DUOLEVER FRONT SUSPENSION
BMW TECH TALK
Imagine a swingarm holding the front wheel, instead of fork legs, and connected to the steering by a hinged arm at the top, and suspended from the frame by a pair of forked arms with a single shock connected from the bottom fork to the main chassis. This is Duolever, developed from an invention by a British designer called Norman Hossack. In theory, it has several benefits over a telescopic fork.
With a fork, all forces at the front wheel – braking, bumps, cornering – are fed through the steering and felt at the bars. Sometimes they interfere with steering in an unhelpful way – if you shut off or panic brake mid-corner, a force appears at the bars as the bike starts to come upright and steer out of the corner. The correct reaction would be to continue to steer (to avoid crossing lanes and running out of road) – but it’s usually a loss of confidence that makes you shut off mid- corner in the first place. So every fibre of your being – as well as the force at the bars – is telling you to do exactly the wrong thing: to brake.
One riding advantage of Duolever is the braking and suspension forces bypass the bars and are fed into the chassis. They have minimal effect on the steering. So in the above scenario, if you experience a loss of confidence mid-corner and close the throttle, no weight is added to the steering – which means there’s no sense of the bike wanting to self-right, so it’s easy to simply keep on steering.
This means if you’re the kind of rider who habitually scares themselves by turning into corners and apexing too fast and too early, then bottling it and running wide (or even sitting up and crossing the centre line), then Duolever may save you.
There are other advantages to the system – a potential for greater strength and/or lower weight, less stiction and greater control over suspension behaviour.
One of the disadvantages of the extremely stiff Duolever system is that at extreme lean angles – say, on a track – it’s hard to feel the grip limit; the bump feedback doesn’t get through to the rider and, as a result, it’s hard to know how hard to push. The same is true, to a lesser extent, on a wet road.
Other disadvantages – at least in BMW’S application in the K1300S – is a long wheelbase dictated by the Duolever linkages, and long-term wear in the system of scissor forks and bushes.
‘Braking and suspension forces are fed into the chassis’ SIMON HARGREAVES
Roll off the throttle in a corner and Duolever won’t make the bike stand up