Jerry Thurston column
For the last 100 years, the final drive chain has been the prevalent way of transferring drive to a motorcycle’s rear wheel.
Over the last 30 years, I have been lucky enough to ride motorcycles that feature many of the types of transmission that have been developed.
Perhaps the most delightful is the simple belt drive, relying on sheer engine torque to pull you from walking speed to whatever the engine will rev to. Provided you are fit enough to paddle away with the valve lifter engaged, once this is dropped and the engine fires, it’s a magical motorcycling experience.
Quirky but fascinating to ride is the Royal Enfield twospeed with the ‘tram handle’ gear lever. When properly adjusted, this allows you to start the bike in neutral and then ease the handle back to take up the drive and get going. Once underway, the handle can be shoved firmly into top gear and you are off, with the combination of a big V-twin engine and two speeds making light work of whatever comes your way.
My favourite of all, though, has to be the Zenith Gradua, with its version of constantly variable belt type transmission. The rider winds a tank-top handle to operate a drive pulley that closes or opens, allowing the belt to ride higher in the V for longer gearing or lower for shorter, all this while simultaneously altering the wheelbase to keep constant belt tension. The feeling of having the motor in its sweet-spot and then altering the gearing for seamless acceleration is one of vintage motorcycling’s seminal experiences.
One of the great joys of a hand change motorcycle has to be mastering the across the tank clutch-less change, at least on one of the gated versions. I revelled in doing this on my Scott Powerplus replica, but sadly the gate-less Sturmey-Archer system, with the low lever attached to the seat tube, makes this an impossibility on my Norton.
On my Velocettes, I experienced the early positive stop gearboxes. I have to be honest here, although they were an improvement over the old hand change, I always found them to be slightly cumbersome, thanks to their long gear levers, where I found that
I had to physically move my leg to operate the long throw mechanism.
It’s almost impossible to criticise more modern gearboxes where you can simply ease the throttle, flex your ankle and it’ll change as fast as you can move. Note I say modern – they weren’t all featherlight. Mid-1970s boxes could be clunky, and after a couple of hundred miles on my BMW R90S, the top of my foot was always sore from changing up.
You don’t need to be a mechanical genius to realise that making the gear change faster and faster is a good thing, as the longer it takes to shift the ratios the less time you have with the motor either driving or helping to slow the machine. Prior to the advent of modern ‘quick-shift’ technology, racers had given this some thought – I cite the crude but surprisingly effective quick change mechanism often seen on two-speed grasstrack bikes or sprinters… A big spring that flicked to the second ratio when it was released.
Today, things are sophisticated to the extent that many machines have a quick shift up and an auto blip to match the revs to the speed when going down the ratios.
Over the last 100 years, motorcycle transmission systems have become increasingly technically refined. So, why do motorcycle manufacturers persist in using what appears to be an outmoded method of power transmission… The conventional chain.
Chain is outmoded possibly, ancient certainly. Da Vinci was reputed to have sketched a prototype roller chain in the 1500s, and at the turn of the 19th century a chap called James Fussell patented his variant, and the chain we all know, the Renold patent design, dates back to the 1880s.
Within the various ways of getting power to the rear wheel, the answer surely has to be the smooth quiet belt, although V-type absorbs a fair amount of power. In the early 1980s, Harley -Davidson put into production a new version of an old idea and revisited the concept of the belt drive, this time with a more efficient flat belt with ‘teeth’ that locked into a corresponding pattern on the ‘drum.’ Perhaps surprisingly for what appears to be a great idea, the take-up has been poor – only a couple of other manufacturers have followed suit and then only on some models.
Aside from the perennial and grubby problem of keeping a chain adequately lubricated, at least so far nothing better has come along… relatively lightweight (especially if you stump up about £500 for a titanium version) and the capability of transmitting a huge amount of power with relatively low frictional losses means the chain stays in vogue.
“It’s almost impossible to criticise most modern gearboxes where you can simply ease the throttle, flex your ankle and it’ll change as fast as you can move.