Cargo Bike Power

If you want to wean yourself away from petroleum dependence, try a cargo bike. A good one lets a relatively fit adult transport 500 pounds of stuff across level ground, so a few bags of groceries are cake. In recent years, increasing concerns about the environment and energy dependence have made cargo bikes a hot topic for makers and tinkerers who want to design an important piece of the future.

The concept isn’t new, of course. Bikes specially designed to transport cargo are nearly as old as the bicycle itself. Starting in the late 19th century, cargo bikes were used in many developed countries to carry items that would otherwise have required horsepower, and they continued to be used to deliver things like bread, milk, and mail until after World War II, when cars and trucks took over in industrialized countries.

But designing cargo capacity into pedal-powered transportation is a challenge that not only presents questions of where, what, how, and how much to carry, it also complicates all the usual bike design tradeoffs — balancing weight, strength, cost, gearing, frame geometry, wheel size, and so on.

It’s a vast, messy, multivariable problem that can’t be optimized for all applications. But overthe generations, a few popular strategies have evolved that do a good job with common types of cargo and terrain. Makers like Joshua Muir and Saul Griffith are adding their own ideas to the field, building a revolution not just in cargo-bike design, but in the way people live.

Classic Carriers

How do people carry loads on bikes? Many popular “cargo bikes” are just regular bikes with cargo capacity added on. Good old-fashioned panniers and bike trailers, for example, come in various shapes and sizes, and you can detach them to regain your bike’s performance. But panniers have limited capacity, and trailers can be difficult to maneuver — tip-prone energy drags, rolling behind and clattering around.

To make room for loads on the bike itself, you can shrink the bike’s front wheel and fork, lengthen the head tube, and attach a basket in front. This is the tradesman’s bike, aka deli bike, butcher’s bike, post bike, or porteur. With the basket attached to the frame, rather than the handlebars, steering is unaffected. One model, the Pashley Mailstar, is still used to deliver mail in the U.K., although they’re sadly being phased out in favor of vans.

For even more capacity, you can move the front wheel forward, connect it back to the handlebars via a pair of curved steering rods, and carry the cargo low (and therefore stable) in between.

Such was the principle behind the Belgian keg bike (now commonly called long john or long haul), originally designed for a land of great beers and flat topography. Popular with messengers,

these bikes carry heavy cargo (comparable to a 2-foot by 1½-foot, 160-pound beer keg) where the driver can easily monitor it, which especially helps riders carrying living “cargo” like kids and pets.

Inspired by this classic design, Portland, Ore., cargo-bike maker Metrofiets created the Beer Bike for a local brewery, which carries two kegs (with taps made from bicycle parts), an inlaid wood bar, a pizza rack, and a wood-paneled sound system.

Tadpoles, aka Christiania trikes (named after the car-free district in Copenhagen where many are made), are sturdy cargo tricycles that carry large loads, including children, between two front wheels. Like other tricycles, they’re less maneuverable than bikes — wider and prone to tipping during turns.

A different cargo-trike approach is to put the two wheels and cargo in back, as with recumbent tricycles, where the driver sits low with legs extended forward.

Life After the Xtracycle

Perhaps no other U.S. company has done more to promote the potential of bicycles to transport cargo than Xtracycle (xtracycle.com), started by mechanical engineer Ross Evans.

In the spring of 1995, Evans began studying bicycle use in the developing world. He noticed, particularly in Central America, that while conventional bikes were abundant, they weren’t as useful to people as they could be.

He set about designing an inexpensive cargo carrier that was lightweight, maneuverable, stable, and able to travel down narrow paths. This led him to develop the “longtail” frame-extension kit, a bolt-on attachment that extends the length (and cargo-carrying capacity) of regular bicycles, sold by Xtracycle under the name FreeRadical.

The kit attaches just behind the bike’s bottom bracket and clamps to the rear-axle drop-outs, moving the rear wheel back about 15 inches (and swapping in a longer chain). The frame extends back to hold the rear wheel and wraps around behind it to support four upright tubes that carry a variety of accessories, like racks and decks for holding child seats or large panniers.

Many of today’s cargo-bike designers were inspired by Evans. The explosive cult popularity of the smooth-riding Xtracycles has inspired a subindustry of compatible add-ons that take the cargo bikes in different directions — like the Stokemonkey electric motor assist kit (MAKE Volume 11, page 82), which lets a rider haul hundreds of pounds up steep hills that would be impossible for anyone but Lance Armstrong to pedal otherwise. You can pedal normally without any motor resistance, but you can’t use the motor without pedaling. As manufacturer Clever Cycles explains, “We don’t believe in replacing human power with electricity; we believe in replacing cars.”

