BMW K 100RS

There are those who will argue, and rightfully so, that BMW had to do something, that even though Max Friz's 60-year-old Boxer motor was most certainly a Good Thing, all good things must come to an end sometime. And for Good.

Thing, that sometime was not far off. The Twin already was laboring to pump out a meager 70 horsepower in its one-liter form, and upcoming noise and pollution regulations would have made maintaining even the present levels of performance more difficult than squeezing blood from a rock.

BMW, more than anyone, had seen the handwriting on the wall, so it stopped building the R100 models altogether, and has drastically cut the number of 650cc and 800cc Twins that will roll off the production line in the near future. The company's brand-new manufacturing facility in Berlin will produce 33,000 motorcycles this year an increase of 20 percent over last year—22,000 of which will be K100 models: the standard, unfaired K100 ($5990), the sporty K100RS you see here ($7200), and the touring K100RT ($7500), all of which share the same basic engine and chassis.

What's even more chancy about BMW's gamble is that the company is playing a hand it dealt itself almost six years ago, back when the decision was first made to build the K100. At that time, the technocrats at BMW were charged with building a machine that would not only meet the projected performance criteria of the Eighties, but one that would offer traditional BMW values— longevity, luxury, serviceability and, perhaps most important of all, exclusivity in a market soon to be inundated with exotica from Japan.

Simply put, the Germans needed to build a machine that the Japanese would not. And in the quest for such individuality, many engine configurations were either tried or at least considered. V-types, square-Fours, far-fetched H-designs, even a horizontally opposed flat-Four was evaluated, although it was abandoned once it was deemed too similar to Honda's Gold Wing. Eventually, the decision was made to build a new machine powered by a dohc, liquid-cooled, fuel injected, one-liter inline-Four laid on its side with its crankshaft running longitudinally. And after making that commitment, the powers-that-be at BMW must have gnawed their fingernails to the quick as new engine designs from Japan started bombarding the marketplace all around them.

Luckily for BMW, there were no direct hits. And finally, after five years of development that included 10,000 hours of dyno time and 400,000 kilometers of test riding, the K100 became a production reality for the European market late last year. Now it's America's turn. And those who have feared that the precious essence of BMW would somehow be boiled away by the brewing of this new formula need worry no more. Because the most endearing of BMW qualities are present—indeed, maybe even enhanced in the K100.

Now, understand that even though the K100RS tested here looks nothing at all like a Japanese bike and even less like its predecessor, the R100RS, it has been heavily influenced by both. The lazy lope and subdued rumble of the flat-Twin engine have been replaced with a more urgent, higher-frequency whine, the same kind of four-cylinder song sung by the inline-Fours from the Orient; yet the bike still has the same air of dignity that marked the R100RS. It gobbles up highway miles in grand BMW style, but also can be snapped into and out of corners with a precision and surefootedness that no Boxer could ever match. It's a bike that can be herded along a twisty ribbon of road in the company of the best high-performance Japanese iron without losing its stately composure. So in effect, it's the best of both worlds.

There's no question that a really fast rider on a really competent Japanese sportbike can get from Point A to Point B on a winding road much faster than he could on a K100RS; but most everyone else can ride just as fast, if not faster, on the BMW while not working as hard in the process. The K100 has the kind of powerband, the kind of suspension and the kind of overall handling that simply make the fine art of riding quickly a whole lot easier.

There is no mystery about how the K100RS accomplishes this feat; BMW merely rethought and rearranged existing technology to fit within some new parameters. In fact, poking around in the RS's twin-cam, 987cc engine reveals anything but cutting-edge hardware. The bore-and-stroke dimensions are un-fashionably undersquare (67mm by 70mm, respectively), the cylinder head is of a bog-standard two-valve design, and valve adjustment is via the same type of shim-and-bucket arrangement that has been bumping poppet valves open for decades. Only the narrow, 38-degree included valve angle is in keeping with current trends in engine design.

But there's a good reason for all of the K100's apparent low-tech: It fits the requirements imposed by the use of a longitudinal, inline-four engine of one-liter capacity. Were the cylinders any larger in diameter, the engine would have to be longer, for the bores already are marginally close together (9mm); and a longer engine would, in turn, mandate either a lengthier wheelbase (which is already quite long) or a shorter swingarm (which, if it were much shorter, would excessively amplify the up-and-down chassis-jacking caused by the shaft drive's torque-reaction). And since that more-or-less locked BMW into a smallbore, long-stroke engine (which is not conducive to high-rpm operation), a four-valve combustion chamber (which reaps its biggest benefits at higher rpm) made little sense.

