The following is from the AMA...
PICKERINGTON, Ohio - AMA (American Motorcyclist Association) Racing announced today that the inspection of the rear tire used by professional racer Kenny Coolbeth in the GNC Twins round of the 2008 AMA Flat Track Championship at Mountain Raceway Park in Maryville, Tenn., June 21 was found to be in compliance with AMA Pro Racing rules, specifically the Competition Bulletin issued on May 29.
"The bulletin specifies that competition tire alterations are not permitted," said AMA Flat Track Director Ken Saillant. "A thorough inspection of Coolbeth's tire undertaken by an outside lab confirmed that it was in compliance."
Saillant added that the AMA will continue to check tires in the field to ensure compliance and will, at its discretion, send tires to an outside lab to assure accuracy and impartiality. "Utilizing a tire that is not in compliance will result in a Category 1 penalty being levied against the rider," he said.
According to the bulletin, all tires must remain as originally produced by the manufacturer. The bulletin, CB40508 FT 2008, can be viewed online.