Mike Burrows is considered by many to be the doyen of British bike designers. Key to his success is a willingness to break the mould and challenge tradition in order to improve his craft. His nonconformist approach has brought a number of innovations which have redefined standards in cycle design. In this film he examines one of the fundamental givens of cycle geometry: fork angles.
The variables which affect the way a bicycle handles include its head angle (the angle the head tube intersects the horizontal) and its fork rake (the horizontal distance between the steering axis and the front axle). These two factors in turn affect a bicycle’s trail, which is the distance between the point the front tire contacts the ground and the steering axis.
In the early days of cycling, a bicycle’s steering axis, and fork, were vertical – look at an image of a penny farthing. The reasons for the evolution towards the titled steering axes of today is something of a mystery, but cycle historian John Allen has suggested the change happened for rather run-of-the-mill reasons: to bring the handlebar closer to the cyclist, and for the front wheel to clear the rider’s feet. Whatever the reason, this standard has stuck for generations, and works perfectly well for upright bikes.
When developing a new recumbent bike though, Mike decided to work out what the best configuration for handling really is. To allow him to test how head angle influences handling, he built a bike with an easily adjustable front set up. He then test-rode each set up to determine which offers the most comfortable and effective steering.
These rides taught Mike that optimum steering in terms of efficiency comes from having a vertical head tube and forks raked slightly back – like casters on a shopping trolley. The reasons are fairly straightforward: a vertical head tube means turning the handlebar will influence the direction of the bike 100% – anything other than vertical compromises steering for up-down movement. Mike’s results tally with research by Tony Foale and Vic Willoughby who, in motorcycle engineering bible Motorcycle Chassis Design, carried out a similar trial using a modified BMW 650.
Despite his findings, Mike acknowledges that bicycle shapes will remain unchanged largely because of the shape we, their riders, are. But it should be noted that forks are angled forward for ergonomic, not handling, reasons.
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