Motorcycle news, Motorcycle reviews from Malaysia, Asia and the world

What is a Counter-Rotating Crankshaft?

You may remember that Ducati touted a counter-rotating crankshaft for the Panigale V4 was introduced. It is now a shared feature among their V4-engined family.

It is all about forces

Inside almost every motorcycle ever built the crankshaft turns in the same direction as the wheels. But in recent years a handful of exotic bikes have started spinning their cranks backwards. If you’ve heard the term ‘counter-rotating crankshaft’ but aren’t entirely sure what it means, what the advantages are or which bikes have one, read on.

(Quick point of order: we’re focusing on bikes with across-the-frame cranks here. Bikes with inline cranks, such as BMW boxers, Honda Goldwings and Moto Guzzi V-twins, can sit this one out. They’re free to spin either way.)

Spinning things like to stay spinning, called inertia, while the spinning motion causes gyroscopic and centrifugal forces.

When you’re riding along in a straight line, both wheels whizzing around beneath you, everything’s fine and dandy. But try to lean the bike over, shifting multiple spinning objects (wheels, brake discs, tyres, crankshaft) away from the plane in which they were quite happily turning, and they’ll resist.

How big this gyroscopic resistance is – which affects how much physical input you need to move the bike off line – depends on the weight of each spinning object, its diameter and the speed at which it’s spinning. One solution would be to reduce any (or all) of the above: lighter wheels (expensive), smaller wheels (wobblier), or slower wheels (boring).

Another fix is to introduce something spinning in the opposite direction. Something like, say, the crankshaft. It might be small, but it can spin really fast. At 100-110 km/h a typical 17-inch front wheel turns at just 1000 RPM; the crank, meanwhile, could be spinning ten times as fast.

Well, alrighty then. Simply spin the crank the other way and you’re reducing the bike’s total gyroscopic resistance. This means less effort is needed to get the bike turn, making for increased agility, lighter steering, nimbler handling and other great road test cliches.

But wait, there’s more! Spinning the crank backwards also gives a second benefit, in the form of an anti-wheelie effect. This is down to a torque reaction from the crankshaft accelerating. When a forwards-spinning crank accelerates, the rest of the bike rotates backwards: the nose lifts and the tail drops. With a counter-rotating crank, the nose instead drops, meaning less wheelie, allowing better acceleration.

So why don’t all bikes have it?

Spin the crank backwards and your rear wheel also turns backwards. To fix this mild inconvenience you have to add an additional shaft inside the engine (an idler gear/countershaft/jackshaft) to keep the rest of the powertrain moving the right way. This extra shaft adds weight, cost and complexity, plus it saps power due to friction.

The trade-off is worth making in MotoGP, where every bike on the 2023 grid uses a counter-rotating crank. It’s not actually an especially new idea in racing: Honda’s 1987 NSR500 had one, as did Yamaha’s first YZR-M1 in 2002, a year before the Petronas FP1 (which used a backwards-spinning crank by virtue of its completely back-to-front engine) in World Superbikes.

Who else uses it?

On the road, just two major manufacturers use counter-rotating cranks today: Ducati, in all its V4s and MV Agusta, in its triples. A tiny number of other two-wheelers have used them in the past, including – of all things – the Aprilia SRV850 maxi-scooter, which shared its 839cc V-twin and CVT with the Gilera GP800 and Aprilia Mana, both launched back in 2008. Curiously, Aprilia never thought to mention this feature until the SRV arrived in 2012.

Understanding Compression Ratio – and Fuel Octane

We have written about fuel octane, or more specifically, what it does and why do we have different RON ratings at the pump. Fuel octane is directly tied to the engine’s compression ratio.

What is compression ratio?

A ratio means something divided by another thing. Firstly, take the cylinder’s volume when the piston is fully at the bottom of its stroke (bottom dead centre/BDC), and add the combustion chamber’s volume. Secondly, take the volume of the cylinder when the piston is fully at the top of its stroke (top dead centre/TDC). Now take the BDC volume and divide against the TDC volume. This is why compression is expressed as 10:1. 11:1. 13:1 and so forth.

