I remember Ted James built a bike with an Alfine disc hub mounted above the bottom bracket. The cranks drove that via the normal chain and the disc mount had a Velosolo cog which then drove a fixed gear hub on the back. Disc must have been on the wrong side though thinking about it.......
Stretchy chain. Need a stretchy chain on two sprockets. And a pusherthing. Or...
... expanding sprockets.
Or, conjoined twin dinglespeed.
I always get to either
a) it defeats the object of a singlespeed or
b) You might as well have a derailleur and cassette
a) it is not a singlespeed so not sure how it defeats the object of one
b) I would rather have a couple of gears in a hub than a derailleuer, cassette, cables, shifters etc, when I only need 2 or 3 gears
Most of my riding life (45 years) has been on bikes with one gear from trackers and BMXes from age 5 to 18 and then fixed and singlespeed from age 30 to 51 so I am really not someone who is into gears but having a simple solution for 2 or 3 gears would appeal to me much more than loads of gears and a derailleur. I tried gears a few months back and the novelty of 11 gears quickly wore off and they just became annoying. I am well and truly conditioned into liking one gear.
900g rear hub for 1 extra gear!
I always get to either
a) it defeats the object of a singlespeed or
b) You might as well have a derailleur and cassetteWould a very simple pinion type gearbox be a go-er?
Pinion
I said it's not that heavy, I didn't say it's light! From a quick browse on the SA site, it looked like 3-speed hubs are pretty much the same weight as a standard hub + cassette + rear mech. Hubs with 5 speeds upwards start to add a fair bit of extra weight.
Single speed for me is about reliability and simplicity, the weight saving is a bonus which I'd happily forego for an extra gear.
If Pinion would make a chainset with 3 speeds in it that was fit for mtb, could fit any frame, didn't cost a fortune and didn't need to be sent to Germany if something broke, I'd snap it up 🙂
(Or Sram could just bring back an improved Hammerschmidt...)
tjagain
Member
There is a very old design for a bike that is two speed that you pedel forwards for first gear and backwards for second.
https://en.wikipedia.org/wiki/Retro-direct
I'm pretty certain I have seen that bike in the flesh- I just can't remember which museum it was! 🙂
Nobody mentioned Schlumf Drive yet?
I like the SRAM Automatix hub, a neat idea and functionally it's great.
I’d guess a front mech with 2 rings and a single rear with a chain tensioner is as good as it’s going to get.
I thought about these ideas for a super-durable touring bike spec once. If you're putting a tensioner on the rear as well as something to shift the FD you may as well use a rear mech, that way you eliminate the FD and consolidate the shifting and tensioning. Once you've done that you may as well have more than 2 gears.. or a hub gear. A hub gear with 3 ratios weighs almost as much as one with 7 or 8. So, SS / 2s Auto / 1x / 3x / hub gear all make sense. To simplify things for eg a backcountry or world tour I'd go dinglespeed, no tensioner, just 2 well chosen gear ratios.
So, my pairs of 4 is wrong, isn't it? It's pairs of 2 (pairs of 1 for a half link chain). I'm getting old, bits of my brain occasionally fall off 🙂
a simple solution for 2 or 3 gears
Me too. If I have gears fitted to my bike I only really use what's closest to my single speed gear and one either side. I'll occasionally bung it in top if I can push it down a hill or bail out to the lowest but I only do that because it's there really. I prefer to honk up most stuff and I'd rather get off and walk to loosen up than sit and spin up a hill.
I'd considered making a three speed cassette and using a short mech but if you're going that far you might as well stick the whole lot on.
I've toyed with the idea of fitting an S2 to my commuter as well as buying ann old SA 3 speed hub for the same application. the trouble is I just find I love the simplicity of having it fixed. even though hub gears are a good solution, fixed is about as simple as life can get... flipflop hub?
one-day I'll build something up with that SA hub...
IME having the same total no of teeth on different sprocket/chainring combos does not equate to a tight chain on both due to the trig difference (in case this hasn't been said above).
I've run a disc brake Sturmey 3 speed off road and quite liked it. The low and high gears felt fairly efficient (compared to the Alfine I commute on) and gear 2 was obviously just like normal singlespeed except with the slightly annoying tick-tick-tick as you pedal. Lack of sealing and chain line were two issues - I was running an Uno chainset at the time and it didn't line up very well, eventually breaking a half link and one of those singlespeed chain spring clip links. With a regular chainring spider (giving choice of chainring position) and a derailleur chain it was fine.
