e.g. Shimano Acera and Tourney.

They have mahoosive jockey wheels, is there any particular reason for this?

It’s the equivalent of 19″ wheels on a Vauxhall Nova, innit?

Centrifugal force innit. The rotational inertia acts against the momentum of the heavy bike to make it easier to pedal.

I’d been wondering this too.
I just bought a tandem with Acera.
Would a better quality/higher priced rear derailleur shift any better, or would it just be lighter ?

to allow the mech to deal with incompetent BIG BIG and SMALL SMALL gear selection id have thought.

something we might see shortly for those wanting 40tooth rear gears.

Why is a bigger lower jockey wheel required for bigger sprockets though?

smoother shifting isn’t it?

I’m sure I was told they would put it on higher end stuff except it looks a bit o^0 and people expect a positive shifting action on the higher end stuff.

when the chains long enough to go round the 40tooth sprocket and you drop down to the 11tooth youll find the chain flaps around as theres nothing to take up the tension.

the big jockey wheel gives the chain something to wrap round and provide tension to the chain.

either that or the larger number of teeth spreads the wear out and keeps the deraileur shifting smoother for longer 😉