The higher the ratio means the fuel air mixture that enters the cylinder is squeezed into a much tighter space. Higher compression is good for making more power as more of the heat from combustion is transferred to kinetic energy in pushing the piston down.

Whichever way we go about it boosting the compression ratio is an easy route to more power. High compression pistons are in essence “bolt-on horsepower”. Modern bike engines tend to run compression ratios in the 10:1 to 12:1 region.

However, there is a limit

But there are limits to how high the compression ratio can go.

Any medium, whether is it just air or the fuel air mixture will get hot as it is compressed more and more. The higher the compression, the higher heat the medium will achieve. And, when the heat becomes too high, the fuel air mixture will self ignite before the spark plug ignites it at the correct timing.

This self-ignition sends shockwaves around the combustion chamber that can cause catastrophic failure. These shockwaves can be audibly heard and has a metallic knocking sound, hence called “knocking” or “pinging.”

In fact, diesel engines work this way. They employ very high compression ratios and compressed air alone until it gets really hot before diesel is injected into the combustion chamber. This mix causes instantaneous ignition. It is also why diesel engines produce that signature clacking sound.

So, how do we stop self-ignition? There are three methods: Lowering the compression ratio, retarding the ignition timing, or using fuels with higher octane rating. We shall explore this in another article.

BMW Motorrad Sales Broke Records in 2024

BMW Motorrad sales broke records again in 2024, with the German marque claiming to sell a total of 210,408 new bikes.

The biggest seller was of course, and without doubt, the new R 1300 GS and the previous R 1250 GS. Their biggest market was once again in their homeland.

Top sales region and countries:

118,727 new bikes were sold in Europe, making making it the most valuable region.
Sales in Germany were up eight per cent with 26,177 bikes.
France was the next best-performing country, with 20,693 units.
Followed by Italy, with 16,617 units.
Central Europe, which includes countries like Poland, Romania, Switzerland and Serbia collectively sold 11,411 new bike sales. It was a 12 per cent increase from the previous year.

Best-seling models:

As mentioned ealier, R1300 GS and R1250 GS were the most popular, selling 68,000 worldwide.
The S 1000 RR was the best-selling four-cylinder model, with 11,610 shifted
The entire four-cylinder family (S 1000 RR, M 1000 RR, S 1000 R, M 1000 R, S 1000 XR, and M 1000 XR) sold 27,147 units worldwide.

Markus Flasch, head of BMW Motorrad, said, “I would like to extend my heartfelt thanks to our customers and community around the world for the tremendous trust they have placed in us once again in 2024. With the strongest sales result in company history, BMW Motorrad remarkably claims the 1st Place in the global Premium Motorcycle segment. Our market leadership in numerous segments and markets in based on our claim to innovation leadership, our highly attractive product offering as well as the consistent strategic focus on brand strength. Based on these success drivers, BMW Motorrad is well-positioned for the future and so I approach the year 2025 with a very positive outlook.”

Making Sense of Engine’s Bore and Stroke

We were treated to an all-new Yamaha YZF-R1 for this year. Poring over the specification sheet we found that the engine’s bore and stroke has changed i.e. larger bores and shorter strokes. And yes, it revs higher.

What is bore and stroke?

To put it simply, the bore is the hole the piston sits in. Stroke, on the other hand, is the length that the piston needs to travel between its highest and lowest points.

But why is that?

The relationship between an engine’s bore and stroke determine, to an extent, how it makes its power. For a given capacity, ‘long stroke’ engines – ie those with a relatively long stroke in relation to the bore size – will tend to be relatively low revving but with strong low down power, while ‘short stroke’ or ‘oversquare’ motors – short stroke with a wide bore – will be able to rev higher. And, because more revs equal more horsepower (horsepower = torque x rpm divided by 5252, so increase the revs and the bhp increases too), manufacturers are always looking at ways of safely increasing the upper rev limit of their motors.

