double crankset and single speed drive train?
 

I've just got my alfine 8 built up, and have just realized what a royal pain in the ass it is to get the lock ring in there for the rear sprocket. I thought I could be on a tour, encounter a mountain, and easily swap out the rear with a 20t or 22t to get my lowest gear ratio equivalent to a 34/28. NOT SO!!

So I'm taking a new approach. the crankset I'm using is a triple. I currently have a 1/8" ss chainring in the middle. I'm wondering if I can put another 1/8" chainring on the inner bolts to make a double. I'm not going to bother with putting in a front shifter. The small chain ring is only there for the steepest climbs. When that happens, I can just jump off my bike, align the chain on the smaller ring, and pedal on.

I'm a little worried about chain offset on my single speed chain. I'm guessing this won't be a big deal, but double checking.

Also, I will be running a spring tensioner on the bike, and the jump from the big ring to the small ring might be a lot for the tensioner to handle. I'm running 46t on the front. Can I run a 36t on the inner ring? or even 32?

I'm not digging this plan. I think the changer is generally included just for the conditions you describe, without the grimy hands.

I think there's something about the Alfine 8 that I'm not getting. It's a IGH? so you can't use a changer?

Why are you using a 1/8" chain and chainring when Shimano IGH cogs are 3/32"? You could be using a derailleur chain, double jockey tensioner (one that takes up shifting slack) and FD with your triple crank. You'd have to replace that 1/8" middle ring with a proper derailleur mid, of course.

double crankset and single speed drive train?
 

Surly used to make a double cog called a "dingle" for just such a thing as the OP. Do they still make it? Might be worth a look.

oh damn I didn't realize the rear cog is 3/32. nevertheless, it says it can be used on a ss chain. I'll just go with the ss setup because I want it to last longer, unless the ss chain is too wide to be used on a double, in which case I'll just get a 3/32" setup.

I still don't want a FD though, because if I do, it'll have to be a clamp on down tube shifter, on an oversized carbon fiber down tube, and that'll be a pain in the ass to find, and mess up the glossy finishing. I'll just step off the bike and do the chain swap manually. I'll rarely do it anyway.

I can, just don't want to. Want to keep the bike as simple as possible.

those dingles are threaded. the igh cogs are slide in with a snap ring.

Well, I guessed that simplicity is part of the appeal but still, do you have to go back to the dark ages? A shifter for your front derailleur could be very elegantly accomplished but probably not if you're completely opposed to an additional cable.

I can always add them if I feel the need to. Right now, I don't feel the need



ANYWAY, the original question is will the spring tensioner be able to handle a jump from 46t to 32t? Will the chain will have enough wrap around the cog?

If you're going to manually move the chain, then the SS chain will work, so long as the chain line for both chainrings is pretty good—1/8" chains weren't designed for a lot of sideways flex. Definitely try to get a 1/8" ring for an inner—stainless steel, of course. 1/8" chains don't play well with 3/32" alloy rings, and dumping the chain off the inside ring can result in frame/paint damage and a locked drivetrain. Get a Deda Elementi Dog Fang or something like it anyway. They're cheap insurance for less than half an ounce.

I actually measured my chainring, and the width is actually 3/32, not 1/8 as advertised, meaning I could run a 3/32 chain. but I've already ordered a 1/8 chain. Why doesn't 1/8 chain work well with 3/32 sprockets?

BITD, I got a 3 cog cluster for my S-A 3 speed, and fitted a cottered triple crank & still used the 1/8" chain it came with.


3 by 3 by 3 ... a 27 speed .. used 3 levers to change gear combinations.


thats 14 t.. same as most road doubles ,so a chain tensioner with 2 pulleys with a distance between the 2 pulleys like a regular RD
should be adequate.

you can always use an old MTB RD as a chain tensioner if you need more slack .

The chain will be fine on the sprockets, but SS chains are not designed to flex sideways like derailleur chains.

FWIW, the Alfine model chain tensioner is designed to allow a double chainring setup, but you need a derailleur chain.

the Bushing 3/32" type was used by all the Pros, etc. before companies like Sedisport

introduced the bushingless chain , now all derailleur chains use that design ..

it begat the whole more 'speeds' the merrier thing, beginning with the 6 in the space of 5, and 7 in the space of 6 ..

I was referring to the single pulley type tensioner

That's an interesting concept that I hadn't heard of before, but it seems like you'd need to travel with a wrench and some latex gloves at all times. Not the end of the world, I suppose as I do that anyway.

By my math, if you have it set up with a 46/20 (same low gear as 34/28), then your top gear will be around 99" which has always been enough for me on tour. How about skipping the complicated setup and putting on the 20T now? :D

greasy finger front shifting the smaller chainring can even be on the outside. ( a Brompton bodge done on their older style 50t chainring cranks )

but if you are buying a new double crank use it as it comes ..

This whole thread is a royal mess. Chain tensioner, manual front shifting, swapping cogs... Why not just stop screwing around and put a derailer drivetrain on? They use these handy little things called shifters that can be mounted on the downtube or the bars. And they give you all the range you'll ever need if you use a triple up front. The system will also be lighter than an IGH.

What am I missing here?

I have a 2 speed Planetary geared crank . and the chain never leaves the chainring,
just the crank arms turn at a different rate than the chainring ..

Is this a Schlumpf crank? Certainly an elegant solution to the OP's plan

mountain drive

^^Best "solution" I've read.

My BSR 3 speed + MD gives an 18~80" range, the direct gear is a 58"..

This is another one .. It shifts with a Cable Patterson Bike - Rocket Fast Shifting | Cannot Throw a Chain

Over drive when engaged , chainring turns faster than the crankarms ..

Interesting concept but comes with quite a weight penalty!

bike weighs 22 lbs right now.