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I have a road bike I use for commuting and I'm about to move 20km further out, so I'm considering fitting a tiny engine to it to assist my ride to work.

However, where I live I have a restriction - the maximum power allowed is 200 watts (about 1/4 HP).

I've seen some kits, but they have huge engines (beats me why they have to be so big).

Further, I'd prefer a diesel engine (no spark/glow plugs) and better economy.

Some brief research has shown that a tiny (5cc or so) diesel engine should be able to produce about 200 watts. A larger one could be de-tuned. There are model aircraft diesel engines of this size, but they're quite expensive.

I've been told a "brushcutter motor" (small two-stroke) could be an option, but they are noisy, smoky and smelly.

I'm not worried about how to deliver the power to the wheel - I'm trying to pick the power plant first then make it work.

Has anyone got any suggestions for:

  • diesel engine
  • very small (200 watts max)
  • not expensive

Edit:

My bike is a Focus Planet TR 2.0 (2012), which has internal hub gears, so the solution can't involve replacing the rear hub. It also has disk brakes front and back, so replacing the front hub may be problematic (not sure).

Regarding range, I will live about 30km away from my CBD and batteries seems to have about a 60km range. Also, recharging takes a while, but filling a tiny tank takes seconds.

Also, I seriously doubt that the pollution created by a tiny 1cc engine exceeds that pollution created by the recharging process of burning coal and pushing the electricity through all the transformers and switches between the power station turbines and a bike battery.

For these reasons, I'm still seeking an internal combustion solution.

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    model aircraft engines do not run on petrol(I believe known as gasoline in USA) or diesel. they run on special fuel, which I believe will be more expensive. Also, if in the UK anything with an engine requires a road licence if driven/ridden on the road.
    – Mark W
    Commented Feb 1, 2013 at 8:40
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    The small amount of smoke they produce is enough to make the rider smell like smoke as soon as he gets indoors. The problem in this case is not the amount of smoke, dirt and noise, but how close it is TO YOU!
    – heltonbiker
    Commented Feb 1, 2013 at 18:35
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    The best solution is probably an electric front hub, unless you really need the range of a fueled setup.
    – Daniel R Hicks
    Commented Feb 1, 2013 at 18:49
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    Joke answer: Legs.
    – Stephen Touset
    Commented Feb 1, 2013 at 19:36
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    @Bohemian Have you considered just buying a scooter or a moped? In the long run it'd be safer, faster, and more reliable than a little 1/4 hp engine strapped to your rear tire.
    – WTHarper
    Commented Feb 5, 2013 at 3:40

3 Answers 3

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There are some bike hubs containing an electrical motor inside. If you google "bike hub motor" and take a look at the images, you'll get the idea.

I think these ones are ideal since they require minimal changes to the overall bike structure, allowing for normal riding if the motor is not working, and they don't burn evil oil: you just plug the bike to the wall and that's it.

The spoked ones should be adequate for building a front wheel with a regular road bike rim.

Hope this helps

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    "they don't burn evil oil" This really depends on where you get your power from. If it's from a coal power plant, not so good. If you charge the battery from a wind generator, that's probably about as clean as you can get. But I agree, an electric motor is a much better idea than a petrol engine, unless you need a very long range.
    – Kibbee
    Commented Feb 1, 2013 at 13:44
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    @Kibbee I have thought about this before, and my "conclusion" is that individual vehicles should not burn oil directly, because this tends to generate noise and smoke INSIDE densely populated areas. The same reasoning goes for public transport (in my city, the main cause of urban noise and smoke are the buses). Even if the smoke will be produced anyway, at least it should be produced away from lots of people.
    – heltonbiker
    Commented Feb 1, 2013 at 15:41
  • @bohemian As already suggested by heltonbiker, a colleague of mine built a electrified bicycle based on such a electrical motor hub. Also from my point of view that's the most simple solution for several reasons: a) you don't have to modify the drive train to attach the motor; b) a small combustion engine would likely emit its power via a high rotation frequency which could need a somewhat complicated transmission system; c) you don't have to start/stop the engine but can control it via a switch on your steering bar whenever needed and it won't influence you much if not needed.
    – Benedikt Bauer
    Commented Feb 1, 2013 at 15:54
  • Thanks for your answer, but my bike has internal hub gears - see edit to question
    – Bohemian
    Commented Feb 1, 2013 at 18:28
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    Bohemian, most electric motored hubs are FRONT hubs :o)
    – heltonbiker
    Commented Feb 1, 2013 at 18:32
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MY first thought was MTFU and get fitter pedalling further. It might not be as hard as you think once you get used to it. However, for a 20k commute, definitely go with an electric hub motor. Loads available off the shelf. Easy to fit and use, very economical and reliable with low/no maintenance. Also nice and quiet.

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  • Thanks for your answer, but my bike has an internal hub gear - See edit to question. BTW, I said I was moving 20km further out, making it a 30km commute. The MTFU option is a better alternative than electric power (also see edit).
    – Bohemian
    Commented Feb 1, 2013 at 18:29
  • I once had a 25 km commute for a few months, and it wasn't that bad. It took me about 1 hour, 15 minutes, which was anywhere from 20 minutes slower, to 20 minutes faster than a car would take for the same trip (some days I got a ride). It was pretty tiring, but I didn't have the best bike at that time either. I got in pretty good shape in a short amount of time.
    – Kibbee
    Commented Feb 1, 2013 at 20:10
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    I commuted for several years 27 miles out, 10 miles back. (The difference was because I took a "short cut" in the morning.)
    – Daniel R Hicks
    Commented Feb 2, 2013 at 2:53
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These guys make small petrol engines for bicycles. I've never seen a Diesel one though.

The advantage here is they supply everything you need. Drivetrain, engine, ignition. The lot.

I'm currently in Bondi, Australia and I see a few buzzing around. They look like a lot of fun.

With these tiny engines economy isn't going to change hugely from Petrol to Diesel.

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  • I'm from Melbourne and I have looked at that site. The engines seem ridiculously large. The smallest engine is 48cc, seems massively large to produce just 200W. (A motorbike engine can produce about .1W per cc, so 48cc seems about 20 times too large)
    – Bohemian
    Commented Feb 1, 2013 at 18:37
  • Where'd you get the .1w / cc from? Also, 48 * .1 = 4.8, a long way off 200.
    – alex
    Commented Feb 2, 2013 at 2:15

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