Quote:
Originally Posted by euromodder
Rear-wheel steering has been tried on some velomobiles because it's far easier to transfer the pedaling power to the front wheels, but was found to be unstable.
To keep them practical, their wheelbase is relatively short, and rear-wheel steering gets rather twitchy at speed.
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I was just reviewing this thread, so I apologize for the long delay, but I must protest. The amount of power-robbing pedal wind-up from even a short lateral shaft can easily be more than the combined deflections from chain stretch and sag, and frame strain to rear wheel drive. I did the math, and you need large diameter carbon fiber shafts to start winning.
A long wheelbase is really no problem on the road, as users of tandems, etc. know.
The Dymaxion cars had rear wheel steering, and Bucky drove hands-off at times. It turns out that the proper geometry is just the same as a regular car being driven backwards, but it needs a damper. The damper takes care of the transient forces from the reverse caster, and in a steady-state turn it still tends to straighten as it should. The two main problems with RWS are that unless the rear track is less than the front, it can get trapped against a curb, and that it takes more time to initiate a turn, but still less than it would with two wheels.
The usual cause of twitchy steering in velomobiles, assuming the toe-in is adequate, is the usual steering ratio. People make trikes from bicycle parts, but they should start fresh. Bikes need really quick steering to balance at low speed, and the steering is never upset by side forces on the rider. Cars use 20 times more hand motion to keep it easy.