automatic gears on a bike ???

[Chris S]

I seem to remember that some bikes in the 1970s had a CVT type transmission - or have I got it wrong?

 

[snailracer]

cadence<>power

power = f(cadence)

 

[mgarl10024]

it doesn't take into account exhaustion!

That would be my thinking. An engine, at a certain rpm, is likely to give the same power as it did last time.
However, I know that as I'm zipping along, I vary on different days - or even at different parts of the ride.
I often find that I'll be starting to spin in a gear, change up because I think I can handle it, then change back down because my legs weren't willing to keep the same cadence and I would be grinding in too higher gear. I guess the system could cope with that.

Then there's hills
- if climbing - I am in a low gear and spinning, I wouldn't want it to change up.
- if falling - I am in a high gear and pedalling slower, I wouldn't want it to change down.

There must be some combination of speed/power/gradient which would give the right gear to be in, but it would need a lot of thinking about and probably would vary too much per person per day per mile....?

 

[snailracer]

There are all sorts of special situations (eg coasting, setting off, etc.) interrupting the main cadence control loop, but automatic cars work fine (often using only springs and hydraulic valves). It's not beyond the wit of Shimano to make it work on a bike, which they have.

 

[GrasB]

The optimum cadence range for a human is actually narrower than that of most cars, which can do 0 - 120 mph with only 5 gears i.e. 24mph per gear.

And there are people who just can't understand gears.

cadence<>power

Not really to both. I make the most power around 80-90 rpm... huge pedal force along with full utilisation of the upstroke. Of course that's anaerobic power, if I look at aerobic power then peek power is around 130rpm for me.

Then there's hills
- if climbing - I am in a low gear and spinning, I wouldn't want it to change up.
- if falling - I am in a high gear and pedalling slower, I wouldn't want it to change down.

There must be some combination of speed/power/gradient which would give the right gear to be in, but it would need a lot of thinking about and probably would vary too much per person per day per mile....?

For me anywhere between 30 & 140rpm is just fine, I've got examples on file where I've gone from 40 rpm to 120rpm without changing gear on climbs & this is without being in bottom gear. It's just how I want to approach an incline & where it's situated in the landscape.

 

[jig-sore]

mmm, good points for and against.

i think i have to agree with the people who are saying its not really worth it. to make it work well (as in avoid all the problems stated above) it would have to be quite complex and therefor expensive. why bother when we have perfectly good ways of changing gear.

i could see a small market in the "3 speed commuter bike" area... but very small

i guess it would be fun to have a go on one though, a bit like those novelty bikes that steer the opposite way !!!. you would soon get fed up though if it kept changing up every time you freewheeled !!!!!

 

[Arch]

As well as the electronic ones (Shimano did a relatively nice to ride four-speed IIRC) there have been several which use centrifugal weights to auto-operate a rear derailleur. Here's one:

http://www.landriderbikes.com/

http://www.youtube.c...h?v=iWOd_0BYm0U

Some amusing opinions on it e.g. here:

http://www.bikeforum...p/t-437895.html

A potentially nicer idea was the Browning system:

http://www2.bsn.com/...s/browning.html

But it never made it commercially.

Hey, googling for the R and M Equinox, the first link that came up was:

http://www.velovision.com/mag/issue2/issue2equinox.pdf

which you wrote ten years ago!