A Four-Week Deadline That Defined a Century
In November 1922, BMW's general director Franz Josef Popp told his chief designer Max Friz to come up with a motorcycle. Friz had the drawings finished within four weeks. Ten months later, in September 1923, BMW showed the R32 at the Berlin Motor Show, and the layout on that bike, a transverse flat-twin with shaft drive, is still recognizably the same architecture BMW builds today.
That's the part that tends to stop people cold. A motorcycle engine sketched out in a hurry in the winter of 1922 is still, in modified form, powering the R1300GS rolling off the line now. Few engine layouts in the history of motoring, two wheels or four, have run continuously for over a hundred years without being replaced by something fundamentally different.
I owned a piece of that lineage for a while: a black 1975 BMW R60/6. The photos in this story are of that bike, and a good deal of what the history books say about the boxer, I learned for myself in the saddle.
Before the R32: Martin Stolle and the M2B15
The boxer twin didn't spring fully formed from Friz's pen. In 1920, BMW engineer Martin Stolle designed the M2B15, an air-cooled, side-valve flat-twin loosely inspired by the British Douglas motorcycle. It wasn't even a BMW-branded bike. The M2B15 was sold as a proprietary engine to other manufacturers, including Victoria, Helios, Bison, and Corona, at a time when BMW itself was banned from building aircraft engines under the Treaty of Versailles and was scrambling for new business.
Those early customer engines were mounted fore-and-aft, in line with the frame, which meant the rear cylinder ran hot with poor airflow. Friz's contribution to the R32 was turning the engine sideways. He rotated the cylinders 90 degrees so they jutted out into the airstream on either side of the bike, solving the overheating problem outright and giving the layout its name. He also added a light-alloy cylinder head for better heat dissipation and specified shaft drive instead of a chain, which suited the rutted, unpaved roads of 1920s Germany far better than an exposed chain ever could.
Stand in front of any airhead and Friz's logic is obvious. The cylinders hang out past the fork legs, fins facing straight into the wind, exactly where a designer who was worried about cooling would want them.
Why the Boxer Layout Actually Works
The transverse boxer isn't just a styling quirk. Two pistons moving outward and inward together, rather than up and down, largely cancel each other's vibration, which is why boxer twins have a reputation for smoothness that inline twins of the same era struggled to match. The weight sits low and central in the frame too, since the cylinders splay out near the bike's center of gravity rather than stacking a heavy crankcase high up.
That smoothness isn't marketing. My R60/6 was smooth at every speed I ever rode it, from walking pace through town to a steady cruise on open road. There's no buzz through the bars or pegs to wear you down, which is a big part of why a 1970s BMW still feels civilized today.
The tradeoff, for eighty years, was a characteristic rocking sensation under hard throttle, as the engine's torque reaction twisted the whole bike slightly on its axis. Riders who grew up on airheads will tell you this isn't a flaw so much as a handshake, a way the bike talks back. I felt it on mine whenever I took the revs up high: a little back-and-forth sway underneath me. I never read it as a problem. It felt like the bike telling me it was working hard and was ready for more if I wanted it. BMW didn't engineer that character away with a counterbalance shaft until the 2004 R1200 series, and plenty of boxer riders still miss it.
From Airhead to Oilhead: A Slow, Deliberate Evolution
BMW's boxer went from 8.5 hp in the 494cc R32 to 16 hp within two years in the 1925 R37, and from there the story is one of steady refinement rather than reinvention. The bikes collectors now call airheads, the air-cooled boxers built from the 1969 /5 series through the last R100s in the mid-1990s, carried BMW through the R60, R75, R80, R90S, and R100 models that built the marque's touring reputation. The 1975 R60/6 sits right in the middle of that run: a 600cc twin from the /6 generation, which brought a five-speed gearbox and the twin-dial instrument pod you see below.
The next real leap came in 1993 with the R1100RS, BMW's first oilhead: a four-valve-per-cylinder boxer, air-oil cooled, displacing 1,085cc and producing 88 hp. Oilheads kept evolving through the R1150 (1999, 1,130cc) and R1200 (2004, 1,170cc), the latter finally introducing that counterbalance shaft. By 2009 the R1200 had gained double overhead cams and 110 hp. The 2019 R1250 brought ShiftCam variable valve timing, and the 2024 R1300GS now makes 145 hp from 1,300cc. BMW even scaled the format up dramatically with the R18 Big Boxer, a 1,802cc engine and the largest boxer BMW has ever built, whose valve train deliberately echoes the old R5 and R51 models from the 1930s and 1940s.
