The engine is basically a bored-out 600cc BMW. The 70.6mm stroke
is common to the entire BMW line, and the R90/6 has a bore of 90mm. Push rods
operate overhead valves, and the 180-degree crankshaft keeps the pistons
op-posed, thereby counterbalancing each other.
Various accessories are located inside, the engine cases. The
alternator and points are mounted under the large cover at the front of the
engine; the electric starter is inside the case above the engine; and the
back-up non-primary kick starter is located on the left side. The starter lever
swings outward and is difficult to use. but fortunately you don't need it very
Constant-velocity 32mm Bing carburetors are mounted at the rear
of each cylinder. Two plastic hoses connect the carbs to the airbox. Two
petcocks. one on each side of the tank, feed the carbs. The markings on the
petcocks are "A" for on. "ZU" for off, and "R" for reserve. The choke lever is
mounted on the left side of the engine case just under the gas tank.
The engine layout is in the BMW tradition, but major changes
have been made elsewhere on the bike. A standard single-leading-shoe drum brake
stops the rear wheel, but the single thin disc brake mounted on the left side of
the front wheel is obviously different. This disc brake system differs from most
others in two ways: (I) The master cylinder is located under the gas lank and
connected to the lever by a cable. Its location protects it in the event of a
crash, but more importantly, conceals it from vandals, who lately have been
ripping off master-cylinder caps like they break automobile radio antennas. (A
warning light in the instrument panel also warns you if the fluid level gets
low.) (2) The caliper is mounted behind the fork leg. In theory, this minimizes
distortion of the fork leg during braking and the consequent tendency to pull to
one side. It also puts the weight of the caliper closer to the steering axis
where it has less effect on steering action.
Another major change for BMW this year is the five-speed
gearbox. Although few people ever complained about gaps in the ratios of BMW's
four-speed, a five-speed better fits the new BMW image.
Quite a few styling changes have also been made. The chrome
panels on the gas tanks of last year's bike are gone, replaced by paint and
pinstripes (in seven available colors) to match the fiberglass fenders and side
panels. The tank itself is tall, fairly narrow, and holds 4.8 gallons. (A 5.8
gallon tank is available as original equipment for an additional $40.) The tank
is easily removed to service the front brake master cylinder
Another stand-out styling change is the instrument panel, which
is in its own case and uses printed circuitry in place of the internal wiring of
the speedometer and tachometer. The printed circuits are more resistant to water
and vibration. Between the speedometer and tach are five idiot lights: neutral,
turn indicator, oil pressure, generator, and brake failure. Also new is a real
honest-to-God ignition key which also fits the fork and seat locks. The ignition
lock is incorporated into the left headlight mounting bolt.
There are two handlebar switches, each with a button. The left
one is the horn (which should be louder) button and a three-position headlight
beam switch (high. low. and flash). The right switch is the electric start
button and the turn signal switch.
The headlight is turned on by the ignition switch, which has
five positions: everything off: ignition off with rear parking light on;
ignition on with no lights; ignition on with taillight; and ignition on with
Under the seat lies the 25-piece tool kit that includes tire
irons, a tube patching kit. and a tire pump. The quality of the tools is very
good, considering they are in a kit supplied with a motorcycle.
Another new feature is an unusual steering damper composed of a
hydraulic cylinder between the bottom triple clamp and the frame and a large
plastic knob atop the forks. The mount that attaches the damper to the triple
clamp can slide from right to left, and turning the knob varies the mount's
distance from the steering shaft. The knob has three positions: 0. I. and 2. The
"0" position places the mount closest to the steering shaft and provides the
easiest steering; the "2" position places steering axis and provides the
The telescopic front forks have internal springs and allow 6.25
inches of travel. Black rubber gaiters keep road crud away from the seals.
The rear shocks are manufactured by Boge and allow four inches
of wheel travel. A built-in handle on the spring base allows three preload
adjustments without any special spanner.
The engine is surrounded by a double-loop cradle frame. The
seat, rear suspension, and rear accessories are supported by a bolt-on rear
subframe. The housing for the driveshaft forms the right fork of the swingarm,
and the driveshaft itself is connected to the transmission with a universal
Center-pull spokes are laced to alloy wheels front and rear. A
3.25 x 19 Metz-eler rib is mounted at the front, and a 4.00 x 18 universal
Metzeler at the rear.
