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RevoPower’s Gasoline-Powered Bicycle Wheel

The Wheel’s basic design.

RevoPower, a Denver-based company, is developing a 2-stroke engine-powered replacement front wheel for bicycles. The 25cc hub engine in the Wheel delivers 1hp (0.8 kW) peak power at 7,500 rpm and supports a top speed of 20 mph. Fuel economy is an estimated 200 mpg.

The Wheel meets CARB/EPA standards for small off-road engines, and features an idle-stop function that cuts off the engine at speeds below 5 mph. (Conversely, the rider needs to hit 5 mph before the engine will engage.) By stoping the engine at low speed or rest, RevoPower avoids the issue of idling emissions, as well as the problem of cooling the engine when the wheel is not rotating.


The company has developed seven prototype engines, two hand-built and five from Komatsu. RevoPower is working with another manufacturer on a stratified charge two-stroke engine with port geometry that will meet the emissions requirements.

The Wheel itself weighs less than 15 pounds (5 kg), and uses a standard one-quart fuel tank (although other designs are possible). Noise emitted by the engine is less than 65 dB at a distance of 7.5 m.

Swapping out a conventional bike wheel with the powered Wheel takes about 30 minutes. The Wheel will be available in 2007, and will cost about $400.

RevoPower has put about $1M into the development of the Wheel so far, and is raising an additional $3-7 million.

(A hat-tip to Richard Earl!)




I am not a fan of small 2 cycle engines. They make noise and pollution, the power output is almost an afterthought. The EPA standards are not very strict and the amount of pollution put out by a one HP engine may exceed a full size 100 plus Hp Prius.
Bikes this size are best served by an electric motor in terms of noise and pollution.
Perhaps someone could post the g/HP or g/mile emissions on these small engines.

Harvey D.

A real misfit where clean electric non-polluting bikes are availble.


Actually, bikes of this size are best served by the use of two human legs. If you're gonna use some sort of external power, agree, however, that electric would be better.


actually the idea is pretty old,

already in 1987 they started to produce these bikes, i own one just for fun of 1988

Eric S. Johansson

is one source of emissions analysis. two-stroke engines persist because they are a huge win for small motor applications. for the same mass, you get twice the horsepower. and yes, because two strokes are terribly dirty, we are going to have to suck it up and convert to weaker motors made even weaker by low-energy density fuels like ethanol is an article on fuel cells and scooters.

As for electric bikes, they are toys. They can't carry any sizable amount of load. If you travel any distance i.e. 20 miles or so, it's effectively a one-way trip unless you have four to six hours to spend in between arrival and departure. for small vehicles like scooters and motorcycles, liquid fueled engines will be a win for the for the foreseeable future.

FWIW, when thinking about scooters, don't think about the 49 CC systems. Think about 150 to 500 CC. I'm buying a 250 CC (four stroke, liquid cooled) because it lets me get up to highway speeds without it overpowering my skill level.


Future scooter owner here.

I've looked at the possibility of an electric bike, and the price/performance ratio wasn't good enough for me.

At least someone is looking into the biggest single complaint about bicycling: The sweat. Now if they could work on the funny pants part, we'd be set.

Mark A

This is a great design idea. The packing of it is very well thought out. And until 2 stroke, weed eater type, engines are totally outlawed, which they arent at the moment, I dont see a big problem here. Of course if everyone, and thats everyone, turned in their 6 mpg excursions and suburbans for 6 of these gas powered bikes, then the resulting pollution problems would need to be taken care of. Of course we would save alot of fuel in doing so.

For now, a nice toy to market, but will not make much of an impact. Who would pay an extra $400 on top of the price of the bike, for this system? Only ones who regularly now use a bicycle. This will not get us out of our 4 wheel vehicles.

Thomas Pedersen

Hmmnnn - navigating dense city traffic with 15 lbs extra weight in the front wheel..? No thanks!

It sounds to me like a dirty, loud lawn mower engine... 65 dB from 7.5 m is quite a lot. Standard cars sound off less than that from 1 m.

