Two years ago, 12-year-old Molly Steinsapir was sitting behind her best friend on a borrowed electric bike when the girls started descending a steep hill in Los Angeles. Molly’s friend pulled the brakes, but the bike began to shimmy, and the girls crashed. Molly, who was wearing a helmet, sustained severe head injuries.

After the accident, Molly’s mother posted a call for prayer on Twitter, rallying hundreds of thousands of new followers who used the hashtag #TeamMolly to cheer for the child’s recovery. But after multiple brain surgeries, Molly died on Feb. 15, 2021.

While Molly’s death prompted an outpouring of grief on social media, the tragedy has taken a new turn. Her accident is raising questions about the safety of e-bikes — specifically the quality of e-bike brakes — and whether the wildly popular bicycles are safe for young people to ride.

Molly’s parents, who are both attorneys, have sued Rad Power Bikes Inc., maker of the e-bike the girls were riding and the largest e-bike company in the United States, claiming that its bikes “inappropriately” are marketed to children and contain “multiple design defects.”

The case, already a hot-button topic in the cycling community, garnered renewed attention this month with the publication of a lengthy investigation by Bicycling magazine. It sparked a viral wave of passionate, sometimes excoriating online chatter about e-bikes and their possible benefits, downsides, price, quality, regulation, and, especially, their appropriateness for young riders.

E-bikes, with their battery-powered motors and pedaling help, have surged in popularity in the United States and around the world as an eco-friendly alternative to cars and a less strenuous and sweaty option for getting around compared to a regular bike. By all accounts, they are the fastest-growing segment of the bike market, with sales topping 420,000 in 2021 and probably exceeding that last year, according to data from PeopleForBikes, the industry trade group for bicycle manufacturers.

There are three types of “e-bikes,” bicycles equipped with a battery and motor. Many are capable of carrying extra passengers or cargo, unlike most conventional bikes. Class 1 e-bikes, the most common, are pedal-assist models with motors that work only while you’re pedaling. They have a top speed of 20 mph. Ride faster, and the motor automatically flips off.

Class 2 e-bikes feature a throttle, so the motor powers the bike even if you don’t pedal. It stops working if you exceed 20 mph, though. Molly was a passenger on a Class 2 model.

Class 3 e-bikes are the most powerful. These pedal-assist bikes can reach 28 mph before the motor stops.

Legally, almost anyone can ride an e-bike. “There is currently no federal law or guideline regarding the appropriate minimum age” for e-biking, said Matt Moore, the policy counsel for PeopleForBikes. “The Consumer Product Safety Commission considers very young children capable of riding bikes, and e-bikes are classified as bikes.”

Thirty-nine states and additional municipalities regulate minimum rider age, usually for the powerful Class 3 bikes, although the requirements vary. Some localities also limit e-bikes, especially Class 3, in bike lanes. You can find more information about local regulations at PeopleForBikes.org.

According to the Steinsapirs’ lawsuit, the bike the girls were riding, a 65-pound RadRunner 1 model bought a month before by the friend’s family as a Christmas gift for an older sister, “began to shake and wobble” when Molly’s friend applied the brakes. The complaint claims the bicycle’s brakes, a type known as mechanical disc brakes, and the skewer and lever holding the front wheel in place, an easily removed mechanism called a quick release, were inadequate to the demands of handling and stopping the bike and contributed to the accident.

Brandie Gonzales, the director of public relations and communications for Rad Power Bikes, wrote in an email that the “entire Rad Power Bikes team extends its deepest condolences to the Steinsapir family on the tragic loss of Molly Steinsapir.” The company would not comment on the incident or lawsuit, she said.

Stacey Stewart, vice president of engineering at Rad Power Bikes, added that the company is “confident in the safety and quality of all of our ebikes and components, including the disc brakes and release mechanism, which are standard in the industry, used on thousands of bikes, and when used and maintained properly, are safe.”

Gonzales also provided a previously unreported letter, dated Jan. 12, from the Consumer Product Safety Commission, in which the agency said it had “completed its review of the information you provided” in response to the agency’s inquiries about the RadRunner 1 bike following Molly Steinsapir’s death. “Based upon the information you provided, the staff does not believe the problem identified necessitates further action.”

But anecdotes about brake issues and other concerns with the quality or handling of some e-bikes are common online and among cyclists of all ages and their mechanics. John Martinous, a 24-year-old teacher in Sanford, Fla., posted on Reddit about his e-bike, a Christmas gift from his parents. Contacted by The Washington Post, he said the brakes had stopped working while he was riding the bike, and he collided with a car turning into a preschool parking lot.