ENGINE AND GEARBOX: If the engine is cold you need the chokes to
start the bike. The engine will fire off and idle immediately, but needs a few
minutes warm-up before it will pull awav strongly. The electric starter button
requires a fairly hard push before it makes contact, but the starter won't
operate if the clutch is engaged with the bike in gear.
The bike has a broad powerband with no sudden power surges
through the rpm range. It accelerates smoothly from 1500 rpm in fifth gear, even
with passenger aboard. At 60 mph the engine is turning about 3500 rpm. only
halfway to the 7000-rpm redline.
Performance isn't generally considered to be the BMW forte, and
compared to some other bikes of similar displacement, the R90/6 isn't a
rocketship. BMW claims only a 14.0-second quarter-mile time for the R90/6. but.
our test bike logged 13.49 seconds at 96.8 mph. not bad for a tourer. We had a
lOOOcc Harley-Davidson Sportster ulong at the drag strip (for a test next month)
and raced it against the BMW The BMW won, hands down.
Unless you get your weight well forward on the BMW, wheelies may
be a problem if you are trying to get a quick hole shot-a fact that firmly
impressed us during our first run at the dragstrip. Our tester wasn't far enough
forward, and the tire spun for a few yards; when it got traction it almost
looped the bike. The reason the BMW is prone to wheelie is that, in addition to
normal rearward weight transfer during acceleration, the pinion on the
driveshaft tries to rotate around the ring gear in the rear end and raises the
whole bike when power is applied.
At 50 mph on level ground, you can accelerate and pass in fifth
gear. If you are riding double or are on an upgrade, you must downshift into
fourth for passing at 50, and if you're in a hurry, a quick jab down to third
will give even more punch.
There is a large flywheel on the crank-shaft to smooth out
engine vibrations, and its inertia also helps low-speed torque. However, the
additional inertia makes the engine less responsive to changes in throttle and
load: because of the flywheel weight, the engine doesn't rev as quickly as. say,
a four-cylinder bike. Nor does it return to idle immediately when the clutch is
disengaged and the throttle closed. Because of this gradual response, it takes
some time to learn how to shift without lurching. The faster the shift, the
bigger the lurch when the clutch is released. The trick is to let the engine
speed synchronize with the transmission speed before engaging the clutch after
In past years, one complaint about BMW's has been that the
gearboxes clunk during shifting. Although the gearbox has been revamped this
year, ours usually still clunked when it was shifted. By downshifting without
the clutch—just blipping the throttle as we shifted—we could usually keep it
from clunking. Normally, though. we just used the clutch and let it clunk. The
only shift that was usually silent was the upshift from fourth to fifth.
With a powerband as broad as the BMW's, a five-speed
transmission hardly seems necessary, but it does bring the ratios closer
together. They are evenly spaced and offer flexibility with however much power
you want for any particular move. For example, you can come out of a 70-mph
corner in any of three gears, depending on how much power you want. You can
change the overall gearing on a BMW. but it's not cheap or terribly easy. You
have to replace the ring and pinion set. which is a complicated job. Unless the
bike is going to be used for something unusual, there is no reason to change the
The clutch lever required a fairly hefty pull, but otherwise the
clutch was flawless. It never slipped or dragged, and the engagement was smooth
HANDLING: The R90/6 is most at home with straight line cruising
and casual cornering. It won't wobble at all on the freeway rain grooves, and if
you are cruising in a straight line, you can take both hands off the bars and
the bike will remain straight and steady. The only time it wiggles while going
straight is if you make a hard shift with the power on: then it gives a slight
twitch due to the offsetting torque of the engine and drive shaft.
Because the R90/6 is designed with long-distance louring comfort
as the foremost consideration, some concessions are made in the area of
high-speed handling. The soft suspension allows the bike to wallow slightly
during fast cornering. We experimented extensively in one turn where it wallowed
at 55-60 mph when pushed very hard. We were unable to make it wallow less with
any combination of rear shock preload or steering damper position. The wallowing
never turned into a tank-banging speed wobble or threatened to wrest control
from the rider, but it made it difficult to take a precise line through those
corners. But as long as you're not stuffing it through a turn at the absolute
limit, the BMW corners precisely and predictably. You can pick a line with
confidence in any corner, bumpy or smooth. It will also change lines willingly
in the middle of a turn.
