yellowss7 Posted September 9, 2013 Share Posted September 9, 2013 Guys, I did a couple of trackdays this weekend, and the car ran great thru the first 7 sessions, on the 8th session a shake/vibration started halfway thru the session that actually vibrated my center mirror loose and it started to turn so I pitted. I didn't feel any looseness in the front wheel bearing. The slicks were picking up a significant amount of rubber, and I cleaned the fronts off as best as possible. I didn't check the rear tires though. I went out for the next session and the shake continued so I packed it in at that point. Last time I had a shake like this I changed over to a new set of slicks an the issue was resolved. That set now has about 8 or 9 trackdays on them. They have plenty of rubber left and still seam pretty sticky. Any suggestions as to what I should check out other than the bearings, the wheel balance or the U joints? Tom Link to comment Share on other sites More sharing options...
MHKflyer52 Posted September 9, 2013 Share Posted September 9, 2013 Hi Tom, Sounds like you might have a tire that is separating from the cords internally. Do you have a set of road wheels and tires that you could put on and see if the vibration goes away. Just a thought but when was the last time you checked the drive shaft connections as a loose flange or missing bolt and nut could also cause the vibrations. Hope this helps. :driving: Link to comment Share on other sites More sharing options...
yellowss7 Posted September 9, 2013 Author Share Posted September 9, 2013 Thanks Martin. I'll put it up on the lift and check out the u joints and prop shaft. Then I'll put the street tires on, and the windscreen and take a ride around the neighborhood and make sure everyone is awake! :seeya: Tom Link to comment Share on other sites More sharing options...
xcarguy Posted September 9, 2013 Share Posted September 9, 2013 (edited) Just want to confirm; vibration, not a bounce. For what it's worth, check for the possibility of a lost wheel weight. Aside form that, I agree with MHKflyer52, possible tire cord separation. Since you've experienced this before and resolved the issue by changing tires, I'd think tire breakdown (cord separation). Edited September 9, 2013 by xcarguy Link to comment Share on other sites More sharing options...
yellowss7 Posted September 9, 2013 Author Share Posted September 9, 2013 Aw come on, I only have 45 to 50 heat cycles on them. :ack::ack: I thought these things should last a lot longer than that. :jester: Like I said, they still have plenty of rubber left based on the wear indicators. Plus yesterday they were really nice and soft as the temp was around 80F and Sunny. Just sitting in the paddock they were hot to the touch. Heading out to the garage now to put the street tires on. tom Link to comment Share on other sites More sharing options...
jlumba81 Posted September 9, 2013 Share Posted September 9, 2013 You could rotate the tires front to back and see if the vibration moves. I've driven with winter tires w separating cords and it gave a nasty vibration 20mph and up. Couldn't afford new tires so I ended up rotating them to the rears and the vibration was more manageable. Link to comment Share on other sites More sharing options...
blubarisax Posted September 9, 2013 Share Posted September 9, 2013 Here is the rubber I collected with Tom on the track yesterday. I scraped a baseball sized lump off right before the run. Can't figure out why the rubber seems to collect all in a line around the tire. -3 Degrees of camber and 20 psi hot. Temps were uniform across the tire and this only happens on the front tires (both of them). http://i913.photobucket.com/albums/ac336/blubarisax/TireRubber2_zps31612486.jpg Link to comment Share on other sites More sharing options...
coffee break Posted September 9, 2013 Share Posted September 9, 2013 Was the vibration associated with road speed or engine speed? Link to comment Share on other sites More sharing options...
yellowss7 Posted September 9, 2013 Author Share Posted September 9, 2013 Can't remember at what speed it became apparent. It definitely shook going thru the bowl, which I take at about 75-95 mph. I definitely shook going down the front straight which was about 95 to 115 mph. Don't remember any issues while braking. Link to comment Share on other sites More sharing options...
