Bomar Shelby

I have the same issue with my 20 inch Champions and the Pirelli Pzeroneros I just went to after switching from Michelins. My fronts have the rimguard fairly flush with minimal gap but my 305 rears have the same large gap as 911finally is reporting. WTH is going on here? first pic is the front second 2 are the rears

jdgamble

I officially change my answer. I missed the rim gap. Was just looking at slight stretch. Those are not on the wheel properly.

BIG smoke

Tire sizes aside. 19" rim, we all know.
Are the wheels original to this car?
Check what wheel is on your car?" Could be a wider rim? And still a lobster.

911Finally

They are original 19" rims Carrera S

Mumbles

At 180 mph oem tires will still give you full width of the tread surface contact, ie 295 tire will be 295mm contact patch at 180 mph. Non oem tires may give reduced contact patch or not full width contact at max speed

This is what I was told from an older P technician.

motopix

Seems doubtful.

Bomar Shelby

Damon@Tirerack.com can you weigh in here?

911Finally

I'm just concerned that the bead will break on my tire at 80 mph. I'm not concerned about the looks as much as my life.

Mumbles

Just passing on what I was told

Petza914

Ever seen how a Drag Race tire stands up upon takeoff from the friction and centrifugal force. I don't see any way that a tire with a certain cross section of tread contact at rest, or maybe a little more due to load, could have essentially that same contact area at 180 mph. The construction would have to be do rigid that the tire wouldn't work well at all as the load on it changes.

Seems doubtful to me as well.

tom030

Bead has not properly seated. Take them back to the installer and insist they reseat the tire.

vern1

Agree. Got nothing to do with oem tires (even if he means N rated)

+1, they aren't on properly

FLA 997

The original picture of the stretched tire is mine.
I posted it on facebook.
I bought new wheels and went with a 12" rear like the GT3, but I kept my original 295s since they have a lot of life left.
The correct size is 305 for this rim however, I think even the 305 is too small.
I'm probably going to go with a 325 like several people have recommended to me.

semicycler

And there's the answer. The photo is from FLA 997 on non-lobster 12" wide wheels using the wrong size tire. The tire is stretched and gapping between the rubber and the wheel. This also explains the severely rounded side profile. FLA 997 is not the original poster of this thread.

The original poster of this thread, 911Finally, is describing a problem on lobster 11" wide wheels but showing a picture of a different 12" wheel as an example. If there is a gap similar to FLA 997's then the bead is set wrong. Honestly we are guessing at OP's issue without real photos though.

911Finally - post a picture of your actual wheel using the same camera angle as the first post.

Iceter

It's an interesting physics question, although a comparison with a drag slick is pretty much apples to oranges. Drag slicks are built with saggy sidewalls intentionally. This allows the tire to absorb driveline lash and actually contributes to traction and allows more of the contact patch to stay hooked up with the tarmac.

I would be curious to know how much the contact patch of a tire changes as speed increases. My hypothesis would be that as tire revolutions increase, centrifugal (centripetal?) force might decrease the contact patch as the tread is flung outward, away from the center of rotation. This should cause the tread to flex and the contact patch to shrink to a smaller area towards the center of the tread.

OTOH, as you probably know, the contact patch changes only slightly with changes in weight (downforce), and the downward force of the car changes as speed increases. To really figure this out, you would have to correct for the downforce (or lack of it) at different speeds.

My dad has a PhD in physics. I might ask him about this next time I see him.