The Cyclecar Project

MTM Scientific, Inc

The Go-Kart Cyclecar Project was inspired by the Cyclecars of the early automotive age. Many fine examples of Cyclecars were built by amateurs between 1910 and 1930 with the desire to 'get on the road' with a simple and inexpensive vehicle. Cyclecars typically have an air cooled engine, large wheels and a narrow-width profile. Many Cyclecars had a single rear wheel to reduce expenses. 

Cyclecar from MTM Scientific, Inc

We endeavored to build a DIY Cyclecar using commonly available off-the-shelf kit parts. This turned out to be surprisingly easy and inexpensive to do. Many of the components are go-kart parts, with other parts carefully selected from EBAY and other sources. For example, the main frame of the Cyclecar is a widely available and inexpensive go-kart frame from Azusa Engineering.

Front End & Steering

The front end of the Cyclecar has large bicycle-type wheels to raise the frame off the ground and provide good rolling resistance to bumps and rough road. The front wheels are spoked with pneumatic tires and ball bearings. The front wheels were originally designed for use as part of a push-type garden cart. We found there were 2 primary issues with using these wheels and tires: The bearings were not designed for high speed or rough service, and the pneumatic inner tubes were prone to punctures and leaking.

Fortunately the issues with the ball bearings were easily and inexpensively solved with a simple bearing replacement. We were able to find replacement bearings of high quality which have provided excellent service. The bearings we used are pre-packed with grease and also sealed for protection from dirt and contaminants.

The issues with the pneumatic tires leaking were rather surprising to us. We found that the fasteners for the spoke seats in the rims had numerous sharp edges. At first we tried to tape-over these sharp edges, but that did not work for long, and the tires would start leaking again. We eventually solved this problem by replacing the original inner tubes with a special 'stop-leak' type. This simple and inexpensive remedy has worked quite well for us.

Using large diameter tires on the front end required increasing the width of the front wheel base to elimate rubbing against the frame during sharp turns. We incorporated 2 design features to solve this problem: We started by choosing the largest and longest wheel spindles available. And, we used shaft spacers to move the wheels outboard as much as possible. The combination of these two design choices resulted in perfect placement of the front wheels, and provides the necessary turning clearance.

The steering linkage to the spindles is a more-or-less standard type of ball end linkages. We opted to weld our pinion arm to the steering wheel shaft for perfect placement. We chose a butterfly type steering wheel to increase the clearance underneath, which makes it much easier to enter and exit the driving seat.

Rear End & Brakes

The rear wheel shaft on the Cyclecar is a live axle. That means the entire shaft rotates with the wheels. The rear axle is supported by two ball bearings at opposite ends. We chose to use a heavy duty 1.0 inch diameter shaft. The shaft has keyway cuts at both ends. Both ends of the shaft are also stepped-down and threaded, which is a great convenience for attaching the wheel hubs.

The rear shaft would have a tendency to drift right or left in the ball bearing supports. We implemented a simple system of spacers to precisely and rigidly position the shaft. The spacers are located at opposite ends of the shaft. The spacers ride between the inner races of the ball bearings and the outside wheel hubs. (The wheel hubs are solidly attached to the stepped-down shaft ends.) This simple system of shaft spacers positions the live rear axle in a fixed location.

The rear wheels and tires of the Cyclecar are unusually large. The large size was chosen to facilitate ground clearance and operation over rough terrain. We searched extensively for suitable go-kart wheels, but they were generally expensive and limited in size. The Cyclecar wheels and tires are actually compact spares from a Ford Escort! We found these wheels readily available on EBAY, at reasonable prices and in like-new condition. The only modification we made to the wheels was to drill a  pattern of 4 mounting holes to match the hubs.

One of the most significant design choices for the Cyclecar was the type of rear wheel drive. The rear shaft is a live axle. We initially attached both rear wheels directly to the shaft to maximize traction.  Traction was indeed accomplished, but the steering was difficult for anything more than a gradual turning radius. We eventually progressed to using a single driven rear wheel drive. In this configuration the traction is still very good and the steering is exceptionally easy and sharp. Since both the wheel hubs and shaft are keyed, selecting the drive mode on a wheel is simply a matter of including a shaft key, or not. We have chosen to drive the wheel closest to the engine, on the driver's right.

