Riding a bike is one of the most recommended forms of exercise for overweight Americans, yet not a single mainstream bike company in America makes a bike designed specifically to accommodate riders over about 300 pounds.

This is the Catch-22 Dr. Rodger Kram found himself considering last year when contemplating a bold research project: making a bike for adult Americans between 18 and 65 who qualify as obese, which the National Institute of Health defines as having a body mass index of 30 or greater. That’s a market of about 35.7 percent of the American adult population, or approximately 73 million people.

“Cycling is an obvious exercise choice for obese people, except that bikes aren’t made for them,” says Kram, an associate professor of integrative physiology at the University of Colorado Boulder. “In fact, a lot of bikes are sold as, ‘Here’s the rider weight limit.’”

Making a bike for big people isn’t as simple as outfitting a frame with sturdier wheels and tires, or swapping to a larger, more supportive seat, although that’s a good start. Kram, whose team comprises students from both the physiology department and CU’s engineering school, points out three current challenges that bikemakers are largely not dealing with: safety, comfort, and durability. The obesity bike project aims to address all three.

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What Overweight Riders Need

Obese riders have particular challenges when cycling, which Kram’s research assistant Rob Foster knows first-hand. Foster, who is about 5’11”, weighed as much as 327 pounds a few years ago before using cycling, running, and attention to diet to reach his current 160 pounds; the weight loss would have gone more smoothly with the right bike.

“When I started riding I was already down to about 260, but I still had issues even at that weight,” says Foster. “It was uncomfortable and hard to ride, and the cheap bike I had didn’t last very long.”

Kram’s team interviewed obese people who’ve used bikes for exercise to gather information about their experiences on the bike, and found that broken seatposts and wheels are common issues. “A taco’d wheel is obviously a problem, but a broken seatpost is extremely dangerous,” says Kram. Almost every place on a bike that carries a load—from crankarms to pedals to the chain—could wind up a hazard if it’s not built with very large riders in mind.

It’s not enough for a bike to simply be bombproof: It has to be comfortable to ride, too, if it’s going to see use, and an obese person’s body requires different considerations from a design team. For one, a saddle must be the right size and shape to properly support them. Rider position on the bike is key in alleviating stress on the spine that could cause issues with disc tissue. Even something as specific as handlebar height helps fine-tune a rider's wrist angle to prevent against fatigue.

Given the concerns, why recommend that obese people ride at all? Why not just advise them to walk, another form of exercise commonly recommended to severely overweight people? About a decade ago, recalls Kram, then-doctoral student Ray Browning (also a former professional triathlete) looked into walking’s mechanical load on leg joints and found that even brisk walking put enormous strain on obese people’s joints, particularly their knees. Walking at a gentle pace on a slightly inclined treadmill was fine, Kram says, but it’s not nearly as inspiring as riding outside. Cycling, as a generally non-load bearing aerobic exercise, could be a better choice, if it were safer and more comfortable.

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The Paradox of Bike Design

But to actually design a bike that meets comfort, safety, and durability needs is a challenge for many reasons: Comfortable bikes aren’t always sturdy enough, and vice versa. And it’s important to note that obese riders are qualitatively different from very tall riders of a similar weight in a very important respect—getting on and off.

The classic double-diamond frame is difficult for obese people to mount, but a standard step-through frame doesn’t always offer the torsional rigidity that these riders need. Past studies by Kram’s lab show that, partly because their musculature has to support such a large load, obese people generate tremendous amounts of power doing something as simple as standing up, so they also create lots of torque when pedaling.

Working with Mosaic Cycles, a custom framebuilder in Boulder (founder Aaron Barcheck is one of Kram’s former students), the team built a prototype and discovered that moving the traditional top tube to a spot midway down the seat tube—and connected horizontally to the middle of the down tube rather than up at the top of the head tube like a normal step-through design—produced good torsional rigidity while preserving a step-through’s easy-to-mount attributes.

Perhaps the most overlooked issue—and the one presenting the most problems for the team—is safety, namely for braking. A few of the bikes marketed toward 300-plus-pound riders use antiquated braking technology like a coaster brake. Even some modern systems may still need tweaking. Using a borrowed downhill bike with 200 mm rotors, Kram’s team tested the stopping distance from 15 mph with an increasing amount of weight on a trailer behind the bike. The results: At 450 pounds total rider weight, stopping distance was almost three times farther than for a 180-pound rider.

