CliffordK

I run a standard 8 speed freewheel and a triple with no FD on my Cargo bike.
I haven't gotten around to building a derailleur mount for the proper spacing for my wide bottom bracket.

I do my light riding mostly on the big ring. Then with heavy riding I drop down to the middle ring, and sometimes hills on the small ring. With some luck, I can shift on the fly, just reach down and bump the chain over. That reminds me, I had planned on adding a 4[SUP]th[/SUP] really small ring.

However, every once in a while I'll bump something with the bike and look down and see it is on the wrong chainring, usually jumping its own from big to middle. Anyway, the moral is that the FD provides a nice chainguide to keep it on the right sprocket.

A unique solution might be to find/build a 2 sprocket rear end, separated say by 10T or so. 18T & 28T?
Then give your double chainring also a 10T jump. 50/40.

This would give you the shift range: 50/18 & 40/28T AND I THINK WOULD WORK WITHOUT A TENSIONER, but would take a bit more work to shift.

spectastic

I hear you on the chain guide. Like someone suggested before, I would probably get something to keep the chain on the ring. I'm also changing my mind on the spring loaded tensioner and going with the other kind that sets in place and doesn't move. That takes away the issue of chain suck, and make the chain much more stable on the rings.

does 50/18 equate to a 40/28? I don't think it does, but I don't feel like writing a proof either..

I don't think I will get anything as exotic as a planetary geared crankset, or a double cog on the rear. Still want to stay within the readily available OEM route, though I do appreciate the suggestions

CliffordK

I don't know if the chain length is exact. But it should be close enough that the differences could be taken up by your slotted dropouts. Plus, if designed right, it would preserve your chainline.

However, I understand your desire to use off the shelf components.

I do more standing hill climbs than spinning... Have you tried your current single Alfine setup? How heavy of bags are you carrying? Perhaps you don't need all this added complication of the multiple chainrings and tensioner.

I did snag a 7 spd IGH a while ago that I've been meaning to try out, but probably not for too many miles with the bike it is on.

pacificaslim

So...only 30-40% more than a modern road bike? (Seriously, that crankset is like 1800 grams and regular double road cranks are in the 600-700 range so that's between 2 and 3 pounds of extra weight for the crankset.)

spectastic

according to you, the modern road bike weighs 15.7 and 16.9 lbs. I think you're mixing up modern with high end. my crankset is more like in the 1000 lb range, with the BB. It's an elita gxp with a new chain ring. the wheels are heavier than usual, due to the disc brake setup, the 32 and 36 spoke count cr18 rims (good for touring), and alfine hub (1600 grams) which substitutes for delicate shifters, cassette, FD, and RD. I could upgrade the crankset, get lighter rims, get a super light road frame (instead of the strong cross frame I have now) but I like the bike the way it is. It's in that perfect sweet spot where cost meets performance. It rides like a champion, and am very proud of it. Can't wait for the rest of the parts to get here so I can swap out the repurposed vintage derailleur and chain for the actual intended setup.

spectastic

I made a spreadsheet for this. On my last tour, I went through big sur, los padres, and did a lot of climbing. I carried only 23-25 lbs, but still needed my 30/28 from time to time. If I do 46/16, my high gear is equivalent to a 53/11 and my low end is equivalent to 39/25. If I do 36/16, my lowest gear goes down to an equivalent 30/28, while the high end is around 53/16. I like these numbers, so that's what I'm probably going to get: 46/36 front, 16t in the rear.

Cross Creek

When choosing your chainring/cog combinations, remember that Shimano recommends not exceeding a 2:1 ratio (on the low end) to avoid over-torquing the hub. Your 36/16 combination is ok, as would be a 32/16 or a 36/18, but a 32/18, for instance, or a 36/20, would exceed the spec. With the typical use that IGH bikes see, I wouldn't be particularly worried about easier combinations (easier on the rider, harder on the hub), but you're planning to tour in mountains—I'm sure you don't want to blow up your hub half way.

spectastic

thanks. got that covered