bloodfont

Hi bikeforums.

With the current rise in popularity of the '1x' drivetrains (gravel bikes and MTB) I've been thinking of their intrinsic issue: crooked chainline. So for example, SRAM Eagle boasts a 1x12 drivetrain which of course puts the chain in extreme positions.

So what if, the chainring would simply follow the chain to wherever it wants to go i.e. to whatever rear cog (not necessarily follow every cog, perhaps 2 or 3 positions, mimicking the double/triple crankset). I’m calling this ‘yaw chainring’ for lack of a better name (although the movements possible are yaw and in-out along the spindle)

Has anyone (person/company) thought about something like this?
Has anyone seen something like this in bike history?

fietsbob

Decades ago I saw an odd crankset prototype, that moved the chain rings sideways to be in a straight chainline
irregardless of what cog you were in on the back..

It never went past prototype. displayed at a bike trade show at Harrogate, UK..

width 'Q' between the pedals was huge, to accommodate the motion sideways.

JohnDThompson 

Yes, I remember seeing those as well and considered it to be a solution in desperate search of an actual problem.

Perhaps with the advent of 12-cog clusters, its time has finally come.

corrado33

I don't think anyone would ever go for it. You'd have to constantly put in energy to "turn" the chainring. With the amount of money spent on things that save 1-5W, I highly doubt someone would put something on their bike that would rob them of that many watts.

If the chainring was free floating I'd bet that the chain would hop off of it quite often. Not to mention it'd require a larger q-factor, which would hurt knees of some riders.

As the above posters said, a solution in search of a problem.

shafter

I've thought about the same thing. How about a cable operated mechanism that could move the chainring and crank in and out along the BB by moving a lever at the handlebars.

But all that would require a major redesign... and whatever you came up with wouldn't be compatible with anything else. All for a rather unimportant goal.

bloodfont

Thanks, guys, awesome replies.

There will be room for all sorts of stuff in the BB with the coming of the new BB standard i.e. larger BB. According to what fietsbob and JohnDThompson said, somebody has already tried it but perhaps of the small BB size back then, there wasn't much you could fit in there.

The free floating chainring that corrado33 wouldn't actually be "free floating", it would just move along the spindle like a MTB suspension fork blade works.

Also, to answer shafter's comment, it could work like an FD, but then it would defeat the purpose of the 1x drivetrain. It should actualy work automaticaly only by shifting in the rear.

scott967

I think it's a real problem, but considering the loads that are being carried, the solution would have to be pretty beefy I would think.

scott s.
.

wschruba

I seem to remember a double chainring crank without a derailleur making the rounds a few months back; it would seem the technology is already there, but the market answered with a resounding "why?"

If your desire for a perfect chainline is tantamount, seek IGHs or a Pinion Drive, if you have deeply stacked pockets.

bloodfont

IGHs or a Pinion Drive would be an option if you were touring or commuting, but I'm talking about MTB and gravel bikes. Those 2 systems just don't cut it in these fields, otherwise everyone would be using them.

wschruba

Seriously curious here, what is your justification for this? Those who are not racing/pushing the limits of the design (having worked selling bikes of all stripes, I would confidently say better than 90% of people) a small amount of extra drag is negligible versus the reduced external complexity. People on bicycle forums (not here, in particular) forget this, since they are the other 10%. As (generously) an "okay" cyclist, I could easily keep up on an IGH--worse than a pinion in terms of weight distribution, if not better protected from crap being kicked up from the front wheel.

To say nothing of the fact the a Pinion Drive (or mid-drive, really), in particular, is the best possible (emphasis on possible...) system for a suspended mountain bike--because the rear wheel is now as light as possible, the unsprung weight of the system is lower than even the lightest comparable derailleur setup...which is the best case for suspension activation.

Gravel and mountain biking are just two different surfaces, and the drive system literally doesn't care. Some systems may be ill-suited to the shocks of, say, a 4 foot drop, but that isn't the fault of an IGH, anymore than it is the fault of a Dura-Ace crank...

I don't consider everyone using something as a sign of it being the best for something. These are similar arguments for why generator hubs are inferior for everyone, or skinnier tires (or now, wider tires) are faster, etc...

Otherwise, a derailleur drivetrain (even with poor chain line) falls into the same category as everything above...it works 'good enough'. Expect a major redesign to encounter the same objections/resistance above.

bloodfont

Nice comment.
So are you saying that the only reason for 'pros' not using IGH/pinion drive is because of sponsors pushing what they want (marketing) and because of weight? I also assume configurability, because if you want to swap cogs on a cassette you can, is that possible on IGH/pinion drive?

And for that matter, why isn't SRAM Eagle a 1x12 using IGH?

martianone

Have preferred the 1xN set up since long before it became a trend. If chain ring is lined up with middle of cassette, not sure chain position is such a big deal.

wschruba

I'm going to assume you aren't trolling, and actually answer your question; yes, of course you can change the drive ratios on the Pinion (and IGH in general), with about the same amount of customization as a 1x derailleur drivetrain... That is, you can change the input ratio of the drive system (or with a Pinion, the final drive). The ability to meaningfully (or easily) change the drive ratio on a "high end" cassette was lost years ago, so the comparison is quite appropriate.

There is a long and storied history of cyclists, both racers/casual users, having technology [read: improvements] they did not want shoved down their throats, if you only look for it.

bloodfont

Thanks for all the comments. My question is pretty much answered. I actually got more info than I hoped for . Here are my conclusions:
- my initial idea (moving chainring) was attempted in the past (was hoping for some links or photos though )
- regarding 1x drivetrains, IGH (or pinion drive) seems to be the future, especially with something like CVT
- we shouldn't be making decisions by what the 'pros' use, since they mostly don't have a say in it

rgconner

Have you considered a planetary gear for the crank? That would give you 2-3 gears with one chainring.

Might be able to make one with modern technology that is not so bulky that it would be prohibitive.