Rat Rods, friction drive moped kit.


May 11, 2020
Rat Rods-
A simple way to convert most available standard bicycles, such as a cruiser, hybrid, mountain, road, trike, etc. Turning an existing bicycle into a fully functional moped is only a couple bolts away for a Rat Rod kit.

Adjustable clutch action, gives this friction drive precise depth pressure and control as well as consistency.

An ADA centrifugal clutch kit is also available to install and allows the kit to idle at a stop with out having too raise the engine to clear the tire.

Uses standard Zenoah 2 stroke hobby engines (22.5cc-34.5cc) resulting in an easy to start, run and maintain power plant.

Paired with a high quality go ped 1 liter gas tank, the result is a moped with reliability, distance, and presents a clean and light alternative to other moped kits.

A disadvantage with friction drive is the slip issues occurring when water meets in between the surface of the spindle and tire. Adjustable clutch pressure
helps, but assisting the motor during wet conditions is the most effective method.


What bicycle should I use?
A steel framed bicycle or a higher quality aluminum is fine. You will need to switch to hubs that use a nut n bolt on axle or use 5mm grade 8.8 thread-all if you decide to keep the skewer for mounting the bottom brackets to the axle. A Quick release will vibrate loose, and could result in the wheel popping off the fork mounts.

If a front shock is present, then the rear moped unit is called for, and vice versa. a slight cost difference, as bracket extension
A cushioned and spring seat will also make the ride more enjoyable.


Requires no to minimal amount of modifications to install, if caliper brakes are used, one will need to be removed and replaced as the front mounted or rear mounted unit requires removal of corresponding brake to mount to use. I am however developing a universal mount to accommodate caliper brakes.

Disc brakes, or drum brakes are preferred as they are more effective.
The stopping forces used for a bicycle going faster than an average non motorized bicycle speed wears these brake systems (caliper more than others) out as well as prematurely, the rims.
Running two brakes (disc or drums) with this system will require a cable splitter or brake lever with dual cable output since clutch lever takes brake lever position(Inquire for options).

My advice is to install a front drum brake hub if caliper brakes are used. This can be ran as a solo brake or split cable and the caliper ran on the non motorized tire. Be sure to include an in line barrel adjuster if caliper is used.

Sizes from 1" - 2.5"
Rim sizes 16-20 (modifications maybe needed, I haven't gotten to mount on this yet) 24,26,27,29 are standard.

Which ever, front or rear mounted. It is important the drive tire be smooth as possible, with the very center a solid contact surface if possible. A higher density rubber compound will last longer as well, as it's more resistant to the wear effect.

Kevlar lined tires help with the stiffness and the puncture resistance helps keeps you staying on the road.
A trip around town or running errands can become lengthy due to a flat tire. (A dual kick stand leg can help tremendously in these situations)
Since I've switched to Armadillo 700x32c anti flats, I haven't had a flat in the nearly daily use of this friction drive and the wear from the friction driving has gotten me over 800 miles in 4 months no problem, with a couple hundred at least left go.

Like most vehicles, a reliable and quality engine is paired with the importance of quality tires.
Width is important for a couple reasons. One, it allows for a wider and better contact surface during friction drive. two, it will be a smother and more enjoyable ride. Three, it will absorb more shock rather than directing it through the rims and spokes possibly resulting in structural integrity issues or complete failure.

3rd bearing support

This kit can be ordered to fit with a 3rd bearing support, with out modifications can fit up to a 1 1/2or a 38mm tire.
Modifying a bigfoot branded 3rd bearing supported spindle in a .625 size can increase the tire width to about 2 inchs.(remove the end of the spindles diameter with sand paper until it fits the goped sport bearing, 15mm). But a method of increasing the spindle diameter on the contact surface is ideal for a higher top speed. Currently developing methods for this, and possibly seeing how much custom milled spindles would fetch for.

All units can be ran without 3rd bearing support.


Options, kits, engines
• Kit "Rat Rod M.1A - fits 1 -1/2 or 37mm tire great for road bikes and hybrids. Works on older cruiser style(huffy, Raleigh, etc) can accommodate the 3rd bearing support, with no modifications.

• Kit "Rat Rod M.2A"
For use on hybrids with 38mm -50mm, or narrower cruiser or mountain bikes with no more than 2" width
Will accommodate modifications for extended bigfoot spindle, allowing 3rd bearing support on 2inch wide tires.
Comes with no support bearing.