For comfort's sake, the suspension, especially the front forks,
offers more wheel travel than most street bikes. However, overcoming centrifugal
force while cornering causes much of the suspension travel to be used up. which
reduces Ground Clearance. When cornering hard the side Stand drags on the left
and the brake pedal grounds on the right. If you lean still farther to the
right, you can nick the valve cover, but that's leaning very far.
Part of the reason that the Ground Clearance is reduced during
cornering is the torque reaction of the bike when the power is rolled off. The
driveshaft tries to rotate around the ring gear and push the motorcycle down
during deceleration: and applying throttle will cause the drive-shaft to raise
ihe motorcycle. The result is that acceleration means more Ground Clearance, and
backing off the throttle means a reduction in Ground Clearance. Most riders will
never be concerned by the resulting dragging of the sidestand and brake pedal,
but riders who corner fast will have to deal with it.
Because of the low center of gravity offered by the horizontal
engine, it's a breeze to flick the bike from side to side in an S bend. The
lower center of gravity also makes the bike seem lighter when you are supporting
it at a stop light. And you don't have to be built like King Kong to back it
into a parking place.
The Metzeler tires are designed for long life at high speed. The
rubber compound is fairly hard, but the tires hold well within the limits
imposed by the bike's power and Ground Clearance.
The seal is long, wide and comfortable. Long hours in the saddle
won't make your posterior sore. The bars are rather narrow (27.7 inches) but are
wide enough for easy maneuvering at low speed. The narrowness is good for
high-speed comfort and touring because it keeps you from being SJMfead out in
the wind. The Magura grips are large and soft enough that your hands won't get
A friction damper on the twistgrip allows you to ride long
distances without o>nsiantl\ having to twist the throttle, fuming a thumb screw
pushes a friction shoe against ihe drum of the twistgrip. but you can still
close the throttle by forcibly turning it back
The only part of you that will ever get sore while riding the
R90/6 will be your left hand, due to the heavy-pulling clutch. But that will
only occur on roads where you must shift frequently.
Because the right cylinder is offset to ihe rear in relation to
the left cylinder. Ihe right footpeg is equally offset behind the
left footpeg. Nobody noticed this unless it was pointed out to them. Two of our
testers were bothered by the right intake luhe. which occasionally hit their
The seat-bar-fooipeg arrangement fits most rulers. You lean
forward on the bars only a little bit. which works out line once you're moving
and there is wind pressure on your chest.
The front suspension, with ils long travel, absorbs big jolting
bumps and tiny road cracks equally well. The rear suspension never pounds a solo
rider, even with the shocks on their stiffest selling: thus sum hack doesn't get
sore after a day of riding. I or the average rider, the best ride is with the
shocks on the softest position: the best position for hard cornering is the
Ihe R9G76 vibrates far less than most bikes. Our lesi bike was
smooth at highway speeds, but during hard acceleration and when the engine was
under load, it And it was noticeable at any rpm, although not enough to cause
Noise can also be fatiguing, but the very low level of exhaust
and mechanical noise from the R90/6 makes a ride to work or a tour through the
country a really pleasant experience for both you and those around you. BMW has
set an enviable standard of excellence in this area.
The passenger is well taken care of; he has plenty of room on
his part of the seat and the passenger pegs are adjustable. Instead of a grab
strap. BMW uses a hand rail around the back of the seat for those not inclined
to hold onto the rider.
THE BRAKES: Feedback and feel from the front brake were
excellent, and the brake required a great deal of force to lock the wheel. There
was no noticeable pull to either side.
The rod-operated rear brake is too powerful and insensitive. It
can be locked easily, especially if the rider downshifts while braking.
Downshifting into first gear while braking would often lock the rear wheel. The
best stopping distance at 60 mph was 137 ft. 6 in.
Although the brakes were quiet when cold, they squeaked when
they got hot. The front brake emitted a soft, high-pitched squeal, and the rear
shoes squeaked louder but with a lower pitch.
Instead of an external pointer to meet Federal demands for brake
wear indicators, the BMW has two viewing slots in the rear hub. You look through
these slots to check the condition of the brake shoes. We thought the slots
might allow water to enter the drum and make the brake ineffective, so we
thoroughly doused the rear brake with a hose and immediately went for a ride.
The rear brake was as strong as ever.
