~ Auto Buzz ~: ANALYSIS: Sepang I MotoGP Test The riders may not be saying much, but the tires sure are.

One central aspect of MotoGP racing that has improved its technology over the winter break is information control. Rider after rider, asked how his sessions at the Sepang test went, uttered bland generalities. “On the whole, the test was positive, with some things giving us encouragement and others needing further work. We will see at Sepang II in two weeks.” Getting nothing from riders, we seek it from the time sheets (Day 3 results are below). Again, not much of note. The two Hondas are right where we’d expect that R&D powerhouse to put them. A Ducati in 3rd? Shall we dance in the street? Not yet. Ducati remains on the special soft tire allowed them by rule. And we know there are one-lap setups, 5-lap setups, and 24-lap setups. Which are we seeing? The top professionals work hardest at race simulations, because it is the performance of the machine and tires over the whole distance that will win—not hot laps. Time and again last year, Andrea Dovizioso warned his fans not to expect him to race at practice pace—the set-up had not matured enough to allow that. For an example of a 5-lap set-up, think of Troy Corser’s rides on the developing BMW S1000RR in World Supers. He looked grand in the lead, but very quickly his tires gave up so dramatically that he’d lose 10 or more positions through the rest of the race.

Andrea Dovizioso Sepang test action shot

What causes such a thing? Much of the small-bump/high-frequency suspension is provided by the springy yet internally damped pneumatic tires. But it may happen that to make the bike respond quickly to control, and to transfer weight rapidly, a stiff setup gets the bike to a given lap time in the time available. But tire and suspension are partners, and as suspension is made stiffer (for example, the front, to support hard braking load), the tire is asked to take over more than its share of flexure. Tires are much less than 100 percent elastic, and the missing energy in each cycle of flexure becomes heat in tread and carcass. How long does it take for this heat to damage tire grip? In a successful tire/suspension partnership, tire flexure is kept within a tolerable range throughout the race. The more the tire is called upon to perform the suspension’s job, the sooner it gives up. This means that hot laps prove little. Look instead at the race simulation lap times. Jorge Lorenzo was pleased with his, which, he felt, would have enabled him to fight for the win against the Hondas. Maybe. Suspension has transcended forks, swingarms, springs and dampers. Those were the old terms of suspension, but those parts can now do only a fraction of the job of limiting the peak loads to which tires are exposed.

Suspension spring rate has to be able to support not only the weight of machine, fuel, and rider, but also those weights intensified by cornering force, which is of the order of twice the static weight. The better the tire grip, the greater the cornering force, and the stiffer the springs must be made to prevent bottoming. Damping force—the friction deliberately provided to keep the machine or its wheels from oscillating uncontrollably after every disturbance—must be in proportion to spring rate. The result is very firm—every new MotoGP rider remarks on how very stiff the bikes and their tires are. When the machine is in midcorner, therefore, suspension is well compressed, leaving only small travel available. At Indianapolis a few years ago, when so many riders fell on the very bumpy pavement, there was not enough suspension to deal with such roughness. So it was that through the 1990s, and intensifying in the MotoGP era, the chassis itself was deliberately made laterally flexible to supplement the suspension itself. Those of us raised on race car suspension ideas are attracted to the concept that the chassis must seek total rigidity, forcing all movement to take place in the suspension (Jan Witteveen, are you listening?). This is fine for cars, whose suspensions are always vertical—but a motorcycle’s suspension loses much of its vertical compliance as the machine rolls to high cornering angle. This is why every team has a constant shuffle of chassis, swingarms, and forks. Making these parts laterally flexible without providing commensurate damping is risky because it invites chatter. That provoked a period of referring to parts by their natural frequencies. Classic chatter seemed to center on 25 cycles per second, so parts whose frequencies were enough offset from that frequency were considered okay—chatter proof. Then, a new thing appeared, of which Honda’s Nakamoto said at the time: “This is not chatter at all.” This was something seemingly in the tires themselves, working as low as 16 cycles. No one is talking about all this, but Yamaha’s Valentino Rossi had chatter in Sepang, as did the Hondas (remember when we thought Hayden was somehow immune to chatter?). Chatter is always there, waiting to burst into song. What chassis lateral flexibility comes down to is encouraging flirting without outright infidelity.

And so the tire must partner not only the mechanical springs and dampers, but also this nebulous world of lateral chassis flex. Thus, no one has the grip he wants at all times. There is no solution, only better or worse compromise. Last year, the Hondas lost grip on rough pavement; this year, the Yamahas spin rather than accelerate—and continue to have some deficit in braking versus the Hondas. Where is the grip? Compromised away to serve other important goals. Yes, someone could stumble onto a complete solution, but in 20 years of trying (remember Muzzy and others, desperately sawing out cross-members?) no one has done so. That leaves us with compromise—and racks of flexible parts that work well in two problem turns but are junk elsewhere. Is there a pattern that the teams just can’t see? Variable flexibility, controlled by yet more data channels? There’s plenty else to work on, but Dorna management is relentless in its efforts to randomize racing by taking one technology after another out of the teams’ control. The spec ECU is here and the software freeze is coming. In the US, unnamed officials once discussed (and, whew, rejected) a proposal for spec chassis. That leaves unending repetitive testing of chassis components. How many engineers, premium fabricators, top test riders, and data analysts can you muster? I try not to think about this, but just look forward to seeing top riders inventing and heightening their art, on machines that continue to represent the best creative thought.

Pos.	Rider	Num	Nation	Team
1	MARQUEZ Marc	93	SPA	Repsol Honda Team
2	PEDROSA Dani	26	SPA	Repsol Honda Team
3	IANNONE Andrea	29	ITA	Ducati Team
4	ROSSI Valentino	46	ITA	Movistar Yamaha MotoGP
5	LORENZO Jorge	99	SPA	Movistar Yamaha MotoGP
6	ESPARGARO Pol	44	SPA	Monster Yamaha Tech 3
7	DOVIZIOSO Andrea	4	ITA	Ducati Team
8	BRADL Stefan	6	GER	NGM Forward Racing
9	SMITH Bradley	38	GBR	Monster Yamaha Tech 3
10	ESPARGARO Aleix	41	SPA	Team Suzuki MotoGP
11	CRUTCHLOW Cal	35	GBR	CWM LCR Honda
12	VINALES Maverick	25	SPA	Team Suzuki MotoGP
13	PETRUCCI Danilo	9	ITA	Pramac Racing
14	AOYAMA Hiroshi	7	JPN	HRC Test Team
15	BARBERA Hector	8	SPA	Avintia Racing
16	PIRRO Michele	51	ITA	Ducati Team
17	REDDING Scott	45	GBR	Marc VDS Racing Team
18	HAYDEN Nicky	69	USA	Drive M7 Aspar
19	BAZ Loris	76	FRA	NGM Forward Racing
20	MILLER Jack	43	AUS	CWM LCR Honda
21	BAUTISTA Alvaro	19	SPA	Factory Aprilia Gresini
22	DI MEGLIO Mike	63	FRA	Avintia Racing
23	ABRAHAM Karel	17	CZE	Cardion AB Motoracing
24	LAVERTY Eugene	50	IRE	Drive M7 Aspar
25	NAKASUGA Katsuyuki	T1	JPN	Yamaha Test Team
26	TAKAHASHI Takumi	72	JPN	HRC Test Team
27	DE ANGELIS Alex	15	RSM	NGM Forward Racing
28	MELANDRI Marco	33	ITA	Factory Aprilia Gresini