Outside the Box

INSIDE TECH By John Sharrard Outside the Box

Other than constantly refining electronics and how they interface with our modern motorcycle, the basic architecture hasn’t changed much concerning the bikes beneath us. The engine, be it gas or electric, is basically between our knees nestled in a main frame. The rear wheel moves vertically up and down (well, in a slight arc determined by the length of the swingarm) attached to the frame to isolate us from bumps while we ride. The fact that the suspension is less and less effective as the bike leans over farther and farther is an engineering challenge that we really have yet to overcome. The front wheel turns left to right on bearings in the front of the frame, and braking duties are handled almost exclusively by single or dual discs squeezed by calipers. Fuel, if the bike uses internal combustion, is usually carried above the engine, which reduced the need for a fuel pump back when bikes were carbureted. As a rider, we sit just behind the fuel tank on a small seat on the frame, holding onto handlebars bolted to the front wheel and suspension. This general layout has been in place for almost 100 years now, which, on one hand could point to a possible lack of real progress in the advancement of

50 Inside Motorcycles

the motorcycle, but, on the other hand, if it ain’t broke... don’t fix it!

Racing or physical competition has been the measure of human and mechanical progress since early Greece, and bikes, like people, continue to get faster and faster as our brightest engineers continue to refine this fairly standard package. In this article, let’s look at a couple different ideas and different ways that some designers have employed to make their bikes a little better while thinking, even a little bit, outside the box.

Chain vs. shaft drive. The vast majority of motorcycles use a simple multi-plate link type chain to transfer power from the engine to the back tire. Since the engine is fixed in the frame, and the rear drive wheel moves up and down anywhere between 125 and 300 millimetres (roughly 5 to 12 inches), some method of power transmission must be employed to function while the rear tire is in motion. The chain drive in this application has worked quite well for years and years.

Pros: The chain drive system is relatively light in weight and fairly reliable. Not perfect mind you, but if maintained, it can give a long trouble-free life. Also, final drive ratios are quite

easy to change, as most aftermarket suppliers will offer two or three front (or countershaft) sprockets, and sometimes as many as 10 or 12 different rear sprocket options in different diameters, which we relate to by changing the number of teeth on the front and rear sprockets. This ability to ‘tune’ the final drive ratio makes customizing the bike’s power delivery very easy, which is essential in a racing application to adjust the top speed and rate of acceleration to different course lengths and layouts. Also, drive chains are very simple to maintain by the average enthusiast, who can clean and lubricate them easily.

Cons: They do need maintenance. If you neglect the chain and the quality of the chain is low, or the conditions are harsh, it can stretch and ruin the sprockets, or even fall off or break, stranding the owner. Chains are currently made from steel, so they rust easily. Not many external parts on a motorcycle are unpainted steel, so the chain needs extra cleaning and lubricating when compared to the rest of the motorcycle, especially after riding in the rain.

As the alternate idea, some cruisers and sport touring machines will use a shaft drive system in place of the drive chain, which is then incorporated into the rear swingarm or suspension system. Pros: Clean and tidy. No dirty or rusty chains to worry about that constantly want oil or grease applied which then flies off all over the tire or rear of the motorcycle. The shaft drive system incorporates gears and bearings hidden inside the swingarm to transmit power from the engine to the back tire. The parts are all neatly inside the sealed, painted swingarm and can run in a bath of oil or grease to eliminate the concern of rust or road contamination, providing the rider with one less thing to worry about. Cons: The shaft drive system with its robust swingarm, bearings, shafts and CV joints, is heavy. The nature of all these parts sealed inside their housings, mean that ratio changes are difficult if not impossible. This doesn’t exclude them from competition, as many of my customers with vintage BMW and Moto Guzzi race bikes can attest, but it makes it very difficult to change this final drive ratio for different racetracks. With a shaft drive, we have removed the highest-maintenance-requiring device on the bike, so riders with limited to no mechanical ability need not worry about constantly cleaning and lubriating this portion of the motorcycle. The shaft drive also does not ‘stretch’ over time requiring a loosening of the axle and adjustment of the chain tension, which can be stressful if the owner isn’t confident in this process,

Front fork design. Another system on a motorcycle that has varied away from a long-held standard is the design of the front suspension. Again, we see the vast majority of motorcycle manufacturers use a sliding inner and outer tube design to permit wheel travel over the bumps while providing bearings and an axle to hold onto the spinning front tire. The lower tubes will hold the brake caliper or calipers while flexible lines allow us to communicate brake fluid and electronic wheel speed sensor data back up to the suspended components above. The damping control systems have awkwardly been stuffed inside these small ‘fork’ tubes, to control unwanted oscillations after bumps and road irregularities have been encountered. This inner/outer tube design with dampers inside now needs seals and bushings to permit this motion while containing a lubricating and damping media, more commonly known as oil. Having oil so close to the

Opposite page: This Moto Guzzi uses a shaft drive in conjunction with a single-sided swingarm. Above: The front shock on BMW’s Telelever front suspension can be seen back in behind the fork.

front brakes and the important front tire has always been a challenge to designers and leaks still occur and need to be addressed quickly for the rider’s safety.

Pros: Everyone has been employing this system for so long that it is very advanced in its understanding and function. Damping and spring cartridges are available to insert inside these tubes to give much better control and adjustability if the rider desires or requires it. Cons: As the sliding fork suspension system cycles from fully extended to fully compressed, the delicate rake and trail measurements up front reduce and the bike becomes less stable, changing the handling quite significantly. Chassis designers must compromise the design and hope we don’t really notice the imperfection as the suspension cycles.

Well, BMW has an alternate design that offers a work-around to this problem. Coined the Telelever system, it still employs the simple slider bushing fork design to permit wheel travel while giving a spot to mount the handlebars, but the damping and preload system, much like out back, is contained in one shock absorber mounted just under the fuel tank. The real change, however, is in the way the shock is mounted between two arms that bolt to the frame behind the shock, and the upper and lower fork tubes ahead of the shock. Now, when the rather conventional forks compress, the bike’s geometry doesn’t get steeper reducing stability, it actually relaxes the fork angle adding stability as the suspension compresses.

Pros: The bike as mentioned above becomes more confidence inspiring through added stability as the suspension compresses, which aids to the enjoyment of the riding experience. The bike is also far less prone to brake dive, which is a limiting factor that aggressive riders must deal with. Conventional fork design dives like crazy when the brakes are applied hard, dramatically reducing or eliminating any suspension travel left over to deal with corner entry bumps. The BMW Telelever design is not affected by this as much, so bumps are still quite manageable even while braking aggressively. Cons: Like shaft drive, this system is heavier for sure, and the newly required shock takes up valuable room where the engine and fuel tank usually meet, which required a rethink of component placement.

Next month, we can look at Ducati’s frame design and KTM’s different suspension systems on their off-road machines to see how they are looking outside the design box! Until then, ride safe and keep it between the ditches! IM