Shrike Philosophy
PHILOSOPHY
The basic design philosophy for the Shrike:
Simplify simplify simplify.
Straight tubes.
Flat body panels.
No compound curves.
Zero tooling.
Complete motorcycle chassis and power unit.
Moderately high performance.
Minimum of specialized components.
This section is a distillation of some of the topics covered in more depth in the “Ask Mr. Shrike” section. There the topics are discussed in much more depth, with different opinions often presented. Please note that the views presented are only my opinions based on my knowledge and experience.
Basic Dynamics of 3Ws:
2F1R (two front wheels, one rear) is vastly superior to
1F2R (one front, two rear) in terms of overturning
resistance under braking, while 1F2R is equally superior
to 2F1R for drive traction and overturning resistance
under acceleration. For street use, I favor 1R2F for
accident avoidance.
FWD (combined with a 2F1R layout), is dynamically superior to RWD. Major advantages are improved drive traction (more weight on the drive wheels), a tendency toward understeer rather than oversteer (a safer condition for drivers with less experience and skill), and greatly reduced rear tire wear.
Optimum CG location:
There is none. There is only a compromise of competing
factors, overturning resistance and drive/braking
traction. There is an optimum theoretical CG height: 0”.
It is unobtainable of course, but lower is better. That
too is a compromise in packaging. You can’t put everything
on the floor.
Side-by-side vs Tandem Seating:
Side-by-side seating is more conventional and widely
accepted while tandem provides constant lateral weight
distribution for more consistent cornering response.
Tandem increases wheelbase (better ride quality, worse
turning circle) and reduced frontal area
Ultimate Performance:
It is possible to provide very high levels of acceleration
and braking, handling, and gas mileage, but not without
compromise in other areas, primarily crash safety.
Rear Tires, car vs bike:
There are two reasons (three counting appearance) for
running a wide, straight-tread car tire on the rear:
longitudinal (braking/acceleration) grip and tire mileage.
Tradeoffs include cost (modification to swing-arm and
exhaust system (in the case of the BMW drivetrain) and,
surprisingly, lateral (cornering) grip. With conventional
swing-arm geometry the rear tire camber changes with
chassis roll. 5° roll produces 5°
positive camber. With a round cross section bike tire the
road contact patch does not change. A flat-section tire
rolls onto the outer edge, greatly reducing road contact
patch.
Front Suspension:
Three types are discussed: VW trailing arm/torsion bar,
double A-arms and McPherson Strut.
Anti-roll Bar (sway bar):
The need for a front anti-roll bar increases with
increasing vertical travel and spring rates. The Shrike
has lots of travel and low spring rates. It needs one. It
doesn’t have one. I have learned to live with out it.
Reverse:
None on the Shrike. It would be nice, and should be
mandatory on all trikes. Methods include factory stock
(some Goldwings and BMWs), starter motor shaft levered
into contact with the rear tire, and a seemingly infinite
number of trick designs. In 160,000+ miles I’ve never been
in a situation where the lack of reverse put me in danger.
Of course it only takes once…
Safety:
Two parts: Active (avoiding the crash) and Passive
(minimizing injury during the
crash).
Active Safety:
Acceleration and braking, lateral acceleration, and
handing responsiveness.
Passive Safety:
The Shrike has a safety cell (a triangulated cage of 2”
diameter steel tubing, a racing seat, and a 5-point
harness, all designed to keep the driver in and other
stuff out. The wedge shape in plan and side view helps
deflect many would-be frontal impacts. I haven’t seen this
combination on any other vehicle.
Engine Choice:
I’d avoid the crotch-rockets and stick with a
comparatively low-stressed motor with a lot of bottom end
torque. The Shrike started with a 650cc four with 60 hp.
That gave adequate performance even at freeway speeds. The
130 hp BMW is overkill. Driving is serious business with
that much power. If I had it to do again, for an everyday
driver, I’d use a version of GoldWing with reverse, ABS
and the usual bells and whistles. Reliability is boring
and so very pleasant.
Body Materials:
Many possibilities, I use Alucobond, it’s just so easy to
work with.
Fuel Consumption:
Surprisingly, fuel consumption in the Shrike is
essentially equal with either 60 or 130 hp, averaging
34-36 mpg. With 60 hp it’s WOT (wide open throttle) much
of the time. With 130 it’s loafing 99% of the time, with
revs almost always below 4000 rpm (70 mph in 6th gear).
Air drag with the early version was terrible, and improved
slightly with the addition of body panels. While it would
be possible, and workable, to compromise the Shrike
concept to get much better mileage, I have no interest in
doing so.
Aerodynamics:
The Shrike is a fairly “dirty” shape, and not likely to be
improved much without more complex (expensive) body
panels.
nortonshrike.com ddnorton1@msn.com Dave Norton ©2016-2025