readygetsetBen

Hey all, just had a thought about using internal gearboxes like pinion to run a geared fixed-gear (or rather a coast-less geared-gear?)and was curious as to whether it had been done before. Does anyone know of a set-up like this? Maybe there's something about gearbox technology that wouldn't allow fixed-gear that I am unaware of?
Thanks everyone!

TimothyH

What problem are you trying to solve?

Why not just run a normal fixed gear?

Ironfish653

So, you want a 3-speed fixie? I suppose such a thing could be made, by locking the sprocket on a 3-speed IGH, but i'm not sure how well it would work.
The actual 'shift' between gears is made, the wheels, cranks and the rest of the driveline are all moving at different speeds. The freewheel allows for those little differences to even out as the gear ratios change.
Basically, what you want to do is like shifting a manual transmission, without using the clutch, or backing off the throttle. It can be done, it just won't be pretty.

FBinNY 

Decades back (prior to WW-II) Sturmey Archer produced internal planetary geared 2 speed fixed gear hubs. I've been riding one on and off for the last 45 years or so. They also produced a 3-speed version later on, and both of these are collectors items today.

I believe that similar hubs have been reprised recently, but can't confirm whether this is so.

Jax Rhapsody

Last I checked they still do.

79pmooney

Sturmey-Archer makes a fix gear 3-speed, the S3X. Sturmey-Archer | Products. The mechanic in my shop and Sheldon Brown who used to come by and hang out both had S-A fix gears.

Ben

fietsbob

Might be a reason to start towards an BS & MS in in Mechanical engineering at a University..

FBinNY 

Sorry, but no. You cannot easily convert a typical 3s (AW type) hub to a fixed version. The system depends on overrunning clutches (freewheel ratchets) to function.

Fixed hubs directly drive the shell through the planet system and use sliding clutches with dead spots between gears to ensure that 2 different gears can't be engaged simultaneously (which would lock up the hub).

FBinNY 

Having ridden multiple speed fixed gears on and off for years, I can tell you that it's like eating your cake and having it too. You enjoy the various benefits of fixed gear riding, yet have expanded hill climbing capabilities.

Or you can set the up hub with higher gearing than otherwise, knowing that you can downshift if/when needed. My 2 speed fixed hub is set up roughly 10% higher than I normally ride fixed, giving me a higher cruising speed on the flats, yet still giving me the flexibility for hills.

Trakhak

I read the opening post as asking whether there is, was, or could be such a thing as a fixed-gear bike with a chainless shaft drive. No mention was made of multiple gearing.

If I read that correctly, here's a Wikipedia page on the topic:

https://en.wikipedia.org/wiki/Shaft-driven_bicycle

Gweedo1

I guess the OP's use of the term "geared-gear" and "gear box" hinted at multiple gears. But the use of the term "pinion" certainly brings up images of a bevel-box final drive found at the end of shaft drives.

Good thread: I can now see how a multiple gear fixie could be of value. Learn something new everyday.

Dan Burkhart 

Sturmey Archer has a 3 speed fixed gear hub in current production. The S3X has the bottom 3 ratios of the wide range 5 speed, (now out of production), with the top gear being direct drive.
The range could be expanded by adding a Sclumpf 2 speed crank set, but the combined gear lash of the two mechanisms would drive any dedicated fixie rider crazy.
I have no direct experience with the Pinion gearbox, and I could not tell you if it has a freewheeling mechanism, but even if it didn't, it would certainly have significant lash, as any gear assembly must.
As the Pinion box becomes more common, as I believe it will for certain applications, it would be interesting to see somebody try it.
Hmmmm.

Dan Burkhart 

Pinion is a brand name of a bottom bracket mounted multi speed transmission.

PINION | DRIVE TECHNOLOGY | | bicycle gearboxes ? made in germany

Gweedo1

Ahahaha...thanks for setting me straight! Like I said...learn something new everyday.

Just took a quick look at that link and...just wow! But..not exactly a bolt on option is it?

JohnDThompson 

FWIW, Sheldon Brown describes a method to convert a 3-speed AW hub into a 2-speed fixed gear hub. Haven't tried it myself, though:

Converting a Sturmey-Archer AW Hub Into a Two-speed Fixed Gear

Dan Burkhart 

Correct. It is not made for aftermarket retrofit. The frame must be designed to have the gearbox housing built into it.

readygetsetBen

thanks everyone, I guess I should have been more specific

My question was whether or not anyone has used a bottom bracket mounted gear system (like Pinion's) to make a geared fixie. I'm well aware of the fixed gear hubs, but I've read that they just don't feel right. Someone was talking about gear lash, could someone please explain that concept to me?

Dan Burkhart 

Any assembly which has gear teeth in mesh must have a a small degree of free movement between those teeth to prevent binding in the mechanism. The term for this free movement is gear lash.
The internal mechanism of a hub has several points of power transmission, each of which must have this lash. It's cumulative, so the more points of engagement along the flow of power, the more accumulated lash in the train.
More info here.
https://www.quora.com/What-is-the-ba...isadvantageous

Retro Grouch 

So that would be a niche market segment of a niche market segment.

readygetsetBen

hahahahahahaha!!

readygetsetBen

Thanks man!

Dan Burkhart 

Yeah, that narrows it down.

Dan Burkhart 

You're welcome. And for more on how fixed gear hubs work, there's this.

FBinNY 

I don't see a problem with using a BB epicyclic (planetary) drive with a fixed gear hub. It might actually be more mechanically efficient, though that shouldn't be a factor.

As for gear lash, that's simply a sub category of backlash which is an issue in mechanical systems. Both because of manufacturing tolerances, and to ensure low friction operation, systems are built with a bit of play. So, there's a bit of free play between the parts when engaged forward and reverse. In a car, you hear and feel it as a click (or clank) when you shift from forward to reverse.

If you've been riding fixed for a while, you know about this already. You keep a bit of slack in the chain to allow for the eccentricity in the sprockets. When you reverse torque the tension shifts from the upper to lower loop, and there's a bit of backlash you can feel in the pedals. IME, with the hubs I've used, the internal backlash is no more than that in the chain, so I don't consider it an issue.

Of course, whether hub backlash is an issue at all depends on the relative precision of the hub vs. sprockets, and how tight you can safely run the chain. Unless it's extreme, you adapt and don't notice it when riding.

JohnDThompson 

Other people here have already explained why some lash is necessary; I can tell you what it feels like on the road. It feels like riding a fixed gear bike with a slightly loose chain. That's all.