rtbcomp
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Er... I'm not sure tanks have wheels that steer rtb.. I don't think you can use that analogy and get away with it! Tanks use skid steer:- totally, utterly, nothing to do with three wheeled bicycles! Sorry, tricycles.
The basic difference between a twin rear wheeled bike with a diff and one with two freewheels is that when going round a corner, the diff bike will drive the faster (outer) wheel, and the freewheel bike will drive the slower (inner) wheel.
The latter bike would probably show only a small tendency to pull, because the front steering wheel is pointing the bike in the right direction (not like a tank). Which you could easily get used to/ allow for.
But if you're really tanking it (no pun intended) round a corner and go onto two wheels, you will lose traction and your little legs will go round at the speed of light. When your inner wheel comes down, the bike will really pull, and you will probably crash into a double decker bus coming the other way. Fini.
Two wheels at the front is generally, better.
I can get away with that analogy - tracks only skid because of their length, OK - try disconnecting the brakes on one side of a car and see if it steers or not when you apply them!
I agree that 2 freewheels will drive the slower wheel, that's what I said.
The diff doesn't drive the outer wheels faster, it compensates for the fact that they go faster by allowing the carrier and planet wheels to rotate about the sun wheels.
I agree that the effect would be slight on a trike, in an earlier post I expressed suprise that they use diffs on trikes, but research showed they do.