The future of the bicycle drivetrain.

dw300

I was thinking about training with a power meter, and of course we now have electronic transmissions.

So, will we get to a point at which Shim/Sram/Camp make a shifter system where you select the power that you want to be cycling at and the computer tells the transmission to automatically changes gear depending on the gradient of the road you are on?

It might mean you could avoid building lactic in your legs marginally better by avoiding short peaks of unwanted strain on your legs on rolling terrain or in gusty headwinds.

Gizmodo

Until you try to accelerate and it drops down the gears so much that you're spinning like a lunatic. Nice idea, might have to add cadence to equation somehow.

BillyMansell

Continuously variable transmissions have been around for years, including on bicycles. Combine one with a gripshift so you can adjust either torque or cadence on the input shaft and Bob's your uncle.

Gizmodo

BillyMansell wrote:

Continuously variable transmissions have been around for years, including on bicycles. Combine one with a gripshift so you can adjust either torque or cadence on the input shaft and Bob's your uncle.

So what's their disadvantages? If they are perfect they would be on every bike right now.

BillyMansell

Gizmodo wrote:

BillyMansell wrote:

Continuously variable transmissions have been around for years, including on bicycles. Combine one with a gripshift so you can adjust either torque or cadence on the input shaft and Bob's your uncle.

So what's their disadvantages? If they are perfect they would be on every bike right now.

No gear system is perfect and they all have both advantages and disadvantages over each other.

The advantages of CVT hub systems is that they're mechanically simple with few moving parts to go wrong, they'e sealed against the elements (but then so are hub gears and Option gear boxes) and they can provide infinite gear ratios within a given range.

The disadvantages are their mechanical simplicity relies upon friction between components for drive which can reduce their efficiency. Also, compared to derailleur systems where the gear range can have a 500-600% spread the gear range is almost half in hub CVTs (about 350% with the last NuVinci CVT hub) and considerably less again with chainset CVT systems. The last CVT hubs were also extremely heavy but then as their use is limited to city bikes there probably hasn't been consideration or investment in making lighter systems.

JamesB5446

The weight thing wouldn't be as much of an issue if you could fit a CVT into the bottom bracket.

rolf_f

I can see the benefits of a CVT setup but automatic shifting on a conventional bike transmission seems a bad idea to me. It's like with cars - on big engined cars with loads of torque, auto transmissions are great. On small cars with low torque, they are horrible. The gearbox doesn't know when to shift and generally gets it wrong. Not badly wrong, just wrong enough to make the driving experience horrible - I can't see it being different with a bike.

It would be interesting though - you'd have to make it work so it shifted smoothly under load because of course the bike is deciding when to shift and not the rider. If you can do all that without a significant weight penalty, you might have something!

Mr Will

I've pondered automatic gears before but it'd probably be better to base them on Cadence rather than power. Set a minimum and maximum and off you go!