Oscillation under load on track day - 996 - any ideas?
Discussion
Hi All,
Went to Donington Park for a track evening on Thursday (great evening, great weather, first time at Donington and really enjoyed it!).
All was going well until towards the end I started to feel some vibration when cornering. It felt like an oscillation similar to what i felt in the past when i had a wheel start to come lose. Came in, torqued all the wheel nuts, went back out with the instructor. Vibration was there again and instructor could feel it too.
We jacked up each corner with the mechanic from the track day organiser (want2race, really nice chaps), pulled on each wheel, nothing was loose. Checked tyre pressures, nothing wrong. Thought it might be tyre deposit or sticking brake pad so went back out for a couple of laps.
Tried braking when the vibration occurred and it didn't go away so we ruled out sticky brake pad. Did two full laps at 50% and it didn't go away so we ruled out deposit from the track on tyres.
Called it a day. Drove home 1h30mn with no problem what so ever (not enough lateral load on normal driving to feel the vibration).
Things that I find weird are: no steering wheel judder, happened under load from cornering on both left and right, nothing in a straight line. Not super loud or violent, but enough that a passenger would feel it.
Had a poke around under the car and saw nothing lose or snapped. Will get it on the ramps at a specialist as soon as i can, but in the meantime any ideas would be very welcome. I'm also not sure i could reproduce this on the road without driving way to fast so not sure how to identify where it might come from. Suspension is relatively new (KW V3, lower control arms, ARB) and had a full geo a few weeks ago. Car felt great from the geo and very easy to drive.
Anyone have a similar experience or any ideas?
thanks!
ps. car is a modified 996.2 c2
Went to Donington Park for a track evening on Thursday (great evening, great weather, first time at Donington and really enjoyed it!).
All was going well until towards the end I started to feel some vibration when cornering. It felt like an oscillation similar to what i felt in the past when i had a wheel start to come lose. Came in, torqued all the wheel nuts, went back out with the instructor. Vibration was there again and instructor could feel it too.
We jacked up each corner with the mechanic from the track day organiser (want2race, really nice chaps), pulled on each wheel, nothing was loose. Checked tyre pressures, nothing wrong. Thought it might be tyre deposit or sticking brake pad so went back out for a couple of laps.
Tried braking when the vibration occurred and it didn't go away so we ruled out sticky brake pad. Did two full laps at 50% and it didn't go away so we ruled out deposit from the track on tyres.
Called it a day. Drove home 1h30mn with no problem what so ever (not enough lateral load on normal driving to feel the vibration).
Things that I find weird are: no steering wheel judder, happened under load from cornering on both left and right, nothing in a straight line. Not super loud or violent, but enough that a passenger would feel it.
Had a poke around under the car and saw nothing lose or snapped. Will get it on the ramps at a specialist as soon as i can, but in the meantime any ideas would be very welcome. I'm also not sure i could reproduce this on the road without driving way to fast so not sure how to identify where it might come from. Suspension is relatively new (KW V3, lower control arms, ARB) and had a full geo a few weeks ago. Car felt great from the geo and very easy to drive.
Anyone have a similar experience or any ideas?
thanks!
ps. car is a modified 996.2 c2
Discombobulate said:
I would remove and take another careful look at both rear tyres before doing anything else.
What am i looking for? There is meaningful rubber from the track day, especially on the rear left, but i don't do enough track days to know if this is too much/ normal/ abnormal. ChrisW. said:
The topic suggests an oscillation rather than a vibration .... have you checked your dampers and settings ?
Damper settings are at the KW manufacturer recommended setting. They were fine all day before that. I checked and settings hadn't moved.Difficult for me to describe this properly but it felt like a regular knocking - maybe 2 or 3 times per second - not too dissimilar from what you would have with an unbalanced wheel.
I just uploaded a video of rear tyre deposit - could this be it?
https://www.youtube.com/watch?v=CinAyr-iSuc
And just to add some fun to the thread here's 1 lap, after having had a session with an instructor and trying to learn the lines. As you can see it was pretty empty.
https://www.youtube.com/watch?v=siEDMMpMyPA
https://www.youtube.com/watch?v=CinAyr-iSuc
And just to add some fun to the thread here's 1 lap, after having had a session with an instructor and trying to learn the lines. As you can see it was pretty empty.
https://www.youtube.com/watch?v=siEDMMpMyPA
Edited by james.a.c.911 on Sunday 6th June 12:28
james.a.c.911 said:
I just uploaded a video of rear tyre deposit - could this be it?
https://www.youtube.com/watch?v=CinAyr-iSuc
And just to add some fun to the thread here's 1 lap, after having had a session with an instructor and trying to learn the lines. As you can see it was pretty empty.
https://www.youtube.com/watch?v=siEDMMpMyPA
That's your problem.https://www.youtube.com/watch?v=CinAyr-iSuc
And just to add some fun to the thread here's 1 lap, after having had a session with an instructor and trying to learn the lines. As you can see it was pretty empty.
https://www.youtube.com/watch?v=siEDMMpMyPA
Edited by james.a.c.911 on Sunday 6th June 12:28
Had the same on my Cayman on a Silverstone track day, my Michelin PS4S looked very similar and I stopped the day too due the noise and small vibration without realising it was the tyres. Afterwards I thought about it an on my cooling down laps I had spent most of it off the line on dirty part of the track to keep out of people's way, in future will stay on the clean line until I need to move over.
I left mine and drove on the road for a while and over time it wore off.
I left mine and drove on the road for a while and over time it wore off.
I had a weird once that wasn't due to pick up-I took a new to me car to the ring and had what I thought was pick up that I couldn't shift. After faffing on for weeks it turned out that mildew had turned dust inside the tyre into a small marble that shifted laterally under cornering.
Cool story etc.
Cool story etc.
Rocket. said:
Had the same on my Cayman on a Silverstone track day, my Michelin PS4S looked very similar and I stopped the day too due the noise and small vibration without realising it was the tyres. Afterwards I thought about it an on my cooling down laps I had spent most of it off the line on dirty part of the track to keep out of people's way, in future will stay on the clean line until I need to move over.
I left mine and drove on the road for a while and over time it wore off.
Ok. I think this confirms the diagnostic!I left mine and drove on the road for a while and over time it wore off.
I spent a bunch of time on cooling laps off the line also (and on a very few occurrences while overtaking) and it was a track evening after a warm, full track day so probably more rubber than usual.
thanks
LaurasOtherHalf said:
I had a weird once that wasn't due to pick up-I took a new to me car to the ring and had what I thought was pick up that I couldn't shift. After faffing on for weeks it turned out that mildew had turned dust inside the tyre into a small marble that shifted laterally under cornering.
Cool story etc.
Ha! How did you find out, when the wheel was off the car?Cool story etc.
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