How stiff does a 3 wheeler's chassis have to be? Given that there are only 3 wheels on the road, there is no real torsion applied to the chassis. Am I right in thinking that it only has to resist bending under its own weight and under cornering, plus some crash resistance and roll over resistance?

I'm no expert but I remember reading some time ago that the chap who designed the DRK said otherwise - his argument was that the last thing you wanted to encounter was rear wheel steer caused by chassis flex!!!

Yes, it would have to resist cornering forces. I should have been more clear, I'm thinking of torsional stiffness. I can't think of any torsional forces it would have to counter. So long as it didn't sag when you sit in it and it remains straight under cornering, something like a simple ladder chassis or a simple back bone would be more than enough.

speak to richard oakes at blackjack....

The cornering force acting at the contact patch of the single wheel will introduce a torsion that has to be restrained by the pair of wheels. If the chassis isn't torsionally stiff enough, there will be a lot of lateral movement of the chassis at the end with the single wheel, as the single wheel rolls and unrolls relative to the end with the pair of wheels. I can't imagine this giving a sense of confidence, especially the over-steery feel if the single wheel is at the back.

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Originally posted by BenTyreman
The cornering force acting at the contact patch of the single wheel will introduce a torsion that has to be restrained by the pair of wheels.

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