“The problem was that I wasn’t able to stop in time,” he said, adding that he wound up scraping his feet along the ground to stop the bike.

Peter Flax, a longtime cycling journalist in Los Angeles, said that after his story on Molly was published in Bicycling, several cyclists and mechanics contacted him to describe brake pads wearing out after only a few weeks of use or otherwise failing to fully stop the bikes when applied. “I heard from lots of people,” he said.

In the article, Flax described his own experience with brake concerns, after the brakes on a Rad Power bicycle he had purchased for one of his teenage sons weeks earlier stopped working. An experienced cyclist, he adjusted the brake cables and bought new brake pads, but the e-bike’s brakes continued to work erratically and burn through brake pads, he said.

After publication, he said, his Twitter feed and DMs filled with messages similar to that from one bike shop manager in Minneapolis, who told Flax that “every single Rad that comes through has brake issues.”

“It’s the Wild West” for e-bikes, said Dave Nghiem, the manager at College Park Bicycles in Maryland.

He and other bike mechanics contacted by The Post said the problems are not confined to one brand, but apply to many models of relatively inexpensive road e-bikes designed for recreation and commuting. These bikes typically retail for less than $2,000 and usually are sold directly to consumers, not through a bike shop. They make up the bulk of e-bike sales.

By law, all bicycles sold in the United States must comply with federal regulations on the safety of their components, Moore, the PeopleForBikes counsel, said. Depending on the bicycle’s weight and the total weight it claims to be able to carry, the brakes must be able to stop the bike within a certain distance, he said.

Stacey Stewart, the Rad Power Bikes VP, said in a written statement that the company’s “internal design and validation methods exceed the minimums required by the US ebike regulations," adding that "[e]very single bike is ridden one mile before getting boxed up. Then we conduct random sample out-of-box testing prior to shipment.”

But not all e-bike manufacturers follow similar voluntary standards. Some inexpensive e-bikes sold online can arrive from their overseas manufacturers without certification that the bicycles comply with all U.S. safety regulations. And many of the parts are unfamiliar to mechanics here, several bicycle mechanics said.

“I won’t work on them,” said Robert Lynn, the service manager for BicycleSpace in Washington, D.C., referring to low-cost e-bikes sold directly to consumers and featuring inexpensive components. “I won’t touch anything with cheap brakes.”

Karl Stoerzinger, a mechanic at Perennial Cycle in Minneapolis, likewise said the store has stopped working on electric bikes people ordered online because he’s often “flying completely blind” on the repair, dealing with unknown batteries and parts.

Some of the cheapest electric bikes people order online are using components that “aren’t really up to snuff,” Stoerzinger said. “If they’re using cheap brakes or something that’s not strong enough, that can quickly be a genuine safety issue.”

Even components that comply with bicycle safety regulations and have worked well on conventional bikes can be problematic on e-bikes, Lynn said, because e-bikes tend to be far heavier and sometimes carry passengers, adding to the weight.

“These things are going 20 miles an hour, which is faster than most people ever ride a regular bike, and then you have to stop all that weight,” he said. “Do that a few times, and you burn the brake pads down real fast.”

Anyone who rides an e-bike, whatever its make, should frequently check its brakes and other components, said Amy Korver, the community education manager for Cascade Bicycle Club in Seattle. (So should anyone who rides a conventional bike, she said.)

If the brakes’ levers get “really close to your handlebar” when you pull them back to stop, that’s a sign the brakes have lost stopping power and you need to get them checked, Korver said.

“You want at least a thumb’s width worth of distance between your handlebar and your brake lever,” she said.

Similarly, if you hear a scraping sound from the brakes or notice that the brake pads’ grooves, which help shed road debris, have worn down, you should have the brakes serviced.

On conventional bikes, the brake pads typically last for as much as 1,000 miles of use, but mechanics warn that the same pads may wear out with less usage on heavier e-bikes. “Those things can wear out in a couple of weeks,” Lynn said.

Accidents involving e-bikes are not due solely to mechanical failures. According to data from the Consumer Product Safety Commission, 53 people died as a result of e-bike accidents from 2017 to 2021. (By comparison, 68 people died as a result of e-scooter accidents during the same period.) In most of these incidents, Moore said, “it appears they are related to crashes with motor vehicles or rider error, rather than product defects.”

