DUOLEVER FRONT SUS­PEN­SION

BMW TECH TALK

Motorcycle News (UK) - - Com­ment -

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

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