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Old 06-01-05, 02:34 PM   #1
hjbiker43
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Compact Crankset?

I'm thinking about replacing my 39/53 crank on my roadbike with a compact, probably a 34/50. I live in the mountains of SoCal and will be having surgery in August, so I'll be needing some lower gears during my recovery. Don't want a triple as I just want to keep it simple. I'm just wondering if I'll miss that 53 and if the shifting will be as smooth as my present setup (12-27 in the rear). I've heard with some compacts, because of the bigger gaps, shifting can sometimes be a problem. Have any of you who have compacts, experienced any of there problems? What's a good brand? Carbon or aluminum?
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Old 06-01-05, 11:57 PM   #2
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HJ, I took delivery of a new Scott CR1 Team Issue two months ago. I did not even use the DuraAce 53/39 that came as standard but immediately purchased and installed an FSA carbon mega expo 50/34 crankset. My reasons were the same as yours; I live South of San Francisco and in a 70 mile Coast ride today, I climbed 6,600 feet. My 12 - 27 cassette gives me a low of 33 inches that equates to 7 mph at 70 rpm (a convenient figure). I find I can keep up with my younger, stronger friends (I am approaching 68) pushing higher gears much easier than before. I agree with the benefits of simplicity of a double (triples are hard to trim with indexed brifters) and with a 10 speed who needs a triple? As for missing the 53, my 50 - 12 gives me a 109 inch top gear, good for about 40 mph. Faster than that and I coast.

My DuraAce shifters, front and rear, perform flawlessly.

I sold the unused D/A crankset and it payed for the FSA carbon which is a bit lighter.

I have only had experience with the FSA and its MegaExpo bottom bracket. It is well made and has given no trouble.

Brian
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Old 06-02-05, 06:58 AM   #3
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I've got FSA 50/34 crankset paired w/ Chorus drivetrain - no problems.
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Old 06-02-05, 11:36 AM   #4
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If you read the pamphlet that comes with a new front derailler, you will find that it can only shift a range of 22teeth difference. I have stretched that to 24t on the tandem, but it will not take 26 comfortably, and that is on a triple. The limits are on the derailler guide itself as the physical size of the cage means that you conpromise and have chain rub at one end of the gearing or the other. How you roadies get away with having a difference of more than 24t I do not know, but to me that means if you run a 50 as your largest sprocket, then 36 will be your smallest. An alternative is to run a larger range of rear cassette, but that would also entail a change of the rear derailler to a long cage version.
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Old 06-02-05, 12:10 PM   #5
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I'm going to cut and paste what I wrote in a similar thread in the Road Cycling forum. You may want to check that one too.

I'll add this, as it didn't come up over there - shifting in both the front and rear - no problems. I'm using a 12x29 cassette and Campy compact FD. My standard Chorus FD worked, but the shifting looked ugly (chain slewing all over the place) and so I popped for the compact version.

Here's the rest of my story:

I'm 51, relatively strong recreational rider, hate climbing but can get up most hills. No knee problems, but, I'm not 20 and indestructible. I wanted to build a climbing specific bike without a triple. Note, this bike is not my sole ride.

What I've found - had many problems with gearing and matching it up to my style (small ring spinner, not a masher.) Had to fix a problem with the 2nd and 3rd cogs rubbing on the inner side of the large chainring due to the geometry of the frame (required a 2mm spacer on driveside BB.) Also didn't like the 50T combinations as I was riding in the biggest three cogs - close to constant cross-chaining. Went to a 48T.

So now I have a 48/34 up front and a 12-29 in the back (also had to modify a Campy 13x29 to put a 12 on to regain the 13 when riding in the 34)

I ride almost all the time in the 48 - most of the 34T combos are too easy for anything but climbing. The upper end of the 48 combos put a lot of bend on the chain, so the FD adjustments need to be precise. More precise than a regular FD set up.

If this was my only bike, I'd take the compact off. While I can probably get used to the differences it requires in my riding style (more shifting, oddball combos) it would not be worth the work.

My sole piece of advice - spend some time looking closely at the gear combos you ride now and compare the ratios to where they would fall with a compact set-up. It may be that you end up on the outer edges of everything like I did and thus need to make some compromises.
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Old 06-02-05, 12:33 PM   #6
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Quote:
Originally Posted by stapfam
If you read the pamphlet that comes with a new front derailler, you will find that it can only shift a range of 22teeth difference. I have stretched that to 24t on the tandem, but it will not take 26 comfortably, and that is on a triple. The limits are on the derailler guide itself as the physical size of the cage means that you conpromise and have chain rub at one end of the gearing or the other. How you roadies get away with having a difference of more than 24t I do not know, but to me that means if you run a 50 as your largest sprocket, then 36 will be your smallest. An alternative is to run a larger range of rear cassette, but that would also entail a change of the rear derailler to a long cage version.
Capacity of a double derailleur (e.g Shimano 105) is 15T. 53/39 is 14T. 50/34 is 16T. It's 1T over spec capacity, but specs are just specs and often conservative at that. There's truly no substitute for trying things in the real world!

