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View Full Version : Double vs. Compact Double



KnottedYet
08-14-2006, 09:15 PM
Help me, please.

I really did try to figure this out myself, but failed.

What is the difference between a double and a compact double?

Say (hypothetically) one bought a Waterford with a double, which from the picture has very little difference between big ring and little. And you KNOW you need a littler little ring! Maybe even a littler big ring, too.

Couldn't you keep the cranks and front derailleur and shifter and just change out a ring (or two)? (and adjust things afterwards, of course)

Someone told me I'd need to get a compact double and change out the cranks, too. And the FD.

Isn't a compact double just 2 rings with a big size difference? Can I fake it with new smaller ring(s) in front?

Switching out the double for a triple would cost me a gazillion dollars, and honestly I hardly ever use my big ring on my commutermobile. Don't use the little ring much, either, except on monster hills.

velogirl
08-14-2006, 10:51 PM
A standard road double is 53-39. A compact is typically 50-34 (although now you'll see some deviations from that). You're limited in the spread between large and small ring (for example, you could put a 50-24 on because the range is too large).

Your LBS might be able to create a custom crankset for you, but that will depend on what rings are available in certain bolt patterns (different cranks have different bolt patterns).

To convert from a standard double to a compact, you might also need to swap bottom bracket and front derailleur.

A cheaper alternative might be to use a larger cassette in the back. Depending on how large you go, you might also need to swap the rear derailleur to a medium or long-cage derailleur. This second alternative is typically less expensive than the first.

Get the frame dimensions (BB shell width is an important one) and chat with your LBS about options. They'll be able to best advise you.

Mags...
08-15-2006, 03:53 AM
I swapped my double for a compact double, and I did it myself. This was pretty straight-forward with my bike as I went from Shimano Dura-Ace double to Shimano compact double. It's all in one piece, the bottom bracket, the right crank and the 2 rings which are 50/34. When the crankset/BB is inserted through the hole in the bottom of the frame, the left crank is then bolted on the left side of the BB.

I didn't have to change any shifters, chain, or derailleurs. The FD was positioned a little too high for the compact, as the original double was sized 39/53, so this was shifted down a little bit - easy. I did have to spend some time fiddling/tuning the gearing into the FD as there was a little rubbing of the chain initially.

You should figure out what sort of cycling you'd like to be doing and there are charts/figures/sums you can do to work out what gearing ratios you'll get between one set-up to another. The range of gearing you get depends on what rear cassette you team the crankset with, for eg. 11/23, 12/25, 12/27. I've got the 12/25 and I've found that in comparison to what I originally had, which was the double 39/53 teamed with the 11/23 cassette, I've got equivalent of 3 lower gears for going up hills than I originally had, and have lost 1 gear at the top end. Seeing as I'd never used that one anyway, it was no problem. I use the larger front chain ring more often now. It takes a little getting used to but I'm happer with the changes.

bike4ever
08-15-2006, 05:14 AM
We also put a compact double on for a customer without changing the front derailleur. I put a compact double on my Lemond this season and needed to change the front derailleur since I am using Campy. We just couldn't get the standard derailleur to work. My crankset is Bontrager Race Lite so I didn't need to change out the b/b.

DebW
08-15-2006, 05:15 AM
Nothing new to say, but I'll say it in different words. Every crankset has a minimum sized chainring it can take because of the size of it's spider arms and the diameter of it's bolt circle (the bolts that hold the chainrings to the arms). You need to find out the brand/model of crankset and it's bolt circle diameter. Then you can find out what the smallest chainring it can take is (probably 39). A compact double is made to take smaller rings (probably 34) than a standard double. Your Waterford may come with a 42 inner, and if so you could go down to 39 for minimal expense. Increasing the cassette size very much will most likely require a new rear derailleur (looks like a short cage in the pic), but going to a compact crankset probably will also.

KnottedYet
08-15-2006, 06:53 AM
Thanks you guys!

Gee, the amount of knowlege on TE is just so cool. You guys are great!

velogirl
08-15-2006, 10:37 AM
We also put a compact double on for a customer without changing the front derailleur. I put a compact double on my Lemond this season and needed to change the front derailleur since I am using Campy. We just couldn't get the standard derailleur to work. My crankset is Bontrager Race Lite so I didn't need to change out the b/b.

I'm a campy girl, too, and I've been running a compact double since they first came out in 2003. I didn't change my front derailleur since there weren't compact-specific FDs available at that time. And I've never had problems with the standard FD.

alpinerabbit
08-15-2006, 10:49 AM
Yep, swapped to a compact double, with a new cassette thrown in (larger Granny gear) - no change to the derailleurs required.

bike4ever
08-15-2006, 01:14 PM
velogirl - I'm glad your campy compact worked out well. We tried everything we could to try and get it to work. I believe it has to do with the Bontrager crankset paired with the Campy front derailleur.

roadfix
08-15-2006, 02:21 PM
Couldn't you keep the cranks and front derailleur and shifter and just change out a ring (or two)? (and adjust things afterwards, of course)

To a certain extent, yes. On a standard double crankset (typically 53/39) the smallest chainring you can mount on it is 38. You can also swap out the large ring to a 50, for instance.
A compact crankset uses a smaller spider arm (110 BCD) to hold the rings and typically come with 50/34 or 36. You can mount larger rings on a compact crankarm if you wish to make that change. One normally sets up a bike with either the standard or compact double depending on their strength & riding style but that's another completely separate subject matter.
You can use your front shifter and derailleur with either setup. No need for a compact specific front derailleur....standard front derailleur works perfectly on a compact double.

KnottedYet
09-01-2006, 07:59 PM
Had a great time hanging out at my good ol' LBS www.recycledcycles.com with a wrench who has a Waterford, too.

He said they could order me a Campy Veloce compact double (50t/34t) for $148. I can get it from Nashbar for $140, but that's as much as they can lower their quoted $170 price. That's ok with me. I love them. They love me. Feel the love and $8.

They have a used Campy Athena bb for $20 (I'll get 10% off cuz they sponser my Team Survivor team). Wrench says it's in darn good shape and should have another 4,000 miles left on it, easy.

They have used Campy Veloce and Mirage front deraileurs (and a couple other Campys in case those are gone when I take my bike in) for between $15 and $25 (and I'll get 10% off that, too). Wrench says they will work fine on a Campy compact, no need to order a compact FD unless I'm planning on racing and need superfast shifting.

He said the labor charge to replace the regular double with the compact stuff would be about $15-20. (feel the love, feel the LOVE)

So, all you bike mechanic goddesses, does this sound like a good deal?

The bike shop isn't being hurt by giving me more than my usual 10% off on the new crankset. I will bring them a six-pack when I take in my Waterford. Feel the love! Feel the bribery! (be kind to my bike, and I'll bring you ANOTHER six-pack....)

velogirl
09-01-2006, 08:21 PM
Yes, it's a good deal. But then again, anytime you're patronizing your LBS I think you're making the right decision. Your LBS will be there to take care of you through thick & thin. Why not give them your business when you can?

ps -- cookies are better than beer. No one will crash riding home after eating a cookie.