On the other hand, the shim-and-bucket valve gear made perfect sense in the K100 engine. Not only does that arrangement meet BMW's requirements for simplicity and long intervals between adjustments, but it allows the camshafts and followers to be easily serviceable just by removing the cam cover on the left side of the motor. So, too, are the K-model's forged, one-piece crankshaft and its attendant plain bearings highly accessible, for they're all located just beneath the easy-to-remove aluminum cover at the right side of the engine.

Like late-model Boxer Twins, the K100 Four uses an electronically applied, nickel/silicon-carbide coating (called "Scanimet") on its aluminum cylinder bores, which are cast as a unit with the upper, left-side engine case. Aside from being non-boreable, this coated surface is superior to a cast-iron liner in terms of thermal conductivity, plus it allows for closer bore-centers, and is lighter and more durable. Durability also was the prime reason for the use of liquid-cooling on the K100. And the fact that previous BMW motorcycles have been air-cooled was no drawback; the company has, after all, been building liquid-cooled BMW automobiles for a long, long time.

BMW's expertise with automobiles also was put to good use in the adaption of fuel injection to the K100. The bike incorporates a variation of the Bosch LE-Jetronic system used on numerous BMW cars for years. This system utilizes a black-box computer (under the RS's seat) that, through a series of sensors positioned in key locations in and around the engine, keeps tabs on engine speed and temperature, throttle position, and the air temperature and pressure within the intake tract. That information is analyzed by the computer, which then regulates accordingly the flow of fuel through the injector nozzle situated in each intake port. But that's all pretty much standard fare for a fuel-injected motorcycle, with one exception: On the K100, a Bosch-built electronic fuel pump is housed inside of the bike's 5.8-gallon aluminum tank as a part of a unique, completely sealed fuel system.

Bosch also supplied the K100's electronic ignition, which is tied into the injection system's computer box so it functions as both a performance aid and a rev-limiter. By comparing engine rpm with the amount of throttle opening, the ignition effectively selects one of two distinct advance curves to work most effectively with the load that's being placed on the engine. In addition, at 8650 rpm, which is just 100 rpm above redline, the ignition automatically retards the timing to deter over-revving. And should the rider ignore that first warning, the computer then shuts off the fuel-injection system altogether at 8750 rpm, and keeps it off until the engine speed drops back down to below 8750 rpm.

That fail-safe capacity is about the most sophisticated aspect of the K100's engine. But otherwise, the bike has an unremarkable, long-stroke, two-valve, relatively low-revving motor that fits right in with the performance program outlined by BMW's engineers right from the beginning: strong torque output at exceptionally low rpm, and a healthy if not spectacular peak horsepower production at only moderately high rpm. That's just what the K100RS has, too. The torque peak is at 6000 rpm, but the engine achieves 85 percent of that peak at 3500 rpm; and the claimed 90 horsepower is delivered at 8000 rpm, still well below the power peak for virtually all comparable Japanese engines.

What those numbers mean is that even though the K100RS isn't going to win any contests of speed with Japanese weaponry of equal displacement, the bike still is no slouch. Actually, it's faster than, say, a Suzuki GS850 shafty in just about every conceivable way, from an idling crawl to triple-digit speeds and everywhere in between. Arid it does that by producing the kind of power that is generally found only on something like a Honda Interceptor—smooth, uninterrupted, linear.

So no matter the situation, whether it's cruising the open highway or clipping along some remote country backroad at a classic sport-touring pace, the BMW always seems to offer you two, maybe three usable gears to choose from. And although the K100RS admittedly is no FJ1100-killing roadburner, it still romped through the quarter-mile in 12.56 seconds and 107.20 mph—not bad, considering that the RS has rather tall gearing, taller, even, than the standard K100's.

There's also an uncanny smoothness in the way the K100 reacts to changes in throttle. Off of idle in neutral, the engine seems to respond slowly, almost with a stumble. But when the bike is in gear and moving along, it offers a nearly perfect compromise between immediate response and gradual reaction. There's virtually no driveline snatch, no sudden lurches, no tendency to fall on its face, just a turbine-like outpouring of strong, steady power.