RELIABILITY AND MAINTENANCE: One of the most important factors
in deciding a bike's worth, and the hardest to measure in a road test, is
reliability. A bike can be a rock-steady rocket-ship that stops in an instant,
but if it self-destructs after 5000 miles it had better have a pretty low price
tag to make it worth considering. Owners of any particular motorcycle always
tend to be a little optimistic about its qualities because their egos are
involved, but we called one mechanic friend who has been working on BMWs for a
few years and asked him how often he had to do top-end jobs and replace
There was a pause. "I've never done a top-end job on one," he
said. "And I don't even know what a BMW crankshaft looks like."
Was there any problem that they commonly had? "Yeah." he said,
"they turn pipes blue."
That was only one mechanic, but we've never heard
anyone say anything different: the legendary BMW reliability comes from more
than the overconfidence of a few happy owners. The new engine size introduces a
variable to that leeendar reliability, but we don't feel that the bore-job will
affect engine life. BMW engineers have proven themselves more careful than that.
Commonly maintained parts are easy to reach: The valves,
carburetors, points, air cleaner and large 12-volt battery are all at hand.
Two maintenance benefits of the drive-shaft are: (1) It only
requires an occasional change of lubricant: (2) you never have to align the rear
The spokes are of the center-pull variety and require less
attention than conventional angled ones which are found on most bikes.
During the test we never had to do anything more than add gas
and oil. We didn't even have to adjust the clutch or brakes after acceleration
and brake testing.
MISCELLANEOUS: The Bosch quartz iodine headlamp is excellent. It
throws a bright, wide beam that thoroughly lights a large area.
Two mirrors are supplied with the bike. The right one on our
bike badly distorted the images over much of its area.
The speedometer includes a resettable tripmeter. something that
is useful for telling how long it's been since you last filled the gas tank. It
was about four mph optimistic at 60 mph.
The BMW sidestand snaps back automatically when the bike isn't
leaning on it. This might be overlooked by someone unfamiliar with the bike: he
may lean the bike upright and then try to lean it back over onto nothing. A
centerstand is also standard equipment.
There is a helmet hook located beneath the seal. You can slip
the D rings of your helmet on the hook and then lock the seat and leave your
helmet with the bike. Unfortunately, a healthy tug will open the seat whether it
is locked or not. And while someone is stealing your helmet, he'll probably take
your tool kit and tire pump too. The lock needs redesigning, along with a
repositioning of the helmet hook. If you try to carry a helmet on the hook while
you're moving, the helmet hits the rear tire.
We averaged 46.8 miles per gallon during the test, or almost 225
miles per tank. We got one bad batch of "premium that made the engine ping when
the throttle was open wide at low rpm. II* the quality of gas seems to be low in
your area, or you plan on touring in areas where high octane fuel isn't
available, your local BMW dealer can show you how to retard your timing to suit
The only problems we had during the test were improperly
adjusted carburetors (which we adjusted and had no further problem with) and
very slight oil seepage around the case joints when the speedometer registered
5200 miles. And the pipes were blue, as our mechanic friend mentioned.
SUMMARY AND CONCLUSION:
The BMW R90/6 is a powerful motorcycle, designed to compete in
the performance-conscious market of 1974. Basically, the R90/6 is a bored-out,
snappy 600cc tourer, but by restyling, adding a front disc brake and several
other innovations and features. BMW has created a strong competitor in its
The R90/6 accents touring, but still maintains an identity as a
sporting machine. The engine is powerful enough for good high speed performance
and yet remains absolutely tractable at low speed. The live-speed transmission
clunk has well-spaced ratios: the clutch is smooth, but heavv-pulling.
The R90/6 is very much at home on the highways and inlerstates.
It is smooth, stable, and quiet at touring speeds but some of the concessions to
comfort and ride, so valuable in a touring situation, limit it somewhat during
hard cornering. Routine maintenance is kept to a minimum, and what maintenance
ihere is can be done quickly.
As a tourer, the R90/6 is not outdone by any motorcycle, but
some of ihe Japanese multis have closed the gap on BMW in many areas where BMW
used to stand alone. And although the prices of Japanese bikes are rising, thev
are still cheaper than the $2950 price of'the R90/6.
So. in the end, ihe R90/6 will have to sell itself by
reputation, reliability, charisma, and unique features that have appeal to some
buyers and are unavailable elsewhere. CG