A gravity bike is a bike that has been modified to run at high speeds by using a hill and gravity to get you going. There are no other means of pedaling the bike so you need to make sure your hill is long enough and high enough to get some good speed. There are lots of variations to the designs but most of them have the rider in a low center of gravity position, most have added frame structure to ensure a safe ride at high speeds and massive brakes to stop. SIN Cycles have built a number of bikes and they walk through the build process of their s1 gravity bike in one of their blog posts. You can see the s1 in action in the video below at the 1:30 mark and a crash of the s1 at around 1:50. :(Â Doesn’t look like the damage is anything that a big hammer and a welder can’t fix though.
