In what many consider one...
In what many consider one of the greatest races of the modern era, Doohan leads Schwantz, Rainey and Kocinski through the chicane at Suzuka, 1991. Just over half a second would cover the quartet at the line.
“Imagine being a tire technician like David,” Rainey said. “You’ve got to figure where you are going to get the performance from the tire. There’s a hundred different parameters; if you just change one of them it can hurt the other 99 of them.” Finding the decisive factor was often a matter of trial and error, and sometimes luck.
“When you design tires, what you’re looking for is what we call a neutral line, stress-free line,” Watkins explained. “And you try to build the tires so the components, when they become stressed, they become equally stressed along their periphery or across their cross section. So what you don’t want is pinpoints of stress.
“Probably a year before at Daytona when we were testing with Yamaha, we were looking at tires without high stress levels in them in pinpoint areas. And we sort of escalated on from that. So by the time we’d finished the 1990 season, we got a pretty good idea. We tried various constructions, but stability was always a problem in the heat. The softer construction worked OK in temperate conditions.”
Rainey (center) won convincingly...
Rainey (center) won convincingly at his home round at Laguna Seca, with Doohan (left) second and Schwantz third. Doohan seems increasingly disgusted with Rainey’s building momentum (the American finished third at Suzuka, and won at Doohan’s home race at Eastern Creek), but it wouldn’t last when the series went to Europe.
He took the problem to a colleague in Dunlop’s textile lab who told him, “Well, it’ll be one or two things. Either you need a high-weight Kevlar or you simply just put a lower twist in it to increase the modulus [of elasticity] that way.” So tires were made with both types of strands and a preparatory test was done. “We found that the higher-molecular-weight Kevlar wasn’t as good as the low twist (the number of twists you put into it). And lower the twists, it becomes very stiff. If you get too stiff, you get no grip, so it’s a balancing act.”
Even more important are the initial stages when the tire is formed. Says Watkins, “It’s the most important bit, because if that’s wrong everything can’t be put right after that, so it has to be made very accurately.” Start to finish, a race tire was made in about 45 minutes, roughly the length of a Grand Prix race. As Schwantz said on a visit to the factory in 1991, “I can burn them more quickly than you can make them.”
Rainey (1) leads teammate...
Rainey (1) leads teammate John Kocinski (19) and Schwantz (34) during the initial laps at Eastern Creek, Australia, where Rainey won his first race of the season. The Dunlops’ grippy qualities in the first few laps would allow Rainey the chance to build an early lead.
“Obviously nowadays with the N-Tech, forms are already curved,” Watkins reveals. “And Michelin lay cords on separately and Pirelli do a similar sort of thing with their method,” Watkins said. “And then that tire goes to the press (where the layers are fused together), and then [much depends on] how it goes in the press and how volatile the rubber is. It’s quite crucial…you can mess this up after all this beautiful hard work in about 15 minutes, because that’s how long the curing time generally would be.” The tires would normally be cured at about 350 degrees Fahrenheit in about 15 minutes, but Dunlop found the best results with Rainey to be a half-hour cure with a much lower temperature. That seemed to give better consistency. “I don’t know the process on how they cured their tires, but I could generally tell there was something different about a batch of tires,” Rainey said. “I was pretty fortunate in my era that I got to test so many bloody tires. So I had a certain feel out of these tires that I was able to use when I went out and analyzed tires.”