Dynamically Adjustable Motorcycle Chassis

The MotoGP world championship contains the most exotic and innovative motorcycles seen in history.

But while engine systems have become more high-tech with traction control, pneumatic valves and variable -length intake systems evolved from car racing, dynamically adjustable chassis technology 'common on four-wheel racers' has yet to appear on today's motorcycles.

A conventional motorcycle's final frame design is a compromise between stability and maneuverability. Rake and trail are only changeable in small amounts, and only after extensive work - changing steering head inserts and/or triple-clamps. Even then, a steep rake/short trail that works well in corners might cause unwanted instability at speed or exiting corners. Anybody disagree?

To address this problem, a American group of designers and motorcycle developers conceived and tested a number of variable-geometry two-wheeled prototypes.

The system adjusts rake at the steering head while the bike is at speed on the track.

Normally, final race setup of a chassis suits the overall circuit 'enough agility for the tightest corner, stable enough for the straightaways' but is then a compromise. A dynamic motorcycle chassis allows extreme rake angle adjustments, changing in real time. This enables performance for each corner to be optimized on the fly.

Such a setup also produces an aerodynamic advantage. If the rake angle changes from a quick-turning 23 degrees to a more stable 'chopper-like' 28 degrees, for example, the front of the motorcycle lowers by a significant 14mm. Drag would be reduced as stability increased.

The center of gravity can be altered in the same fashion and is another feature to exploit, helping with braking and turning. A high c-of-g helps drop the bike into the turn. Lowering the c-of-g mid-turn then makes the bike easier to pick up on exit.

Electronics capable of controlling such a system already exist. GPS can tell the motorcycle which corner it is entering, while current sensor technology is also capable of linking the system to lean angle.

Perhaps the most important feature of a dynamic motorcycle chassis is safety, particularly on streetbikes. Current sportbike trends replicate the extreme geometry of race machines, often resulting in nervous handling. Honda's use of an electronically controlled steering damper on the Honda CBR-1000RR suggests that more extensive electronic manipulation of a motorcycle chassis is in the near future.