Attempting To Understand Superbike Torque Curves

Comparing apples with oranges, Aprilia RSV4 vs. Ducati V4 S vs. Ducati V4 R.

dyno chart for RSV4 1100, Panigale V4 S and Panigale V4 R
This chart compares the horsepower and torque output of a 2019 Aprilia RSV4 1100 Factory, a 2019 Ducati Panigale V4 S, and a 2019 Ducati Panigale V4 R, as tested earlier this year on Cycle World's Dynojet dynamometer.Cycle World

Sometimes things just don't make sense. Here are horsepower and torque curves for three 2019 superbikes: Aprilia RSV4 1100 Factory, Ducati Panigale V4 S, and Ducati Panigale V4 R. At first glance, I saw that red hp curve of the V4 R sagging 20–24 hp below the other two hp curves from roughly 7,000 to 11,000 rpm, with only the "red rush" of the R model's higher rpm beyond 13,500 to justify it.

And looking below at the torque curves, there is the V4 R giving up 12–15 percent to the V4 S and more like 18 percent to the admirably robust curve of the RSV4 in the range of 7,000 to 9,000 rpm, but continuing past the other two from roughly 13,500 to the V4 R’s signoff at approximately 15,800.

Yet, at the same time, Cycle World's testers really liked the apparently torque-weak V4 R, choosing it as "Best Superbike of 2019." How could that be? Were they mesmerized by the R's racy gleam? Or was I missing something important that was lost in these curves?

Then I had another thought: Let’s look up the overall gear ratios—crankshaft to rear wheel in top gear—for all three. Here they are:

Aprilia RSV4: 5.1 (engine revolutions for each rear wheel rotation)
Ducati V4 S: 5.7
Ducati V4 R: 6.3
Ducati Panigale V4 R dyno
The Ducati Panigale V4 R made 204 rear-wheel horsepower—more than the Aprilia RSV4 1100 Factory and the Ducati Panigale V4 S—and 76 pound-feet of torque, which is fewer than produced by either the RSV4 or the V4 S. But there’s more here than meets the eye…Jeff Allen

Aha! The superbike homologation special V4 R is geared down 21.5 percent more than the Aprilia and 11.1 percent more than the streetable V4 S. Because it is torque at the rear wheel that actually accelerates the motorcycle, I decided to "normalize" the V4 R's torque curve as a means of taking out its lower overall gearing, that is, more revs at any given speed. I therefore recalculated V4 R's numbers to take account of the lower gearing (this multiplies the torque by a factor at every point) and to compress its 15,800 actual rpm to compare torques not at equal engine speeds but at equal road speeds. This, after all, is what the road testers would have felt.

Part of the V4 R’s appearance of lower torque is owed to its smaller 998cc engine displacement; the V4 S displaces 1,103cc and the RSV4 1,078cc.

Rather than do this for all three bikes—26 data points—I simplified things a bit by normalizing to a rough average of the two gearing differences.

Part of the V4 R’s appearance of lower torque is owed to its smaller 998cc engine displacement; the V4 S displaces 1,103cc and the RSV4 1,078cc. When I finished my approximate normalization, I got three curves that compare the torques at the three rear wheels at similar road speeds.

When I did this, I saw that the rear-wheel torque of the V4 R is actually marginally greater than that of the Aprilia, but of very similar shape, save for a dip between 6,000 and 7,000 rpm. It is also usefully above the curve for V4 S.

Now we see how it all works. The V4 R, by spinning at higher rpm but with lower gearing, can actually produce more rear-wheel torque than the larger-displacement engines of the others at nearly all points in the rear-wheel rpm range used for maximum acceleration. And that is what the test riders felt, surely an important element in their decision to choose the V4 R as “Best Superbike.”