Good advice Allen. I've faced this issue with multiple builds and on a couple I just went with smaller tires, but on others I took a different approach.
Many builders use 2.25" cruiser wheels and this makes even the 1.95" tire squat into a wider profile than if mounted on a narrower rim and I've had chain scrub on both sides, motor and pedal, of the 1.95" tire perfectly center and chain lines straight on both chains. I'd say this is uncommon, but has occurred. I'll also add that the chains at rest and with the wheel being rotated by hand would appear to have 3/16" or more of clearance on each side of the tire and each chains slack was in the half inch range of tension. The problem with rub was occurring under power of operation and was caused by the ever so slight side to side movement of the chains.
The solution I've come up with is to run a spring loaded chain tensioner on both motor and pedal chains, mounted closer to the front of the tire where the rub occurs. What this looks like is the tension roller is in front of the tire on the motor side of a 2stroke engine and the pedal chain tensioner is located a bit further back on the chain stay to allow free operation of the pedal. When fitted and adjusted properly the chain can only travel vertically as the roller prevents any side to side motion of the chain. I learned that on the pedal side chain the rub was worse (without the spring tensioner) when the bike was under motor power only and not when pedaling. Maximum slap occurred when the pedal chain was slack and the bike under power. The spring tensioner acts as a support idler/locator in this example.
I'm a big proponent of running spring loaded chain tensioners for several other reasons as well, but that's another conversation. I run 2.25" wheels and tires on 3 different factory frames with no tire or stay rub using minimal axle spacers and 3 bolt hub/sprocket adapter on each. I also avoid running these wider wheel/tire combinations tire at low air pressure as the tire squats and widens at low pressures.
Rick C.
