S550 Strange Vibration at Watkins Glen 5/2

[cjatrains]

So I was at Watkins Glen 5/1 and 5/2. On day two, 3rd session, I started getting a very noticeable vibration coming through the chassis. I only had one dry session on Monday, on the long 3.45 mile course. No issues Monday other than me being in a new car, and temps below 50. On day two, the first two sessions on the short NASCAR circuit were going well, temps almost hit 50, track was dry.
On the 3rd session, after T1 RH corner, exiting around 70 to 75 and accelerating to T2 also RH entering the Esses, I feel this alarming vibration in the chassis. I was entering T2, RH between 90 and 100 mph, as those were my entry speeds in my C7.
Initially, I figure it's just the track surface, or pick up or something on my tires. Vibration mostly disappears after cresting the hill T3 LH at 110 and I don't feel it the rest of the way around. Next lap same vibration same spot on course, between T1 & T3 ??? I am like what's going on. Do I have a tire going down... Is the pavement torn up which is uncharacteristic for WGI
As I know it's my last session of the day, I keep driving, try a different line, vibration isn't going away.....
Obviously made it through the 20 minute session, a little worn out from worrying. I go cool and the car down, go the gas station, pack up and drive home 400 miles. I have checked the rear left axle shaft 32 mm nut, marked it, and turned the torque wrench up to 250 pounds, it wouldn't budge. Lug nuts were all fine as a torqued them twice daily. After driving all the way home, the only thing I could find that might even begin to maybe cause this was a ribbon of melted rubber about 1/4 to 3/8" wide all the way around the circumference of the tire approaching the edge of the first rain groove in the Cup 2. I am suspecting that ribbon was larger and more pronounced when I was on track last session, as it survived a 400 mile journey home.

Anyone have any thoughts about what might have been happening, and more importantly what I need to be checking out ??? Thanks

 

[RES_22]

Weird that you saw that much pickup on only one tire....hmmmmmm???

Check and scrape any residual pickup from all 4 tires, then go check the balancing. Rebalance as required and tape the weights carefully.

Next trip to the Glen, monitor for pickup and/or rotate side to side at lunch.

Good luck.

 

[cjatrains]

Thanks for the ideas. I plan to rotate tires before I go back in July. I didn't mention it, but another S550 I met at the track told me to check my wheel weights and look for any other large globs of rubber inside the barrel. Both of those inspections didn't reveal any weights missing or any large rubber deposits. I am kind of thinking that ribbon of rubber was my Cup2's rubber, just moving it from the shoulder toward the center of the tire. It's early in the season at the Glen, it had been raining buckets for weeks, and it really never sunny or above 50 degrees, so I am thinking we weren't getting much pick up. But then again, I didn't do the track walk Monday night, and while I have been to 23 track days in 3 years, I am by no means an expert on any of this. Had just developed a good feel and understanding for my C7 platform after 18 days at the Glen, but then sold the car last October and bought the Mach 1 in November.

 

[blacksheep-1]

A quick diagnostic on the track would be to put the car in neutral, that would isolate everything from the tranny back, and remove the engine and mounts from the vibration list.
From then on, it's sort of just eliminating different things, tire balance would prolly be the next easiest to isolate, at that point it is prolly driveline related.
As stated above, clag can be a weird thing, you can try scraping everyhting off but sometimes you pick up as much crud driving through the paddock as you do on the track. I use dto scrape every tire used for the race, but it's all gone by the time the car gets to the end of the pit lane anyway, so now I only do it for disgnodtics.

 

[cjatrains]

Thanks Blacksheep-1: Yes Neutral is a great idea if and when it re-occurs, to isolate drivetrain issues.