLS for a day or two (with some luck I will not want to hang myself) Then about 6 hours north to the start of the boundary waters.

Randy

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Nice! Weather looks iffy but enjoy bud!
Gotta keep the in-laws happy tho! Haha