Another Compact Crank Question
I've read a number of threads on here about this subject, but was unable to find an answer to my question. I'm thinking about outfitting my bike with something that some locals call a mega-range compact crank. The locals in question are all set up on Campy components. The setup that I'm thinking about is a Shimano 105 groupset with a 52-36 on the front, and as wide a range as I can get in the back (11-32 would be nice, but maybe 11-27).
My question is, will the long-cage version of the 105 derailure work decently on a double-crank, or should I go with another component combination entirely? The Shimano 105 long cage was designed for a triple-crank, and gives you an extra 8 teeth of capacity (29t short cage, 37t long-cage). I want the extra tooth capacity to widen my range for all of the mountain and hill riding that I do.
I'm not a racer, not that worried about componet weight, but prefer that the gears lock right into place, especially on climbs. My current rig has a 52-42 on the front, and a 14-28 on the rear. The only time that I use the 42 ring, is when the slope is greater than 10% or so, but I could definitely use another bail-out gear for some of the longer and steeper mountain roads around here that exceed 15% grade near the top (nasty for me at the end of a 1-2 hour climb). Thanks.
Low car diet
Beyond capacity, rear derailleurs also have a limit of the largest rear cog it can handle. All newer road long-cage RDs are rated for a 27-tooth. You might be better off with an SGS (long cage) Deore or Deore LX, which is about equivalent to a 105, but for MTBs and can handle up to 32T.
How many speeds are in the back? If it is 8 or 9, you can easily find an 11-32T cassette. If it is 10-speed, I've only seen one (I thought it was at Nashbar.com, but can't find it now...I think it was made by IRD???).
Not sure if any front derailleur can handle 52-36 very well. Normally 36 is paired with 50. But, people do use 50-34, which is the same tooth difference (6), so you might be okay. But as you mentioned you'll need a compact crank to handle the 34T or 36T ring which takes a 110 mm Bolt Circle Diameter crank (normal Shimano is 130 BCD). If that is the case, I don't know if there are 52T rings with 110 BCD meant for a double setup (as opposed to single speed missing the ramps and pins to aid in shifting).
It's possible just replacing the 42T you have now with a 39T, putting on a 11-32T cassette, and Deore/LX MTB RD will get you the gearing you want. Try messing around with Sheldon Brown's gear calculator: http://sheldonbrown.com/gears/ I suggest using "MPH @ 90 RPM" and running your current setup and then compare it to the 52-39T/11-32T setup and see if it will get you low enough.
Last edited by JiveTurkey; 11-07-07 at 11:15 AM.
The Improbable Bulk
I'm having a bike built with 105. It has a 50/34 compact and 11-28 SRAM cassette.
It needs either a medium or long cage 105, but I was told that it will work. As mentioned earlier, since 50/34 works, I see no reason 52/36 wouldn't... ideally the 52 has ramps and pins. I am not sure about who manufactures 52 tooth rings in 110 bcd.
I believe that the 28 is as large a cog as you can use with a 10 speed Shimano.
EDIT: To directly answer the question, a long cage derailleur can work for any combination of chain rings... including 2, whether compact or standard.
Low car diet
Just realized you probably have a 14-28T freewheel and not a cassette (the 14T high gear is a giveaway), which means it is probably a 6- or 7-speed. I saw a 13-34T 7-speed cassette on Nashbar.com, they also have the Deore RD on sale for $18. You'll have to look elsewhere for the 39T chainring, but after reading your original post again, you may not need it as the difference between 28T and 34T is pretty big, giving you that bailout gear. You might need new shifters (downtube??) if you're going from 6- to 7-speed.
Low car diet
Shimano can do 10-speed beyond 28T, you just need a MTB-type derailleur (e.g., Deore) to handle the larger cogs and greater capacity, and a wider-range 10-speed cassette. Found an 11-32T and 11-34T 10-speed cassette at Harris Cyclery, but they're expensiive ($160): http://sheldonbrown.com/harris/k7.html#10
Originally Posted by Little Darwin
Your setup of 50/34T and 11-28T is probably plenty low enough for most people though, except for loaded touring.
Thanks for the info, guys. Somehow, I forgot to mention above that I'm in the market to buy a half-decent used bike to perform these upgrades on. My old 1988 Trek Aluminum is going to be retired to the trainer in the basement soon. As JiveTurkey indicated, it is an old 12-speed bike that has just gotten too costly and time consuming to find decent parts for these days (fixed 126mm rear hub width on an Aluminum frame, 1 inch threaded headset, 6-7 rear speed road freewheel, etc.). Besides, I could really use that bail-out gear to haul my 200 lbs butt up steeper slopes. Maybe if my RPMs were above 30 on steep climbs, I would do hills more often and burn some more of this fat off? It sounds good, anyway.
With all of that in mind, it looks like I will be looking for a used Triple-Crank bike. I don't want to have two "special parts" bikes that I ride regularly. I just don't like the idea of getting a bike with 3 chainrings, when I will only use both of the smaller chainrings on hills over 10% grades. I'm so used to only using the 52 tooth chainring to ride everywhere else. I actually spend a vast majority of my time in the hardest 3 gears in the back too (16-14 teeth). I guess that it is a combination of being used to downtube shifters (fear of fingers in the spokes...yes, after all of these years), and being too lazy to shift? Most of the guys that I ride with like to spin fast all of the time, but I like to vary my speed and resistance while commuting and on my non-fast training or recovery rides.
I ran a 52-36 compact with 12-23 and 12-27 9-speed cassettes on my two wheelsets (one for pace lines, one for charity rides and serious climbing) for a couple of years before switching to a 50-36 with 11-23 and 11-26 cassettes. The chain rub with a triple front derailleur is annoying but it will work. Switching to a double FD got rid of the rub.
I'd be inclined to spec a 52-36 with a 12-28 IRD cassette and a double RD but you would be pushing the 29 tooth capacity of the latter. Proper chain length and B-screw adjustment would be very important. A triple RD would be less temperamental. Climbing 15% grades with a 36-27 gear was a chore but it's more or less the same as the 30-23 gear on a triple.
The Improbable Bulk
Leave it to Sheldon Brown and his comrades at Harris to find a way to do 34 teeth on 10 speed cassettes.
Originally Posted by JiveTurkey
I know it would take a mountain RD, but I didn't realize anyone was making larger cogs for 10 speeds yet.
Not a great technology hurdle to do it, just didn't think anyone had done it yet.
I actually had considered using an LX derailleur on mine just to allow for larger cogs when available, but I am one of those types that doesn't mind pushing up the hills I can't ride. At 50 years old, I have other things I care more about than the ego boost of never walking. But I should be OK on almost any hill anyway, especially as I lose weight.
Thanks for the heads up on the 34 tooth 10 speed cassette in case I run into anyone that wants/needs one.