The Cyclecar uses a standard drum and shoe style go-kart braking system. This approach to the brakes turned out to be ideal, since the frame is designed for easy mounting of the components. The only challenge with the brakes was securing their axial location on the rear shaft. As supplied, the brakes are intended to be attached using a shaft key and set screws on the driver's left. We found this method worked at first, but eventually the set screws would loose their grip and components would began to move. We solved this problem by adding special split-shaft collars on either side of the brake hub. The shaft collars are designed to securely grip the shaft, and they can be easily positioned to any desired location along the shaft. By using shaft collars on both sides of the brake hub, we also captured the shaft key inside the brake hub.

The Cyclecar uses a chain drive to transmit power from the engine to the wheels. A large chain sprocket is attached to the rear axle. The sprocket is also fixed to the shaft using a key. The position of the sprocket on the shaft is fixed by using another pair of split shaft collars, identical to the method of locating the brake hub. The sprockets are designed for standard Number 35 chain.

Engine & Jackshaft & Clutch

The Cyclecar uses a 4 cycle internal combustion engine with 97cc displacement rated for 2.7 HP at 3600 RPM. We purposely chose to use a small engine for overall economy, and focused on creating a drive system with good mechanical advantage to effectively use the available power. The big rear wheels and high RPM engine requires a large ratio of speed reduction to develop good low speed torque.

The large ratio of speed reduction from the engine to the wheels is accomplished using a double reduction chain drive system. A small sprocket on the engine drives a large sprocket on an intermediate shaft called the 'Jackshaft'. A second small sprocket on the jackshaft drives the large sprocket on the main axle shaft. The overall speed reduction ratio is the product of the two individual reduction ratios.

The usual challenge with using a jackshaft is the mechanical mounting arrangement. The jackshaft must be supported with ball bearings because it is rotating. At the same time the jackshaft position affects two center distances, and the chain lengths between them: 1) Jackshaft to engine, and 2) Jackshaft to rear axle. We found a mechanical kit on EBAY specifically designed for adding a jackshaft to a small horizontal shaft engine. The kit uses a rectangular steel channel with a heavy duty shaft supported by ball bearings mounted in pillow blocks. The engine mounts to the top of the channel. By using this arrangement the engine and jackshaft mount become an integral unit... only needing adjustment once to obtain proper chain length between engine and jackshaft.

The modular engine-and-jackshaft assembly is mounted to the Cyclecar frame in the location where just the engine would normally be positioned. The Cyclecar frame has a mounting plate with slots designed for an adjustable center distance to the rear shaft axle. The slots are used to adjust for proper chain length between the jackshaft and the axle. We found this simple arrangement to be rugged and easy to work with.

A centrifugal clutch is part of the power train. The clutch is directly mounted on the engine's output shaft. The clutch allows the engine to reach operating RPM before power is sent to the chain drive. We used a standard go-kart centrifugal clutch for this purpose.


The brake and throttle pedals are standard go-kart types. We included an inexpensive engine kill switch button on the frame, which the motor was designed to readily accept. The bucket seat and seat cover are also standard go-kart design.

We did make a small optional change to the front of the frame. We welded an extension on the front to serve as a foot rest. We found that pre-fabricated tubular steel parts are readily available on EBAY for building dune buggies. The front extension is actually designed to be a pre-formed grip handle.

A logical improvement to the Cyclecar design would be to add rollover protection. We actually rolled over the Cyclecar by making a sharp turn at high speed. So be careful! We found that the existing chain drive ratios provide a nice compromise between speed and power. For example, driving the Cyclecar on grassy turf was no problem, even for an adult.

The Cyclecar does not have a suspension system to reduce shock and vibration. We found that the most effective method of improving the quality of the ride was to operate with low air pressure in the rear tires. A true suspension system would be a worthwhile project to consider for improving this design. Another improvement might be to cut the frame at the midpoint and weld extensions in place to extend the overall length for more leg room. A nice paint job, or even some fiberglass body cowlings would also be worthwhile.

We have created a 37 page booklet of instructions for building this Cyclecar. The plans include 27 detailed photos. The photos are labeled to make it easy to understand and build the Cyclecar. The plans also include a complete list of parts, with useful information about where to purchase the items. As a special bonus, we have also added a helpful reference material section. If you are going to build this project (or anything similar) it will be much easier using these plans!

Free Cyclecar Plans

The Cyclecar Plans can be downloaded for free as a ZIP file download. We are making these free plans available to encourage hobbyists to explore and experiment building projects. Good luck! Regards, MTM

Download MTM Scientific Inc's Cyclecar Plans ( ~70MB Zip File)