BMW released stunning images this week of a new concept motorcycle that nobody saw coming, featuring the resurgence of an engine configuration we all thought was long-dead. In recent years Triumph has stamped itself as the master of modern triples, and now BMW has made a clear statement of intent that it's bringing the inline six back to the bike world. The Concept 6 showcases a brand-new 1600cc engine that's four inches narrower than any previous production six, and produces truly prodigious power and torque throughout the rev range. And it's housed in a cafe racer body that has to go down as the sexiest motorcycle design BMW have ever produced. Sensational stuff... We can has production model plz?
Inline six-cylinder motorcycle engines don't make a huge amount of sense on paper - for a given engine capacity, they tend to be heavier and considerably wider than a comparable four-cylinder. They deliver power, grunt and smoothness advantages, but historically, not enough to compensate for their weight. Even so, when Honda's CBX1000 debuted in the late 1970s, its exotic engine and six snaking, chrome headers made it an instant cult classic that still turns heads to this day.
But the CBX was, at its heart, simply a branding measure - a monument to Honda's engineering prowess and a demonstration that the company could build exciting, excessive machines. It fascinated the punters and delivered ball-tearing performance for its day, but the engine's power was gobbled up by its excessive weight, and its imposing width played merry hell with the bike's center of gravity, resulting in handling troubles that could never be compensated for - at least when it was placed alongside four-cylinder wonders like Suzuki's GSX and the later V-4 Honda Interceptor.
Today there are precious few production sixes on the motorcycle market. Honda's Goldwing is the only major contender; the GL has been gradually increasing its engine capacity over the years but sticking to a flat six format since 1988. Testers frequently describe the current-generation GL1800 engine as the smoothest powerplant they have ever sampled.
Still, the idea of high-performance six-cylinder motorcycles has pretty much wandered off the radar in recent years. Suzuki's Stratosphere concept of 2005 raised a lot of eyebrows, but there haven't been any hints that the "New Katana" will actually get off the ground. So when BMW released details of its Concept 6 cafe racer this week, perhaps the biggest surprise was the strong language in the press release promising that the new Bavarian inline six isn't just an engineering exercise:
"The new BMW straight-six will further expand the K-Series in the foreseeable future. The first model to be introduced will be an innovative and luxurious BMW touring machine."
So, having established that a Beemer Six is indeed on the way, let's take a closer look at the Concept 6.
The Concept 6 engine - 1600cc of pure, 6-cylinder grunt
The Concept 6 design team was determined not to let the engine blow out to the party-pooping width of the CBX's imposing donk - and it looks like they've done a good job keeping it acceptably narrow. Each cylinder is still slightly oversquare (its bore is slightly larger than its stroke), which will help it spin up and develop horsepower at higher revs, but the stroke is relatively long compared to the ratios used in BMW's inline fours, keeping those cylinder bores as narrow as possible while retaining the ability to rev.
There's very little space in between cylinders, and the alternator and other electrics have been relocated from the side of the engine back behind the crankshaft in the spot above the transmission. The overall result is a motor that BMW claims is four whole inches narrower than the previous thinnest inline six on the market - and only slightly wider than a big inline four.
With a capacity of 1600cc, and all the extra exhaust headers and gear required by an inline six, it's still going to be a very heavy powerplant, but BMW have used a trick from their K-series sportsbikes to neutralize the negative effects that big lump of metal could have on the bike's handling. With the engine tilted forward by 55 degrees, the main bulk of the cylinder bank is kept low, pushing the centre of gravity down and forward, which should help keep the bike flickable and fun in the twisties.
Peak output will reportedly be similar to the K1300 series engines - somewhere around 170 horsepower - but the big six will belt out a massive 130 Nm of torque from just 2000rpm. For reference, the torque monster Suzuki GSX1400 peaks at about 125 Nm at around 4700rpm. The new engine's torque peak is unspecified, but it should rev as high as 9000rpm, making it a hugely flexible powerplant that BMW believes will be "the ideal power unit for a range of different motorcycles." Yummy!
The BMW Concept 6 Cafe Racer
It's a pity the first new-age Beemer Six is going to be a tourer - because this sporty concept is an absolute stunner. Looking like a marriage between the K1200R and a Buell Cyclone, the Concept 6 is a techno-masterpiece of design.
Interestingly, the design team chose not to fetishize the big engine or display acres of header chrome a la the Honda CBX - but then, their hands were forced by the engine tilt, which pretty much puts the exhaust headers out of view under the bike's belly. An inline engine at that sort of angle is always going to look a little awkward, but the lines through the rest of the bike are absolutely gorgeous, particularly in the way the tank integrates with the miniature front fairing. Even the tail-light is beautiful - a red-hot trail of fire extending directly from the rider's backside, representing exactly the kind of reaction you'd expect a 1600cc inline six to engender.
The front end suspension is a Duolever system like what you'd see on a K1300R, the rear swingarm doubles as a shaft-drive and torque reaction is nullified by its Paralever 'ankle.' The primary cue that the bike is a six-cylinder comes from the three flared exhaust chambers that exit low and wide just behind the rider's feet - a muscular look that is echoed in the chunky intake ducts peeking out beneath the tank.
The dash takes the interesting step of eliminating the tacho, instead showing a readout of how much torque is available at the current engine speed - the theory being that with an engine this grunty throughout the rev range there's no need to go hunting for a redline.
The Concept 6 sweeps aside the rest of the BMW range in terms of exciting design - and even tops the fantastic Lo-Rider concept for pure visual thrill. In typical BMW style, it looks more like a finished bike than a concept - and the kind of bike only BMW could build. Maybe, if we wish hard enough...