Five For Nineteen: A Few Questions (And Answers) For The New Year

Twist that thang. M4 ECSTAR Suzuki Superbike rider Jake Lewis has a tight grip on the go-fast control.

1. Why do motorcycles have twist throttles?

Your daily driver, SUV, pickup, or even your UTV has an accelerator pedal right there on the floorboard. Your ATV or snowmobile has a throttle lever on the right handlebar that you operate with your thumb. And your personal watercraft has a similar throttle lever that you squeeze with your index finger.

So, why does your motorcycle have a twist throttle? Control and modulation are the answer. Ask any motorcycle road racer, and they’ll tell you that throttle control is one of the most important aspects of racing. It’s why throttles have evolved from being cable-operated mechanisms to far more precise “throttle-by-wire” setups. A gas pedal on a bike is a bad idea because your hands, even in a glove, have way more feel and better control of minute adjustments than your feet do. And a thumb-lever or index-finger-trigger is almost as difficult to modulate as an accelerator pedal, especially over a long distance or after many laps. Twisting a throttle is precise and, because of that, preferred on motorcycles.

2. Why do all modern road racing motorcycles have one rear shock instead of two?

The obvious answer is cost. Manufacturing two rear shocks costs twice as much as one rear shock in many instances. But if you’ve ever bought a set of twin rear shocks for your vintage Honda CB450, they don’t cost anywhere near as much as that aftermarket rear shock that you just bought for your Suzuki GSX-R1000. So, cost isn’t the only reason that modern racebikes have one rear shock. Performance is the real reason. Single-shock rear suspensions began to take over the sportbike world in the 1980s because, with their associated linkages, they proved to be far superior. For one thing, no matter how well-made a set of twin rear shocks is, there are going to be manufacturing differences that, however minute, cause those two shocks to perform slightly different from one another. Also, a single rear shock has less “stiction” than two rear shocks, so one is better than two in the case of rear suspension.

3. Why do all MotoAmerica racebikes have double-sided swingarms?

The whole purpose of a motorcycle swingarm is to support the rear wheel and pivot around an axis attached to the frame or engine so that the rear suspension can compress and extend.

Traditionally, swingarms are double-sided, with two bars or “pipes” that extend back along both sides of the rear wheel to the rear axle. Endurance road racing led to the development of the single-sided swingarm, a design that helped facilitate quick rear-wheel changes because the wheel was attached by a large single nut, or at most, five lugnuts like on a car, and there was no need to remove the axle, chain, or fiddle with the rear brake to extract the wheel.

MotoAmerica is sprint racing, so lightning-quick rear-wheel changes are not necessary because pit stops for fuel or tires are not required. In addition, modern technology has led to “quick-change” mechanisms for double-sided swingarms that, while not still not quite as fast as rear-wheel changes on single-sided swingarms, are “fast-enough” to get the job done.

However, there are currently a couple of manufacturers who do offer sportbikes or Superbikes equipped with single-side swingarms. Several Ducatis, as well as KTM’s 1290 Super Duke models, spring to mind. And, while we thought there might be a Ducati Panigale V4R Superbike on the grid in MotoAmerica Superbike in 2019, so far, that hasn’t materialized, meaning that every motorcycle racing in every MotoAmerica class, at least for now, is equipped with a double-sided swingarm.

The reason is cost. Generally, bikes that are equipped with single-sided swingarms are higher-end motorcycles like the flagship Ducati Panigale V4R, and that’s because single-sided swingarms are much more expensive to manufacture because the design is much more complex.

Also, removing the rear wheel from a single-sided swingarm is quicker, but you’ll probably need special, proprietary tools to remove that huge, single fastener holding it on along with a special paddock stand designed to lift a single-sided swingarm-equipped bike instead of a common, run-of-the-mill double-sided swingarm stand.

Weight is also an issue. Single-sided swingarms are thick masses of material that, even if they’re made of magnesium; carbon fiber; or some other exotic, lightweight, unobtainum material, still may not be as lightweight as a more traditional, double-sided swingarm.

Chain reaction. The business end, and side, of Toni Elias’ Yoshimura Suzuki Factory Suzuki, with a chain and sprockets delivering more than 200 horsepower to the rear wheel.

4. Why do all MotoAmerica racebikes have chain final drives?

While the vast majority of motorcycles send power from their engines to their rear wheels via a chain-drive system, chains are not the only way to get the job done. Some manufacturers, including BMW, Moto Guzzi, Honda, and Suzuki offer touring-oriented motorcycles with shaft drives, while other OEMs, including Harley-Davidson, Yamaha, and Kawasaki, have several cruiser models that feature belt drives.

However, in Superbike racing, chain-drive is omnipresent, and here’s why. Track configurations dictate that adjustments must be made in the gearing of racing motorcycles in order to have the correct ratio that nets the right rpm and extracts maximum horsepower from the engine. The best and easiest way to change the gearing on a motorcycle is to increase or decrease the number of teeth in the rear sprocket, the front (or countershaft) sprocket, or both. Most race teams are equipped with an assortment of sprockets – particularly rear sprockets – and changing them to achieve a different gear ratio is as easy as changing the rear tire.

With a shaft-drive motorcycle, changing the final gear ratio is either not possible or next to impossible because shaft drive gearing is fully enclosed in a complicated final drive assembly. That assembly and the associated gears are proprietary to the manufacturer, meaning that there are no aftermarket companies who make different-size gears the way there is a plethora of aftermarket companies who make different-size sprockets. In the case of belt-drive motorcycles, theoretically you could change the front and/or rear cogs of the belt drive, but like shaft-drive gears, different-size belt cogs are not readily available like sprockets are.

Also, in the case of shaft-drive motorcycles, the shaft system transmits more of the shock absorption to the bike and rider, particularly when accelerating or decelerating. Shaft drives also have a tendency to lock the rear wheel if the downshifts don’t match the road speed, which is obviously not a good thing on a road racing motorcycle.

Belt-drive is fairly common in cruiser bikes, but it’s non-existent in sportbikes and Superbikes. That’s because a rubber belt is just not as strong as a steel chain, and belts can’t withstand the kind of horsepower that a racebike generates.

5. Why don’t MotoAmerica racebikes have automatic transmissions?

All of the motorcycles competing in MotoAmerica’s various race classes are equipped with standard transmissions that feature six forward gears. And, even in this era of sophisticated electronics that operate no-clutch quickshifters and autoblip fly-by-wire throttles, the transmissions on racebikes are not automatic. A left-hand-operated clutch lever and a left-foot-operated shift lever are still required to get a MotoAmerica racebike moving around the racetrack. Motorcycles equipped with automatic transmissions do exist, and scooters have featured continuously variable transmissions (CVT) for decades. But MotoAmerica racebikes have standard transmissions because the OEM street-going versions of those motorcycles also have standard transmissions. And standard transmissions are not only less costly to manufacture, but they are also more efficient than automatic transmissions.

That said, however, some MotoGP racebikes have “seamless” transmissions that do not momentarily go into neutral when changing from one gear to the next. They engage the next gear ratio while the current ratio is still driving, so there is no “clunk” when shifting. It is technically still not an automatic transmission and it has also not yet trickled down to production motorcycles and then to MotoAmerica racebikes. But, seamless motorcycle transmissions may someday become the norm in the MotoAmerica paddock, so stay tuned.