There is, however, a glitch or two in the K-bike's performance program, not the least of which is what seems like a rather fragile clutch. Indeed, in the middle of only the third run down the dragstrip, the single-plate dry clutch in our K100RS fried itself to a crisp. Then there's the matter of the vibration radiated by this new-wave BMW. Despite being rubber-mounted in the front, the engine buzzes noticeably more than a Japanese inline-Four of comparable size, and certainly more than any Boxer Twin ever managed on its worst day. It's a fairly high-frequency vibration, too, that is strongest right at about 55 mph in top gear, and it's felt most often through the footpegs. And the vibes didn't go unnoticed by the heat shield on the muffler, which self-destructed its front mounting

So that improvement, along with the use of three low-lash cushion mechanisms in the driveline (one spring-type cushion and two hard-rubber types) in place of the the two in the Boxer (both of the coil-spring variety), has eliminated most of the driveline free play that made riding the old bike smoothly such a chore. Gear changing on the K-bikes is therefore not the least bit clunky or noisy, and off-on-off throttle transitions are not greeted with the lurching made infamous by the RI00 models.

Better yet, the K100 exhibits less of the up-and-down chassis-jacking that is always a concern on shaft-driven bikes. Some of that is due to the fact that the bike has slightly shorter suspension travel than the Boxer has, some is due to the fact that the rear suspension has stiffer spring rates with more preload and thus will not let the bike move up and down as dramatically. There still is a pronounced rise and fall, especially in the lower gears, but the problem is less exaggerated than it is on the R100 series.

Consequently, low-speed cornering in particular requires a bit of throttle-control to prevent excessive vertical chassis movement. But unlike the opposed-Twin BMWs, which often hammered their undercarriages into the road surface when the suspension compressed quickly, the K100RS has an abundance of cornering clearance in any case. The bike must be ridden extremely hard before first the footpegs, then the sidestand tang and the centerstand, graze the pavement. And even when something solid does smack the macadam, the RS remains unflinchingly stable.

One reason why the bike displays such good road manners is its use of fairly sticky Metzeler Perfect tires, an 18-inch up front and a fat, 17-incher in the rear. Another is the rigidity of the front fork, a Fichtel&Sachs-built assembly using 41.4mm stanchion tubes held in place by thick aluminum triple-clamps. The fork also features a front axle that has a huge, 22mm diameter to maximize the rigidity of the entire assembly, and the axle also is offset 2.5mm to the rear to increase the trail a like amount.

That sturdy fork is equipped with two very powerful Brembo brake calipers pinching slotted, stainless-steel discs that are 285mm in diameter. The brake pads are semi-metallic and provide consistent, effective stopping ability in both wet and dry conditions. But although the front brake is powerful and requires only two-fingered actuation to slow the RS at moderate speed, it calls for a fistful of digits around the lever during high-speed braking. Despite its high-effort action, though, the front brake does not fade, even when used aggressively for long periods of time.

Not so the rear brake, which can be overheated with exceptionally hard use, sometimes badly enough to stop working altogether. And when used in combination with engine braking from fairly high rpm, the brake can also initiate some mild rear-wheel chatter, which is aided by the soft rates of springing and damping in the rear suspension.

BMW has always used long, soft suspension on its motorcycles, it seems; and although the K100RS has a tad less travel at both ends than the Boxer models of recent years, it is nonetheless plush, compliant and responsive to bumps of all sizes. The fork action is above reproach in just about every respect, with the possible exception of the dive it exhibits during severe braking. The fork offers no external adjustments, but the single rear shock has a ramp-type collar that allows the spring preload to be set at any one of three positions. At its lowest setting, the rear end is pleasantly supple on the highway, but compresses and moves around too much during aggressive cornering. At its highest setting, the shock is best-suited for hauling a passenger and a few days' worth of luggage. Thus the middle position is the most useful and versatile, offering above-average compliance, sufficient ride-height, and adequate resistance to bottoming.