Shimano 3 speed has "silent clutch" freewheel but I think it still does tick-tick-tick in gear 2. Also got a couple of Sachs 3 speeds knocking around that I must try sometime.
I was looking at the Pedersen book this morning - will have to upload some pictures of the "frictionless 3 speed hub"
IME having the same total no of teeth on different sprocket/chainring combos does not equate to a tight chain on both due to the trig difference (in case this hasn’t been said above).
Yep, been pointed out above and a good point. I reckon there will be twin-magic gears though, you'd just need multidimensional matrix of calculations or something to find them.
I thought about these ideas for a super-durable touring bike spec once. If you’re putting a tensioner on the rear as well as something to shift the FD you may as well use a rear mech, that way you eliminate the FD and consolidate the shifting and tensioning. Once you’ve done that you may as well have more than 2 gears.. or a hub gear. A hub gear with 3 ratios weighs almost as much as one with 7 or 8. So, SS / 2s Auto / 1x / 3x / hub gear all make sense. To simplify things for eg a backcountry or world tour I’d go dinglespeed, no tensioner, just 2 well chosen gear ratios.
Yep, I agree with most of that logic. I used to run single speed cog out back and triple out front, but just go 1x10 nowadays.
That said there are still some arguments for the former, like cost (single speed cogs and normal chainrings are cheaper and last longer than cassettes and narrowwide's) and weight distribution (as it massively reduces weight at the rear and adds somewhat less at the front). Another problem though nowadays would be front mech clearance.
Schlumf Drive
I thought it'd been mentioned, but perhaps not? Expensive things and I thought they required some-sort of frame modification, but they're to some degree just what I want.
I reckon there will be twin-magic gears
Only if you have ratios which are x:y and y:x, which will give you a useless setup.
There may be gear pairings which give tolerably similar chainstay length, but they'll be extremely few and far between, and if you want to use the same length chain I suspect they're essentially non-existent. (I've not done the maths… wouldn't be hard to write a bit of code to work out all the combinations with readily available components and figure out which come closest.)
jameso
Subscriber
I like the SRAM Automatix hub, a neat idea and functionally it’s great
Looks like they're no more unforts:-(
I was thinking last night about replicating SA AW ratios with a derailleur set-up. So, using my SS as an example, gear 2 would be direct (in this case 36/18 = 53"), gear 1 would be 39" and gear 3 would be 70.49".
So, that would equate to a cassette with 24, 18 and a high of about 14.
So the next question is, what is the largest gap one could reasonably have between cogs and at what spacing? 8sp, 9sp, 10sp?
Only if you have ratios which are x:y and y:x, which will give you a useless setup.
There may be gear pairings which give tolerably similar chainstay length, but they’ll be extremely few and far between, and if you want to use the same length chain I suspect they’re essentially non-existent. (I’ve not done the maths… wouldn’t be hard to write a bit of code to work out all the combinations with readily available components and figure out which come closest.)
You may have worked this out already (I'd didn't realise at first), but because the length of each chain doesn't have to be the same like it does for a conventional ("conventional...") dingle-speed set up, the options open up. What does have to be satisfied for each pair is that the effective chain length* divided by chain pitch is a whole number.
So you could run one chain as a 1:1 gear ratio (22t rear 22t front, 28t rear 28 front, it doesn't matter.) Then for the second gear, say you wanted a 2:1 ratio, you could try a 16t at the rear and 32t front, if that didn't work, change the front for a 32t, or a 33t, or 34t. If still no luck change the rear for a 17t and the front to a 34t, then again try 35t front, 33t, 36t... etc.
A spreadset calculation should tell you the answer soon enough. Think I'll try it in fact...
*As I understand it, this is the length of the chain from the sprocket to the chainring. I may be wrong...
Where I've said "effective chainstay length" I've meant the distance between the BB axle and the rear hub axle with the chain taut.
I need to draw myself a diagram to make sure I've got my head straight before I get back to this 🙂
This link (posted earlier in the thread) does some calculations for you-
https://eehouse.org/fixin/formfmu.php
You only need to know the chainstay length and it'll give you an indication of what'll work-ish. Here's my bike (supposed to have 415mm stays but it's closer to 418mm as I measured it) in it-
[img] 
[/img]
The colours in the chart indicate which ratios should use the same chain length.
