Low Observability Motorized Bicycle


New Member
Local time
10:46 AM
Nov 3, 2008
I live in a state (PA) that requires motorized bikes ("Mopeds") to be titled, registered, and insured, even though no special operator's license is required and there are no inspection requirements. This would be a nuisance that I would put up with, except it seems to be virtually impossible to get a homemade bike registered & titled (see other posts in this forum).

The reason I'm building my bike is to have some simple 'pedal assist' when I go out on my weekend motorhome trips in the mountains and back country of PA. I just want to use the engine when necesary, pedal the rest of the time, and 'stay off the radar screen'.

For this reason, I'm wondering if anyone out there has put any thought into 'low observability' installations that aren't eye-popping obvious to the casual drive-by observer (aka 'Police'). I think there are a number of measures that could be taken, starting with the style of bike frame, then what the gas tank looks like and where it's placed, where the muffler is mounted and how loud it is (very important), and even some sort of shrouding that obscures the engine.

Is anyone doing this, and would you care to discuss?

yes -- if you look around on this site -- you will find what you need

I have seen rack engines hidden in milk crates

and as you mention -- keeping the noise down -- I think -- most important

you might want to go into the legal threads and just download some of the laws
that you like
if you have a drivers license and are not riding crazy
it would be an up tight pooolice that would give you a ticket
and with gas prices being the way they are
the judge will probably throw the ticket out

a kid down the mountain just went to court the other day
driving a MB without a license and a couple of other things
judge dropped all -- our time may be a coming !!!

ride that thing
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MM is right about the milk crate. It hides a lot.

A pusher trailer is another solution.

With anything you come up with, aside from hiding it visually, sound control (to Major Tom :rolleyes:) should be near the top of your list of objectives.

I've thought about this with my recumbent. If you've seen a recumbent with a tailbox... something like that over my subaru. It could be insulated and I even drew up some air intakes to keep it running cool.

So far I haven't had any problems with police but I haven't really ridden that much. I can't see the local cop giving me trouble as I've known him for 20 years. But the state troopers seem to have a bug up their rear about almost everything.
Stealthiness is the reason I built an electric MB. I'm not getting the 20 miles per charge as advertised but I do make the 8 hilly and part dirt path miles with charge to spare. I'm on my 3rd controller and second set of batteries in almost two years of daily service.
I like the idea of a rack mount gasser in something like a motorcycle trunk but you'd have to figure out how to get enough air moving around it. A milk crate would work but I personally would want to paint the motor and everything black. Maybe black nylon on the sides and rear but leave it open on the front, top and bottom would work to ventilate and hide the motor.
The Tanaka motors have an integral centrifugal fan which pulls air across the cooling fins on the cylinder head. Muffler wrap (or similar insulating treatment) applied to the muffler would also help ensure that heat is expelled in the exhaust gases instead of transferring through the muffler casing.

Assuming a milk-crate-based stealthing approach, it would also be a good idea to have some form of exhaust redirector/diffuser to get those hot gases out of the crate. One of the objectives of my GEBE motor/mount customization program is to get the exhaust soundwaves emanating straight down towards the ground to make the noise output a bit less directional. Seems to me like this would also be a good goal for any stealthing project.

Rack-mount vs frame-mount is probably an ideoogical debate all by itself. For my money, I like the idea of putting the motor weight down low on the frame.
However, as I said in my original post, and others have agreed, noise is the key. There are some good threads on 'dampening' the noise that comes right out of the engine/gearbox housing, but muffler improvements seem to be more elusive. Can anyone point us to a description, and possibly a video/sound clip of some dramatic noise improvements? Can we make these little engines just whine like some high-end scooters?
Harder to hide the engine in the frame. Also, tougher to make the frame mount engine quiet if for no other reason than the stock muffler on engines usually used on racks is usually very quiet. The exception would be something like a frame mount Honda, but take it from me- it's bigger yet and harder to hide.