Getting the perfect fit

A sidecar combination is not simply a chair bolted on to the side of a motorcycle. Mick Payne explains the principles behind setting up a sidecar.

As you will know from last month’s Bit on the Side, Keith Wash passed away before Christmas. He was a good engineer who has left a legacy of which most people involved in sidecars will be aware.

I’d known him for many years and when I originally met him for a feature in Motorcycle Sport I was riding my first ever outfit, an MZ ETZ 250. This was bought brand-new as a complete unit, put together by the guys at Wilf Green’s and supplied by Mick Surman of Aylesbury.

Keith chatted about the Hedingham’s torsion bar suspension, lead, toe in and lean out. As a fellow engineer and designer I understood the principles of torsion bars but the rest was meaningless to me. From Keith I learnt the arcane basics of setting up a sidecar and these instructions have never left me. These relate to sidecars on the left but the principles apply to all fitments.

Imagine arbitrarily bolting a third outrigger wheel to a motorcycle with no concern as to where it goes. The logical position might be to line the rear wheel of the bike and the sidecar one on an imaginary line through the rear wheel spindle and set up parallel to the machine’s centreline. This is how it was done at first, but it didn’t take too long for charioteers to find that if the sidecar wheel was moved forward a few inches then stability would be improved. This is lead.

Toe in relates to the position of the sidecar wheel, too. In this case it applies to whether the wheel is in line with the bike wheels, as the chair wheel is undriven and therefore causing drag it would cause the machine to pull to the left. The answer is to set the wheel steering very slightly towards the bike, only by a small amount, though. Then, as the rear wheel pushes the bike forward, the effect of the sidecar trying to steer towards the motorcycle gives the feeling of everything running in a straight line.

Chatting with David Angel of F2 Motorcycles, his opinion of setting up a chair is: “I have to consider the rider’s weight and whether they regularly carry a sidecar passenger.” This will also affect the last variable, that of lean out; this is how much the bike leans away from the sidecar.

Imagine David’s dilemma or that of any other sidecar fitter – the rider might weigh anything within the range of human beings and there may or may not be a passenger, payload or dog in the chair.

Of course, roads generally aren’t constructed flat. Before the days of the potholed surface, roads were constructed with a water shedding crown form thanks to the Romans. This means that if a bike and sidecar were constructed parallel, then the bike would be leaning leftwards because of the camber. Lean out compensates for this so the bike should have this small amount of adjustment dialled in. All these adjustments are arbitrary and are down to the individual rider/driver; probably no two sidecarists will agree.

Thanks to David Angel for his help and I can recommend visiting his website simplysidecars.co.uk for further information.

Somewhat predating Mr Payne’s first adventures with a sidecar, here is Mr McFarlane of McFarlane Ironfounders, Chapel Lane, Wigan, at the controls of his 1913 Triumph combination and showing the very limited lead used in the early days of sidecars.

These photos show the beams that David Angel had made up in order to set up sidecars. Here they are being used to check a new Chang.

A diagram in an old Velorex fitting instruction leaflet showing toe in and lead…

… and lean out.