And it is in those fast, sweeping corners where the K100RS really shines. Its suspension squats evenly and predictably as the apex is reached, and mid-turn corrections can be made with little effort. The bike is no featherweight, but it carries the bulk of its heft which is the engine, primarily in typical low BMW fashion. And so, despite its narrow, 24-inch-wide handlebar, the RS can be flicked into a corner or side-to-side quickly and easily. You'll never be tricked into believing that there's a 16-inch front wheel residing at the front; but with its steep (27.5-degree) Steering Head Angle and short (3.9 inches) front wheel trail, the RS is responsive and uncommonly neutral-feeling at all lean angles, even when braking in a turn.

It's easy to see, then, how a rider can lock himself into a smooth, relaxed, but extraordinarily fast rhythm on the K100RS without even trying hard. That's a fair description of sport-touring, an activity at which the RS performs brilliantly. The seating arrangement is better even than that of the fabled R100RS sport-tourer, for while the two are roughly equal in the swervery, comfort-wise, the K-bike is roomier and more luxurious for use on the open road.

The seat, for example, is padded with softer, thicker foam; and the footpegs have been moved back ever so slightly compared with those on the Boxer, which cants the rider a bit more forward and takes some of his upper-body weight off of his tailbone. And the low, narrow handlebar is designed to keep the rider tucked in behind the fairing so he's out of the airstream.

One interesting trick BMW employed to keep things calm behind the fairing is the use of an adjustable airfoil just at the top of the windscreen. The foil causes a venturi effect at the top of the screen, accelerating the flow of air back toward the rider's head. This little wing does not enlarge the envelope of still-air around the rider, but instead just smooths and directs the flow so that the air that does hit the rider's helmet is relatively free of turbulence.

We have no wind-tunnel numbers to substantiate our feelings about the aerodynamics, but we can attest to the fact that the fairing does an excellent job of protecting the rider. One of our testers got caught in a sudden downpour without his trusty rainsuit, but when he stopped he discovered that only his boots and the top of his helmet had gotten wet.

That's the kind of thing that can forever endear the K10(?RS to its owner. So too can a host of other well-thought-out niceties, such as: turnsignal housings on the fairing which snap off easily in the event of a tip-over; a taillight that can be popped off in seconds with no tools; an easily removable cam cover and crank-case cover that feature self-centering bolts and reusable rubber gaskets; a rear wheel that can be detached in minutes; and, of course, BMW's highly acclaimed toolkit, which can actually handle some major engine work, including crankshaft removal. Then there are some real BMW breakthroughs, like a centerstand that is wide enough to provide stability when in use, and a centerstand that not only can be deployed from the saddle, but that won't retract unexpectedly and let the $7200 K100RS flop on it side.

What's more, the sidestand incorporates one of the slickest interlock devices ever to hit the market. The sidestand is linked to the clutch via a separate cable so that squeezing the clutch lever also automatically retracts the stand if the bike isn't resting on it. If it is, the clutch lever simply won't move. And since the engine will not start in gear without the clutch disengaged, BMW has made it virtually impossible to ride away with the sidestand down.

BMW has also made it impossible for anyone, regardless of their allegiance, to ignore the new K100. The bike has already been voted motorcycle of the year in five European countries; in Germany alone, BMW motorcycle sales have increased a staggering 120 percent since the introduction of the K100 last fall. And with the recent export of the entire K100 family to the U.S., BMW plans to increase its worldwide sales by more than 50 percent.

Ah, but to reach that sales goal, BMW figures that it will have to attract 35 percent of its K100 buyers from the ranks of Japanese-bike owners. And that's a sword that can cut both ways. Because should the K100 prove too successful, should this upstart motorcycle from Germany make any kind of a noticeable dent in the market-share of the Big Four manufacturers, you can bet your bottom Deustchmark on one thing: The Japanese will figure some way to flop an inline-Four on its side and put together a K100-clone that'll sell for thousands less. Maybe it won't be a good clone; maybe it won't take sport-touring to a new all-time high the way the K100RS has; but it'll be there, and the mere presence of a Japanese-built K100RS-replica could dilute the market for such a bike just enough to cause big problems for BMW.

We hope it doesn't come to that. We hope that the Japanese will ignore the small slice of the market that BMW might be able to capture and instead concentrate on bigger, more lucrative segments of the sport. We're willing to wager that they'll do just that. And so is BMW, obviously.

The difference is that we've got nothing riding on that wager. But BMW has bet the whole store on it.

Source Cycle World 1983