Hub with a single direct drive

[prState]

Bear with me as I try to explain!

First, if I understand the basic disadvantage of a hub gear is loss of efficiency, or to put it another way, more intervening gears that have to be turned in between the power source and the tire. It's not good for power, but it's great for flexibility.

Okay, but here's what I'm wondering about. Can you have a design that encorporates the hub (3, 5, 7 gears whatever) but also has one single gear, as direct and power efficient as possible for just one gear. And that gear would be one high gear. (think maybe a front and rear sprocket working entirely seperately, welded into a modified bike for instance**)

For instance, a normal Agattu, which you ride normally most of the time.

However, on a flat, or wind to your back, or some downhill, you switch out to your single efficient high gear (which let's say is geared to work at 23 or more mph with the motor), and you pedal along taking advantage of the motor at higher speed with the best power advantage of a single geared bike working in a perfect range.

And when conditions change, you switch back to the hub gear system?



**I don't know what the best way to approach such a system, that's just my general idea

 

[flecc]

Could be difficult to design such a multi-speed for both rider and motor, though one very simple solution would be to have a neutral in the hub gear linked to a locking pin between the rear sprocket and hub shell, giving direct drive.

The Swizzbee has a crack at this in a complex way by having a motor, belt driving one side of the centre of a rear wheel hub and the rider derailleur gears driving the other side. The hub centre itself is a sort of differential which sums the two power inputs as the drive into the hub shell and so to the wheel. That means the rider can always use the gear they want, knowing the hub differential will match in the motor power to optimum effect.

However, in practice it seems to work better for speed rather than for hill climbing, and the bike costs around £2500.

I proposed another solution for the hub motor. Taking a standard epicyclic gear drive hub motor, my suggestion was for the motor to drive through the epicyclic to give a lower ratio up to a fixed speed, then automatically switching to direct drive of the hub for the upper ratio, in which e-bikes spend most of their life. That would give both optimums for all conditions. The rider would still have derailleur gears regardless of whether the hub motor was front or rear wheel.
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[Miles]

Bear with me as I try to explain!

First, if I understand the basic disadvantage of a hub gear is loss of efficiency, or to put it another way, more intervening gears that have to be turned in between the power source and the tire. It's not good for power, but it's great for flexibility.

Okay, but here's what I'm wondering about. Can you have a design that encorporates the hub (3, 5, 7 gears whatever) but also has one single gear, as direct and power efficient as possible for just one gear. And that gear would be one high gear. (think maybe a front and rear sprocket working entirely seperately, welded into a modified bike for instance**)

Most of them have a direct gear already! For 3 speeds, it's usually the middle gear. For the Shimano 8 speed, it's 5th gear. For the S.A. 8 speed, it's bottom gear. The Shimano 7 speed has 1:0.989

 

[flecc]

As Miles says, the direct gear is in the middle generally, What I proposed above was the possibility of the opposite of the Sunrace Sturmey 8 speed.

On that where all gears above bottom are indirect, the chainwheel and rear sprocket are almost the same size to make the primary drive low enough, with even a spider available to give a lower gear by using chainrings for rear sprockets.

The problem with my proposal would be the opposite. With all indirect gears lower than direct drive as you'd like, the primary drive would have to be very high geared. With typical chainring the rear sprocket would be around 9 to 11 tooth, far too small for permanent use including high loadings due to the wear. The smallest acceptable would be around 13 tooth, but that could mean a chainring around 60 tooth or more on normal wheel bikes to get acceptably high gears. That gives poor ground clearance with the possibility of the chainwheel hitting the ground over kerbs, steps and the like. On a smaller 20" wheel it would be more restrictive, and impossible on 16" wheels for the smallest folders like the Brompton where the top gear would be too low with any usable sprocket combination.

As ever with bikes, around two hundred years of thought have got to around the optimum anyway, any change introducing new and often worse problems.
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[Miles]

Good points, flecc.

Another thing to bear in mind is that the efficiency of a hub gear will go up with increase in torque throughput.

Is top gear necessarily the one that you want to be the most efficient, anyway?

