As the MotoGP teams were putting their Laguna Seca pageant back into its shipping cases Sunday evening, I spied Jeremy Burgess. We talked briefly about tires and their temperature. He remarked, as Yamaha satellite rider Cal Crutchlow had said at an earlier round, that factory rider Jorge Lorenzo has his steering stem so far forward no one can figure out how he can brake like that.
What needs explaining here is that MotoGP steering heads are not the tubular affairs with which we grew up. In fact, they are much larger, often-oval affairs that permit not only changing the rake angle but also allow a fair amount of fore or aft movement of the front wheel. Insert plates, bored in pairs for the desired rake angle and front/rear position, are used to achieve these changes. Burgess’ rider, Valentino Rossi, is said to have his front end fairly far back in the head, which, by shortening the wheelbase, achieves a faster build up of weight on the front tire as braking begins. Lorenzo, the leading exponent of high corner speed, brakes earlier and more moderately than most of his competitors. This is not just a personal preference; the grip required for high corner speed would be upset by sudden brake application.
Think of the problem: As you approach your braking point for a corner, your front tire has been cooling since the last turn. Therefore, it lacks maximum grip because the cooler a tire becomes, the harder it gets and the less able it is to achieve maximum rubber-to-pavement contact by filling the pavement’s texture. If you just give the brake lever a good yank, the cool tire will slip rather than grip. If this happens at any angle of lean, the result can put you into the gravel. You must first “plant” the front tire by braking just hard enough to begin weight transfer to the front, compressing the fork and squashing the footprint to a larger size. Making the front tire carry most of the machine’s weight quickly drives its temperature, and its grip, upward. As grip increases, you can squeeze the lever progressively harder. This calls for judgment, not brute force. Braking force must rise with the available grip.
I asked Burgess about this variation in tire temperature during braking and through corners. He said Yamaha had reason to believe that Honda has an advantage in combined braking and turning, such as occurs in spades after Laguna’s Turn 1. Here, Rossi recorded the highest speeds of the weekend, 167 mph, but because bikes are quite leaned over through this fast left, they cannot brake at maximum rate for upcoming Turn 2. According to Brembo, whereas maximum deceleration for Turn 6 is 1.4g, only 1.1g can be achieved for Turn 1.
Why might the Honda have an advantage here? As all teams have access to the same disc, caliper and master-cylinder technologies, the answer must lie in differences in how tires warm up during braking. Does the Honda transfer weight to the front more quickly, possibly by having a higher cg?
Each team has precise data from on-board GPS and sensors to record exactly where their riders first apply brakes and how they vary brake pressure on the way into the corner. The closer to full operating temperature the tire is initially and the faster the rider can raise its temperature by braking, the shorter the braking distance can be.
I mentioned the statement made earlier this year by Bernard Gobmeier, that Bridgestone could fix Ducati’s lack of mid-corner front grip in two weeks. Burgess agreed, saying that in the previous era of tire competition, Michelin had made a special tire to suit Kevin Schwantz’s style.
The claim of a spec-tire series is that “it’s the same for everyone,” but Ducati’s plight makes a lie out of that statement. In effect, the present tires require Ducati to build a Honda or a Yamaha. The current Ducati, a second per lap off the pace, is clearly not a solution. Some Ducatisti imagine that if only Casey Stoner would come back, a new golden age could begin, but Stoner’s 2007 championship on a Ducati took place on special Bridgestone tires custom-designed for Stoner’s style and the Ducati’s design; the spec tire era had not yet begun.
There are no simple, equitable answers to this situation.