Yamaha M1 Shocker!
YAMAHA M1 SHOCKER!
ROUNDUP
YAMAHA RECENTLY TESTed at Jerez, Spain, revealing the novelties it has been working on during the off-season. Most notably, Norifumi Abe rode an experimental four-stroke YZR-M1 with twin shocks. This has apparently been done to make room for the exhaust header to come up between the shocks from beneath the machine to a muffler that pokes up through the tailpiece behind the seat.
Although setting a style that will soon appear in showrooms is certainly one reason for the appearance of current MotoGP bikes, I suspect something else is at work here. All companies involved in racing have been working hard to build into their chassis some degree of lateral flexibility-without introducing undesirable effects like flex steer or fore-and-aft fork flex ure. During the two-stroke 5 00cc era of Grand Prix racing, it was customary to use an arched "banana" beam on the swingarm's non-drive side to provide extra pipe clearance. This was considered perfectly okay at the time because until just before the end of the two stroke reign, any shape was satisfactory as long as it was stiff enough to handle the two strokes' non-uniform torque development.
Today, all that has changed. Current tires allow machines to lean over so far in corners that the normal suspension (which in this condition has precious little travel left anyway) is going in the wrong direction to absorb bumps. What's being sought now is some kind of "lateral suspension" that can absorb low-amplitude, high-fre quency disturbances before they can make the bike chatter, hop or skate. But if you apply lateral force to a banana swingarm, the differently shaped structures of its two beams are going to bend in dif ferent ways. What is desired is an arm that is "stress-symmet ric," so that under lateral stress it flexes like a parallelogram, allowing the rear wheel to move side-to-side, but without twist. This is the type of swingarm we have been seeing lately, whose side beams are very deep verti cally to resist twist, but quite thin laterally to permit some flexure in that direction.
There are other potential gains. One, as noted above, is the cre ation of something new for mo torcycle buyers to want. What law says that sportbike mufflers must forever resemble fallen-over mailboxes made of carbon-fiber and titanium? How many other wise good-tempered women in shorts must receive the infamous painful burns to their inner calves before a more suitable place for hot smokestacks is found? Final ly, side exhaust systems-like side radiators-are unacceptably vul nerable to crash damage. An upthe-center system is much better protected. The obvious problem is isolating the rider/passenger’s nether regions from pipe and muffler heat.
Another interesting feature of the Yamaha that Abe tested is a pair of bolted-in struts-or possibly, extremely compact force dampers-that extend forward from the tops of the tall rear uprights carrying the swingarm pivot. They receive the thrust of the twin shocks, transferring it forward to the steering head, past the sides of the carbon-fiber airbox. Their purpose is to remove flex from the suspension anchorages. The sidebeams of the new chassis angle downward almost directly from steering head to swingarm pivot, which is why the uprights must be extended upward as suspension anchorages in the first place.
Reportedly there is also a new engine version called the M3, the cylinder block of which is tilted further forward than previously. Current engines are the full 990cc rather than some previously smaller displacement, and fuel-injection has replaced the carburetors used in the Ml’s first season.
—Kevin Cameron