At one level that’s understandable; it’s three times the mass. But it’s troubling from a safety perspective because it means larger riders may not be able to stop in time to avoid obstacles. “Even hydraulic disc brakes aren’t giving us the amount of braking power we need,” says Kram.

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The Industry’s Oversight

Despite the obvious potential market of 73 million Americans, the bike industry hasn’t shown much interest in making a bike for severely overweight riders.

That’s not to say there hasn’t been any; it’s just that these designs are at the fringes of the industry. Custom builders like Zinn are experienced at making bikes for big and tall riders, but they come with custom prices. A handful of small companies (Zize, Worksman and Day 6, to name a few) make bikes expressly intended for riders over 300 pounds, but not everything about them is necessarily appropriate; a couple of models from Worksman and Day 6, for instance, use coaster brakes, and some still use the double-diamond design overweight cyclists find difficult to mount.



Regardless, none of the “big four” brands—Trek, Specialized, Giant, and Cannondale—make bikes expressly intended for riders over 300 pounds. In fact, all four manufacturers use cautionary language in their owner's manuals that hint at rider weight limits, such as not guaranteeing the warranty for riders past a certain weight (typically 300 to 325 pounds, depending on the make and model). All the bikemakers we spoke with added that the weight limit, if it can be called that, is there primarily out of an abundance of caution and to limit legal liability. They characterized it as a recommendation, not a requirement, but it’s there nonetheless.

As well, the independent bicycle channel has done little to market to this prospective buyer for a number of reasons. One: major bikemakers' product lines are often global, with only small tweaks for different markets, and obesity isn’t quite as much of a public health problem in other bike markets like Europe. (That’s not to say it’s not an issue; more than 20 percent of adult Europeans qualify as obese, according to the World Health Organization). Also, in the US especially, the bike industry is chiefly made up of lifelong enthusiasts who market and sell to other enthusiasts in turn.

Eric Bjorling, a spokesman for Trek, recognizes that the bike industry hasn’t historically pursued non-traditional markets well. While Trek has worked with overweight and obese riders (both individually and via outlets like the reality TV show “The Biggest Loser”), and CEO John Burke has spoken bluntly about the challenge of obesity for employees and employers, Trek hasn’t made a concerted push to design for or market to the overweight—although its Shift line has some of the attributes Kram’s team is targeting.

“We as an industry need to take a hard look at what we’re doing to grow cycling,” Bjorling says. “I say that not looking at [overweight riders] as a category, but to make cycling accessible for as broad a range of people as possible. Companies are starting to look at how the market is aging, with things like e-bikes, but that shift hasn’t happened on the weight side.” He admits he “doesn’t have a great answer yet” for why that hasn’t happened. “I hope to soon though,” he says.

The engineering horsepower certainly exists at bike companies to create bikes for big riders, Bjorling says: University efforts like the CU research project might offer some valuable insight. Kram says the team’s intention is to put their research results in the public domain for any bikemaker to use. Partly for that reason, he’s crowdfunding the final phase of the project, with proceeds going to create a final prototype based on what his team learns. The team’s crowdfunding campaign ends May 16 and has a relatively modest $3,000 goal. (Because CU is a public university, donations are tax-deductible.)

Strong Potential

Bikemakers aren’t entirely convinced that the market for overweight-specific bikes is there, despite the potential numbers involved. But Kram is. Early in the project, his research team led a focus group with about 60 hospital patients who were both morbidly obese, and yet motivated enough to change that they’d had bariatric surgery.

“We asked how many of them rode a bike as a kid, and about 60 hands went up; practically everyone likes to ride bikes,” he says. “Then, we asked how many of them had ridden in the last year. Maybe two, three hands.” It hurt to ride, attendees said. Finally, Kram’s team asked, how many of you would ride to lose weight if it were safe and comfortable?

“About 60 hands went back up.”

Joe Lindsey Joe Lindsey is a longtime freelance journalist who writes about sports and outdoors, health and fitness, and science and tech, especially where the three elements in that Venn diagram overlap.

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