• Kit "Rat Rod M.3A"
For use on bikes with tires bigger than 2".
Will accommodate tire sizes up to 2-1/2" and offers no spindle support.

kit options
I can order a zenoah engine (22.5 -29cc )and a gas tank, spindle and have the unit ready to bolt on the bike. The stock zenoah muffler will not fit this kit, a CY/rovan muffler fits correctly and will be included instead.
10% parts cost included in price reflect installation. I prefer a newer zenoah model with dual bearings on the spindle drive side, this will increase engine life with no 3rd bearing.

No engine kit:
You can order the engine, spindle and gas tank yourself and do the install as well. This will save you a little bit of money and you either benefit from having to do the install, or may not have the handy skills to do such a thing yet.

Both kits come with struts, axle adapters, frame, universal mount, engine spacers and gas tank spacers, thumb throttle(with ready to install linkage carb mount) and clutch lever with cable also included. Full detail manual included.

If interested, can do a close, matching paint on the frame and pieces, extra cost reflection in total price. Otherwise, standard clear coated with black gloss enamel on the 6061 aluminum.

I do not warranty the engine, gas tank, spindle, throttle, or clutch lever.
Lifetime Warranty on the moped unit includes frame, struts, clutch arms, universal mount. Covers wear and tear.
No coverage on engine,carburetor, spindles or gas tank.

Why I choose Zenoah
CY engines and rovan are cheaper alternatives, but you do get what you pay for. Zenoah is high quality and certainly worth the money.
A couple of cheaper test engines have given me issues. From bad seals out of the box, shredding rings within 100 miles and having to drill out a carb pump vacuum hole in the jug because it was filled in with castings.
The cheap engines have been cheap, with one that lasted a couple months only to strip a crankcase case bolt upon inspection.
My zenoah f270 runs smooth and has plenty of power for my 60 pound bike and 160 pound personal. Out of the box running, minor carb adjustments for the high altitude and has given myself months of reliable service

Two ways are use to start the engine, either by pull cord or by dropping the clutch.

I recommend pull cord, and only dropping the clutch when it's been used in the last 20 mins and is not to cold.
These engine should warm up for at least a minute, a couple on cold weather. Correct engine temperature is optimal.
1. Engage the clutch, lifting the engine off the wheel. Keep hand on clutch lever! Put the engine into choke position (refer to engine manual for full run down), prime 2-4 times, pull the cord until an attempt to sputter alive, open choke and pull until the engine idles.
2. Being observant, mount the moped and start to with a couple pedals to get going.
3. Depending on spindle size, engage the engine by releasing the clutch, at about 5-8 mph.(dropping clutch at a dead stop to accelerate WILL wear a tire out fast)
4. Gentle throttle acceleration is key with friction drive mopeds. To much will rotate the spindle faster than the relative speed of the tire and result in premature tire wear. If you notice a surge in rpm(engine "revolution per minute"), then ease on the throttle, if a lot of "slipping" is occurring, adjust clutch spring pressure, or replace worn down spindle, or resurface spindle for more grip.
5. Do not try to run the engine at a high mph with no throttle (engine braking). This will cause seal damage or prematurely run down piston rings. Disengage clutch when coming to stop or slowing down with no open, or partial open throttle.
6. Before shutting off, allow engine to stabilize to normal idle for at least 30 seconds. (Not included in the kit, but a handle bar kill switch or button is recommended.
Dropping clutch
Get to at least clutch engagement speed(5-8 mph), release clutch and engine will catch and start. If engine seems to not want to start using this method, simply pull start, or refer to step 4, "slipping".
in conjunction with the drum brake.

If interested, Contact me via private message or email @ toemas.smith@outlook.com

We can discuss the bike, and its intended use to help build a kit to fit right and send you on the road.


May 11, 2020
I will be updating this thread with more pictures. I needed to get some of the build in its entire complete form, but I was in a rush that day and now we have 18" of snow in the forecast! No riding till the weekend! Any questions please feel free to ask.


Active Member
Sep 11, 2021
Wow thats an incredibly well designed kit! Like the third bearing! I had a 24cc Zenoah in a gasser model heli.
Ran like a Rolex and made good power for its displacement. Cant imagine a better engine for your kit. Im impressed!


May 11, 2020
It took trial and error to get there, lot of shop time!
Making something practical, simple, but with some serious features.

I love the clutch design, and it uses steel bushings press into the aluminum to protect it and make it last longer on the pivots, using marine grade grease the maintenance is like once a year at the most.

I also updated the post, for those who like centrifugal clutch setups, this can also run those ADA no problem. No getting off the bike to raise or lower your engine. You can still just engage the clutch lever.