Flat Spotting?

Hi All, I think I have a case of flat spotting on my tires.

 

Before I get into my story, here are the specs of the tire that could have flat spots..

 

Kumho Ecsta XS 245/35/18

 

My car is aligned within reason to factory spec, so no huge amounts of negative camber up front (IIRC, -0.9* or so up front). I am pretty low on coilovers however, but I don't think that would contribute to my problem since the wheels are aligned.

 

Anyway, I switched over to my Kumhos in mid April, and everything was fine. A few weeks ago I noticed a slight vibration when going speeds over 50 mph. My first thought was that a weight was lost from one of the wheels. I rotated my wheels front to back, and had the same vibration.

 

This past weekend I switched to my All Season wheels/tires (17 x 7.5" wheels and 225/45/17 tires.. Bridgestone Pole Positions A/S). I got my car up to highway speeds and even went up to 80 mph and no vibration what so ever. Had to be one of the wheels balance issue I thought.

 

So I took my summer wheels (w/Kumho tires) to my tire guy, he put them on the balance machine and all are balanced correclty. He claims that they are "flat spotting". Why would they do this? Could it be because the rubber on the Kumhos is much softer then standard tires? I mean, I know that they still have a few thousand miles of wear left, I would hate to have to get a new set of tires so soon.

 

Anyone else have these same Kumho tires and ran into this issue?

I may try the Dunlop Starspecs next, but I would have to jump up to size 255/35/18 as they are not available in 245's.

 

Any thoughts?

22 views and no one has any ideas? someone has to have run into this problem before...

When you say flat-spotting, you don't mean like when you lock up your wheels on the track and wear a flat spot into the tire? I assume you are talking about when your tire deforms into a certain shape when it has been loaded in a certain manner over a long period of time (if your car sits for the winter for instance). If that is the case, then simply driving on them for a while should get the flat spot to rub out.

The former.

 

I am thinking that I will just put them on for autocross days, drive the crap out of them on the track and just go with the starspecs for next season.