The Towing Cycle


The towing bicycle was an old 1970's Peugeot road bike fitted with some newer parts to make it more suitable.

The Towing Cycle

 

 

 

 

 

 

 

 

The bike in its original state was not suitable to tow the sidecar.

The brakes were poor, the tyres were too thin, and the 5 gears were all too high.

The old Bike - Click for a larger image.

 

 

 

 

 

 

 

 

The bike was rebuilt with some new wheels and larger 'touring' tyres.

The new wheels incorporated drum brakes and a hub gearbox at the back.

 

 

 

 

 

 

 

 

The gearbox was a Shimano Nexus 7. A seven-speed hub gearbox with ratios of :

 

 

 

 

 

 

 

 

The rear sprocket was selected to have 21 teeth to give ratios low enough to tow the sidecar and yet high enough for commuting (the bikes other use).

A typical mountain bike has ratios from 28" to 84". This number refers to the equivalent wheel diameter with a direct drive from the pedals. The Nexus 7 didn't have such a broad range but the 7 gears given with the 21 tooth rear sprocket are shown on the right.

 

 

 

 

 

 

 

 

These gears were OK for commuting but were still to high to tow the sidecar uphill. So the front chain-wheel was reduced from 46 teeth to 42 teeth. This gave new gearing as shown on the right.

Old 46T Chain wheel

New 42T Chain wheel

 

 

 

 

 

 

 

 

As the sidecar experiments showed, the sidecar would need to pivot against the cycle for the bike to handle properly. The pivot was a 12mm diameter steel bar connected to the bike at 2 points. However the pivot needed to be located directly under the chain-stay to avoid it clashing with the pedal.

 

 

 

 

 

 

 

 

Click to enlarge

The main mounting used the back wheel axle. This mounting point was a strip of 3mm steel plate with a steel block welded in place and drilled to take the 12mm bar.

Once attached on the bike the bar was used to twist the metal strip until the bar was directly under the chain-stay.

The front mounting was a clamp, which was positioned and angled so that the bar was horizontal. This clamp was positioned as far forward as possible without obstructing the pedals or the rear wheel.

 

 

 

 

 

 

 

 

The rear mount would take the main weight and motion of the sidecar. The front mount was designed to stop the sidecar twisting in towards the bike during speed changes and to stop the sidecar tipping nose-down under braking.

This image shows the clamp set. Note the front mount (shown at the top) had a v-groove cut at the correct angle to suit the chan-stay angle whilst keeping the pivot bar horizontal.

 

 

 

 

 

 

 

 

Click to enlarge

This photograph shows the assembled pivot. The pins and washers were required to stop the bar and sidecar sliding out of place.

 

 

 

 

 

 

 

 

The final bike and sidecar pivot were tested with the ballast load.

Performance was good with much less movement than with the wooden test chassis.

The gears were low enough for a reasonable incline, but more thorough testing would be needed to see if they would cope with all circumstances.


 


Update

After several hundred miles of use, the conclusion on the towing cycle was that it was good in many ways, but the rear hub was disappointing. In particular the back-pedal brake was difficult to use. The gearing of the rear hub was also slightly unpredictable, with some gears feeling rougher than others, all in all not the best solution.

In fact the sidecar worked just as well with an old Hercules Balmoral with 3 speed hub gear.


 

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