It's the handlebars, if you want the bars at the rear of the bike, the chain is on the right, if you want them on the front the chain is on the left.
Simple ! Well that's what Wombat told me and I believe him.
Others say that it has something to do with the off-set of large tyred bikes and left and right side balance bias. Particularly with wider belts.
The gear-box drive can be made with longer or shorter shafts to suit.
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Ride on !