Too bad they wasted $1M on that project... :-(

Rafael Seidl

Eric -

two-strokes do not get twice the power out of the same displacement, for several reasons:
- displacement is bore * stroke of the piston
- the bottom quarter of each stroke is reserved for gas exchange
- combustion products are retained in the chamber (10-30% EGR depending on scavenging method)
- fresh charge must be compressed to effect scavenging, in small engine typically in crankcase

Bottom line: typical power gain relative to four-stroke is more like 50%. The price is HC emissions as high as 30x those of a four-stroke engine of similar power. Note that it is possible to build four-strokes small and powerful enough for chainsaws, with substantially reduced HC emissions.;site=a4e/lng=en/do=show/alloc=3/id=2712

As for recharge times, with modern batteries it should be possible to bring those down to 15 min off a regular 110V 15A household circuit. Assuming a 50% efficient charger and 14V battery voltage, you'd need a 14.5Ah battery. Btw, some of the fancier electric bikes are rather expensive toys:


Sid Hoffman

I'm also concerned about the noise, like others have mentioned in the standard scientific method is to measure sound levels at 1 meter. In fact, the rider's head is probably not much more than 1 meter from the wheels anyway.

Noise levels generally drop in half for every doubling of distance, although this is where it gets confusing since the real sound level drops in half ever 3 db, even though human perceived levels are every 10db or so. Even if we take the more conservative 3db, 65db at 7.5 meters would be 74 db at 0.93 meters, which is very loud. At 10db doubling, it would be over 90db at 1 meter.

Agreed that a human/electric hybrid bicycle makes more sense both from noise and clean energy perspective.

Eric S. Johansson

Rafael Seidl: thanks for the correction on power output. I'm looking forward to a pollution tax + buyback program on engines to drive 2strokes out of general use.

And yes, e-scooters are expensive toys. when they can match the range and speed of a 250-300 cc scooter, I'll think about them. ;-)

thanks again for the correction.


"As for electric bikes, they are toys. They can't carry any sizable amount of load. If you travel any distance i.e. 20 miles or so, it's effectively a one-way trip unless you have four to six hours to spend in between arrival and departure. for small vehicles like scooters and motorcycles, liquid fueled engines will be a win for the for the foreseeable future."

Most electric bikes out there fall into the category you describe. However over the last couple of years there's been some huge improvements in wieght loss speed and range. I've personally built lightweight bikes that go 30 miles at 20mph no pedalling.
There are lots of excellent kits out there for cargo see

There's a little less available in the way of complete bikes but there are some great models out there.
Have a look at the ezee torque

One of the great things about electric bikes is that you can expirement with some fantastic battery tech that will takes years to be adopted in cars. Some people are even starting to use a123 systems cells

Anyone looking for info on electric bikes should take a look at or the yahoo group power-assist Newbies are very much welcome!

John W.

Nick F thanks for the links! They are helpful.

Two-strokes, historically anyways, have indeed produced roughly twice the ponies of equal sized four-strokes, because of double the powerstrokes, and simpler engine design with less power-sucking mechanisms like cams, rocker arms, related bearings and chains, etc, etc. Anyone who grew up with dirtbikes knew the two-strokes in their powerband were scary fast: a typical 250cc two-stroke would put out around 50-55 horse compared to roughly half that for a 250cc four-stroke equivalent, at least a decade or more ago. I'm not in the scene anymore so I'm not up on the current generations. Mind you, four-stroke dirtbikes have had a major renaissance lately, and have come a long way, so I can believe two-stokes are not as advantageous anymore, power-wise. However, I do doubt very much the power advantage has been cut in half.

That said, I'm not promoting two-strokes, because they do polute much more, though they have been cleaned up substantially in the last several years. Golden Eagle Bicle engines has a very good engine-assist set-up too: and though they don't have the slick in-wheel packaging of this setup here (it sits outside of the rear wheel usually), it does have this advantage: you can use any engine you desire, including clean four-strokes.

Eric S. Johansson

NickF: I'd like to see stokemonkey work with: ( I have a folding model) :-)

fuel cell scooters

electric scooters

dirty search for electric scooters


It would be interesting if something like this could be fueled by an ethanol/svo blend or some other biofuel/blend that works well in a 2 stroke. That way they could market a 'green' fuel for their otherwise dirty motor for those a bit more concerned about emissions and get more free press.

This would make an interesting addition to an electric bike, giving it a third source of power. Hills around here mean lots of opportunity to recover energy, so gas alone doesn't make enough sense.

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