So they're saying hair spray can stop them from rotating...

https://rennlist.com/forums/racing-and-drivers-education-forum/691614-tire-rotating-on-rim.html

It would be interesting to know if it occurs because of hard acceleration forces, hard braking forces, or hard cornering forces:confused::confused::confused::confused:

If you bother to read all the printed material you get when the tires have been replaced you see see that you have to be careful with hard acceleration and brakind for a couple of days to prevent exactly this problem from happening.

Who bothers to read that!?? haha!

Haha, well I’m pretty gentle on my street tires but I don’t think that I’ll be avoiding hard acceleration/braking on my track tires! ;)

So in off road motorcycling, many tubeless tires and rims use a Rim lock device to lock the bead down to the rim. Off road car/truck racers have to lock the beads down on to the rim so it makes perfect sense that a sports car on a track would do the same thing.

I have a theory on this, for all it's worth.

Disclaimer: All my racing experience is in my old '02 VW GTI 1.8T. I've only done HPDE and open lapping in the Boxster as I collect parts for my Spec build.

Theory: All rotation happens under braking, but the fronts are rotating further around the rim than the rears. I further theorize that the driver's side is rotating counter-clockwise, with the passenger side going clockwise.

Reasoning: I don't feel like these cars generate as much rotational force under acceleration as braking. The only time I could see a great deal of acceleration force occurring is in standing starts, which I don't think occurs very often. Think about when you hear tires: under braking, or in corners, never under acceleration out of a corner. I haven't had any telemetry hooked up in the Boxster, but in the VW, with ~215HP at the wheels, I could not break 1G under acceleration, but could regularly in braking and cornering.

Anyone have any in-car telemetry they could share showing peak forces during acceleration and braking?

Hopefully, none if us will experience breaking forces, only braking forces!

Here is my thoughtful and deep theory of why the rear tires move on the rims -

Braking forces are much greater than acceleration or cornering forces, but my guess is that the rears rotate on the rims when accelerating out of a slower corner (the greatest acceleration) and you go over bumps or curbs; something that is going to disrupt the grip. I'm talking about the "flat curbstones" that are often at the exits on the outside of turns.

Think about what the rear tire copes with while exiting a second gear turn - it's gripping the pavement while under (for our relatively low-powered) hard acceleration. As you exit the turn, you ride up onto to the curbing, which normally is not smooth; the curbing has a washboard design. The tire is going through a consistent grip/no grip action, experiencing a rat-a-tat-a-tat of forces to it's sidewall. The tire moves a tiny amount on the rim each time this happens. Do that enough times, and the tire ends up moving on the rim enough to notice.

Okaay..... I'ma be THAT GUY: It's BRAKING. Not Breaking. Though, honestly, I've had plenty of BOTH at the track, haha.

And no, as the images show clearly, the tires are rotating in opposite directions on the wheels, so they are not both happening under braking forces.
Also: I hear tire noise coming out of nearly ALL slower corners. You're suggesting that it's impossible to oversteer on these cars at corner exit, which is of course wrong. It's quite easy to do. So add-into the equation some sticky tires that don't break (not brake) traction as easily, and you've got a perfect environment for this sort of rotational movement under power.

I would have invoiced $1.15 for correcting that error. :cheers:

Most likely because of the low air pressure for off road traction.

This is precisely why.
When we're off-roading / Rock Crawling, we air down a LOT. When we're building a purpose-built machine that'll do that regularly, we use beadlocks. Not because the low-pressure has inherently less grip to the wheel (it might?), but because lower pressure means more sidewall flex. the sidewall flex is what deforms the bead, and creates a "loose" bead, which slips tires on wheels and sometimes deflates a tire altogether.

This is why I think Racerboy's idea has some distinct merit.
If there's something I do plenty of at the track, it's use the curbs. :dance:

You go ahead and be that guy ... I do it too. No one is above mistakes. Thank you, corrected my post.

Also, I don't see how it is "clear" that the the tires are rotating in opposite directions. Whether a clock goes one way or the other, both directions will ultimately arrive at 2.

And you hear squealing from your tires, under acceleration, coming out of corners?

Hmmmm ... that's a good point. Had not considered that the vibrations could cause slipping.

ooohhh... yeah, I see that you're suggesting one of the tires may've slipped almost all the way around, and only LOOKS like it went the other way because of it's final position. I'll admit that didn't occur to me. You're right, of course, that it is possible. But I still think it unlikely.

There is, as I said below, very little force applied to the rear tires under heavy braking. Weight transfers forward and all the work is being done at the front wheels. The very design of the car shows you where the forces are: Smallest brake is in the rear because it doesn't take much braking force to overcome the available traction when the weight is moved forward. But biggest tire is also in the rear because they need to be, to accommodate the torque being applied under acceleration.

And yes, absolutely; If you aren't hearing tires complain when you go to the gas, then you could be going to MORE gas. :-)
I'm talking about mid-corner, when you're trying to get the drive. It's very easy to get too greedy :troll: with the throttle and snap the back end around. You're flexing that sidewall for all it's got laterally, and then you stick forward motion to it as well. The carcass flexes more and you overcome the available traction. Now apply stickier tires to the mix. There's more force being applied to that rear-tire bead under this scenario than there is under heavy braking.

I wonder how we could test this ... something to show the direction of movement, in respect to the rim? Something attached to the rim that would "draw" on the tire if it moved counter to it.

I like the way you're thinking.
I wish I were planning to get back out this year. I was hoping to this weekend... but.... Kids... y'know? ;)

There's a big NASA event at my local track in October.... maybe I can rationalize that.

It seems that, since we're checking tire pressures regularly anyway, adding some marks every time we can see movement would allow us to track the direction. We may also see a pattern in tire temperatures / pressures relative to that movement. (What if it's a COLD bead that slips more easily?)

Local being Miller?

Formerly miller. Now UMC. But yup. You been out here?

Yah, my only NASA National event podium (3rd) was there, in GTS-2, back in 2010. Love that track and facility.