EricJ

My rear tires slipped/rotated on rims at the last event.
15x9 6UL (Gen 3), 205/50/15 Toyo RRs, 26 cold\30 hot.
NB N/A (TTE) Miata, Torsen II, light weight flywheel.

I started marking my valve stem positions with my latest set of RRs and found the right rear tire had slipped about 6" on the rim and the left rear about 4" in 4 15 minute sessions. Fronts didn't appear to move on the rim.

The track was MSR-Cresson with one longer tight left 2nd gear accelerating corner and one shorter left 2nd gear accelerating corner. Right corners are all under deceleration or 3rd gear.

Do I need to re-balance the tires?
Do I need to change where I get my tires mounted? Could they be using too much liquid during the install?
Or do I just need to ignore it and drive the car?

emilio700

iTrader: (3)

WD-40 or hairspray helps them stick. Gen 4 6UL's have corrugations on the bead surface for that .

aidandj

iTrader: (5)

This was recently discussed somewhere on the site. WD-40 actually vulcanizes the rubber and makes it stick on better.

Leafy

iTrader: (1)

Its normal. I stopped balancing my race tires once I noticed it, but I never exceed 75.

Arca_ex

iTrader: (2)

If make marks like that on pretty much any track car that doesn't have a knurled area where the bead seats, you'll notice they slip.

Ignore it.

This is also the reason I will balance my wheels without a tire on it, and just slap race tires on and off without issues. (Sometimes the bare wheel will take 1, maybe two weights at the most. Most don't require any at all.)

bbundy

Yes if you have your tire guy start with a clean rim and use WD40 instead of the usual tire goop they stick to the rim like an order of magnitude better and rarely if ever rotate. Seems to work even on 245/40 Hoosiers mounted on 10's on a 300+hp car with significant aero down force adders.

EricJ

OK, I'll start using only gen 4s for the RRs, I can put my rains on the gen 3 set.
And I'll bring a can of WD-40 for mounting.

amptramp

Running 205's on a 9 inch wheel is a hefty tire stretch. Cornering forces may actually be pulling the tire bead off the rim, only to reseat themselves on a straight section of road. With this amount of stretch, you would need more than 26 psi cold / 30 psi hot to keep the tires seated on the wheels. Go to a narrower wheel size and your troubles should disappear. Or go to 245's for tires.

emilio700

iTrader: (3)

Piece of friendly advice; If you aren't actually sure or don't have direct personal experience WRT to a complex technical question, don't post guesses and proposed solutions fro those guesses. So ah, no, 205 EHP or race tire are not pulling off the 9" bead in cornering.

Arca_ex

iTrader: (2)

Umm no... I run 205 Hoosier R7's below 30PSI on track (hot) all the time. Have not ever debeaded one. Even if you did debead one in a corner, it likely wouldn't reseat itself going in a straight line. Also 245's on 9" is not very ideal. Have yourself a neg cat.

MartinezA92

iTrader: (4)

dude what

amptramp

OK, so I didn't get universal buy-in to my explanation. Could someone please answer why the OP's setup, 205/50-15 tires on a 15x9 wheel is the hot setup for an autocross car? I would have thought the wheel width could be less just to remove weight and keep the tire close to its original dimensions. Typically, people don't recommend more than 7.5 inch width for a 205 section. Does a larger rim width translate into extra responsiveness? If so, does it make a difference to lap times? Perhaps he has the wrong bead sealing glop in the wheel with the wheel spinout he is getting. Or perhaps this is a effect of the Torsen he is using. Decades ago, drag racers used to screw the tires to the rims - not universally accepted but at least the tire didn't rotate on the wheel and this was with the low pressures (under 15 psi) that were used at the time.

BTW the last autocross I attended as a spectator was won by the lowest powered car with the smallest tires - a Lotus Elan running stock wheels and tire sizes. This was not a close win either - he did 47.+ seconds and the nearest car was at 51.+ seconds.

aidandj

iTrader: (5)

FTFY

dasting

The larger wheel puts more rubber to the ground, and increases responsiveness and feedback. There was no mention of autocross application in the OP, he clearly states it's used on track in Time Trials, which effectively doesn't have wheel width requirements.

If a rear tire debeaded mid corner, the only outcome I can think of is the tire immediately deflating and the car spinning.

Savington

iTrader: (31)

Typically, people do recommend more than a 7.5" width for a 205 section tire. Specifically, this community has accepted as a whole that wider wheels are faster and more responsive for a given tire size, and there is little debate on the topic at this point.

Directly, yes

Yes, as proven repeatedly by direct A-B tests

Dietcoke

We use permatech hi-tack sealant for drag slicks on wheels at next to no pressure instead of tire goop. It will stop them from moving, period. Stuff's a wicked rubber cement.

Dunning Kruger Affect

Where did the OP bring up autocross?

Also, how does a Torsen work?

And a 3rd request: what tires are readily available 245 in 15"?

Thanks.

amptramp

^

The OP did not bring up autocross, but autocross does have some of the same handling issues as racing with tighter turns.

Here is the explanation of a Torsen in a video:


Although it does ensure traction from both wheels in a straight line, its tendency to lock wheels together may make for interesting behaviour in turns with some tendency for the rear end to get loose.

Hoosier apparently has A7 and R7 tires in 245/40-15 third and fourth entries down on this page:

245 15 at Tire Rack

Not cheap and not for the street but listed as available.

emilio700

iTrader: (3)

No, no it doesn't.

miata.net is the place for posting conjecture, speculation, starting baseless rumors and being polite. miataturbo.net is the place to state your opinions based on direct personal experience or verifiable data, and enjoy foul language.

https://www.miataturbo.net/wheels-ti...40-15-a-86511/
https://www.miataturbo.net/wheels-ti...-rc-1-a-77840/

amptramp

FTFY