Engine layouts: firing order and shake
Two motorcycles with the same number of cylinders can sound, shake and grip completely differently. It comes down to two things: when the cylinders fire, and how the pistons are arranged so their shaking cancels out. You can play with both below.
Same 720°, different rhythm
Every four-stroke engine fires each cylinder once for every two turns of the crankshaft: 720 degrees. How an engine spaces those bangs around the clock changes how it sounds and how well you can feel the rear tire. Pick three engines, press play, and watch. Better yet, turn the sound on.
Keyboard: Space plays and pauses, R restarts, F toggles full screen, Escape exits it. Sound plays one engine at a time; press the sound button to move from the first to the third.
How to read it
Each dial is one full cycle, so the hand makes one lap for every two turns of the crank. The numbered markers are the cylinders, in the order they fire, and each one flashes when it goes. The yellow arc is the longest quiet stretch between one bang and the next.
On a wide screen, the strip underneath lays the same rhythm out in a line across four turns of the crank, so you can compare engines beat for beat.
Things to try
- Put the 90° V-twin next to the 270° parallel twin. The dials are identical, which is why a Ténéré 700 sounds a little like a Ducati.
- Set the speed to Brisk, turn the sound on, and listen to the single, then the 270° twin, then the crossplane four.
- Compare the 360° twin with the boxer. Same rhythm, very different motorcycles. Whatever makes a boxer special, it isn't the beat.
Why don't twins shake themselves apart?
The shake in an engine doesn't come from the explosions. It comes from the pistons: lumps of metal flung up, stopped dead, flung down and stopped dead again, twice every revolution. There's a main shake once per revolution, a smaller faster buzz twice per revolution, and rocking when pistons push opposite ways in different places. Every layout is a different way of lining pistons up so those cancel.
Press play on any engine and watch the outline. The motion is exaggerated so you can see it, and the yellow arrow points the way the engine is being pushed.
V-twin
Boxer twin
Parallel twin
Why not just add a counterweight for each piston?
Every crank carries counterweights, but they have a limitation that took me a while to see. A counterweight spins: it pulls up, then sideways, then down, then the other way. A piston only shakes up and down along its cylinder. So a spinning weight can cancel only part of one piston's shake, and the rest just becomes sideways shake instead of up-and-down. The shake doesn't go away; it gets pointed somewhere else. That's why a single needs a separate balance shaft.
A balance shaft is what the name suggests: a second shaft alongside the crank, geared to it, carrying a weight set off-centre. It spins the opposite way at the same speed, and the opposite direction is the whole trick — two weights turning against each other have sideways pulls that cancel and up-and-down pulls that add. What is left is shake along one line only, and that line can be aimed straight back at the piston’s. A balance shaft is, in effect, a dummy piston built out of spinning parts. The price is another shaft to drive, a little more weight and a little more friction, which is why no engine carries one it doesn’t need.
The magic of the 90° V is that its two pistons together make a force that already spins, and a spinning force is the one thing a single spinning counterweight can cancel completely.
Why exactly 90°? Each cylinder shakes the engine back and forth along its own line. At 90° those two lines sit at right angles, covering the diagonals equally, and together they trace a circle. Narrow the V and both lines lean towards vertical, so the shake flattens into a tall, thin oval — mostly up and down. Only at 90° is it a true circle, and only a circle can be cancelled outright by one counterweight. Put a counterweight on a narrower V and it erases the circular part, leaving a smaller circle spinning backwards — the wrong way for anything on the crank to catch, which is exactly what a balance shaft is for. Step the angle through 90°, 60° and 45° above and watch the outline change shape.
What about narrow V-twins?
In a narrower V, the pistons move more nearly in step, so their shakes don't add up to a clean spin. The fix is an offset, or split, crankpin: each rod gets its own pin, a few degrees apart. Split them by the right amount (60° for a 60° V, 90° for a 45° V) and the shake spins again, so one counterweight cancels it. Honda's 52° V-twins, like the old Transalp, use this idea.
