3x2 drivetrain for touring
 

I'm figuring out the drivetrain for a vintage light tourer.

I'm considering a 26/38/50 Biopace triple up front with an alloy 29T and a steel 15T rear cogs. The resulting gear inch range is 24 to 45 for the large cog and 46 to 88 for the small cog.

The idea is to switch between the two rear cogs manually. This allows the system to run under a single-pulley tensioner without a rear derailleur, so half the pulley drag and good chain alignment. It also allows for a no dish rear wheel for durability.

Does this work? What's the best way to fit two cogs with no dish? Any hub recommendations?

FWIW the way 3x2 was typically done back in the day was by employing a Sturmey-Archer AW three-speed hub with either two cogs and a rear derailleur, or two chainwheels, a tensioner and a front derailleur.

https://cimg1.ibsrv.net/gimg/bikefor...74b92685a1.jpg

What problem are you trying to solve by ditching the rear derailer? IME rear gear changers work better than front, especially with triples. The added loss from 2 pulley wheels versus 1 is insignifcant.
If I were building a bullet proof trouble free ride, I would start with an old Shimano 600 6 speed cassette hub, the original version with flat cogs and a screw-on 13. Those are light, the axles are supported at the ends for maximum strength and make a 6s wheel with about the same offset as a 5s, which is way better than any modern wheel. You might even be able to modify it for even less dish if you replaced the 13 with a simple lock ring, or maybe get more gears by using 8s cogs and spacers. Use it with Simpex retrofriction downtube shifters. IF you only want 6 gears you don't need a front derailer at all, which mostly eliminates chain drops. Or you could go really old school with 5s wheel on 120mm spacing, and use a SunTour Ultra 6 freewheel. Wider spacing results in too much axle bending with those old freewheel hubs. All of those parts are probably more available than a 2 speed freewheel (which I've never seen) or even Biopace chainrings.

Hope this helps.

em

+1 Front shifting under load is far more problematic than rear shifting. The major negatives I see with your proposal are:

1. The gaps between adjacent gears are going to be huge (46% from 26T to 38T and 31% from 38T to 50T) so finding a comfortable gear is going to be difficult particularly under varying road conditions.
2. Stopping to shift manually in back is going to get real old real fast unless your are in very uniform terrain.
3. A dishless rear wheel is not the great benefit it might have been years ago. Modern rims and spokes are much more durable and a moderate dish say 6 or 7-speed with 126mm spacing or 8/9/10-speed with 130 or 135 mm spacing) is no problem.

Thanks for the Shimano 600 suggestion, is that the narrowest cassette available? Ie, with the lowest dish?

It's not just the number of gears though, it's the gear spacing. As pointed out, it's not obvious that I will be able to accomplish two cogs on same side with standard parts but I see a few theoretical benefits to this setup that I'd like to test out:

- Half the pulley drag, especially with road debris on
- Better chain angle
- Stronger rear wheel
- Simpler/lighter overall transmission

Good point about stopping to shift manually, will think about this further.

Gears are set up so that I engage each gear at 60rpm and hold it until 90rpm before shifting back to 60rpm in the next gear, do you think that's still gonna be too wide of a spread?

That's an acceptable spread for me, unless I'm training with a competive group. You only need close gears to stay at maximum power long enough to close gaps. You are at least as efficeint at 60 RPM as at 90, but you have a lot less power. With a wide gap, sometimes you need to relax and just go a little slower, or put in the effort to stay in a gear that's a little higher than you want. It doesn't make much difference in your time to your destination. IME my commuting times were at least as fast with a single speed as with my race bike, mostly because when I had a lot of gears I always ended up in one of the low ones. YMMV

em

Pulley drag is negligible. Use ceramic bearing pulley whells if you are concerned about that, but it doesn't make any difference. IME even most racers don't bother with that.
The fixed tensioner will always be misaligned by a half space. Maybe that's noisy, or maybe it even causes ghost shifts when you work the front derailer.
Typical 5s offset offset is fine, even with old school 350 gram tubular rims. It's bullet proof with modern rims.
A cassette-derailer might be lighter than a 2 speed freewheel rig. Changing gears with a downtube friction shifter is simpler than getting off the bike.

em

The idea of a 6 speed Uniglide hub is good. I’d go a bit farther and find a 7 speed Uniglide/Hyperglide freehub body with a thin flange and mount it to a deep flange hub. I’ve done this with a Hyperglide body and a shim and didn’t have an issue with the hub bevel. You should pick up a couple mm’s in freehub body width.

