Tires, grips, pedals and brakes needs to have high friction, while all rotating parts needs to have low friction.
invention of bicycle
yes, the bicycle is an invention
a bicycle for transportation
Between its invention, and into a few years after the invention of the Safety Bicycle.
1817
The brakes! And the tires (no friction = no traction).
In the bearings, where you want as little friction as possible.
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The bearings
Because friction stops momentum of force from moving the bike
The invention of the multi-speed bicycle increased the usefulness of the vehicle. It made it easier to pedal up hills giving it much more range.
The brakes and the tire treads.