Can a few millimeters affect the MotoAmerica championship?

Is that enough to make a difference? Well, we know a change in tires can have a decisive effect in a championship, because we saw it happen last year in the Supersport class. We may have seen an impact on the Motul Superbike title chase in the first weekend of the new tire’s use.

Editor's note: The MotoAmerica Motul Superbike series returns to racing this weekend in conjunction with the Superbike World Championship at WeatherTech Raceway Laguna Seca. Josh Herrin will also be riding in the WSBK races as a wildcard, meaning he'll do four races this weekend.

First, what is the “big tire?”

The new rear Dunlop slick is a 200-width tire with an aspect ratio of 60 instead of 55. Aspect ratio is the height of the tire, from the bead that seals against the rim to the high point of the tread, as a percentage of the width. Dunlop Technician Tony Romo explained that the change is one that several tire manufacturers are making with their race tires right now.

Why? The taller tire has a slightly different contour that provides a bigger contact patch when the motorcycle is leaned over, allowing riders to carry more corner speed. Though it has been extensively tested and revised by Dunlop — the KR451 is now on version 22 — the MotoAmerica teams got their first chance to try the tire in preseason testing. Most riders preferred the new tire, but even those who didn’t were able to turn faster lap times on it, said Romo.

“You could look at their data,” Romo said of the riders who were unenthusiastic about the change. “They were carrying almost two mph (more) in some corners, which is huge. But they would say, ‘My timing is off entering the corner.’ They have to change their timing. Not so much their riding style, but just how they tip it in. How you attack the corner, when you let off the brake, when you get on the gas. You’ve got to find that again.”

How a tire affects a championship

This is not unknown territory for Dunlop. In mid-season last year, Dunlop changed the spec tire for the Supersport class to a 180 width but kept the height the same as the wider tire the Supersport riders had been using. Up to that point, Yamaha teammates J.D. Beach and Garrett Gerloff were tight in the points race. But the new tire suited Gerloff’s high-corner-speed style of riding more than Beach’s dirt-track-derived style. Gerloff found a higher level of confidence after the change and reeled off a series of wins that got him the championship and a seat on the factory Yamaha Superbike team for this season.

Naturally, as the spec tire supplier, Dunlop does not want to be seen as affecting the championship. Romo said the top pros adapt quickly and the taller tire does not require radical setup changes. That’s something that will also be important when the tire becomes available to expert club racers late this summer.

“There are quite a few guys who have tested this tire in club races and it’s almost just plug it in and go,” Romo said. “It really hasn’t required a lot of setup changes. Maybe a little bit of ride height in the rear, lowering the rear a couple of mil (mm), raising the front a couple of mil, but it’s not huge. You don’t need a different link or a different shock. You don’t need a whole pro team out there to adapt.”

And while that may be true, at the top level of MotoAmerica, small changes can affect a rider’s confidence, and thus results. Not surprisingly, the riders on the podium were positive about the new tire while those who had a tough weekend had a different perspective.

“I think Dunlop did a real good job with the big rear tire,” said Cameron Beaubier, who entered the Road America weekend tied for second place, 35 points behind, and left as the new points leader. He said the real difference may not have been seen at a fast track like Road America but will show up more at tighter circuits. “I think throughout the year, the other tracks we go to, we’re going to notice a difference in times.”

Meanwhile, Mathew Scholtz also came into the weekend tied for second with Beaubier but left in fourth place after crashes in both races. “We didn’t get a lot of laps on (the new tire) at that test, and we kind of knew going into this weekend that we wouldn’t be up to speed right off the bat,” Scholtz said. “We are going to try to test the new tire before we go to Laguna for the next round.”

The KR451 slicks are manufactured in the United States and Romo proudly points out the U.S. flag imprinted on the sidewall. They will be exported to countries around the world, from Australia to South Africa, and by late summer the new, taller slick should be available for club racers to try.

By then we should also know if a few millimeters of added height has made a difference in the nation’s top professional roadracing series.