tire moving on rim at the track

[particlewave]

I’m shocked that you guys are so shocked by this.
Seriously...

[piper6909]

Originally Posted by particlewave

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.

[maytag]

Originally Posted by particlewave

I’m 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. ;-)

Sent from my SM-G970U using Tapatalk

[blue62]

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

[piper6909]

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

[ianacole]

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?

[maytag]

Originally Posted by ianacole

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 breaking, 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 breaking. 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 breaking, 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 breaking and cornering.

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

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.

[Starter986]

Originally Posted by maytag

Okaay..... I'ma be THAT GUY: It's BRAKING. Not Breaking

I would have invoiced $1.15 for correcting that error.

[ianacole]

Originally Posted by maytag

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.

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?

[maytag]

Originally Posted by ianacole

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?

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.

[Racer Boy]

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.

[ianacole]

Originally Posted by Racer Boy

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.

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

[ianacole]

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.

[maytag]

Originally Posted by ianacole

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?)

[ianacole]

Originally Posted by maytag

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?

[maytag]

Originally Posted by ianacole

Local being Miller?

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

[ianacole]

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

[maytag]

Originally Posted by ianacole

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

NICE!!!

yeah, it's sorta mecca for me. I've been involved at various levels since it was just a rumor.
For nearly 20 years, I spent far too much time on the road between here and 2nd-creek, Mountain-View, PPIR and Pueblo. Not to mention Vegas, Pahrump, Willow, Aroyo Seco, thunderhil, Buttonwillow, etc etc.
The irony here, is that our customer base is largely made-up of people who don't know just how good they've got it here. I tell them we used to have to pit in the gravel, drag our own generators and porta-johns to the track, etc.... yeah... they don't understand. And then they start ********************ing because they don't like a policy, or they have to pay $25/day to rent a garage for the weekend. (an air-conditioned garage, with power, compressed air, laser-flat floors, restrooms).
They just don't have a clue what a gift that place is to motorsports enthusiasts in the region.
I'll defend Larry Miller all day long and twice on Sundays against any of the haters.... just for this one gift he gave to me.

[maytag]

Originally Posted by ianacole

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

oh, and way to sand-bag me.... got me telling you that you can "go to the gas earlier", and telling you how the brakes work..... hahaha. Jack-waggin!!!! I've never been on a NASA podium..... hahahaha.

But I HAVE won HPDE before. I know I did, because I left feeling like I had. hahahaha

[ianacole]

I did not get to experience 2nd Creek, but have turned a lot of laps at PPIR and Pueblo (broke my back in an accident at Pueblo). If you have the chance, come out and turn some laps at High Plains, and if you want to go a little further east, give Hastings a try. Wonderful tracks. Did the 25 hours of Thunderhill in 2009, that was a hoot, and just beautiful out there.

If the current users don't like it there, send 'em to Pueblo - they'll have a new found appreciation. When I learned that Larry wanted to build in CO and was told "no" I couldn't believe it. What a lost opportunity.

And definitely not trying to sand-bag While I've turned a few laps, I still have a LOT to learn. I still can't even heal/toe And winning HPDE is what motivated me to go wheel-to-wheel