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Rather than resort to radical gears such as a very small granny chainring (such as 20T) and a very large rear cog (40T), both of which can cause some problems for derailleurs as well as other problems (such as chain tension issues), why don't they just have more reasonable gears and have a 2 speed internal hub gear to basically give you 2 ranges of however many speeds you have?

For example, suppose you have a 2x10 setup but the lowest gear is nowhere near low enough for steep hill climbs. Perhaps it is 20 gear inches. Instead of tweaking the cassette for a lower gear, it would be nice if there was an internal hub gear that would reduce everything by 50%. Then your new lowest gear would be 10 gear inches which would let you climb just about anything (at very low speed) but the point is then you wouldn't have to use the lowest gear cuz everything would be lower and you could select the proper gear (perhaps 3rd for 4th gear for example).

I would think a small 2 speed internal hub wouldn't add much weight and the dual range of gears would be very useful. The higher range of the internal hub would just be a direct drive so it could be considered 1 speed internal hub but with a lockup (direct) high range.

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    It would add a lot of weight and money. You're paying for both systems now. Where do you want to install that third shifter? Also it raises the cost a lot to have both gearing setups. It's a neat idea of comfort and commuter cycling though – BEVR1337 Jan 20 '16 at 16:35
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    Google "dual cassette internal hub" – paparazzo Jan 20 '16 at 16:39
  • More cost but a hell of a lot more fun. A dual range 7 speed for example would be great. The high range could be geared tall like 4:1 max gear and 1:1 low gear. The low range would give you a super crawler 0.5:1 gear and also make the gears much closer as far as speed range, thus giving you more of a selection at the lower speeds (such as when I climb one of those spiral entrance ramps to a walkway bridge). That is a situation where I would want very closely spaced gears. Someone should make a super light 2 speed (actually a 1 speed with lockup) internal hub and market it. – David Jan 20 '16 at 16:46
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    Gear spacing on the dual range 7 speed would be 26% between the 7 gears. This seems reasonable. One thing I dont like about closely spaced gears (on a bike or even a motorcycle) is sometimes it is hard to determine if a shift actually took place. For example, if your cadence drops from 100 to 74 that is much easier to detect than say 100 to 90. The 4:1 cassette spread is just an example and can be spread out over ever more gears (such as 9) or tightened up to maybe 3:1. It is a flexible concept but the "halving" gear is the most important allowing for both street and offroad use. – David Jan 20 '16 at 16:53
  • I am not a moderator and don't represent the rules. But the purpose of the site is specific (real) questions. Why this would be cool and someone should build it is out of scope in my opinion. – paparazzo Jan 20 '16 at 17:17
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The closest to that is the Sachs DD3 "dual drive" hubs that are a 3 speed IGH with a standard cassette mount, available in 8,9 or 10 speed cassette versions. According to this site the ratios in the hub are 0.73,1,1.36 giving 1.86 between high and low gears. That's wider than a double chainring setup but narrower than most triples (a 20/30/40T triple has a ratio of 2.0 for example).

Those apparently weigh less than a triple crank and derailleur, but since you want that as well as a double or triple you will be adding the weight, as well as the cost and complexity rather than substituting it. Sheldon Brown has done this with the older 3x7 version and seemed to enjoy it.

The issue is the size or complexity of the shifts. Rather than just having two overlapping gears from two chainrings, you now have 6 or 9 overlapping gears in much of the range (so there's lots of ways to get a given gear ratio). When shifting from high to low in the hub you either experience a big jump in final ratio or have to shift significantly on your other levers at the same time. If you went from, say, hub low on the 15T cog on the cassette to hug high, you'd probably want to shift to about 25T cog so the jump was a normal step between gears. Typically that will be three or four cogs.

The Schlumpf Mountain Drive gives a 2.5x gear down in the bottom bracket but I'm not sure they're still manufactured. I've used one of those and found it effective but the jump in gears was huge. It was more like shifting between low ratio and normal in a 4WD vehicle than a normal bicycle gear change. Typically I'd go from bottom gear on the derailleur system to the smallest cog on the cassette when I changed, but often the bike would almost come to a halt when i did that because I was going up a hill and not pedalling hard for the 2-5 second gear change cost me all my momentum. I fear that a similar shift in the rear hub would have the same effect.

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If you really want that wide a ratio, the widest ratio chainset combined with the widest ratio cassette commercially available would get you very close. There are crank sets that can take chain rings from 22 to 50 teeth (finding a front derailleur that could do this range might be hard), and an 11-40 cassette. Cross-chaining would be a bad thing given how much the rear derailleur would have to tak eup.. This works out to just less than 9:1. (The components I've linked probably aren't compatible with each other but demonstrate what's possible).

That fact that this is possible but bikes aren't sold with it probably gives you your answer.

Sheldon Brown did try putting a hub gear on a bike with front and rear derailleurs to get a 63 speed bike, OTB chainrings Sheldon Brown's OTB showing a 51 and 26 tooth chainring. There's a 7 speed freewheel and a 3 speed sturmey archer IGH there too, and his final version had a triple on the front for 63 gears (3*7*3)

  • Yes I think I remember reading about that. My idea though is to have a simple gear 50% gear reduction in the hub (or somewhere else like bottom bracket) such that it is either on or off, meaning 50% reduction or direct drive lockup. So there would not be 2 gear ratios there would be only 1. When riding on the road you would use the lockup mode and perhaps when riding on grass and/or up large inclines you could use the 0.5x mode. Something that simple (conceptually) should be light and reliable and can be made small. It would also take a bike with 4:1 gear ratio spread and widen it to 8:1. – David Jan 21 '16 at 13:10
  • Another cool benefit is in the low range, you can still use all the chainrings and all the cogs, but they will be much lower range, thus you will be shifting more often. The lower gears will be so close as far as road speed range that you might shift every crank rotation in some cases. I think a dual range concept allowing all the cogs and chainrings is a very good idea. Since my idea is to have a single reduction of 0.5 (50%) and a lockup 1:1, it is technically only a 1 speed cuz the lockup is not a gear it is just a direct link to transfer power. – David Jan 23 '16 at 14:34
  • How about something like 20-32-50 in the front and 11-44 in the rear, giving a spread of 2.5*4 = 10? Makes sense to me. The lowest gear could spinout at 3 MPH (walking speed) and the highest at about 30 MPH. That translates into about 4.8 km/h and 48 km/h. – David Feb 6 '16 at 16:55
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    @David subject to the derailleurs being able to handle the step size and chain length difference, yes. But I suggest you don't need to spin out at walking pace. 50-60 rpm at walking pace would be enough. On good ground I can go down to very slow walking pace by giving the pedal a little push then backpedalling the same amount before coasting. – Chris H Feb 6 '16 at 18:02
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There are 2 stage BB gearboxes from Schlumpf.

The mountain drive offers 1:1 and reduction of 2.5:1 (easier gears)
They also have a speed drive which is 1:1 and 1:1.65 (harder)
and a high-speed drive which is 1:1 and 1:2.5 (much harder)

Gear change happens by pressing the middle of the crank with your heel, one side for up and the other side for down. Note there is only one chainring, but it turns at a different speed to the crank arm when in gear.

Recently taken over by Haberstock in Germany, their web site is
http://www.haberstock-mobility.com/index.php/products.html

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