Fancier funny front end
Bimota’s new supercharged Tera adventure bike sets out to fix the Tesi’s front-end flaws
While dozens of attempts to come up with a superior alternative to the telescopic fork have fallen by the wayside, Bimota’s longrunning obsession with funny front ends has remained undimmed.
Starting back in 1990 with the launch of the original Tesi, the swingarm-based front suspension system was designed by Pierluigi Marconi (who remains at the company) and lives on today in the supercharged Tesi H2 hyperbike.
What’s more, with Bimota now on a firm financial footing as part of the Kawasaki Motors empire, the hub-centre-steered front has been given yet another significant overhaul for the incoming Tera adventure bike.
Missing detail
While the Tera’s Ninja H2SXderived 197.3bhp supercharged engine and variable ride height suspension grabbed headlines, the redesign of that Tesi-style front slipped under the radar when the bike was revealed at the end of 2023.
On closer inspection though, it might be the most significant element of the bike as it addresses key shortcomings that plagued previous hub-steered models.
Like the Tesi’s design, the Tera’s front swingarm suspension is designed to eliminate problems that telescopic forks can’t surmount. For all their elegant simplicity, telescopic forks are unable to separate braking and bump forces, and the angle they have to adopt to get the right steering geometry inevitably encourages brake dive.
The Tesi-style front swingarm concept solves those problems but introduces new ones of its own, including unwanted friction and play from its various steering linkages and bearings, as well as
limiting steering angle to about 20 degrees – far less than the figure on many road bikes.
The Tera solves those problems by keeping the hub-steering and dual-sided front swingarm arrangement but introducing a completely different way to connect the steering.
As on the Tesi, the front hub steers on the axle, with the rake and trail controlled by a pair of rods that run parallel to the swingarm back to the frame, creating a parallelogram arrangement that prevents the steering geometry from changing as the suspension compresses. The same rods also work as brake reaction arms, helping to control brake dive.
Complex system
On a Tesi, the steering is via a third rod, also running parallel with the swingarm, that goes back to a combination of two bell cranks connected by another, intermediate linkage near the swingarm pivot, and then another rod that travels up to a lever below the steering head that turns with the bars.
It’s complicated, with lots of bearings that can add friction and joints that could introduce slop. It can work well when finely engineered and properly set-up, but it’s not ideal for transmitting subtle feedback to the bars or control to the front wheel.
The Tesi’s rod-operated steering also has limited lock that makes tight manoeuvres impossible.
Fresh thinking
The Tera’s solution is to bin all those rods and connect the bars to the front hub via hinged, knee-like linkage above the front wheel, rather like the steering on Hossackstyle front forks used by bikes such as the BMW K1600 GT and the latest Honda Gold Wing, to allow much more steering lock while reducing play and friction.
It’s also something that was tried with a Tesi-style front swingarm on the Vyrus 968 M2, which was designed as a Honda-powered Moto2 racer back in 2011 and reached the street in a small run of
‘More lock while reducing play and friction’
‘Strada’ versions later that decade.
But for the Tera, Bimota have added two, short, parallel steering links between the top of the knee joint and the bottom of the steering stem below the bars.
These are the focus of new patents and allow the steering stem to be mounted at a different angle to the steering axis of the front wheel as well as further back than it would be on a bike with conventional forks, all without harming the steering or suspension geometry.