Living With a 1975 R60/6
The /6 cockpit is simple and clear. A speedometer and a tachometer sit side by side, with a column of warning lights between them for the turn signals, oil pressure, generator, neutral, and brakes. Everything you need at a glance, nothing you don't.
The detail that surprised me most when I first got on the bike was the ignition. It's on the left-hand side, and at first it felt a little strange. It made sense quickly, though, because I'd owned a Porsche with the same left-hand ignition. Porsche put the key on the left for its racing team because it made for a faster start than a right-hand ignition, and the placement carried over to its road cars. Finding the same quirk on a German motorcycle felt like a small nod between two companies that took engineering seriously.
What really set the R60/6 apart, though, was reliability. It was the most reliable bike I have ever owned. Maintenance was simple: regular oil changes, keeping the brakes in good shape, and keeping the other fluids fresh. That was about it. It never gave me the kind of trouble that makes you nervous about riding a classic any real distance from home.
Where it shone was on winding back roads. The R60/6 was comfortable enough to ride all day, and it felt right at home on two-lane roads with some curves in them. The highway was another story. It would do it, but it wasn't where the bike was happiest, so I mostly kept it on the back roads and off the interstate. For a 1970s 600cc twin, that's an honest tradeoff, and on the right road it didn't matter at all.
Collecting the /2 and /5: Where the Boxer Story Gets Personal
For collectors, two model families anchor the boxer's mid-century reputation. The /2 series (built through the 1950s and into the late 1960s) represents BMW's postwar recovery: mechanically simple, hand-finished, and increasingly hard to find in unmolested condition. The /5 series, launched in 1969, was the bike that modernized the boxer for a new decade, introducing a new frame and the airhead engine architecture that carried through the /6 and /7 bikes of the 1970s.
Both series are collectible for reasons beyond nostalgia. They're simple enough for a competent home mechanic to maintain, parts support through BMW's own archives and specialist suppliers is unusually good for bikes this old, and the shaft drive means no chain to replace every few thousand miles. My own experience with the R60/6 bears that out. That combination of character and practicality is rare in the classic market, where plenty of equally old British and Italian machines demand a much higher tolerance for fettling.
Why Airheads Are Climbing at Auction
Airhead values have been moving upward for a straightforward reason: they're the last BMW boxers built before electronics, catalytic converters, and fuel injection changed the ownership experience. A clean R90S or late-model R100 delivers the mechanical directness collectors are chasing, at a price still well under what equivalent-era Italian twins command. Riders who came up on modern oilheads and liquid-cooled boxers are increasingly the ones bidding on airheads, drawn back to the rougher edges their current bikes have engineered away.
That generational pull, combined with a genuinely finite and shrinking supply of well-kept examples, is the same dynamic that's lifted prices across the wider classic market for Ducati and Norton machines of similar vintage. The difference with BMW is how usable these bikes remain. An airhead bought for weekend rides can still happily spend a full day on the back roads, which keeps demand coming from both collectors and riders who actually want to use what they buy.
A Century, More or Less Unbroken
What makes the boxer's history worth telling isn't any single technical leap. It's the continuity. Friz's 1923 layout, cylinders poking into the wind and shaft drive out back, has absorbed four-valve heads, liquid cooling, variable valve timing, and a near-tripling of displacement without ever being abandoned. Few engineering decisions from the 1920s are still shaping showroom motorcycles a hundred years later. Having owned one of the airheads in the middle of that story, I understand why people get attached to them.
If you're chasing your own piece of that history, whether it's a /2 restoration project, a /5 or /6 tourer, or a modern R nineT built to echo the originals, it helps to know where values are heading before you buy. Browse BMW model histories and airhead auction values on RunMotoRun to see how the market for these engines is moving.
Image credits: My 1975 BMW R60/6 in profile: the transverse boxer, shaft drive, and pinstriped tank that define the airhead era.; Head-on view of the R60/6: both cylinders sit out in clean air, the idea Max Friz built the R32 around in 1923.; Left side of the R60/6 engine, with the Bing carburetor, finned cylinder, and rocker cover that give airheads their look.; Left side of the engine: the same layout mirrored, with the fuel lines and petcock running down from the tank.; The R60/6 instrument pod: speedometer, tachometer, and a center column of warning lights.; Looking down the bars toward the gauges, with the key in the ignition on the left side.