My first post on this website!
bookishboy:
It sounds like your father is prime canadate for an electric assist. Have a look at this:
http://ecospeed.net/index.html
I rode one of these yesterday. I is a very funny feeling to get that kick in the back. From my ride I would look at the bikes suggested at the website first.
The electric drive goes in the middle of the chain, the transfer/drive assembly has a freewheel in it. The net result is you can peddle as much as need then hit the thumb switch accelerator and get a boost. This is an inline boost, it actually uses the rear cluster to drive the rear wheel. This would ensure the knee gets exercise to strengthen it.
Pick the bike first then put the electric drive on it.
A second choice would be:
http://www.bionx.ca/en/main/default/31.shtml
Here you can set the amount of assist wanted, the onboard computer will even figure out the weak leg and adjust for it.
See also:
Can You Really Exercise on an Electric Bicycle
http://www.evworld.com/view.cfm?sect...ue&newsid=7623
-- Brandy