The catch is the same one that runs through this whole page. Moving the pins also moves when each piston reaches the top, so it changes the firing rhythm. A perfectly balanced 60° V fires with gaps of 240° and 480°. Harley's 60° Revolution Max engines split the pin only 30°: that roughly halves the shake, lands the rhythm on 270° and 450° like a 90° V-twin, and leaves the rest to balance shafts. Split pins also make the crank weaker and the engine wider, so if there's room for a full 90° V, a single pin does the job. Switch on offset crankpins above and try each angle.
So does the firing order cancel the shake?
It's a great guess, and it's exactly what I assumed about the V-twin. But no. The shake in these animations comes from the pistons alone. It happens every revolution, including the three strokes out of four when a cylinder isn't firing. Firing makes a separate vibration: every bang kicks the crank forward and twists the engine back the other way. That's the rhythm the Firing Wheel above shows.
What links the two is the crank. Put two pistons on one crankpin at 90° and physics hands you two things at once: a shake that adds up to a single force spinning with the crank, which one counterweight can cancel, and, as a side effect, a 270° and 450° firing rhythm. Nobody chose that rhythm to cancel vibration. It came with the geometry. Switch the counterweight off above to see how much work it's doing, and try the 45° V to see why a Harley shakes the way it does.
That's also the story of the 270° parallel twin. Engineers borrowed the V-twin's crank timing to get its rhythm and feel, but they couldn't borrow its balance, because the pistons don't sit at 90° to each other. The rhythm came free; the balance shaft is the price.
The short version of the video
This page goes with my video on engine configurations and firing orders. If you'd rather read than watch, here's the whole argument in a few minutes.
The rhythm I expected, and the one that wins
I assumed the best engine would fire as evenly and as often as possible, like a drummer who never misses a beat. More pulses, spaced perfectly, should mean smoother power and more grip. For the highway, that's mostly right. For the dirt, it's mostly wrong.
The clearest proof came from Grand Prix racing. In 1992, Honda made its fearsome NSR500 far easier to ride without adding power or touching the frame. They changed when the cylinders fired, bunching all four bangs into one short burst followed by a long quiet gap. Riders who knew both versions described it as a different motorcycle.
American flat track makes the same case from the other direction. Harley’s XR750 dominated the sport for decades, including on the fast mile tracks, while Yamaha turned up with a more powerful, perfectly even 750 twin and struggled to put its power down. More power, a better rhythm on paper, and it still couldn’t hook up.
Engine by engine
Singles fire once every 720° and then take a long nap. By my logic that should be the worst traction engine ever built, yet 1960s desert racers found big singles hooked up better than twins of similar power. Some went as far as re-timing their twins to fire both cylinders together. Singles buzz, run out of breath on top, and can be fussy at very low revs. They're the right engine for dual-sport riding and tight, technical trails.
Parallel twins look the same from the outside, but the crank decides everything. A 360° twin fires perfectly evenly and shakes like one big single; it suits retro and relaxed road bikes. A 180° twin goes bang-bang, pause; it's compact, revvy and cheap to build, and a great choice for commuters and newer riders. A 270° twin keeps one piston moving whenever the other is parked, and it fires with exactly the same rhythm as a 90° V-twin. Nearly the whole middleweight adventure class runs one: the Ténéré 700, Africa Twin, Transalp, Tuareg 660, V-Strom 800DE and F 900 GS, with KTM's twins and the Husqvarna Norden using a close cousin at 285°. If you want one bike for highway, fire road and two-track, it probably has this engine.
V-twins at 90° can cancel their main shake with a single crank counterweight, which is why Ducati and Suzuki's V-Stroms love them, though the engine is long and awkward to package. Harley's 45° twin shakes on purpose; the loping idle is the point, and it's built for cruising. KTM's 75° twin in the Super Adventure is a big, fast adventure engine that still talks to you in the gravel.
The boxer is the exception worth knowing. BMW's flat twin fires perfectly evenly and is very well balanced, yet the R 1300 GS is one of the most successful adventure bikes ever made. Its strengths come from elsewhere: a low center of gravity, durability and comfort. It's the long-haul, two-up, around-the-world engine, and proof that rhythm isn't the only thing that matters.
