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Old 09-20-2019, 03:49 PM   #1
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tire moving on rim at the track

So, I'd heard of this; someone had posted here on the forum. Curious, I marked my track wheels with new tires (RE-71R) before a 2-day event. This is the right rear
wheel after 2 days:



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Old 09-20-2019, 05:31 PM   #2
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That's mind-blowing. The question is, was it the acceleration or braking that did it? If that's a pick of the right tire, it would be braking. If it's the left tire, then it would be acceleration.
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Old 09-20-2019, 06:09 PM   #3
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Actually. I think it’s the left rear. I get my hands mixed up! ��
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987 air intake TB and plenum, Mantissport 2 litre sump, UDP, Bilstein B6 with H&R lowering spings, re71-rs for track, other stuff.
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Old 09-20-2019, 06:19 PM   #4
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Here's a recent thread about it. You'll see I wasn't convinced, until I experienced it in dramatic fashion.

https://r.tapatalk.com/shareLink/topic?url=http%3A%2F%2F986Forum%2Ecom%2Fforums%2Fs howthread%2Ephp%3Ft%3D73341&share_tid=73341&share_fid=31135&share_type=t&link_source=app

You can see my marks on the sidewalls, which lined up with the valve stems at the beginning of the day.

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Old 09-20-2019, 06:23 PM   #5
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The original pic doesn't look like all that much of a shift. I remember other posts' showing +/-6" IIRC from track days. I would imagine the rears show far more of a shift than the fronts?

EDIT: Maytag looks about right.
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Old 09-20-2019, 06:34 PM   #6
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Originally Posted by NewArt View Post
Actually. I think it’s the left rear. I get my hands mixed up! ��
Then it must be happening during acceleration. I was expecting the opposite. I didn't think they had enough torque to do that.

But then again, it looks like all 4 tires moved, so it has to be during braking. Are you sure it came from the left (driver's) side?

Last edited by piper6909; 09-20-2019 at 06:39 PM.
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Old 09-20-2019, 06:41 PM   #7
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Originally Posted by maytag View Post
Here's a recent thread about it. You'll see I wasn't convinced, until I experienced it in dramatic fashion.

https://r.tapatalk.com/shareLink/topic?url=http%3A%2F%2F986Forum%2Ecom%2Fforums%2Fs howthread%2Ephp%3Ft%3D73341&share_tid=73341&share_fid=31135&share_type=t&link_source=app

You can see my marks on the sidewalls, which lined up with the valve stems at the beginning of the day.

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I noticed each pair of tires rotated in opposite directions. Is one pair fronts and one pair rears?
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Old 09-21-2019, 04:33 AM   #8
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Quote:
Originally Posted by rexcramer View Post
The original pic doesn't look like all that much of a shift. I remember other posts' showing +/-6" IIRC from track days. I would imagine the rears show far more of a shift than the fronts?

EDIT: Maytag looks about right.
Yeah, I thought that the previous post was an anomaly, but I now see that this is common for track tires. Maytagís pictures bowled me over! The movement of my tires is negligible in comparison.
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987 air intake TB and plenum, Mantissport 2 litre sump, UDP, Bilstein B6 with H&R lowering spings, re71-rs for track, other stuff.
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Old 09-21-2019, 06:33 AM   #9
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Yeah, I thought that the previous post was an anomaly, but I now see that this is common for track tires. Maytagís pictures bowled me over! The movement of my tires is negligible in comparison.
The guys at the track that day told me that's very common. I'd have never believed it, had it not happened to me.

And piper, as for what tire is what in my photos, I don't recall now. But I'd think it only makes sense that the rears spin under power (so the wheel turns "forward" in the tire) and the fronts under braking (so the tire turns "forward" on the wheel).

Dunno.

