Motorized Bike, 150mpg?
 

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I have been working on this bike for a while and finally have it working pretty good, reliable enough to take for 50 mile rides. I don't have a full tank of gas through it since I put the bike computer on it, but my guesstimate is that it will go 150 mpg at an average speed of 20 mph.

Its pretty fun. Not legal yet but I think it could be if I can get a moped sticker for it.

It would be much better with a freewheel hub on the rear wheel, then the motor could be shut down for EOC and pedaling. Right now, if the wheel turns, the motor turns and there is a lot of resistance.

This kit is called a "Dax Titan" and is about $400. It would work well on a recumbent with a fairing. Top speed is 30mph but on my bike 20mph is more reasonable, it gets a little bumpy at 30. A front suspension fork would be a good thing. It is 50cc and about 1.5 horsepower.

More pictures of the drive train? I would have gone more powerful 2 stroke vs. that 4 stroke.

You can only go so fast before you have to make it conform to all the motorcycle regs. Blah.

4 stroke has the edge re: noise, emissions, fuel efficiency, longevity.

I can see what I need to of the drivetrain. It likely has a centrifugal clutch which then leads by chain- it appears at a 1:1 or close to it ratio- to a jackshaft which then leads by chain- it appears to have a 4:1 reduction- to a fixed sprocket secured to the wheel by bolts threading through gaps between the spokes, with probably some sort of multi-piece disk on the back side to clamp them.

Edit: http://thatsdax.com/TITAN_INSTALL_PAGE_1.html

Ohhhh, I see. The engine has a built-in gear reduction before the clutch!

I'd long thought that I'd try to put a v-belt pulley on the rear wheel and forego clutch and trans, either by pivoting the whole engine or by using an idler. Then easy pedalling capability would be retained.

Wouldn't a centrifugal clutch allow freewheeling and EOC? I thought the clutch would only grab when the crankshaft is at speed, not the chain drive-connected part.

Well not really. The whole assembly is "locked together" at engagement speeds plus; no matter what you do with the throttle it all needs to slow down and/or slip enough to allow weighted clutch pads to disengage. That's how my go carts and things worked anyway.

On this set-up the two chains and jackshaft always turn whenever the wheel turns so whether the clutch is disengaged or not there is a fair amount of driveline resistence to coasting.

Frank has it right, the drivetrain (chains, jackshaft and gear reduction system) always turns with the wheel which causes considerable friction/resistance when pedaling with motor off.

The centrifugal clutch will let go only when it stops spinning and the springs can pull it back, which occurs at idle speed. So you almost have to come to a stop before the motor is disconnected from the drivetrain.

This is a very simple, inexpensive drive system. However with a freewheel on the wheel, it would allow the motor to be shut down for coasting, and there would be far less resistance when pedaling.

Here is a freewheel hub

HD Rear Axle kit

The answer to the mpg question is...

Tank
0.282 gallons
$0.67 to fill tank
$2.389 gallon price

43.222 miles
17.7 mph avg speed
30.1 max speed

153.3 mpg

Not too bad!

My "Goped' averages 180 MPG, it's so funny, 180 MPG... who gets that? Good job on that 153mpg.

have you checked your local laws for motor bicycles? 20mph is I think the slowest speed limit out of any state, most states see a 20mph motor bicycle as a biycle, not a moped, but as I said check you laws, my state it' 30mph and all you need is the city $3 bicycle registration sticker.
150mpg sounds about right, my two stroke moped gets just over 100mpg and has wide small tires.