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Comment by jrockway | Hacker News Reader

The weight of the bike doesn't matter. A 20 pound bike plus a 200 pound rider is about the same as a 30 pound bike plus a 200 pound rider. You're the heavy part, not the bike. (People complain about citibikes being too heavy, but I rarely get passed even on a citibike, so my guess is the problem's the rider, not the bike.)

Also, I don't think a quick release will work for this. The motor needs to push against the bike in order to move the wheel relative to the bike. A quick release will slip.

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Not necessarily. QR systems such as Maxle are sturdy enough for competitive downhill use.

Also 10 pounds is a huge difference not just in the effort needed to propel the bike forward but also in terms of maneuverability, especially as it is rotating weight. And in city usage you often have to carry the bike down stairs etc. where again 5 kg and a messed up center of gravity is a big deal.

I bike about 5000 miles a year in the city and have never needed to carry my bike down stairs while riding. Once you get it home, you might need to lug it up to your apartment, but it's well within the realm of possibilities for a healthy adult to carry a 40 pound bike up a few flights of stairs. (Then again, it's also rather easy to pedal the bike around without a motor. But I digress.)

Most European cities will make you carry your bike from time to time or make huge detours. But, like you, I'm not the target customer for this so maybe people in general are more careful with route planning.

Also, I don't think a quick release will work for this. The motor needs to push against the bike in order to move the wheel relative to the bike. A quick release will slip.

Look more closely at your bicycle. The axle doesn't turn in the dropout. Rather, the hub shell turns around the axle. That's why the bearings are mounted in the shell rather than in the dropouts.

Actually I think their pill-shaped peg that slides into the dropout but won't turn within it is kind of brilliant. A very simple solution, and there is no reason it couldn't accommodate a quick release skewer.

I agree that bicycle weight is a fairly minor consideration for commuting in moderately hilly areas; I've ridden a longtail that's close to 50 lbs. for years. Maybe I don't notice the weight because I am a fat bastard.

I know how wheels work. Look closely with a bike that is internally-geared or that has a drum brake. The hub is secured to the frame or has an antirotation washer installed to prevent the hub from rotating.:

http://sheldonbrown.com/sturmey-archer_tech.html

Remember Newton's law of motion here: for every action, there is an equal but opposite reaction. As the motor drives the wheel forward, the resistance from the street will try to spin the motor backwards, causing the hub to spin in the dropouts. That's why a quick release alone isn't adequate for internally-geared hubs, drum brakes, or motors.

You assume that they need anti-rotation washers, but it's clear from the video that they have a better solution: the pill-shaped peg I mentioned already. See here for the device installed with a QR skewer for a test ride:

http://www.blogcdn.com/www.engadget.com/media/2013/10/flykly...

You are not alone in having bicycled and taken physics!

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