power only (no pedals) setup...?

Probably the wrong forum, but has anyone ever mounted an engine on a mountain bike, so that the sproket on the engine drives one of the 2 front sprokets on the bike that are normally used for high and low range selection?

My thought was to remove the pedals, hook it up in this fashion and add a set of foot pegs to the bike to rest my feet on, this would allow the rear gear selector to still be utilized increasing the range of speeds, and decrease the engine power needed (being that I"m 6'3 and 275lbs, this is somewhat important, and where I live there's alot of hills)

If this can be done, I am very intrested in how it was set up. I have a machinist available if I would have to make parts that's not a problem.

 

[jl ws-6]

Again, here in CT the only law I have found is that if it's under 50cc (and who is to say what is and what isn't in this case) there is no registration, insurance, license required, and it is not subject to signal light rules and whatnot

 

[brendonv]

Just coz u hav pedals doesnt mean u gotta use em u just hav to hav em to be classed as a bike so yeh just keep em on.

 

[jl ws-6]

I will evaluate that situation when I get there. A set of posts mounted where the pedals are so they're like a foot peg would be fine, Pedals may stay, they may not, probably not.

 

[brendonv]

if they dont stay its classed as a motorbike so make em stay!!!

 

[jl ws-6]

I don't care about that in all honesty, if I were to get bothered by a cop, I'd probably laugh at them.

 

[brendonv]

and they will be laughing at you wen they give u a 500 buck fine.

 

[jl ws-6]

you obviously don't live in connecticut. They have alot more important things to worry about then me on a motorized mountain bike trust me.

Besides, I've got a couple PDA cards from state troopers that are friends of mine on being a state lieutenant, I highly doubt they'd even give me a fine with those in my pocket.

 

[duivendyk]

The problem of inplementing a drive setup by powering the front chainwheel is that it is difficult to get the required reduction from engine to it.I will explain why,it turns out that a speed of 20 mph corresponds to 270 rev/min at the rear wheel (26" wheel).
Lets assume a rear sprocket cluster of 13/34t (7 speed) and a three speed front set of 28/38/48 t.This is what's on my Raleigh bike.Lets assume you drive the 48t sprocket with the engine and have the rear chain on the 28 t sprocket.The rear ratio implies a range of 34/13=2.6.Lets assume a min. speed of 12mph,that means a max.speed of 31mph (for the same engine speed),so your actual speedrange would be quite a bit larger.Let's figure out the rpm of the chainwheel at max speed.31 mph means 31/20 *270=418 rpm at the rear wheel.The chainwheel rpm becomes 13/28*418=194rpm.Now that we know this we can figure out the required reduction between the engine and the 48t chainwheel sprocket.
Let's assume an engine speed of 6000 rpm, we get 6000/194=31.This reduction requires a 2 stage reduction,a minimum sprocket size is 10t (there may be smaller ones to be had), which implies a reduction of 4.8,so additional 6.5 reduction is required.Some engines have built in or add-on reductions usually around 5:1,so you can get around a 24 total reduction.This implies an engine speed of only 4700 rpm at 31 mph.If you had a big enough engine (enough torque) this might be OK.At the low end, with an engine speed of 5000 rpm the chainwheel rpm becomes 5000/24=208 rpm and the rearwheel speed 28/34* 208=171rpm or a road speed of 171/270* 20=12.7mph.
Summing up,you need a reduction of at around 25+ between engine and chainwheel for adequate overall performance.This is based on a wide range derailleur drive with a max ratio of 4.5 (48/28* 34/13).If you had less range you would need more.If your engine does not have the required internal reduction you have to get it via an intermediate jack shaft chain drive,that will take a sizable sprocket.You also have to watch out for the reversal of rotation with an engine gear reduction!

 

[jl ws-6]

So a jackshaft setup will work if you had say a 10 tooth sproket on the engine, and say a 50 tooth sproket on the jackshaft, then another 10 tooth on the other side of the jackshaft running to the biggest of the front sprokets.

It sounds like it is doable, but not easy.


Would it be possible to put a shorter rims on the bike, say 24 inch? Other then moving the brake calipers, I don't see this as being impossible.

 

[HoughMade]

I don't know about Conn., but it is possible the presence or absence of pedals does not make any difference. It does not where I live.

"Motorized bicycle" means a two (2) or three (3) wheeled vehicle that is propelled by an internal combustion engine or a battery powered motor, and if powered by an internal combustion engine, has the following:

(1) An engine rating of not more than two (2) horsepower and a cylinder capacity not exceeding fifty (50) cubic centimeters.

(2) An automatic transmission.

(3) A maximum design speed of not more than twenty-five (25) miles per hour on a flat surface.

The term does not include an electric personal assistive mobility device.

IC 9-13-2-109

No mention of pedals. If Conn. has a similar law, do what you want with the pedals.