Thanks Deno. Yes, its a 2.5 multiplier so 18T will equate to a 45 chainring, which will be more comparable to my non-assisted bike, if I use the middle to small sprockets. The larger sprockets will be useful reserve for more severe inclines as I get older! I'm not sure of the length of my current chain which is mfrs original equipment: do you reckon I would need a longer chain for 3 extra teeth?