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Old 09-21-2019, 08:27 AM   #10
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Well, so much for precision wheel balancing!
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2004 986 S
987 air intake TB and plenum, Mantissport 2 litre sump, UDP, Bilstein B6 with H&R lowering spings, re71-rs for track, other stuff.
https://www.youtube.com/user/12shoes2
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Old 09-21-2019, 08:57 AM   #11
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Well, so much for precision wheel balancing!
Yup. That's exactly what I said in the other thread. Never paying to balance track tires ever again

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Old 09-21-2019, 09:50 AM   #12
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So, do street tires do this in day to day driving? Anyone checked?
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987 air intake TB and plenum, Mantissport 2 litre sump, UDP, Bilstein B6 with H&R lowering spings, re71-rs for track, other stuff.
https://www.youtube.com/user/12shoes2
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Old 09-21-2019, 10:54 AM   #13
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Originally Posted by maytag View Post
The guys at the track that day told me that's very common. I'd have never believed it, had it not happened to me.

And piper, as for what tire is what in my photos, I don't recall now. But I'd think it only makes sense that the rears spin under power (so the wheel turns "forward" in the tire) and the fronts under braking (so the tire turns "forward" on the wheel).

Dunno.

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If we know which side the wheels/tires came from and the direction of the rotation, we can determine if it's braking or accelerating causing it. I suspect that even an S doesn't have enough torque to cause this under acceleration.

My theory is that it's caused by breaking, and the front tires rotate more than the rears, because the fronts brake harder.

I probably won't track until next year, and if I do I probably won't drive it as hard as some people on here because I don't have the skills. So it would be great if someone would try the experiment and note which corner each tire/wheel was on. Maytag, would you be so kind?
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Old 09-21-2019, 12:43 PM   #14
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Originally Posted by piper6909 View Post
If we know which side the wheels/tires came from and the direction of the rotation, we can determine if it's braking or accelerating causing it. I suspect that even an S doesn't have enough torque to cause this under acceleration.



My theory is that it's caused by breaking, and the front tires rotate more than the rears, because the fronts brake harder.



I probably won't track until next year, and if I do I probably won't drive it as hard as some people on here because I don't have the skills. So it would be great if someone would try the experiment and note which corner each tire/wheel was on. Maytag, would you be so kind?
Well what I do know, is that you're looking at a rear laying flat and a front from the same side leaning against it, in both images. I just don't remember which image is left or right.

As you can see, they're rotating opposite directions on the wheels.

There's very, VERY little braking going on on the rear wheels, especially at the racetrack where brakes are usually on VERY HARD, or not at all. There is SUBSTANTIALLY more torque being applied to the rear wheels under acceleration than under braking.

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Old 09-21-2019, 02:37 PM   #15
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Well what I do know, is that you're looking at a rear laying flat and a front from the same side leaning against it, in both images. I just don't remember which image is left or right.

As you can see, they're rotating opposite directions on the wheels.

There's very, VERY little braking going on on the rear wheels, especially at the racetrack where brakes are usually on VERY HARD, or not at all. There is SUBSTANTIALLY more torque being applied to the rear wheels under acceleration than under braking.

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Ok. I didn't think they would put out that much torque to rotate the tires on the rims. You know more than I do, so I'll take your word for it.

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Old 09-21-2019, 02:43 PM   #16
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So, judging from the position of the valve stems, unless the rear tires rotated over 270 degrees, the top pic should be the tires from the left, correct?
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Old 09-21-2019, 10:34 PM   #17
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How in the world does this happen and not break the bead/seal? Are the tires getting hot enough to somehow soften the bead enough to allow this? That’s pretty crazy. I’ll have to mark mine next time out...
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Old 09-22-2019, 07:35 AM   #18
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Iím shocked that you guys are so shocked by this.
Seriously...
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Old 09-22-2019, 09:25 AM   #19
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I’m shocked that you guys are so shocked by this.
Seriously...
I'm shocked that you're shocked that we're shocked!

Seriously, I'd never think that was possible unless I saw the pics. But then again, I've never tracked.

Last edited by piper6909; 09-22-2019 at 09:30 AM.
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Old 09-22-2019, 10:05 AM   #20
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Iím shocked that you guys are so shocked by this.

Seriously...
I know..... everyone at the racetrack was so dismissive of this, when I was surprised by it. They've seen it for so long, at such extremes, they couldn't imagine I didn't know about it.

Now I do. ;-)

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