TheDingo8MyBaby Posted September 9, 2013 Share Posted September 9, 2013 Here is the rubber I collected with Tom on the track yesterday. I scraped a baseball sized lump off right before the run. Can't figure out why the rubber seems to collect all in a line around the tire. -3 Degrees of camber and 20 psi hot. Temps were uniform across the tire and this only happens on the front tires (both of them). http://i913.photobucket.com/albums/ac336/blubarisax/TireRubber2_zps31612486.jpg The reason you're seeing pickup only on the inside is due to the camber, probably on the cool down lap when you're only running on the inner section of rubber. Tom: I would agree with others about swapping rubber front to rear. You can also have the wheels balanced (make sure they do dynamic balancing) to ensure they aren't the issue. Typically with wheel vibration issues, you primarily feel it in the steering wheel and less overall in the car. Link to comment Share on other sites More sharing options...
blubarisax Posted September 9, 2013 Share Posted September 9, 2013 The reason you're seeing pickup only on the inside is due to the camber, probably on the cool down lap when you're only running on the inner section Good point, that's the first answer that makes sense to me. Guess I need to stay on line during the cool down lap to check the theory. Thanks, Karl Link to comment Share on other sites More sharing options...
jlumba81 Posted September 9, 2013 Share Posted September 9, 2013 Shake only at high speeds may be caused by something flapping around in the wind. Link to comment Share on other sites More sharing options...
WestTexasS2K Posted September 10, 2013 Share Posted September 10, 2013 Sounds like a tire seperating or a weight came off. Try rebalancing while its on the balancer you may be able to see if there is a small knot or out of roundness with one of tires while its on the machine. Link to comment Share on other sites More sharing options...
Croc Posted September 10, 2013 Share Posted September 10, 2013 Tom - you are describing the exact same symptoms I had on the sevens track day when I lost the wheel weight off the rear right. It may only have been 10 grams or so but it made a hell of a vibration without it! Link to comment Share on other sites More sharing options...
yellowss7 Posted September 10, 2013 Author Share Posted September 10, 2013 Thanks everyone for your suggestions. I took the wheels and slicks over to see if they balance. Hopefully I'll get them back tomorrow and see how it feels. Tom Link to comment Share on other sites More sharing options...
yellowss7 Posted September 12, 2013 Author Share Posted September 12, 2013 Just picked up the wheels and slicks from the shop. The track that I've been running on has 11 turns of which 9 are rights and only 2 are lefts. Wear on the left side tires was apparent and for whatever reason, the tires and wheels without weights were 147 grams out of balance. :ack: I had two new slicks and those on the wheels without weights were only 46 grams out before balancing. So based on that it appears that somehow the tires ended up 100grams out of balance. Hopefully this resolves the issue. I will attempt to run another trackday on Saturday and I'll report back with the results. Thanks again for your suggestions! Tom Link to comment Share on other sites More sharing options...
Croc Posted September 12, 2013 Share Posted September 12, 2013 so.....the left to right variance (F to F and R to R) was 100 grams each and each wheel was balanced vertically if not laterally (on that wheel)? and that would be explained through Lightning Circuit being a clockwise running circuit. so far so good.... But why would that cause vibration? Vibration arises from weight imbalance reacting to centrifugal force and normally rubber is evenly distributed around the rim of the wheel? I think of the example of a L/R staggered set up for a oval course where tires can be shaved to give a cutoff "cone" profile to fit the banking - those cars do not have wheel vibrations? What am I missing from this new piece of evidence to explain the vibration? Link to comment Share on other sites More sharing options...
yellowss7 Posted September 14, 2013 Author Share Posted September 14, 2013 Just got home from a great day on the track. Putting two new slicks on the front and rebalancing the two other wheels, seems to have resolved the shake problem. Car ran real strong today with the nice 65 degree weather. 8 more member track days left this season. Can I finish the season without buying any more tires. :cuss::cuss::cuss: On a sad note, I looks like I will finally have to retire my original brake pads after 12 years on the car, over 60+ trackdays, and 8 seasons of autocrossing. I'm still hoping to finish the season on them, but I'm going to have to monitor them closely. It's going to be close. :ack: Tom Link to comment Share on other sites More sharing options...
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