MotoGP Extreme Lean | Ask the Geek

A recent MotoGP video I watched showed some of the differences between Moto3, Moto2, and MotoGP bikes. Using data from Phillip Island, it said that in corners the Moto3 bikes are up to 7.5 mph faster than the MotoGP bikes. I would like to see the stats on lean angle because it would seem the MotoGP bikes have a greater lean angle. Is this so? Is it a tire thing or maybe a body position thing? The Moto3 riders don't appear to be dragging elbows as much as the MotoGP riders do.
David Grummett
Brampton, Ontario, Canada

While we don’t have access to lean angle data for each of the MotoGP, Moto2, or Moto3 bikes, it certainly does appear that the MotoGP bikes use more lean angle than the Moto2 bikes, which in turn use more lean angle than the Moto3 bikes. And this would seem contradictory to the video, which says the smaller bikes are carrying more corner speed. There are a couple of factors at work here that explain why this is the case.

As we typically see on racetrack data, smaller bikes with less power carry more corner speed than larger, more powerful bikes. This is not necessarily because the smaller bike is capable of that higher corner speed but because of the way the two bikes are ridden differently. The quick way around a racetrack on a powerful bike is to maximize corner exit speed to best use the bike's power on the straight, and this requires a sacrifice in mid-corner speed. Close to the apex of the turn, however, the big bike is making a tighter arc than the smaller bike as part of that sacrifice; even though the bigger bike is going slower at the apex, that tighter arc requires the same lean angle as the smaller bike. This can be shown mathematically using the formula for lateral acceleration:

Where "a" is lateral acceleration, which directly relates to lean angle; "v" is velocity; and "r" is the radius of the corner. As we saw in our test of the Kawasaki ZX-10R, Suzuki GSX-R750, and Yamaha YZF-R6 a few issues ago ("Displacement War," Dec. '14), with identical tires all three bikes were capable of the same lateral acceleration and lean angle, but the R6 typically carried more corner speed than the larger bikes.

That still doesn’t explain why the MotoGP bikes seem to have more lean angle that the smaller Moto2 and Moto3 bikes. Much of this is explained by the tires: The wider tires on the MotoGP bikes may have more grip than the narrower Moto2 and Moto3 tires and hence be capable of higher lateral acceleration and lean angle. Another factor is that a bike with wide tires must be leaned more to achieve the same lateral acceleration than a bike with narrower tires. As a motorcycle leans, the contact patch is offset to the side of the bike’s centerline, increasing the lean angle required for a given lateral acceleration. The wider the tire, the more the contact patch is offset and the greater the discrepancy in lean angle.

Yet another factor due to wide tires is the effect of the center of gravity height. A lower center of gravity also increases the required lean angle for a given lateral acceleration—again because the contact patch is not in line with the bike’s centerline. Over the past several years, MotoGP bikes have been lowered more and more to cope with increased power, both from the engine and brakes. While the lower center of gravity stops wheelies, it does force the riders to use ever-increasing lean angles.

As we know, hanging off the motorcycle is one way to reduce lean angle for a given lateral acceleration, at least partially offsetting those factors that increase the required lean angle. Combining it all—wide tires, low center of gravity, and body position—gives the elbow-dragging lean angles we see more often in MotoGP than the smaller classes.

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