What Are Counter-rotating Crankshafts & How Do They Help?

Performance motorcycles seem to get more powerful by the day, even as emission norms grow stricter and stricter. The original powerhouse, the BMW S1000RR, manages 213PS even in Euro5 guise, while the CBR1000RR-R Fireblade goes one step further, putting out 217.5PS despite meeting the latest emission standards. But what about making a bike quicker through the corners? Well, chassis and suspension technology continues to progress at a steady rate, but what if the engine could help make the bike handle a little better? Sounds impossible, doesn’t it?

Gyroscopic Effect

Ever wonder how a spinning top remains upright or a bike in motion doesn’t fall over? Well, the answer comes from something called gyroscopic effect. Without getting into nitty gritty physics textbook stuff, the spinning or rotating motion of the two wheels is what keeps a bike upright when on the move. But that same gyroscopic effect caused by the spinning wheels is also what makes a bike difficult to lean over, since it always wants to maintain a perfectly upright position.

The gyroscopic effect is directly proportional to the mass of the rotating components (in this case, the wheels) as well as their angular velocity (how quickly they’re spinning). This explains why it requires more and more effort to lean a bike over as speeds rise. It also explains why switching from aluminium wheels to something lighter like carbon-fibre or magnesium wheels can result in a bike that feels a lot more agile and light-steering.

Counter-rotating Crankshafts

Great knowledge about wheels, but what does any of this have to do with engines? Well, all the gyroscopic force doesn’t come from the wheels alone. What else is spinning on the bike? What’s causing the wheels to spin. Yep, the engine. And the crankshaft is usually the heaviest moving component in an engine.

So when a crankshaft spins forwards (in the same direction as the wheels), it adds to the gyroscopic effect of the wheels and makes the bike even harder to steer or lean. But if you make your crankshaft spin backwards (in a direction opposite to that of the wheels), the gyroscopic effect created by the rotating crankshaft partially cancels out the gyroscopic effect created by the spinning wheels. This results in a bike that feels lighter to steer and is more willing to tip into corners quickly. Much like bolting on some lighter wheels.

So, Any Disadvantages?

Well, obviously, a crankshaft that spins backwards still needs to drive the wheels in a forward direction. So an extra gearing element has to be added in the form of a ‘jackshaft’, whose sole purpose is to ensure that the wheels spin forwards.

As any engineer will tell you, no system is 100 per cent efficient, so even the most well-designed jackshafts out there tend to sap 1 to 2 per cent of the engine’s power. What most engineers will also tell you is that good design is a matter of compromise, and the 1 to 2 per cent power less is more than compensated for by the increased maneuverability of the motorcycle.

So Who Uses Them?

The one battlefield where cornering performance is of paramount performance is MotoGP. It’s no surprise then that all 6 MotoGP manufacturers - Honda, Yamaha, Ducati, Suzuki, Aprilia and KTM - use counter-rotating crankshafts on their prototype machines. But what about road bikes? Well, the reverse-spinning crank on the Ducati Panigale V4 is a big contributor to its nimble handling characteristics, and all the current MV Agusta triples employ the technology too.