Shrike Philosophy
PHILOSOPHY
The basic design philosophy for the Shrike:
Simplify simplify simplify.
Straight tubes.
Flat body panels.
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 1R2F 1F2R (one front, two rear) in terms of overturning resistance, while 1F2R is equally superior to 2F1R in drive traction.
FWD (combined with a 2F1R layout), is dynamically superior to RWD. Major advantages are improved drive traction (more weight on the drive wheels) and 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:
Ha!
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 compromising 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 Shrike) and, surprisingly, lateral (cornering) grip.
Front Suspension:
Three types are discussed: VW trailing arm/torsion bar, stock double A-arms and purpose-designed A-arms with push-rod linkage to rising-rate springs.
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 deal with 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 140,000 miles I’ve never been 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:
Braking:
Acceleration:
Handling:…………….
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.
Body Materials:
Many possibilities, I use Alucobond.
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