But as with the Belgian keg bike, longtail bikes aren’t all work and no play. The pedal-powered Margarita blenders and bike-based sound systems of Rock the Bike (Volume 11, page 76) were all originally built on Xtracycles.

Joshua Muir’s Small Haul

Frame builder Joshua Muir (francescycles.com), who co-founded the influential Bike Church Tool Cooperative in Santa Cruz, Calif., loves to go bicycle camping with his 60-pound black Labrador, Soupy. In Belgium, a long john might enable a trip like this, but the steep roads of the Santa Cruz Mountains require something lighter.

So Muir designed a high-performance cargo bike, the Small Haul, which takes the classic long-john design as a departure point. In place of its rectangular cargo area, the Small Haul has an oblong, stretched-fabric load basket supported by thin, integrated frame tubes that curve out gracefully between the front wheel and the down tube. The resulting space frame looks more like part of a racing yacht than a traditional work bike.

Muir saved even more weight with the Small Haul’s steering system. The classic long john includes idler steering, which uses lots of metal: an extended steering column connects down to two metal rods that run under the cargo basket then curve back up over the front fork. In addition to being heavy, the idler arms can get stuck when debris or cargo jam up the steering.

Instead, Muir adapted a less-common design based on sheathed cables, which bikes already use to transmit forces to brakes and derailleurs. The Small Haul’s two steerer tubes, one under the handlebars and the other over the front fork, each attach to a perpendicular pulley. On each side of the bike, one cable end wraps backward around each of the identical pulleys, connecting the two.

The resulting system weighs less than a pound, handles like a regular bike, and is strong enough for Muir to haul Soupy, dog food, and camping supplies in front, plus other gear in panniers on the rear rack. The only nonstandard parts are the two aluminum pulleys. The Small Haul, including generator light, fender, rack, and pump, weighs approximately 37 pounds. (Muir also builds a heavier Cycletruck, which follows a more traditional idler-steering design and can carry 200 pounds.)

Unlike many custom bike builders (and all major manufacturers), Muir minimizes the energy and toxic materials he uses, sourcing components locally whenever possible. “I don’t own a car, and drive little,” he writes. “Most all of the materials I use are sourced within the U.S., and some come from the Bay Area. I build framesets by hand, one at a time, slowly.”

Saul Griffith’s Cargo Trike

Since the birth of his son, Huxley, in April 2009, regular MAKE contributor Saul Griffith has been designing and building cargo bikes. His aim, he says, is to create vehicles that can haul groceries and kids up steep San Francisco hills, eliminating the need for his family to use a car locally. With a fall 2010 launch date, Griffith’s line of bikes will be sold as custom builds through his company Onya Cycles (onyacycles.com). If demand for any of the models takes off, he plans to start mass-producing them to sell at much lower prices.

Like Muir, Griffith has studied the past, including the bike-design “bible,” Archibald Sharp’s Bicycles and Tricycles, first published in 1896 (now printed by Dover Publications). But where Muir draws on his years of mastery, handcrafting lugged, steel-tube bicycle frames, Griffith takes a higher-tech 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.

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 and angles, and found the optimal combination, assuming a typical range of steering radii.

The result, converted from Matlab to metal, is a tricycle that feels uncannily like a bicycle, with a one-minute learning curve that teaches riders to ignore the sight of a big cargo basket swaying side-to-side in front of them and to just ride normally.

Cargobiketopia Rising

As a transit planner and bike activist, I’m thrilled about what Muir and Griffith are doing, as well as many others who are designing not just new bikes but also local bike-sharing systems, maintenance collectives, and plans for reclaiming bike-friendly roadway and path infrastructure (often located along old rail rights-of-way, canals, or rivers).

Building level, regional bike routes has so far been carried out piecemeal, and mostly in the name of recreation. But bike routes could also become an arterial network for transporting people and cargo throughout re-localized communities. Combine this with “intermodal” connections to express buses and trains, and you’ve got a sustainable transportation system with quality of life as the driving force.

Such a system would knit communities together, rather than drive them apart. The able-bodied could transport cargo and other people around, and everyone could live, breathe, and congregate in safety, moving around without a wall of armor surrounding them.

Many people seem to be yearning for a new kind of transportation system, and whatever the future holds, the freight-carrying bicycle will be an important part of it. It’s cheaper, more fun, healthier, simpler, more elegant, and more conducive to community than the alternatives. And designing, making, and pedaling new variations of cargo bikes around our cities and towns should keep us busy for many years to come.

Thanks to Stephen Bilenky and Erik Zo for helpful background information.