Motorized Bicycle - Episode 019

[31 October 2007]

I took the motorized bike for a test-ride today, about 2.5 hours total and about 3.5 tankfuls of fuel used, and the parts that are "finished" worked generally fine. I did not have a speedometer yet mounted but by my earlier estimates (when I had it on the RANS Fusion, that did have a speedometer/odometer) I rode it at least 60 miles, possibly over 70 miles distance. The belt showed only a very-minor fraying on the side that it nudges against the drive pulley (on the engine/clutch shaft) from an earlier test-ride and the belt does not appear to have changed after this ride, and everything else worked basically properly. The additional muffler still needs a bit of work, but that's a minor point.

I really noticed on the open road how weak the 35cc engine can be. This is not so much a limitation of the engine power itself, but a limitation of the one-speed drive setup. I searched online for various moped reviews, and found that a lot of one-speed mopeds get the same remarks--they work fine on level ground, but do very badly up hills. There were even times when I had to turn and ride on level ground into a ~20 mph wind, and the bike would only go ~8-10 MPH. The little 35cc engine doesn't make much power until it gets pretty high into its RPM range, and when it has to start under a higher-than-normal load (such as going up even a minor hill, or into the wind) it never gets into its upper RPM's at all and struggles along at low speeds.

This leads me to begin pondering how I might build a {something} with better power, but more power causes a lot of problems of its own. Ultimately, whatever I build, I would like to have it look somewhat-like a pre-war motorcycle--so I've listed the following objectives:
---the hubs must be stronger than bicycle hubs, and they must be serviceable (parts should be easily available),
---the hubs need to use wire-spoke wheels, so that larger-diameter rims can be laced onto them,
---the hubs would ideally use drum brakes, but this may not be practical,
---the engine should have enough power to propel two people well over typical roads at ~45 mph, and I estimate that this would require at least 100cc's engine displacement mated to a multi-speed gearbox,
---the transmission I would greatly prefer to be automatic, because this opens up more placement possibilities.

This last note about the engine leaves open the possibility of using moped, scooter and motorcycle components. An automatic transmission is not as "sporty" as a manual one, but since racebike-like performance isn't going to be the point anyway, this doesn't matter much overall.

From this list, I assume that-
---most mopeds do not have anything more than a two-speed transmission, if even that. And more importantly, the lower-priced mopeds being imported now aren't from manufacturers with a reliable presence in the USA. The Japanese motorcycle companies build very solid mopeds, but they're also far more expensive than the Chinese and Indian offerings. The cheaper imported ones are roughly the same cost as an older motorcycle, from Japanese companies, that is built considerably stronger. Because of this, I do not believe that any moped I could afford to use would be suitable.

---most scooters that are lower priced are unattractive for the same reasons that the above mopeds are. Additionally, I don't have the skills or equipment to build a fork well, but many mopeds and motorcycles use a fork design that has lots of space above the front fender, that may easily adapt to a larger-diameter wheel. Scooters don't have this extra space, being built for small wheels. I have not seen any scooter that used wire-spoke wheels, and the rear-end drive units of many scooters are only suitable for smaller-diameter wheels as well.

Overall--it seems to me that if you want to build something that's really stronger than bicycle parts and <50cc engines, you should just go straight to motorcycle parts because the minor advantages of using moped or scooter parts aren't going to offset the hassles they'd cause.