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Copyright 2002, 2003, Robert S. Cascaddan, MBA
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“Attracting a New Generation of Riders to the Sport of Motorcycling”
“Disruptive Technology = Revolutionary Changes”
A Qualitative Analysis
By
Robert S. Cascaddan, M.B.A.
In the off-road market of the 1960’s and 1970’s, low
weight and narrow firing-angles (power-pulses concentrated within a relatively
few degrees of crankshaft revolution) gave a handling advantage that offset low
power and heavy vibration[1]. Development resulted in Dirt Bikes with very
low weights. Due to their low weight,
two-stroke engines predominated.
Environmental concerns and recent rule changes, however, have resulted
in a shift in focus to four-stroke engines with twice the displacement. Development is focused on building
four-stroke singles that are light enough to be competitive with
smaller-displacement two-strokes.
This four-stroke technology is easily adaptable to the
on-road market. In fact,
single-cylinder motorcycles with dirt bike lineage, known as Super Motards, are
already beginning to compete in the on-road motorcycle market. Sport Bike riders are switching to Super
Motards because they are FUN. Weights are low enough to revolutionize handling
and make the use of expensive space frames and box-section dual-spar frames
unnecessary. In addition, concentrated
power pulses give the rider a better feel for traction[2].
Only two technical hurdles separate lightweight
single-cylinder motorcycles from widespread acceptance in the on-road
market. The first hurdle is the
vibration that plagues high-performance single-cylinder engines. The second hurdle is the high maintenance
presently required by compact, powerful singles.
Rupert Beindl has built a prototype Twin-Crank Single
as a test platform for a 990cc Four-Stroke Twin-Crank Parallel-Twin intended to
compete in the 500 cc Grand Prix racing class[3]. Twin-Crank layouts have also been used on
two-stroke 500 cc Grand Prix racers.
There are three primary advantages to the Twin-Crank layout. The first advantage is that piston side
thrust is completely eliminated. The
second advantage is that primary imbalance can be eliminated for each cylinder
separately without inducing secondary imbalance. The third advantage is asymmetry between the strokes.
Elimination of side thrust significantly reduces
friction within the engine – increasing available horsepower. In addition, according to Bike, the
layout allows lighter pistons, shorter piston skirts, less ring wall pressure,
and larger bores. Elimination of side
thrust also decreases engine wear.
The Twin-Crank layout provides the potential to
completely eliminate both primary and secondary imbalance (vibration) in
singles, parallel-twins, and triples with simple crankshaft
counter-weighting. The elimination of
vibration allows engines to be run at higher RPM and frames to be constructed
lighter. Singles, parallel-twins, and
triples are simpler to produce and more compact than other layouts. As an added benefit, these engine layouts
produce charismatic sounds.
As a result of offset cranks, the intake and power
strokes in a twin-crank engine take more degrees of crankshaft rotation to
complete than the compression and exhaust strokes. The Bike article specifies advantages for each
stroke. The intake stroke is longer, so
there is more time to draw in air/fuel mixture and cool the piston crown. The compression stroke is shorter, allowing
less time for heat to transfer. Also,
higher piston speed results in more turbulence in the air/fuel mixture. The power stroke is longer, allowing more
time for the expanding gas to push on the receding piston. The exhaust stroke is shorter, resulting in
higher exhaust gas speeds and more effective exhaust tuning[4]. The result, particularly when combined with
a higher redline, is more horsepower.
Rupert Beindl claims that his 650 cc Twin-Crank Single
puts out 115 bhp at 12,000 RPM[5]! Some substantiation of this claim is
available from Daytona singles race winner, Steve Marlowe, who claims that
Rupert Beindl’s twin-crank single breezed past him during a practice. Steve Marlowe was sufficiently impressed to
go looking for the bike that had breezed past him and bring the technology to
the attention of Bike Magazine.
Providing displacement
in a single-cylinder engine requires the piston and connecting rods to be
large. For purposes of illustration, consider
that the same bore and stroke required to make a 625cc single would result in a
1250cc twin, a 1875cc triple, or a 2500cc four-cylinder engine. Significant wear results from the forces
caused by the size of the moving parts.
In a twin-crank engine, however, the forces that cause this wear are
cancelled or distributed over a larger area.
In addition, maintenance issues caused by vibration are eliminated.
One further issue remains. In the process of making single-cylinder engines incredibly compact
and light, engineers have reduced the oil capacity of these engines to a bare
minimum. Consequently, not only are
frequent oil changes made extremely important, they are also rendered more
complicated and time consuming to perform.
In addition to changing the oil and filter(s), all air must be bled from
the system.
One solution may be to
increase oil capacity and pay the weight penalty. Longer-term solutions may involve use of better oils or
filtration to extend oil change intervals.
Another possible solution may involve technology that makes oil changes
simpler and less time-consuming.
Lighter lubricants are another possibility. Only time will tell where development will lead.
The Sportbike Tuck evolved for use on the
racetrack. Aerodynamic drag is
significant at speeds in excess of 100 MPH.
At these speeds, narrow clip-on handlebars reduce unwanted steering
inputs, as well as reduce drag. In a
recent article[6], however, Bike
Magazine questioned whether Sportbike ergonomics compromise a motorcycle’s
ability on the street. On the street
and in tight corners, a narrow bike with wide handlebars, an upright riding
position, and a seat that allows the rider to slide his weight forward to
weight the front wheel is more fun and provides maximum control for stunts,
tight corners, evasive maneuvers, and sliding.
This riding position can be seen
on the street in the growing Super
Motard genre. Despite severe vibration,
and the fact that none of the major manufacturers sells a 2003 model Super
Motard in the United States, this genre is experiencing considerable
growth. For 2004, KTM has announced
that they will reenter the U.S. Super Motard market with 4 models – the 450
SMC, 525 SMC (scheduled for August 2003 Release), 625 SMC, and 660 SMC. More recent rumors, however, suggest that
the 660 SMC will not be available. Rumors
are that he 450 SMC and 525 SMC will to be non-street legal, and the 625 SMC
will be street legal in the United States.
It is unknown if other manufacturers will offer Super Motard Models in
the U.S. Super Motards are very light
and are used for tight corners, wheelies, stoppies, and sliding. Those who ride Super Motards say they are
attracted to them because they are more fun than Sportbikes. This same riding position can also be seen
in the fastest growing segment of the sport – Youth Motocross. As a result, many riders who may one day
consider riding on the street will have grown up with this riding position –
the Sportbike Tuck will seem unnatural to these young riders.
[1] Ed Youngblood, John Penton and the Off-Road Motorcycle Revolution (North Conway, NH: Whitehorse Press, 2000).
[2] Kevin Cameron, “Big Bang Theory,” Cycle World, May 1992, 16.
[3] Kevin Cameron, “Baindl’s Twin-Cranker,” Cycle World, February 2001, 32.
[4] Ibid.
[5] John Robinson, “Four-Stroke GP Missiles Are Coming Bringing Technology You’ll Soon Be Riding on the Road. We Look At One Astonishing Possibility for the Future of Speed and Power,” Bike, July 2001, 130-134.
[6] Hugo Wilson, “Back Hurting? Fuel Light On? Feeling Skint? Blame These Guys > They say racing improves the breed – and while we’re all delighted with better handling and brakes – but how much does track heritage actually compromise your bike’s ability on the road?,” Bike, December 2002, 74-78.