Touring - Need some guidance building up a 700c Rohloff bike
Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.
10-03-09, 09:00 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, 02:48 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, 03:23 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, 08:39 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
Powered by vBulletin® Version 4.1.12 Copyright © 2014 vBulletin Solutions, Inc. All rights reserved.