Re: correct rim size for Skyhawk frame
I run a single freewheel myself- and match the chains as best as I can with half-links- which is not always an exact science and one chain- the motor usually may stretch more than the other and need re-adjusting- I have 22 teeth freewheels and I think the bikes have a 42 and 44 front- an easily pedalling gear!
but I HATE tensioners- the weight, the failure risk, the extra links
On the other hand I have run a derailleur in the past- and it's not a bad gig- simply because a derailleur automatically tensions the pedal chain then- all you have top do is sert the motor chain -
and you can also get now a lightweight 3 speed freewheel on ebay, that's almost as light as a single freewheel, but still gives you some pedalling ranges-