Maker
TYKE LIKE TRIKE: Saul Griffith carries his young son, Huck, in an early prototype of his cargo trike. The triangular
wheelbase and innovative tilt-steering system ensure that the trike stays safely upright while it’s stopped, traveling in a straight line, or turning at any normal radius and speed.
approach. For example, he uses CAD to model
every piece of a bike, from the frame and wheels to
the smallest component, trying them out virtually to see how they fit together. “Someday,” he
predicts, “everyone will design bikes like this, and
there will be a new kind of ‘digital artisan.’”
Griffith’s line features three types of bikes, all
of which he designed to replace cars for different uses: a light-hauling “runabout” that can be
carried up stairs; a family-oriented longtail, where
kids can ride in back; and a tadpole cargo trike for
the heaviest hauling.
All three models use BMX wheels, which Griffith
favors because they’re cheaper and stronger than
27-inch or 700mm wheels, and they facilitate
greater stability by keeping the center of gravity
lower. (Smaller wheels also present marginally
greater rolling resistance, but smooth tire tread
and proper inflation matter more.)
The three bikes also have electric motor assist
from an internal-hub motor with a planetary
gear that can be set to different gearing ratios.
Power comes from a lithium polymer battery and
provides a range of 10 to 40 miles, depending on
weight and terrain.
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Of Griffith’s three designs, the cargo trike may
be the most revolutionary. Traditional tricycles are
naturally stable while standing still or going in a
straight line but are notorious for tipping when you
turn, with even greater danger if they’re motorized
and carrying a heavy load. To remedy this instability, bike designers since Archibald Sharp’s day
have created tilt-steer systems that let wheels lean
into the turn, although these have never appeared
in a mass-market trike.
Most two-wheel steering systems use Ackerman steering, originally invented for horse-drawn
carriages, in which the wheels connect to angled
steering arms linked together by a tie rod. This
allows each wheel to turn at a different radius
around the same point, reducing friction and
energy loss from tire slippage.
For Griffith’s tilt-steer system, he extended the
Ackerman geometry into three dimensions so that
each wheel tilts as well as turns at its own angle.
This required some “gnarly geometry,” he says; to
arrive at his final design, Griffith wrote and ran a
7,000-line simulation program that modeled all of
the system’s basic elements, analyzed the energy
loss under any possible set of their dimensions
Photography by Leila Hekmat