I'm running standard 105 double derailleur with 50/34 compact with no shifting issues. It's not absolutely as smooth as the 53/39 was, but the difference is barely noticeable. Haven't had a single thrown chain or baulked shift, even under load. Take the time to set it up properly (height, angle, limit screws) and it will work fine. I use a 12-23 cassette for flatter rides (which gives a really tight spread of ratios), and switch in a 12-27 when I'm hitting the climbs.

(btw, not 50+ but shouldn't have any impact on an opinion on this topic!)

*edited to fix my stupid typos... had 50/36 when I meant 50/34. 50/36 is within the 'specs' for a standard FD, 50/34 is outside, but will still shift nicely when set up properly*
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Old 06-02-05, 01:54 PM   #7
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I have to duet the above by Stubaca. I built a commuter using a 105 front der and Stronglight Impact (aka Sugino) 50/36. This is used with a 9sp SRAM 12-26 and a Shimano chain. The STI handles it as well as my other two 9sp Ultegra (53/39 and 12-25) setups. I think the key, if there is one, is positioning the front der. both height and angle. My commuter does not have the greatest chainline but it shifts smooth as all get out. The 53 is not missed at all and the 36 is a useful shift from the typical 39. I have not tried the 50/34 combinations yet...maybe that is where the requirement for a "compact" front der comes in...don't know.
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Old 06-02-05, 02:04 PM   #8
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Quote:
Originally Posted by fsor
I have to duet the above by Stubaca. I built a commuter using a 105 front der and Stronglight Impact (aka Sugino) 50/36. This is used with a 9sp SRAM 12-26 and a Shimano chain. The STI handles it as well as my other two 9sp Ultegra (53/39 and 12-25) setups. I think the key, if there is one, is positioning the front der. both height and angle. My commuter does not have the greatest chainline but it shifts smooth as all get out. The 53 is not missed at all and the 36 is a useful shift from the typical 39. I have not tried the 50/34 combinations yet...maybe that is where the requirement for a "compact" front der comes in...don't know.
Just edited my post above... I meant to type 50/34 up there, but had a brain fart and typed 50/36...
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Old 06-02-05, 02:33 PM   #9
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My commuter is rather a truck...if I did it over again, I would have tried for 50/34 rather than the 50/36 that I did use. I have the option of some mild off-roading with really neat hills and a little lower would have been helpful....oh well, next time.
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Old 06-02-05, 03:43 PM   #10
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Good to see some Chimers-in from Road Forum and my Compact Crank thread.

As they can attest, I floated this same question out there and received lots of great replies.
Read here:
Compact Cranks: Who uses them, what kind of riding do you do, and ... are you older?

I'm going to go for it.
My crank is a Shimano 105 w/Octalink, so I will hold out for a set like that instead of going to an ISIS BB. The Ritchey WSC is such a beast, and it gets good marks and is practically priced... I'll just monitor the net and look for the best deal when it comes up. I'm off on a week tour in 2 weeks... so I won't get it done by then (too bad), but I'll have the rest of the summer to tackle the roads.

From where I'm standing, some of the losses would be:

Losing the very highest gears (over 40MPH). That is Nooooo problem with me. I'm happy to coast at 35MPH

Working mostly in the 50 cog with the 34 for hills alone. That's okay. I've yet to change to the 11-12T cog yet!

Some loss of overlap in gearing. Me? It's not like I'm a Criterium racer... I just shift until I find it.

I see the use of STI as an adaptive skill. Until February of this year, I was using DownTube friction shifters, choosing from a range of FIVE gears, of which, on any given front gear, 3 were really useable. After 700+ miles this spring, I'm beginning to understand where I am in the cassette, and where I need to shift to on the cassette PRIOR to moving up/down in front.
I look forward to the new range of gears (and the process of removing and installing a new crank myself!)
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Old 06-03-05, 11:24 AM   #11
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Quote:
Originally Posted by stapfam
but to me that means if you run a 50 as your largest sprocket, then 36 will be your smallest. An alternative is to run a larger range of rear cassette, but that would also entail a change of the rear derailler to a long cage version.
Must have had brain fade on this reply as 50 -36 is only 14t Sorry about that but I should have put in another proviso aswell. The largest jump I can get on a Triple is 14t. Beyond that and there is a time lag before it goes up onto the larger sprocket. In fact 14t is not as crisp as I like.
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