One of the major factors determining an engine’s upper rev limit is piston speed. For every revolution of an engine, the piston moves up from the bottom of its stroke (bottom dead centre or BDC) to the top of its stroke (top dead centre or TDC) and back again. So in the case of the ’04 R1, the 77mm wide piston goes from a standstill, travels 53.6mm up, stops, and comes back down again. At 10,000rpm it makes this journey just over 166 times each way every single second, at an average speed of 17.9 metres a second.

The stresses on a piston and conrod at high revs are massive. If the piston is forced to travel too quickly something’s going to break. Put very simply, if you reduce the distance the piston has to travel – ie its stroke – it doesn’t have to travel as fast and can make that journey more often. So that’s what Yamaha chose to do with their new R1, reducing the stroke by 4.4mm and adding 3mm to the bore. Last year’s R1 redlined at 11,750rpm, while this year’s redlines at 13,750, and makes its peak power 2000rpm further up the RPM scale.

Another way of reducing driveline stresses

Another way of reducing stresses is by using lighter materials for the pistons and connecting rods. Every moving part has momentum, and momentum is calculated by acceleration multiplied by mass. So, the more mass a moving object has, or/and the faster it moves, the higher its momentum. Lightening these parts will reduce stresses and also lets the engine rev faster.

How does an Assist Clutch Work?

We have covered the subject of the slipper clutch, now let us look at the assist clutch function. The assist function is an evolution of the slipper clutch and is fitted to an increasing number of motorcycles these days.

Why do we need the assist function?

Previously, harder clutch springs are required for high powered motorcycle engines in order to force the clutch plates and friction plates together, in order to maximise power transfer. Cutch springs that are too light can cause the plates to slip past each other, especially under hard acceleration.

Problem is, the clutch lever will feel very stiff as we need more finger pressure to overcome the springs’ force. It becomes even worse when the bike is accelerating hard and at speed, as the clutch’s centrifugal force pushes the plates in. Not only that, the gear lever can also feel really when using a quickshifter.

So how does the assist function work?

As with the slipper clutch, there are also ramps on the clutch’s pressure plate. However, these ramps face the other way, which cause the pressure plate to push inside onto the clutch plates for more positive engagement. In other words, less of the engine’s power is wasted from clutch slippage.

The takeaway from this is we can now use lighter clutch springs, allowing for a lighter pull on the clutch lever. It is especially useful when your motorcycle does not have a quickshifter. Additionally, shifting with the quickshifter can be potentially faster and the gear lever feels softer.

How does a Slipper Clutch Work

The slipper clutch is a common feature in road motorcycles nowadays, compared to when it was used in racing exclusively. Even some “performance” kapchais are equipped with it.

Why do we need a slipper clutch?

We are familiar with that deceleration when we shut off the throttle, or when we downshift. That is called engine braking or back torque. It is especially strong on four-stroke motorcycles with bigger engines that produce higher torque. The higher the engine’s torque, the higher its back torque too.

This engine braking can become intrusive, especially when we downshift to aggressively or we accidentally downshift to a gear that is too low. It can cause the rear wheel to hop, or even lock up momentarily. It is not something we want as we are tipping the bike into a corner, and certainly when the road is wet.

How does it work?

That is exactly why the slipper clutch was developed for: To reduce the engine’s back torque through the clutch plates to the transmission and to the final drive.

Slipper clutches usually consists of ramps that would cause the clutch basket to disengage or in other words, “slip” when the rear wheel tries to drive the engine faster above a certain deceleration threshold.

These angled ramps let the clutch faces which are normally meshed together under acceleration and normal riding to pull apart and disengaging the plates when there is too much back torque. Consequently, the rear tyre continue to rotate. It also decreases wear and tear on other transmission and engine parts due to the engine overrevving.

However, on some more sophisticated bikes (read: expensive), the slipper clutch works in conjunction with an electronic feature called engine braking control which regulates the engine speed to avoid clutch hop altogether. But that is a story for another day.