Touring - Need some guidance building up a 700c Rohloff bike
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10-03-09, 10:00 PM
I am now the proud owner of a Rohloff-specific, EBB, 700c, disk brake (Avid BB7) custom-made 'dirt road' frame (think the attached drawing explains it better than I can).
Many of my sojourns will include rather long, and rather steep, mountains.
However, I have never built up a Rohloff bike, and neither has my only LBS (I live in a somewhat boonie place in Tokyo). I am trying to make some decisions about cranks and chain, and have come to the conclusion that I need some guidance!
The chainstays are pretty widely spaced, which I am assuming limits my choice to MTB cranks. I am currently thinking about Shimano M770, with a single 44t ring (Rohloff has 16t sprocket). Rohloff specs don't recommend 9 speed chains though (apart from the uber-expensive Rohloff 9 speed chain) - so I am wondering about which chain to use.
Sorry to be stumped on what is probably a no-brainer 'conundrum' for me, but I really and a bit befuddled right now.
It seems to me you could use more or less any crank; the critical thing will be to get the right length of the BB spindle to ensure the best chain line. By "any crank" I mean pretty much that; a cheap option with lots of choices in the US, for example, would be a "Bulletproof" bmx crank, available in a wide variety of crank arm lengths; and you get to chose the chain ring separately, so you can have any size there. I, personally, would avoid a MTB crank because they usually have 175 mm arms, which I consider frightfully long. Of course I have no idea what's available in Tokyo; if you go to a store, be sure to ask about BMX cranks. If you shop on ebay or internet, you should be able to find pretty much anything.
Get a chain that suits your chain ring. If you get a BMX crank, with a thick BMX chainring, you may need a BMX chain. I don't think the BMX chain is stronger than others, but the thicker chainring will wear longer.
I have a Rohloff hub retrofitted to an old (1984) tandem that originally had a 6-sp freewheel and triple crank. I am still using the original crank, with the middle chain ring (44T) moved to outer position, and the original crank, shortened to fit. So I'm running a 44-15 combination. I've gone over some pretty brutal hills with that, and never needed a lower gear. I'm sure I would have used it if I'd had it, though!
The Rohloff chainline measurement is available on the Rohloff site. I can't recall what it is at the moment, but they designed it to run a single chainrring in the middle ring position on a MTB triple.
I run MTB cranks on both my Rohloff bikes. They are widely available and cheap. On my Thorn I've got a square taper shimano BB and a cheap Alivio crank. Nothing fancy, but it works great. I use 8 speed SRAM chains I get for $16 on all my IGH bikes. The straight chainline is very easy on chains.
If you want some bling for your bike a Phil Woods square taper BB has a fair degree of lateral adjustment so you can totally dial in your chainline. Unfortunately it comes at a high cost.
Enjoy the new bike....:thumb:
10-05-09, 03:48 PM
Looks very nice. Don't worry too much about the chain, I don't think 8sp/9sp matters that much. I run 42/16 on my Rohloff 700c pothole-basher with 175mm mountain cranks and love it. I'm 195cm though so everything's got to be big.
Chainline for the Rohloff is 54mm, as mentioned on Sheldon's site (http://www.sheldonbrown.com/chainline.html). I solved the chainline issue by buying a cheap Shimano cartridge bottom bracket with the right BB spindle length to fit the cheap MTB crank and strong steel 42t chainring I had on-hand.
Getting the cabling done right is the most tricky thing. Good luck with that. Get the right diameter (stainless) cables so you don't have to re-cable it anytime soon.
10-05-09, 04:23 PM
Many thanks for these replies.
In fact I will be using 175 cranks, as the frame was designed with 175 in mind.
I am keen to hear more about cog sizes for 700c bikes ~ would 42/16 be suitable for road riding in 50% mountains 50% flat terrain? I can't find any resources online to help 700c riders calculate Rohloff gear ratios.
I got a White industries crank, partly because I didn't trip over a 175mm bmx crank. Another option are things like a sugino messenger. One thing about the triples is that they can run a chain ringguard. something is useful since the chain will be on the "outer" ring all the time.
I would question a 700c wheel for your use, though it will certainly work. Rohloff seems a better match for a 26" wheel. Basic issue is what size of low gear you need. Best case you already know. Then go to:
dial in your numbers and get your low gear. The rest just falls in place.
10-05-09, 09:39 PM
Thanks for the link to the sheldonbrown calculator!
I came to the conclusion that for me, with 700c wheels and 32 tires, a 42 cog would give a range of gear inches very close to the 27 gears on my MTB. (104 <> 19.8).
I am leaning towards XT cranks, with short bolts to accommodate a single cog, on the outside. + 42 Salsa cog.
Rims: Mavic A 317 disc
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