Terry, if the wheelchair motors still have the original gearing, it's rather normal to gear up if a smaller wheel is used.

On the other side, it's difficult to calculate end speed with only wheelsize known. Somewere we need more information, like RPM of the axle.

Also, wheelchair motors come in a lot of flavors. From 125W from small indoor wheelchairs to 750W from large mobility scooters With worm and wormwheel gear, timing belt, or epicyclic gearboxes. And then the wheelsizes. From 125mm solid wheels, to 26" bicycle wheels, and everything in between.