Today we solve a mystery. The mystery of the red disc on rear of cycle.
What is on that rear wheel?
A reader wrote in with this question:
Hi coach,
Saw some bikes with red discs on the center of their rear wheels. They passed me in the bike lane. I’m wondering what that red disc on rear of cycle is called. What is it?
Sincerely,
Red Robin
Hi Robin,
Now this is something you don’t see everyday!
You might think it is a really big dork disc. But it’s not.
Nor is it a disc brake. (Nor a drum brake or coaster brake.)
It’s kind of the opposite of a brake actually!
If this is what I think it is – and it’s the only red disc I’ve seen – you’re seeing people use the Copenhagen Wheel.
It’s not just a sleek red disc that snaps into a bike’s rear wheel – it’s a replacement wheel that will transform your existing bike into an e-bike!
Did it look like this?
It actually looks somewhat like an aerodynamic disc wheel or cover like a triathlete would use. But you probably aren’t seeing those riders on your morning commute!
The Story of the Copenhagen Wheel
This device was invented at MIT, as part of the “SENSEable City Lab.”
It began as a partnership with the city of Copenhagen in 2009 and eventually became the basis of a startup company called Superpedestrian in 2014.
You can still see the project website at MIT.edu.
And there is a school newspaper article with some further information.
Superpedestrian CEO Assaf Biderman describes it as:
“a self-contained unit that snaps easily onto the back of any ordinary bicycle and turns it into an electric hybrid. With extra power at the riders’ feet… the wheel promotes cycling so that long distances or steep up-hills are no longer a barrier to a comfortable ride.”
Source: Forbes.
I have not actually seen one of these in real life, so it’s best if you watch this video to learn what it is and how it works:
If you watch this teaser video, you’ll see they have big plans for the future:
They also have an official product release video that will make you want to order one!
Would I be correct to assume you are in the Boston metro area if you’re seeing this in the wild? Or are you in Europe perhaps?
Either way, it’s cool you got to see one!
What ever happened to the Copenhagen Wheel?
The wheel eventually became publicly available in 2017.
Now in 2022, it’s no longer available. I’m not sure what happened.
The company has switched focus and now operates fleets of electric scooters.
There are other e-bike conversion wheels nowadays. One popular option is from iMortor, which works as a replacement front wheel.
Want some extra power to your pedals?
There are other e-bike conversion kits nowadays. But they usually involve a motor and battery and a bunch of wiring.
Even though it’s been more than 10 years since this was invented, there’s nothing else quite so simple and user-friendly!
So, that red disc on the rear of that bicycle is called a Copenhagen wheel. If you see one, try to ask the rider about it!
This article was originally published on September 25, 2014. It was last updated October 25, 2022.
Levi Bloom is an experienced endurance athlete who has been training and competing for over 17 years. A former Cat 1 road and mountain bike racer (professional class on the regional circuit), he is now a cycling coach (USA Cycling Level 3 Certified) and sports nutrition coach (Precision Nutrition Level 1 Certified).
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