Parallel universe: The surprising comeback of parallel twins.

Parallel-twin engines might be considered stodgy and uninspired, but they’re poised to make a big comeback, particularly with adventure bikes.

Parallel twins haven’t had an exciting reputation in years, ever since the demise of the Brit bike industry, which had used them to conquer racetracks and salesroom floors around the globe. Since the 1970s, V-twins (or L-twins, as Ducati calls them) have been the go-to engines if you want twin-cylinder fun. So why are parallel twins making a comeback?

There are three reasons for the resurgence of the parallel twin: They’re cost-effective to build, they’re versatile compared to triples and four-cylinders engines, and they pollute less than single-cylinder thumpers.

The parallel twin of the Versys pollutes less than the single-cylinder KLR, although they’re the same displacement.
Passing gas

We went over this last summer, but single-cylinder engines, once the powerplant of choice for big-bore duallies and budget adventure bikes, are on the way out. Thumpers won’t die off completely, but once emissions kill off the current crop of 650 singles, they won’t be as readily available as they are now.

One of the biggest reasons for the demise of the big singles in the 450-650 cc range is the fact they pollute more than twin-cylinder engines in the same displacement range. In the next few years, the government will tighten emissions restrictions further, making it even harder to keep these simple engines on the road. As a result, we’ll see a move towards twins.

Entry-level sportbikes like the Kawasaki Ninja 300 use parallel twins to keep prices down.
Saving graces

Parallel twins are economically advantageous: they save manufacturers money when compared to other engine configurations. Inline fours and triples have higher manufacturing costs, due to the number of cylinders and pistons.

Even when compared to a V-twin, a parallel twin is cheaper to make—there are fewer camshafts, less machining is required, and assembly time is lower.

On a halo bike like the BMW R1200 GS Adventure, these savings aren’t a big deal. On bikes like the Honda 500 series, the few pennies saved add up to big dollars very quickly.

For machines like the made-in-China Suzuki GW250 series, those savings are even higher. The Honda 500s will be sold in first-world markets but the Suzuki 250s will be sold in developing markets around the world. It’s imperative to keep the price as low as possible to make sure as many buyers as possible can afford it, no matter if their pockets aren’t deep.

Honda’s 500 parallel twin serves in a sport bike, a naked bike, an adventure bike, and now powers the new Rebel 500.
Swiss Army engines

The parallel twin engine is arguably the Swiss Army knife of the motorcycle world, and it’s been that way for decades. The Brit bike powerhouses like BSA, Norton and Triumph used parallel twins for standard motorcycles, for their sporty machines, for desert racers and even for ill-advised cruisers.

Then the Japanese took over where the Brits left off, with bikes like the Yamaha XS650 series, the Honda CB350s, the Kawasaki KZ400s, and the Suzuki GS400s. All those basic platforms came in cruiser, cafe, and standard models; some even came in scrambler clothing.

The parallel twins worked in a wide variety of bikes because of the basic characteristics of the engine. A vertical twin is compact like a single-cylinder motor, but doesn’t vibrate as much. A final gearing change makes it even easier to turn into a torquey cruiser or a high-strung street rod. It’s much easier to build a tidy chassis around a shorter parallel twin than a longer V-twin.

The KTM 790 Duke is one of several new models with parallel twins that are about to hit the market.
The future

In case you missed this piece about Honda’s latest application for its 500, the Big Four are turning back to the parallel twin, after ignoring it for several years in pursuit of more glamorous motors. From the late ’80s to 2008, the name of the game was specialization, towards bigger, faster, more advanced bikes. But not now. The generally crappy economic climate faced by the middle class in the developed world, plus the specific issues faced by the motorsports industry (called out last week in Bloomberg) means the OEMs have to change how they do business.

So now, Kawasaki and Honda both have cruisers, naked bikes, adventure bikes, and sport bikes built around their entry-level parallel twins. Yamaha has a new budget twin powering its R3 platform, which is rumoured to be headed to an adventure bike soon as well. Given that Suzuki is the master of parts bin engineering, it’s likely the company will continue to morph its GW250 into new models.

But it’s not just the Japanese manufacturers who see the advantages of the parallel twin. Triumph recently updated both its T120 and T100 vertical twin platforms, and is using the updated liquid-cooled motors in cafe racers, standards, scramblers and soon, cruisers (or so we’ve been told). More currently, KTM is working on a new parallel twin platform, the Scalpel. BMW is updating its long-running F800 platform.

Those new bikes are likely to hit this fall’s show circuit. They’re not the most exciting bikes in their manufacturers’ respective lineups, but pair those bikes with more expensive machines like Honda’s Africa Twin or the Yamaha Super Tenere, and they are definitely proof of a comeback for the parallel twin. The days of the thumper might be passing, but we’re about to see the revival of a time-honoured engine design that’s been underappreciated for too long.

6 thoughts on “Parallel universe: The surprising comeback of parallel twins.”

  1. it’s funny how fashions come and go. I remember reading an article in Britain’s Bike magazine that rated the best to worst engine configurations. The agreed upon worst was the parallel twin. It made me chuckle at the time as I remembered fondly a few of those twins I’d owned. At the time the article was written there weren’t many around but now they’re having a comeback. Likewise their praise

    1. As a side note, by far the most fun I’ve had recently on two wheels has been on a KTM690. A remarkably smooth single that puts out 70+ HP

  2. What Zac said PLUS smaller pistons operating in the ‘sweet spot’ of the rev range improve fuel economy and lower emissions. That, in conjunction with multiple speed automatic transmissions is what you’re seeing across the board in cars and light trucks now, for exactly the same reasons.

  3. Ummmm, the Versys pollutes less because it’s a parallel twin? I think the lions share of the ‘greeness’ is probably coming from modern electronic fuel management as opposed to an aging carburetor.

    1. Smaller cylinders = less deformation of rings and piston = less blowby = less pollution.

      It’s part of the reason why H-D is moving to liquid cooling. They’ve already had EFI for years, that’s not the issue. It’s that the hot cylinder/pistons are deforming, and the only way to lessen pollution is to keep them cooler so they deform less. But eventually, this problem will be the end of all big-cylinder bikes, whether they be thumpers or V-twins, without extensive antipollution gadgetry added on.

      1. I’m pretty sure Harley-Davidson was moving to liquid-cooling because someone in Milwaukee heard that it made them “cutting edge”. They may even discover 20th century materials soon.

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