Re: Question for "Friction Drivers"
In the end, it's up to how you and your individual setup performs on the hills around you. A negligible amount for you might be very satisfying for another rider.
I've used every friction roller size from 1.125" to 1.50". Each one had their positives and negatives. Since I need to keep up with traffic with very few hills, my favorite is the 1.5" spindle.
Gears on the bike is the biggest difference. With a 24-speed bike, pedal-assist plus ANY roller size would work for me.
On a single-speed bike, roller size is more important for hillclimbing.