Bike sizing by Ivor Biggin
I see more people out on new ebikes than ever. What I notice most about them is not the use of Hi-Vis clothing, although this is certainly eye catching, but the fact the bikes are sized wrong for the rider. Ebikes are sized the same as non ebikes, in that they are measured from the middle of the bottom bracket axle to the top of the seat tube ( where the seat post clamp fits ). If you're standing astride a mountain bike there should be three inches of clearence between you and the top tube ( for maneuverability).On road bikes this should be one inch. Hybrids between two and three inches.
A frame that is too small means that the seatpost is often extended past the maximum safe use height. Additionally for comfort, the handlebars have to be raised to match, making them higher than is safe. The riders leg isn't extended enough and over a few miles this can cause cramping of the thigh muscles. Bikes that are too large mean reaching the handlebars comfortably isn't possible and the bike is difficult to handle. This can also mean over extending the leg and causing knee problems.
Regardless of bike type, to get the right saddle height; with your foot at the bottom of the pedal stroke, you should have a slight bend in the leg ( about 80-90 percent of full extension).