The New Parallel-Twin

Story by David Booth//
February 21 2023

Somewhere between the time Honda introduced its torsion springed CB450 in 1965 and when the last Triumph Bonneville rolled off the Meriden production line in 1983, the parallel-twin became motorcycling’s powertrain pariah. Indeed, for those who actually lived — and rode — through motorcycling’s four-cylinder revolution, vivid is our recollection of parallel-twins as junkers. Kawasaki’s 440 LTDs and the Honda CB 450 Nighthawk were the worst of our industry, pumped out without passion or purpose. Seriously, if a 440 LTD were the last bike on earth, I’d have to decide whether I wanted to continue motorcycling.

Fast forward a decade or two and my, oh my, how the times have changed. Litre bikes have become so powerful that few can ride them and even fewer can afford their high-techery. Four-cylinder middleweights, meanwhile, are all but extinct, their combination of high cost and minimal development over the years all but killing the segment. In fact, look around and you’ll find that, amongst the Japanese at least, the four-cylinder engine that ruled the motorcycling roost since 1969 — the year of Honda’s CB750 — is not in much favour. Suzuki has dropped out of the superbike segment and the four-bangers that it still does sell all date back to the early 2000s. Honda’s fours are also pretty long in the tooth, too. MV Agusta has all but dumped fours as well and BMW seemingly continues on mainly because it wants to race in World Superbike. The days of inline fours dominating mainstream motorcycling are quickly coming to an end, replaced by…

The return of those once lowly parallel-twins. And while the (new) Triumph soldiered on with twins and Yamaha stayed the course with its Super Tenere and TDM 900, it’s Honda that really started this re-legitimization of the classic two-cylinder format with its 2016 Africa Twin. And, though many of us — including yours truly — thought it would remain an anomaly, pretty much everyone has copycatted the world’s largest motorcycle manufacturer. Yamaha followed with its Tenere 700, Aprilia with its 660 and Kawasaki, well they really never did give up, its 649-cc — powering both Ninja and Versys — the one mainstream twin that defied time.

Initially, the introduction of new parallel-twins followed a common theme: most manufacturers introduced their parallel-twins as budget bikes. Thus, Yamaha introduced the MT-07 and soon, the R7. Ditto Aprilia and its adventure-style Tuareg. And yes, Kawasaki had, as I mentioned, the Ninja 650, but, just as with Honda’s CB500R, no one in their right mind took it seriously as a sportbike.

I think KTM has to be given credit for lending the lowly parallel-twin some performance bona fides. Where all of the bikes mentioned in the above paragraph — with the possible exception of the recently introduced Aprilia — were lo-po machines that exuded ease-of-use over scintillating performance, the “Ready to Race” Austrians refused to accept that putting two pistons in a line would doom it to mediocracy. Where previous parallel-twins were tedious torquers, KTM’s 790, 890 and soon-to-be 990s all rev their nuts off, the 890 pumping 119 horsepower in its most prodigious guise. That would seem sufficient enough to encourage the Austrian trendsetter to dare to render a legitimate sportbike — the much-anticipated RC 990 — powered by a parallel-twin.

Yamaha’s Tenere 700, meanwhile, is considered the true off-road adventurer’s primo ride and this year Honda is bringing back not only its famed Transalp adventure tourer but also the much-missed Hornet naked, their shared parallel-twin replacing both a V-twin and an inline four. Look around and it appears that the once lowly twin is replacing the majority of higher-tech engines. Hell, Suzuki, which many had given up as dead, actually released its first all-new motor in more than 20 years and it is, you guessed it, a parallel-twin (with a 270-degree crank and two counter-balancers).
So why all this focus on parallel-twins?

The answer is three-fold. First, and most obvious, is that they’re easier to package. V-twins, at least the longitudinally-mounted versions, are longer and fours are wider. Both alternatives have either more exhaust pipes to route or a more complicated pathway. And since twins have less piston — and, more importantly, ring land — circumference to hide unburnt gasses, they more easily meet stringent Euro5 emissions standards than short-stroke, big-bore fours.
More importantly, especially in this day and age, is that they’re cheaper to build. They have 50 per cent fewer pistons, valves and connecting rods compared with a four and half the number of cylinder heads, camshafts and cam chains as a V-twin. The crankshaft is more compact, it’s easier to stack the transmission shafts, and the induction system is way cheaper to engineer. Other than the addition of the counter-balancers needed to quell their vibrations, everything about a parallel-twin is cheaper and/or simpler.

That’s especially important as the age of internal combustion is (supposedly) coming to an end. Keeping R&D dollars devoted to ICEs low is essential if motorcycle makers are to make a smooth, economical transition to electric powertrains. There’s not much point in developing a radial-valved, four-cylinder engine — as MV Agusta famously did for its comeback motorcycle, the 1999 F4 — if they’re going to be banned in a few years.

In the meantime, they build cheap and cheerful parallel-twins.


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