Big Ass Cass-ettes for 10sp Road

3

by Mark V on Jul 31, 2010 at 9:48 PM

hello 10sp mtb 1.jpg I’ve been running SRAM and Shimano 10sp wide-range cassettes for almost a year now with road shifters, as well as having installed them on a number of custom bikes. They work pretty well. In fact, my SRAM Red shifters/X.9 mtn rear derailleur/XT 11-34 cassette shifts with crisp perfection. I don’t have really strong preferences for SRAM vs Shimano cassettes, and I’ve installed SRAM, Wipperman, and Shimano 10sp chains. But there are certain recipes for shifters and derailleurs.

SRAM Double-Tap shifters (Red, Force, etc): for 11-32 cassettes, you can use either the longer cage Apex derailleur (which is nice and inexpensive), or any of the 10sp mtn rear derailleurs. The Apex rear derailleur is rated for a 32T cog and might not work for cassettes bigger with cogs bigger than that (eg, 11-36). In my experience, you can’t often cheat the max cog rating of a SRAM derailleur. Better to go with the 10sp mtn derailleur. Make sure you choose a cage length with enough chain wrap capacity to deal with the combined ranges of the chainrings and cogset. Also, SRAM’s unfortunate nomenclature for mtn components can be confusing. For example, there is a X.9 rear derailleur that is 10sp and several generations of X.9 that are 9sp. Only the 10sp stuff will work.

Shimano STI: for 10sp road cassettes and chains, the best choice is 9sp Shimano mtn rear derailleurs, though older 8sp might be passable. New Shimano 10sp mtn derailleurs are completely INCOMPATIBLE with any road shifters. Also, the Shimano 9sp rear mtn derailleurs seem to be a fairly tolerant of exceeding the rated max cog size (ie, they were never meant to accept cogs bigger than 34T but in practice they’ll work on a 36T with margin to spare). Again watch the chain capacity.

Campagnolo: you’re screwed, thanks for playing. Well, not completely. Campagnolo doesn’t make cassettes with cogs larger than 29T,and Campag 10sp spacing (cog-to-cog) is physically wider with different mounting splines than the Shimano/SRAM standard. And Campagnolo rear derailleurs aren’t meant to work with cogs bigger than 29T….so what part isn’t completely screwed? Here’s some voodoo that I’ve tried. Take Campagnolo 10sp Ergopower shifters, SRAM 10sp mtn rear derailleur, and a SRAM or Shimano 10sp mtn cassette (on a wheel with the Shimano-type splines). It seems all wrong, but if you calculate cable pull for shifters vs cog-to-cog spacing vs derailleur ratios, it works out. Even better, other people like Lennard Zinn have been doing this with SRAM road derailleurs for a few years. Now that the SRAM mtn derailleurs (10sp) have the same ratio as the road derailleurs, this magic mix is even more useful. I’ve installed that on one customers bike so far.

Note: all this info sets aside issues of cranks. front derailleurs, and front shifters. That is a very complex story of integrated systems, shit that sorta works, and then stuff that just doesn’t. The basic rule is don’t mix and match there.

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Comments: 3

The fixed wheel is “back,” but derailleur bikes have marched on from the five speed straight block (with chainrings for intermediate gears) to wall climbers. I still feel like I can get over anything in a 34/27.

Old 8sp Shimano derailleurs work great with 9sp.  My derailleur’d bike has an 8sp era XTR short-cage derailleur (the nicest looking XTR derailleur that they’ve made) mated with a 9sp XT 11-34 cassette.  44/30 chainrings up front on a Ritchey 94mm BCD crankset.  On my tandem I’m using an 8sp era XT derailleur with a 9sp cassette.  The rest of my bikes have internal hub gears.

It’s perfect for Seattle.  I don’t drop into the 30 unless I’m pulling my trailer or riding up Dravus.  In cyclocross season I can switch to a single 38t ring.

http://alexandchristine.smugmug.com/Bicycles/Framebuilding/Ivy-T/14349199_vUdTW#1177362042_k8fEi

From 7sp to 9sp Shimano mtn derailleurs, all basically have the same ratio. The different generation derailleurs vary in pulley and cage dimensions, so later gen model work better with the super narrow 10sp chains necessary for 10sp cassettes.  Also, certain early 90s gen derailleurs had a rather narrow upper pivot bushing and thus were sloppier laterally, especially over time.  As a general rule, I recommend staying within 1 generation of the shifter when choosing a derailleur, with no real penalty for going newer on the derailleur.  So 8sp shifter/7sp derailleur = ok, 10sp shifter/9sp derailleur = ok, but 10sp shifter/8sp derailleur is probably not the best choice.  But if forced to choose between a N.O.S. M900 derailleur and a totally knackered M561, I’ll take the brand new derailleur.

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