No rules besides u cannot use a shopping cart,bicyle to build off of and u cannot use a motor or pedals with chain. I am going to use bicycle wheels. 2 rear and one front. where should i go from here? Anything goes really. ill post some pics from the past cpl years of what people did Obv the bike's are not allowed anymore because there not really making anything and they were way to fast. but no one said u could not use bike parts. So what do you guys think to to make the fastest downhill cart? U get a pusher to get you off the line. Its about a 1/8th mile Ive read the soapbox derby sites about how 2 cheat and such but there limited to alot of rules where here this barley is any. Alot of people told me the road bike tires would be your best bet.. so where from there?