Triples normally fire every 240°, a smooth compromise between twin and four that suits sport-touring and mountain pavement. Then Triumph did something unusual on the Tiger 900: a T-plane crank that fires with gaps of 180°, 270° and 270°, deliberately making a smooth triple less even so it behaves more like a twin in the dirt.
Fours come in two flavors. The classic flat-plane four fires every 180°, the purest version of the perfect drummer, and it's superb for highway miles and a top-end rush. Yamaha's crossplane R1 scrambles that into gaps of 270°, 180°, 90° and 180°, and V4s from Ducati and Honda chase a similar uneven feel.
Shake is a separate problem
How much an engine shakes is a different question from how it fires. The shake comes from the pistons themselves, and each layout cancels it differently: the boxer's mirror-image pistons cancel almost everything, a 90° V-twin gets rid of its main shake with one counterweight, and parallel twins trade one kind of shake for another depending on the crank. The same crank decision that sets the balance also sets the firing rhythm, which is why a 270° twin fires like a 90° V-twin. The animations above show it in motion.
So why does uneven work?
Honestly, the experts still argue about it. There are three main theories.
The tire needs a breather. Space the power pulses out and the tire gets a moment to recover grip before the next hit. It's intuitive, but not everyone is convinced the gaps create more grip.
It's about feel, not grip. Cycle World's Kevin Cameron argued in 1992 that a bunched firing order doesn't add traction at all. What it does is let the rider sense the tire starting to slide, so the rear steps out gradually instead of all at once. A rider who can feel the edge can ride closer to it.
Get the noise out of the signal. The crank has to speed each piston up and slow it back down, twice every revolution. Speeding a piston up borrows a little energy from the crank; slowing it down hands the energy back. So the crank's speed wobbles slightly on its own, on top of the real pushes from combustion, and that wobble reaches the rear tire mixed in with the power. Yamaha's crossplane staggers the pistons so that while some are slowing down, others are speeding up, and the wobbles cancel. What you feel through the throttle is the combustion, not the clutter.
All three theories share one hero: the rider. An uneven engine isn't magic. It gives you better information, and on a loose switchback, information keeps you upright. It isn't free, either. Uneven firing is harder on gearboxes, usually needs a balance shaft, and gives up a little top end, which is why smooth, even engines still make sense on the highway.
But won't the gaps make it stall?
This was my own nagging worry. My first bikes were small singles that loved to stall at the worst moment, usually on a hill, leaving me fighting to keep the bike from falling over or rolling back down on top of me.
It turns out the gaps weren't the problem. Uneven firing rearranges the bangs; it doesn't remove any. And the longest gap in a 270° twin is 450°, well short of a single's 720°. What carries an engine through the quiet stretch is the flywheel effect: the spinning mass of the crank's counterweights and the alternator rotor. Weight near the rim counts for much more than weight near the center, and a steel ring under a pound, bolted to a dirt bike's rotor, noticeably reduces stalling. Small singles tend to have light flywheels, little low-rpm torque and one big compression stroke to climb over, and that combination is what put me on my back on those hills. A 270° middleweight twin is one of the least stall-prone engines you can buy. If hill starts still scare you, hold the bike on the rear brake while you feed out the clutch, and it can't roll back.
Which engine for which rider
- Single: dual-sport, tight trails, technical terrain
- 360° parallel twin: retro and relaxed road riding
- 180° parallel twin: commuting, newer riders, budget touring
- 270° parallel twin: the middleweight adventure all-rounder
- 90° V-twin: sport-touring and road-biased adventure
- 45° V-twin: cruising
- Boxer: long-haul, two-up, round-the-world touring
- Even triple: sport-touring and mountain pavement
- T-plane triple: road-biased adventure that still wants grip in the dirt
- Flat-plane four: highway miles and top-end rush
- Crossplane four or V4: track and fast road riding
The even-firing engine is the best drummer for a highway. The sloppy drummer is the best one for a dirt road.
Firing intervals come from manufacturer materials and published technical references. Some engines vary by model and year. If something here is wrong, write to press@secondkickstart.com and it gets fixed.