7 Mar 2010


Some trikes are designed to use ordinary "two sided" bike wheels. This can save the builder the expense and difficulty of obtaining a single-sided trike wheel and matching axle. The problem with such abuse of ordinary bike wheels is that the results are usually much heavier. The relatively thin bike axle must be adequately supported at both ends. Such an arrangement on a trike can look rather clumsy with the extra struts or bars required to attach both ends of the axle to the machine. Trying to support anything using only one side of a normal bike wheel axle will quickly end in tragedy. The bike axle will bend or break very quickly indeed. Trike axles are always much more sturdy because they are designed to take all the loads on one side only. Though recumbent trike builders have discovered the much heavier axles of competition BMX bikes can be used one-sided with reasonable reliability.

Here is a case in point on a "sociable" trike. These machines tend to be found at seaside resorts as hire vehicles for holiday makers. I captured this one outside a coastal bike shop in the queue for repairs and maintenance. Notice how the framework overhangs the rear wheels to reach the outer ends of the axle.

Another view showing the v-belt, front wheel drive and twin pairs of pedals. I can just imagine the fights over who does the steering! Obviously intended for slow speeds well away from traffic.

Here's a Monarch invalid delta with a wrap over rear end to provide support to ordinary bike wheels. Not too offensive to the eye from this angle since the designer has managed to make the flattened bar look like part of the whole. Perhaps the extra weight is important to keep the very narrow track safely flat on the road? Anyone attempting high speed cornering on this trike might well end up in the gutter!

I don't know why, but the strange angle on that rear bar and the forks which it forms just jars my sense of decorum.  It is much too low to offer a proper hand rest for the owner. Or to aid lifting the trike over a kerb or doorstep. So it just looks like an ugly add-on to me. Otherwise a clean enough design but with unnecessary complexity in the secondary (lay-shaft) drive axle and sprockets. This feature will also increase friction and weight. Probably adding to maintenance problems if any real mileage is covered. That said, a lay shaft is a common feature of many delta, invalid trikes and even used to obtain very high gear ratios by record breaking, fully faired recumbents.

The elderly owner of this trike seemed happy enough riding along a village centre high street. With the through traffic completely ignoring the 30kph (20mph) speed limit as usual! Nothing must ever impede the mad progress of the brainless driver. This, despite the many school kids crossing the main road to buy their sweets and fizzy drinks at the local supermarket. The original, independent supermarket, which used to be on the school side of the road, was lost to competition from a new build by a major supermarket chain. One which deliberately chose to build on the "wrong" side of the road where they could "borrow" an existing municipal car park!

This neat and apparently simple Bomi has two wheel drive and a familiar frame form for the invalid delta trike.

My own Kynast was bought on a whim, for small change, at a flea market just to see how a differential trike behaved. It has a bad puncture in one rear tyre so needs my attention before getting a proper workout on the road. I only rode it around the garden once and then it became a constant nuisance taking up room in the bike shed. It has a simple joint in the middle of the main tube to aid storage. Upon loosening a bolt the trike falls in half.  I'm not disabled but have no real qualms about riding any trike built for this market. It's a machine with pedals to get about on. What's the problem? Note the scale of the rear carrier framework. Probably ideal for carrying a hot air balloon basket, I should think.

An underside view of the complexity of the internal geared hub and back-pedal (coaster) brake acting as lay-shaft to an (almost) fully exposed differential. Great fun to try turning the wheels independently and watch the little bevel gears whiz round inside the rudimentary, pressed. metal shields. The short rear chain tension can be adjusted by moving the lay-shaft axle in its cut-out slots. Plenty of reinforcing loops are provided for the rear axle though rather crudely welded in this example.

It is vital that two wheel drive axles align perfectly or friction and wear would quickly destroy the drive mechanism at the centre. The heat from brazing or welding tubular frameworks together will often produce enough distortion to cause misalignment of the two axles. This must be corrected for. A massive jig may hold the rear axle assembly together during welding. Or the axle housings carefully reamed after welding to regain alignment. No attempt has been made to save weight here. Presumably the extra weight and low centre of gravity help to ensure stability under most riding conditions. A lightweight trike can easily tilt between the ground contact points of any two wheels. Depositing the unfortunate rider onto the ground or giving them a nasty scare. A heavy trike will offer a much greater margin of safety on steep road cambers or when dismounting a pavement edge. Few road engineers give a second thought to the needs of disabled tricycle riders or wheelchair users.

Later Kynasts are far more sophisticated and far better finished:

I don't ask me why but for some reason I missed taking an overall shot of this trike in my haste to capture the detail. Note the very low step-over/step through crossbar on this model and the "town and country" tyres. Stepping astride a disabled/adult trike, before taking one's seat, has to be as easy as possible. Or it may be too much for some elderly or infirm riders to manage. Having to throw one's leg over a typical horizontal (gent's bike) crossbar would make an invalid  trike almost worthless for most of its intended owners.

Conversely, on a lightweight racing trike, a crossbar is essential to allow the rider's knee to be crooked safely over something solid as they lean right off the off the trike on the inside of fast or sharp corners. As show in the link below of Steve Avery looking very determined as he hangs off his very sophisticated trike on a corner to compensate for centrifugal force during a tricycle race:


Here's a website packed with older trikes. The link is to a Holdsworth Worthy:


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