With that, I’d just run a 2x4 (44-28 with 13-34) spaced to 5 or 6 speed with and use friction shifters. I’d center it to get the best chainline.

The caveat is longer rear derailleur limit screws and how tight you can set the high-low.

John

Get a rim with an offset spoke bed.

You can do that but more gears is a slippery slope. If you think you want 7 soon you'll want 8 then 9 then12. All that gets you into fancy cogs with shaped teeth that put sideway stretch on ultranarrow chains, and if you have close gears you're gonna want to shift more often so you'll want Ergo shifters. That's all racing stuff but for touring it's better to keep it simple with 6s old school downtube friction shifters and wide chains, especially if reliability and simplicity are your main concerns. It seems like the OP is over the more-gears-is-more-better syndrome anyway.
FWIW Jobst Brandt thought 7s was the optimum, even for his death march tours in the mountains.

em

Nope. No slippery slope for me.

My point was if you can bury a freehub body by setting it deeper in the hub you can reduce the OLD a bit, or at least reduce the DS hub to lock nut distance for less severe dish. As it is, the OP will probably have to spread the rear dropouts to fit any freehub.

Using a UG/HG lets someone pick between a lockring or threaded 1st position cog and use HG cogs for the remaining three. I’m guessing running a 13-17or18-24-34 centered on the freehub body might give a good range over both chainrings.

I’d opt for bar ends or Gevenalle over downtube. I’m not touring, but I’m using Kelly TakeOffs on my road bike. Took a while to get used to the hand gyrations, but now it is second nature. Hard to find these days.

John

If you want simpler, do a 1x setup rather than what you propose. It just doesn't seem simpler to have to manually change the rear. None of the points you have listed are any real issue. I tour on a 3x9 setup. I have 36 spoke wheels, and have carried a lot of weight with no issue. The wheels are going strong after 11 years. Chain angle is a non-issue. You want lighter weight for the drivetrain on a bike that is going to be used to carry a lot more weight. That doesn't even begin to make sense. The amount of weight you will save by ditching the rear derailleur and cassette, is minuscule compared to the overall weight of you and the bike, plus any load you will be carrying.

I've used bar end levers and those Sun Tour wingnuts, but I neither of them indexed with whatever derailer I was using. I liked racing with them with 6s but not much with 8s, which required a lot more shifting (obviously, I'm old). With fewer gears and less frequent shifting, I'm happy to reach for the downtube shifters if only to stretch my back a little. YMMV

em

While this is getting OT from the OP’s question. I ride a 3x8 with a 14-36 cassette. It is really more of a 2x7, with the inner ring or 36t cog available.

I ran downtube Retrofriction until 2015 and then downtube index. I went to the Kelly’s a couple years ago. Not planning on going back.

John

Great point, I'm also curious about chain dropping off given that tensioner is one pulley instead of two. Maybe that's why racers don't use that

Exactly, the idea is to leverage the symmetric setup to run a lower spoke count. 36 spokes is nice but I don't need this wheel to last 11 years

How much weight do you intend to carry whilst touring with this gear combination? How steep or long are the grades or hills you'll encounter?

There's a bicycle store about 15 kilometers from me that had a number of 1/8" three cogs freewheels when I was there last just before Covid hit.

People used to tour on single speeds or three speeds so your proposed setup should work although you might find yourself walking a fair bit. Pushing a loaded touring bike up a hill is no great joy in inclement or hot weather.

Cheers

Looks like an option could be a 5-speed hub/freewheel with some spacers and only 14- and 28-tooth cogs on?

That would be 25 gear inches lowest gear so ~7kmh at 60rpm

I'm planning 20L max storage so let's say 200lbs gross weight

I had Kelly Take-Offs on one bike years ago and liked them at the time. Now I have Gevenalle shifters on three bikes and they are much lighter and more ergonomic than the Kelly's and I highly recommend them. I have used bar-ends in the past and found them awkward but more convenient than downtube shifters.

You probably misunderstood what I meant by a 1x setup. I mean one chainwheel up front, and a cassette and derailleur in the back.

I agree that Gevenalle are an improvement. What has stopped me has been the price of couple mounts on Tektro levers.

If I could buy just the mounts for $75, I’d probably give them a try. I like the design and the ability to clock the lever at the best angle. Maybe one day.

John

I didn't. How do I get a 25 to 90 gear inch range with that arrangement?

36T chain ring & 11-40 cassette.

For that weight and wheel dish I'd rather carry a lighter 11-25 steel cone and two front rings, plus chain line is worse. This is the worst of all worlds