Thread: Top Speed
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Old 09-08-2011, 09:39 PM
Scootmeister Scootmeister is offline
Motorized Bicycle Elite Member
Join Date: Mar 2011
Location: North Carolina
Posts: 243
Default Re: Top Speed

I learned while racing gokarts and motorcycles that three things determine speed: HP/weight ratio, gearing, and roll resistence which usually is determined by the quality of your equipment, especially bearings. Using this formula I built a motorized bicycle with a homelite chainsaw engine, 58.2 cc, 3.33 HP, rated at 7500 RPM with a magnesium frame and chrome cylinder. Mine has a Mikuni carb, about 16mm (some came with Tillotson, Walbro). I mated this short-stroke quick reving engine to a freewheel jackshaft and 3-speed Shimano rear. With a 46 tooth rear sprocket and 15 : 1 initial gear ratio driving the 3-speed, in 3rd gear I get about 53 MPH. With a change in gearing and a final ratio of 16 : 1 I get about 50. Both are way too fast on my cantilever bike with springer front end. The optimum setup is a 19 :1 ratio which gives me a top speed of approx. 44. The Sun Rhino Lite XL wheels and sealed bearings roll true with little resistance. Running the final drive chain directly to the Shimano hub eliminates the vibration from rag joint or other extaneous hardware. My KMC BMX chain runs smoother than 415 Chinese chains.
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