Copyright 2004, Roadracing World Publishing, Inc.

Dunlop racers at the CCS/Formula USA event at Daytona International Speedway were warned of tire growth with the company’s new 195/70RX-17 slick rear tire, which may cause problems if tire-to-swingarm clearance is not big enough.

Notices posted everywhere in the Daytona paddock during the weekend read, in part:

“Attention: Dunlop Superstock Riders: Tire Growth At Speed Notification: Dunlop’s 2004 rear 17″ slick tire for 750cc and 1000cc machines is a 195/70R-17 KR108. This tire is much bigger in diameter than the original equipment tire on your motorcycle. It may foul on the front of the swingarm at speed if wheel adjustment is not correct. The inflated diameter of 195/70R-17 is 659mm (25.95″). Most OEM tires measure about 628-633mm (24.72 – 24.92″). In order to allow for tire growth at speed you must leave a minimum of 14mm of clearance between center of the tire and the inside front curve of the swingarm. Failure to do so may result in the tire contacting the swingarm while it is rotating. Contact between the tire and swingarm at speed will result in tire smoke which may in turn, cause you to be Red-Flagged by race officials. Tire/Swingarm contact will also cause tire to operate at higher temperatures adversely affecting tire performance. Spacers of 14mm thickness are available at the Dunlop Garage. Please pick one up on your first visit to the Dunlop Garage and use this spacer each time you position, or re-position your rear wheel.”

The unprecedented warning of potential clearance issues due to tire growth results from problems experienced by Dunlop’s sponsored AMA Superstock riders at a recent test at California Speedway, which does not have speeds as high as at Daytona. Teams at that test had to run longer wheelbases than they wanted to achieve adequate tire-to-swingarm clearance. One top rider’s crew chief at Daytona said the extra clearance required for the new Dunlop limited his gearing choices.

Michelin’s Jim Rhodes said growth at speed is not an issue with Michelin tires, and said they normally advise their riders to maintain at least 3mm-5mm of tire-to-swingarm clearance. “Our rear tires have virtually no growth,” said Rhodes.

Pirelli vendor Moose Kuykendall said a 17-inch rear Pirelli slick grows no more than 3 percent at 185 mph, which, according to calculations e-mailed in by various readers, may approach 13mm. We will consult with Pirelli’s Eddie Roberts when he arrives in Daytona and report back with a definitive answer for the brand.

Dunlop has also posted notices at Daytona advising Superstock riders to set the air pressure of the 195/70RX-17 at 38 psi. Michelin’s men said depending on which 17-inch slick being used, their recommended tire pressures range from 22 to 32 psi. Pirelli recommends 34 psi for its 17-inch slick on a 1000cc motorcycle.