Torque and "torquey" have two very different meanings. Torque is a physical measurement with a precise definition. But when riders say a particular bike feels torquey, what they mean is not that it produces high torque on a dyno, but that its engine can accelerate the bike strongly at almost any rpm in its operating range.

The opposite of torquey is peaky, which means instead of having torque uniformly distributed across its operating range, its best torque exists only at higher rpm, where it can make a lot of horsepower. When you ride a peaky bike in its midrange or low-end, snapping the throttle open gets you only moderate torque, resulting in weak acceleration. But if you tap down two gears, putting the engine up at 9,000 to 10,000 rpm, the bike rockets forward because now it is operating up where it makes its best torque.

Want grunt? You’ve got it. On the Cycle World dyno, a 2018 Harley-Davidson Softail Fat Bob powered by a 114ci Milwaukee-Eight V-twin produced 82.32 hp at 4,660 rpm and 111.39 pound-feet of torque at 2,260 rpm.
Want grunt? You’ve got it. On the Cycle World dyno, a 2018 Harley-Davidson Softail Fat Bob powered by a 114ci Milwaukee-Eight V-twin produced 82.32 hp at 4,660 rpm and 111.39 pound-feet of torque at 2,260 rpm.Harley-Davidson

The result is that if two bikes—let's say a Harley-Davidson Big Twin and a Suzuki GSX-R1000—make a top-gear roll-on from 3,000 rpm, the Harley pulls smartly ahead until the Suzuki can rev up into its rpm range of best torque, at which point it evens the score and then pulls away rapidly.

These two kinds of engines represent the achievement of different goals by differently slanted compromises.

A touring or cruiser engine needs strong torque at low rpm to start and accelerate a heavy bike, so it is given quite short valve timings with almost no (or in some cases, negative) valve overlap. Such short timings run out of breath as the engine revs up, but because nobody tours or cruises at 150 mph or tries to break 10 seconds in the quarter-mile, it doesn't matter. It's a compromise. The touring rider needs and likes bottom torque and doesn't mind if the engine runs out of breath as it nears its peak rpm of 5,500.

A peaky engine results from the longer valve timings that can continue to fill cylinders well at higher rpm, such as 12,000. Short valve timings close the intakes before the cylinders have had time to fill at higher rpm, causing an engine to run out of breath. To overcome this, intake closing is delayed after bottom dead center for 50 or 60 degrees, and the intakes are made to begin opening 20 or more degrees before top center. At low and mid rpm, this late intake closing allows the rising piston to pump back out some of the intake charge it has just taken in, reducing torque at those engine speeds.

At higher rpm, this pump back does not occur because intake velocity is then high enough to just keep coasting into the cylinders even though the piston is rising on compression. As a result, peak torque is moved to higher rpm. It’s a compromise: giving away bottom-end and midrange to move the torque to high rpm where it becomes high horsepower.

In physical terms, torque is a force, tending to rotate something around an axis. It is measured as a force—ounces, pounds, kilograms—acting on a lever arm of a specified length (inches, feet, meters). This gives us the familiar pounds-feet or kilogram-meters in which torque is specified in manufacturer brochures or road tests.

When Cycle World tests a bike on its dyno, the results are presented in the form of two curves on a graph—one for horsepower, the other for torque.

Big speed requires big power: Ducati and Honda MotoGP bikes ridden by (from left to right) Andrea Dovizioso, Marc Márquez, and race winner Danilo Petrucci surpassed 215 mph this past June on Mugello’s 1,100-meter-long front straight.
Big speed requires big power: Ducati and Honda MotoGP bikes ridden by (from left to right) Andrea Dovizioso, Marc Márquez, and race winner Danilo Petrucci surpassed 215 mph this past June on Mugello’s 1,100-meter-long front straight.Ducati

The ideal toward which all manufacturers strive is to have high torque, constant over a wide range of rpm, resulting in a nearly horizontal line on the graph. Indian’s dirt-track racing engine, the FTR750, achieves this—flat, constant torque—from 7,000 to 11,000 rpm. Because horsepower is just (torque x rpm)/5252, the horsepower curve resulting from this flat torque is a sloping straight line, rising from left to right.

Real life is not ideal, so actual torque varies because such things as intake and exhaust-pipe resonance and airbox effects exist. They cause local variations in the height of the torque curve. In the case of a traditional touring or cruiser engine, the torque rises to a useful amount at as low as 1,200 rpm, peaks somewhere in the usual range of 2,500 to 3,000, and then slopes gently downward after that. Why? This is the “running out of breath” effect mentioned earlier. As the engine revs up, there is less and less time for cylinder filling, so the short valve timing and moderate port sizes of such engines cause cylinder filling to become less and less complete as the engine revs up, so torque falls.

In the case of a peaky or "light-switch" engine, longer valve timings and larger port sizes move the range of best cylinder filling away from bottom and mid, up to higher rpm where it can contribute to high horsepower. Why does a sportbike need all that power? It takes about 75 hp just to overcome aerodynamic drag at 150 mph, and the MotoGP roadracers that sportbikes imitate need every bit of their approximately 260 hp to reach peak track speeds of 210-plus mph. How big are they? Just 61ci, same as Harley's original EL "Knucklehead" of 1937.

While the rider on the torquey bike can stay in top gear pretty much all day, to get the best out of a peaky engine requires constant gear changing to keep the engine in its rpm range of best torque.

How can we have both? One promising technique is variable valve timing, which has potential to give us both stump-pulling low-end and strong top-end that doesn’t wheeze out. A great many smaller auto engines and a few motorcycles have VVT.

But when the late, great Don Tilley built bikes for the AMA’s spec Harley-Davidson 883 roadracing class, rules didn’t permit such a radical solution, so he had to find a compromise that won races. He saw that “the young fellows who loved those big numbers” weren’t winning with peak power, putting all their torque up high and losing time in slow acceleration off the turns. And the “stock-is-best” conservatives weren’t getting anywhere either. Their down-sloping torque curves came off the slow turns really well but lost out on the straights.

That goal was a torquey engine—the feeling of good acceleration at any engine speed—with high averaged torque across the rpm range actually used.

Don got to work boosting torque everywhere in the range of rpm actually used on the track. Valve timing was optimized neither for the bottom nor for the top, but rather for the broad middle. Valves and ports were streamlined but not increased in size. The smaller the intake port, the higher the intake velocity, keeping the fuel-air charge in motion all the way to top center, producing fast, efficient combustion. Higher compression boosts torque at all rpm.

“We won a lot of races with averaged horsepower,” he told me. That goal was a torquey engine—the feeling of good acceleration at any engine speed—with high averaged torque across the rpm range actually used.

Torque by itself is just a force, like the torque employed to tighten a bolt or the force on your hand as you lean against a wall. It can’t accomplish anything until it is combined with rpm, when it becomes a force acting at a speed.

The “torque people” are right when they say that torque is the force that accelerates your bike. The “horsepower people” are right when they say that the force accelerating your bike has to be capable of speed, that is, horsepower is torque times rpm, divided by a constant. Bikes with a lot of torque only at low or moderate rpm can’t make the power to overcome aero drag at higher speeds.

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