December 2, 2008 If center-hub steering like that found on the Bimota TESI 3D isn't radical enough for you, perhaps this'll do the trick: Tier Motorsports have released a set of concept illustrations featuring a Yamaha R1 that's been modified with a single-sided front swingarm. The aim of the design is to provide a completely vertical steering axis for the front wheel, making for a much more direct and responsive steering effect than is possible with angled forks - and the idea also opens up the possibility of virtually frameless bikes, in which both the front and rear swingarms mount directly from the engine and no heavy steering stem/headstock is needed. Fascinating stuff.
Telescopic forks, which have become by far the most common front-end suspension solution on modern bikes, are far from a perfect design. Their angle and leverage exert powerful forces on the steering head of the frame, necessitating heavy, reinforced frames. They cause the bike to dive forward under braking forces, changing the steering geometry and reducing the suspension travel available to deal with bumps and maintaining traction.
Motorcycle buyers, however, have generally resisted change to the trusty forked front end. BMW's telelever front suspension has been the only commercially successful alternative in recent years - and possibly mainly because its workings hide behind the bikes' bodywork and the system looks pretty much like a set of forks. It does an admirable job of separating braking, suspension and cornering forces.
The hub-center steering employed on the Yamaha GTS1000, and more recently the Bimota TESI 3D and Vyrus 985, employs a front swingarm suspended by a monoshock - a similar arrangement to what you'd usually find on a rear wheel. The difference is that the wheel hub tilts back and forth on a central pivot, pushed by two large steering arms that are operated by the handlebars. By all accounts it provides an uncanny ride experience with huge mid-corner front end confidence and exceptional performance on the brakes deep into a corner.
This latest design from Tier Motorsports re-envisions the hub-center model using a single sided front swingarm and a four-bar tilting mechanism in the hub that allows the wheel to pivot on a perfectly vertical axis for maximum responsiveness to steering inputs. Presented here as a Yamaha R1 mockup, the system could bolt straight in to modified engine cases, removing the need for a strong, heavy frame at the front end of the bike.
Otherwise, the system should enjoy most of the advantages of hub-center arrangements as well as their drawbacks - high costs, limited steering lock, and a perception among the oddly conservative motorcycle market that it doesn't look like a 'real bike.' Still, these striking mock-ups certainly stir the imagination and it would be great to see what designers could do with the concept given a blank sheet. Here's hoping the Tier Motorsports system makes it up to and through the prototype stage so we can get a closer look.
More information and photos at TheBikerGene.