Younger riders can be especially vulnerable. “A lot of kids aren’t used to riding on these fast devices,” said Makenzie Ferguson, the injury prevention coordinator at Children’s Hospital of Orange County (CHOC) in California. “So, they might not have the skill or knowledge on how to maneuver them.”

In an article on its website, CHOC noted that it had treated more than 80 pediatric injuries from e-bike riding in the past three years. Ferguson said the injuries generally have involved kids about 14 to 16 years old, but some have been younger. She noted that the count only includes cases within their hospital system in Orange County and there are “probably more” injuries treated at other emergency rooms in the area.

“Usually, they’re riding, and they lose control,” Ferguson said. “Maybe they hit a curb or something or they’re not used to the weight of the bike.”

The resulting injuries can be more serious than after crashes on a conventional bike, some recent studies show. In a 2019 Israeli study of 196 pediatric emergency room visits related to bicycle accidents, more young people crashed conventional bikes, “but injuries of higher severity only occurred among the E-bikers,” the authors wrote. A separate 2019 study of 337 pediatric hospitalizations after biking and other traffic-related accidents likewise found that serious injuries, especially to the head, were far more common among young e-bikers than those riding conventional bikes.

In the context of overall e-bike ridership, though, the incidence of such accidents and injuries among children is low. In fact, the proportion of e-bike accidents among middle-aged and older riders is rising. A 2022 study of 82 cyclists treated at a Swiss trauma center, for instance, found that the median age of the injured e-bikers was 60.

All e-bike riders, whatever their age, would probably benefit from education about and practice with their bikes, especially if they are new to e-cycling, said Ash Lovell, the electric bicycle policy and campaign director for PeopleForBikes.

Find an empty parking lot or other open, traffic-free space to practice starting and slowing your e-bike. An e-bike’s acceleration can startle new riders, as can the distance required to fully stop them.

PeopleForBikes plans to release educational materials focused on e-bike safety this summer, Lovell said. The group produced a video last year about safety for all types of bicycle riders. The Laguna Beach Police Department in Southern California also produced a video last year about e-bike safety and regulations.

Everyone interviewed for this article expects e-bike ridership to continue growing, even soaring, in the coming years. “PeopleForBikes believes that electric bicycles are the future of bike riding,” Moore said.

There is, after all, plenty to love about e-bikes, he and others point out. They are faster than conventional bikes, making them useful for commuting and daily chores. They are accessible to people with health conditions or other issues who cannot easily manage conventional bikes, or who worry they are not in sufficient shape to complete a ride or keep up with fellow cyclists.

They also reduce car trips and, proponents say, help save the planet. A 2020 analysis of 76 studies found “the personal use of e-bikes is associated with a reduction in motorized vehicle use,” while an ongoing citizen-science study from the Climate Action Center found that e-bikes are 20 times more efficient than electric cars “at fighting climate change.”

More prosaically, e-bikes can be good exercise. In a 2021 study, e-bike riders’ heart rates rose into the range considered to be moderate exercise, though they hovered slightly lower than when the same riders pedaled a standard bike. A 2022 review of research about e-bikes concluded, “E-cycling improved aerobic fitness.”

But whether children and young teenagers should be riding these bikes remains an open question. The time frame for litigating the Steinsapirs’ lawsuit is uncertain.

For now, “parents have to decide which activities their children should engage in,” Moore said, “whether that is cycling, swimming, skiing or contact sports, all of which have known risks of participation.” His group, PeopleForBikes, “agrees with the majority of states,” he said, that “most children aged 16 or older are capable and competent to operate an electric bicycle without endangering themselves or others.”

Flax agrees, but with caveats. “There are so many categories of people for whom an e-bike can have a profound impact” on their lives and well-being, he said, adding that he often commutes in Los Angeles on an e-bike. “I remain an evangelist” for e-bikes, he said.

But after reporting on the lawsuit and e-bike safety, “I’d probably buy something different” for his teenage sons, he said. “I’d still buy them electric bikes,” he said. But those bikes would probably cost more, and they would have better brakes.

Do you have a fitness question? Email YourMove@washpost.com and we may answer your question in a future column.

Sign up for the Well+Being newsletter, your source of expert advice and simple tips to help you live well every day

Well+Being shares news and advice for living well every day. Sign up for our newsletter to get tips directly in your inbox.

Coronavirus vaccines can affect periods, a study showed, confirming what many women had been saying.

Normal marital hatred is real, and here are some ways to respond to it.

Is coffee or tea better for you?

Even if you exercise, sitting all day can cause health problems.

There are many things beyond our control, and these 8 ways can help you feel less anxious about them.