Has anyone ever designed or manufactured an automatic transmission (or automatic shifter?) for cycling?
I imagine such a device would automatically change the gearing to allow the rider to maintain constant cadence or constant torque on the cranks.
I used to daydream about the existence of such a system many years ago when riding my first (battered, second hand) racer as it was such an ordeal to change gears.
http://www.landriderbikes.com They were very heavily advertised several years ago but currently they seem to show up more on craigslist than on TV.
I have ridden one - it used weights thrown out by centrifugal force and springs to move the derailleur in and out. Horrible is all I can say. Maybe it was me not being used to it, but things like not being in the gear you left it in, and less than smooth changes - which you have not idea when they are going to happen, especially under power. The only redeeming feature was it was a borrowed bike I could give back at the end of the weekend holiday.
That said, for cruising around a by someone who otherwise would not ride, and only on flat, even ground), its would do the job.
Trek had a bicycle a few years ago named "Lime" which had 3 speed automatic gearing. I don't think it sold well. It used a gearing system called "Coasting" that was created by Shimano and actually controlled by a computer chip from signals from the front hub.
"A dynamo is fitted on the front hub that gauges the revolutions of the wheel. It sends this information to a computer chip housed near the pedals on most of the bikes.
From there, the chip, which controls the planetary gears located on the back hub, determines whether to shift up or down. All the chip needs to make its determination is for a rider to pedal four or five times, according to Shannon Bryant, Coasting project coordinator for Shimano."
There's the Nuvinci Harmony.
It uses the Nuvinci N360 CVP hub, which is a continuously variable transmission, meaning there are no shift points. The Harmony controller changes the ratio based on cadence, or it can be adjusted manually.
As the Nuvinci system has been mentioned in other answers, I'll mention one more.
SRAM makes the Automatix hub now. It's a 2 speed system (ratios 1:1, 1:1.37) with a centrifugal clutch. There's no manual shifting possible and no cables involved.
There have been attempts over the years, but never particularly successful. One I recall used a 5-speed rear hub that was shifted by weights on the spokes, similar to a centrifugal governor.
I expect that, with the new electric shifters, there will be some new attempts at it in the next year or two. With a computer it should be possible to be reasonably "smart", especially if mated to some sort of torque meter.
I know Im a little late for this posting but this is the first time I came across such question. I do own a Trek Lime, purchased back in 2007. This is a fully automatic bicycle. It has 3 speeds a front hub dynamo (speed sensor), a shifter module-solenoid (computer) under the center frame, and the 3 speed auto-shifter hub in the rear wheel. As far as I know there has always been autoshifting bikes out there, they're rare and not very cheap, but a joy to ride.
This post would deserve to marked as outdated or having a fresh start (or a clean up), as most of the answers are now outdated or redundant, and the accepted answer is a dead link.
As of August 2023, I'm aware of the following automatic transmissions for bikes, in practice limited to e-bikes (probably because of the weight of most systems and the lesser efficiency — in the case of Shimano and the derailleurs, the explanation given is to have the possibility to lower the torque when changing gears):
I have one with an automatic, its a six speed.
It works really well actually, you just pedal nice and it does a real nice up/down shift in the gears; its not a hard riding bike, it's a nice causal ride, great for me and the dog, but it will up shift and down shift on its own. It seems to be an older bike.
I picked it up at a garage sale for ten bucks; it has 3 weights on the back wheel that have the name dad on the and small piece of plastic the size of a dime that rides in a groove. If I'm not riding it wont shift.
The only stickers on the bike are ones that say metro and automatic.
I have searched the web for about three years and find nothing of the likes of it.
Check out the new Autobike http://www.autobike.tv. It uses a CVT.
Enviolo stepless hub (formerly marketed under the NuVinci brand) comes either with either automatic or manual shifting. But in most offerings I have seen it pre-installed, it is a manual shifting (TR). You probably need to get it separately and install yourself if you are after experimenting with the latest greatest technology.
These hubs allow shifting while standing and also under load. This reduces the need of planning in advance: shift before the hill and not under load, shift into gear you want to start from before you stop, ease the load on pedals while shifting, etc. Usual chain based transmission likely would not be convenient if the automatics just moves the derailleur in an unpredictable and probably unsuitable moment.
Not really, the one from Nu Vinci is closest but
Has manual shift
the weight factor is an issue.
The major problem in developing is the input power is too low for a fully mechanical system to respond smoothly and if you include electronics it becomes too complex. But I believe some solution is possible.
I don't know much about it and it doesn't seem to be publicly available yet but Bioshift is the most recent variant I know of.
It basically seems to be an extension for Di2 electronic shifting.
