Bicycle Sidecar Design

The Bicycle Sidecar was developed so the whole family could go cycling together.


Bicycle Sidecar









To test out the theory of a sidecar on a bicycle, a 3rd wheel was added to a road bike, to see how it handled.

The extra wheel was a 12" front wheel from a child's cycle (free from the local tip).

It was mounted in a simple plywood frame and was attached to the cycle with a 3 point mounting system. The lower mounting point was attached to the rear axle thread. The 2 upper mounts were joined to the luggage rack with cable ties.

Click for a larger image.









On the road the extra wheel made cycling 'interesting'.

Straight lines were no problem. Turning right as also acceptable whether you tipped the cycle to lift the 3rd wheel, or just let the extra wheel take the weight and cornered flat.

However turning left was a problem. The bike couldn't lean left because of the wheel and you couldn't corner flat because there was no wheel on the outside to give support.

With practice - normal cycling was possible but the left-hand bends required a much slower speed.









Next the extra wheel was loaded up with 18kg of ballast to simulate a sidecar with passenger.









This weighted set-up was impossible to ride safely.

Left hand turns became slightly easier, with the extra weight on the inside to hold the cycle flat, but everything else was worse.

Even travelling straight was difficult because the wheel would change the angle of the bike depending on the flatness of the surface it was travelling on. A change in the camber of the road could send the cycle careering one way or another. It was simply not controllable.









This sidecar problem was confirmed by some text found on the internet which read :-



"Cycle sidecars have to be of the banking type because the rigid framed type used on motor cycles tend to lift the third wheel on every downward pressure stroke of the right hand pedal. Watsonian overcame this problem by making the inner member of the sidecar a tube which was attached to the bicycle by the means of two clamps secured by wing nuts. The ability of the tube to revolve within these clamps provided the necessary hinge. These clamps were on the lower edge of a plate which was bolted to the rear spindle nut and the chainstay & seatstay of the bicycle. The rest of the chassis was made of riveted flat steel strips and held a 14 inch wheel within a copious mudguard. Two levels of wheel mounting were provided to allow for attachment to cycles with 26 or 28 inch wheels. The chassis was said to carry up to 112lbs in weight."


Quote taken from the "National Autocycle & Cyclemotor Club" website.









Further confirmation came from an article in 'Newnes Practical Mechanics' December 1950, which again was kindly provided by the National Autocycle & Cyclemotor Club.

This article gave plans for a single seater sidecar which was mounted so that the cycle could tilt for greater controllability. The sidecar was made from an angle iron frame with an aluminium bodywork.









Prototype B

Based on these experiment results and this new information, another wooden prototype was fabricated - this time with a pivot connecting it to the bike.

To allow room for feet on the pedals, the sidecar had to be mounted quite far back. The front pivot mounting was in-line with the rear axle and a second mount was 200mm behind this on a extended beam.









The first road test without any weight in the sidecar was easy. The extra wheel just bobbed along beside the bike and cornering felt normal.

The sidecar was almost unnoticeable when the cycle was moving but getting started was different because the cycle couldn't be tilted to lift the required pedal. The reluctance of the cycle to tilt when stationary was because the cycle was pivoting about the contact point between the tyre and the ground; but the extra wheel was required to slide sideways to allow this to happen, because its pivot point was higher up on the bike frame.

Click for larger image.









With the weight added to the sidecar cycling was still good. It was even possible to stand up and pedal the cycle, when going uphill.

The extra weight meant the sidecar wheel was very reluctant to slide to allow cornering but this was not noticeable when moving. The faster the cycle was going, the better it handled.

The flexing in the wooden mounting meant that when pushing hard, there was a pulsing with each rotation of the pedals, due to the inertia of the weight in the sidecar, but this could be improved with a metal construction.









Sidecar Frame Design



The CAD drawing on the right shows the frame layout with key dimensions. The angle iron was 25mm x 25mm x 3mm thick.

The height of the wheel mount was designed for the 16" wheel, but adjustment was factored in, for different towing cycle heights.

The main frame width of 320mm was chosen so 300mm wide coach-work could be made.

The 180mm distance from the main frame to the pivot was chosen to allow clearance for the pedal.

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