Automatic bike transmission concept is wild and spiky—and could be a big shift

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Written By Sedoso Feb

Enlarge / Haven Mercer’s prototype front assembly for an automatic bike transmission.
Haven Mercer

Depending on how you look at it, either a lot or not very much has changed about the way bikes shift gears since the mid-19th century.

A lot has been refined along the transmission path, in which your feet push cranks, those cranks turn a big gear, and a chain connects that big gear to a smaller gear on the rear wheel. Shifting has picked up lots of improvements, be they electronic or wireless, as have derailleurs and internal gearboxes. Materials and tolerances have only improved over the decades.

But in almost all cases, you’re still manually adjusting something to move the chain and change gears, depending on the resistance you’re feeling on the bike. Even the most outlandish recent ideas still involve indexed movement between different-sized gears.

That’s why “Automatic Transmission System for a Bicycle,” a US patent filed by Haven Mercer and published on November 23, has caught the attention of bicycle enthusiasts, myself included. If it works like it says it does (as shown in a brief video demonstration) and can be produced as a reliable product at scale, it could make for some interesting bikes. It’s not meant to replace manual shifting entirely, the patent author told me, but it could allow for bikes that go up hills and speed across flats without much thought at all from the rider. It might even offer some e-bike efficiency.

It also looks, at a glance, like a nightmare to clean and maintain, but it’s a prototype, so give it some time.

Haven Mercer’s automatic transmission bike, as demonstrated by the inventor. Watch for the front and rear sprockets expanding and contracting.

Shifting with your feet

Mercer’s system takes the chainring and rear gear and makes them able to expand and contract based on torque. In the front, it does this by replacing a single ring with eight pulley wheels, pushed to their longest extension when there is no tension on the cranks by springs. Each of those pulleys is on a one-way bearing so that when torque is put on the cranks (to go faster or climb a hill), the springs compress, the pulleys fold in, and the whole front element becomes smaller.

On the rear hub, six pulley wheels are pulled into their smallest size by the springs. When force is applied, the pulleys move out and the sprocket as a whole expands. The gearing (so to speak) adjusts as the rider applies and removes torque from the pedals.

There are two chain tensioners below the rear mechanism. They both pick up slack when the front and rear are expanding or contracting at different rates and guide the chain as it comes in at different angles from the front chainring. Mercer’s patent suggests a few different setups an automatic-gear bike could have, including with traditional front derailleur cages, a small guiding sprocket in place of a front cage, and other configurations.

No more panic-shifting

Haven Mercer lives outside Minneapolis, Minnesota. He has worked in auto body repair, alloy development and welding, hard drive design, and, as a number of his patent submissions suggest, for gaming companies. He struck out on his own as an inventor and engineer in 2019. This automatic bike transmission system is “the first patent that is completely owned by myself,” he said.

Mercer went on a bike ride more than a year ago and thought about how riding most bikes requires a good deal of thinking about gearing. “There’s the basic thought of ‘I gotta push this lever forward to go lower—wait, now it’s too low, so I gotta pull back,'” he said in a phone interview. Then there’s the sudden stress of realizing you have to rapidly shift on a steep incline or decline or start again from a dead stop after you were cruising in a higher gear. His invention aims to mostly eliminate those issues.

He built his prototype using a mixture of self-made parts and pieces commissioned from Protolabs. There is more work to be done, especially in finite element analysis and balancing the spring forces. Asked about cleaning and maintenance issues for so many moving parts, Mercer noted that chainguards and other coverings could be more easily applied to his system than traditional bikes, as his chain stays in a single plane, with little side-to-side movement.

Mercer has taken his protoype bike on trail rides and street rides, and it works, though there is a lot of tuning work ahead. He sees potential for not only casual riders, commuters, and perhaps even mountain bikers, but on e-bike systems, too. Mercer can imagine automatic gearing resulting in less torque required from an electric motor to get moving or achieving higher speeds with a smaller motor size.

An option, not a replacement

Mercer is well aware of what certain bikers might think about having less control over gearing, especially after his patent appeared on Pinkbike and Outside’s Velo site. Commenters there were knowledgeable but “kinda harsh,” Mercer said, in an aside that I can only describe as Minnesota nice. He has seen the older post at The Retrogrouch, linked by commenters, about expanding chainrings’ failure to catch on throughout history. “Neat stuff, but definitely all different than my concept,” he noted. Mercer said he appreciates the deep knowledge and enthusiasm experienced bikers bring to the discussion but thinks they might have the wrong idea.

“I always imagined it going along the same line as when automobiles got automatic transmissions, and it got easier for more people to drive a car,” Mercer said. Lycra-clad weekend warriors, gearheads, professionals, and retrogrouches may always prefer direct control of their cogs. “I just think the vast majority of people out there are in the same boat, where they find themselves in too high a gear going uphill, and it can be a pain to get to a low-enough gear quickly,” he said.

I asked Mercer if he was intimidated by the nature of bicycles’ history, that the sprockets he was looking to replace had not seen the kind of changes his patent proposed in more than 100 years. Being a solo inventor, Mercer said he doesn’t have the same resources as someone working in a larger corporation, bouncing ideas off others and doing deeper research. That also means he’s not likely to shoot his own ideas down.

He’s seen the numerous other patents related to automatic bicycle gearing, but he believes he has something unique—”If it had been done before, we would see it out there. It seems to me like a pretty nice innovation,” Mercer said. Strangely enough, he has been in this position before. When he worked on a new method for dispensing roulette balls, he heard some notable backlash from gaming veterans. “You would think I had ruined roulette forever, based on what I heard.”

For now, Mercer plans to focus on seeing the patent through its review process. He could license or sell it after that. Until then, he will try to keep moving, adjusting as he goes.

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