 

[halfmedley]

Any thoughts/experience on the new Shimano Alfine hub, Flecc? What advantages does it offer over the Nexaves? Incidentally, I wonder why the Shimano Capreo groupset hasn't really caught on.

 

[flecc]

I've no personal experience of the Alfine halfmedley, it's tempting to wonder how much of it is marketing rather than gain. Shimano have this penchant for putting marketing before efficiency with hub gears at times.

The lack of takeup of the Capreo surprises me too, you'd have thought the small wheel bike manufacturers would have leapt to adopt it. Maybe it's Shimano's bulk pricing for the relatively small folder market that's the problem. I considered it's rear mechanism momentarily for the Q bike, but it couldn't span the freewheel sprocket range I wanted.
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[flecc]

Good points, flecc.

Another thing to bear in mind is that the efficiency of a hub gear will go up with increase in torque throughput.

Is top gear necessarily the one that you want to be the most efficient, anyway?

True Miles, and Sunrace see the advantage should be the highest efficiency in bottom gear where the difficulty for a rider is normally greatest as in hillclimbing. There's other bonuses too. The more symmetrical front/rear sprockets of mid diameter are more efficient than a large to small combination. The possibility of parallel chain runs not far apart is ideal for full chaincase enclosure, perfect for the utility market where hub gears live.

Not so good for an oilbath chaincase like the old Sunbeam though.
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[Miles]

With my dual-drive setup, the middle one of the hub gears is set for the maximum allowable power-assisted speed rolleyes, so you get the best efficiency when cruising with the motor. Top gear is for going down hills, un-assisted, of course..

 

[flecc]

Yes that's the cleverness of the DualDrive, adding the hub gear without the need for a further loss of efficiency in most usage, and a major reason why I think so highly of it.

Odd that Shimano have never copied it, though again it may their obsession with the mass market. Maybe it's also convenient to leave openings for tiddlers like SRAM and Campagnolo in the gear market to avoid accusations of monopoly.
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[Miles]

Any thoughts/experience on the new Shimano Alfine hub, Flecc? What advantages does it offer over the Nexaves? .

AFAIK the Alfine has identical innards to the premium Nexus. The economy version has been discontinued, hasn't it?

 

[Miles]

Odd that Shimano have never copied it, though again it may their obsession with the mass market. Maybe it's also convenient to leave openings for tiddlers like SRAM and Campagnolo in the gear market to avoid accusations of monopoly.
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I seem to recall that Sunrace-Sturmey were going to bring one out, as well?

 

[Miles]

If anyone wants to learn about the history of bicycle gearing, I recommend reading "The Dancing Chain" by Frank J Berto.

 

[flecc]

I seem to recall that Sunrace-Sturmey were going to bring one out, as well?

I vaguely remember a mention, but Sunrace have been slow in progress with all the changes. The 8 speed took much longer too appear than expected and then had failures until revisions.

I also understand the Alfine to be just the premium Nexus at it's core, but I'm not sure if the standard one is discontinued yet. I'm sure I saw a reference to both versions somewhere in their site quite recently.
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[Miles]

And of course, we're all waiting to see what the SRAM "Hammerschmidt" will be......

 

[flecc]

And of course, we're all waiting to see what the SRAM "Hammerschmidt" will be......

Is Schmidt their chief designer?
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[Miles]

No idea. I never expect marketing stuff to make any sense...

Rumour has it that it's some kind of crank based gearing system to replace the front derailleur - something the Dual-Drive already does...

 

[flecc]

No idea. I never expect marketing stuff to make any sense...

Rumour has it that it's some kind of crank based gearing system to replace the front derailleur - something the Dual-Drive already does...

Interesting. Forgetting their intentions, perhaps a more efficient alternative to the Schlumpff Mountain and High Speed drives for singe speeders and 'bents?
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[Miles]

Interesting. Forgetting their intentions, perhaps a more efficient alternative to the Schlumpff Mountain and High Speed drives for singe speeders and 'bents?
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More affordable too, I guess..

 

[Miles]

Is Schmidt their chief designer?
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It would seem so - or one of them..

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