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2006-07-25 5:57 PM

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Subject: what are compact cranks for?
i have heard about these. what do they actually do? what is the preformance differences between these and normal cranks?

cheers


2006-07-25 6:00 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?
Less teeth so you can spin faster/easier.  People change them out mainly for hilly areas or races.  Another option would be to change the rear cassette to a 12-27 or 12-25. 
2006-07-25 6:24 PM
in reply to: #493043

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Subject: RE: what are compact cranks for?
so for a climbing course like IMLP you could go compact but for a flat course like Florida you wouldn't? why not just get a tripple if you want the extra gears?
2006-07-25 6:29 PM
in reply to: #493064

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Subject: RE: what are compact cranks for?

scott_loong - 2006-07-25 6:24 PM so for a climbing course like IMLP you could go compact but for a flat course like Florida you wouldn't? why not just get a tripple if you want the extra gears?

More expensive conversion. In addition to the new crankset, you would need new shifters and prossibly a new front derailleur.

2006-07-25 6:30 PM
in reply to: #493064

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Subject: RE: what are compact cranks for?
scott_loong - 2006-07-25 6:24 PM so for a climbing course like IMLP you could go compact but for a flat course like Florida you wouldn't? why not just get a tripple if you want the extra gears?
something like that, but as auto posted t is easier and better IMO to just change the casette for hilly/flat courses. Plus, a triple crank is heavier than a double...
2006-07-25 6:34 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?

I've never done those races but I would agree with your assessment that people may opt for a compact crank for IMLP.  I probably would (well first the rear cassette) because I'm just not a strong biker.  The thing is, not everyone will...many people will still stay with what came with the bike because they are strong bikers.  Oh, for compacts, you'll lose some speed toward the top since you have opted for less teeth.

The problem with the triple is not only is it heavier but also you'll probably have to change out or at least make adjustments to some components like shifters and/or front derailer.  I'm not 100% sure because I didn't decide to go this route, I went with the rear cassette change to a 12-27.  Also, the triple, at least on my MTB, always gave me more problems.  Not sure why, but the derailer just always seemed to get screwed up on the triple.



2006-07-25 10:00 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?
Compact will allow you to spin way past any normal cassette configuration on a standard 53/39 crank.

Compact crank with a 11/23 betters the climbing ability of a 12/27 and has a higher top speed than the 12/27 as well. 12/25 with a compact climbs even better.

Compacts save your legs for the run by keeping up the rpms. For the weight weenies the compact crank and the 11/23 will also weigh less than a 12/27 and a 53/39 crank.

If you are running a Shimano BB it is also really easy to go back and forth from compact to normal crank in less htan 5 minutes.
2006-07-26 3:44 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?

My old bike had a triple and my new tri bike has the shimano compact crank w/12-27 cassette. I love the new configuration...much easier to shift and better to climb hills with. I hate my triple and would never recommend it to anyone...harder to maintain, drops chain easier and more finicky. Compact has the same gear range but a little less on the faster end...but I don't really pedal that much when I'm going over 30 ...not an issue with me.

I live in MA which is hilly and having a compact helps me climb hills better and not burn out my legs. Max helped me figure out gear inches on my current bike and then compared them to different combinations on a potential new bike. Key was that I needed one on the low/easy end when climbing steep hills, keeping my cadence in the 80's and still make it up. Knowing my limitations or concerns on my original bike had my coach help pick out the right set up for my new bike, and it works fabulous.

Last year my normal cadence was high 70's or low 80's now I like to ride in 95-97 range so having a compact crank allows me to spin up the hills. When I get to be a stronger cyclist, I'll change my cassette. 

 

2006-07-26 4:04 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?
Compact (50/36) with a 11/23 is faster on the top end and will climb better than a standard 53/39 with a 12/25 or 12/27 on the back.
2006-07-26 4:07 PM
in reply to: #494036

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Subject: RE: what are compact cranks for?

Nob - 2006-07-26 4:04 PM Compact (50/36) with a 11/23 is faster on the top end and will climb better than a standard 53/39 with a 12/25 or 12/27 on the back.

Didn't you say that yesterday (two posts ago)?

2006-07-26 5:08 PM
in reply to: #493069

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Subject: RE: what are compact cranks for?
the bear - 2006-07-25 4:29 PM

scott_loong - 2006-07-25 6:24 PM so for a climbing course like IMLP you could go compact but for a flat course like Florida you wouldn't? why not just get a tripple if you want the extra gears?

More expensive conversion. In addition to the new crankset, you would need new shifters and prossibly a new front derailleur.



And possibly a new rear derailleur (long cage) and a bottom bracket.


2006-07-26 5:22 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?
seems like my kind of setup. i DO need a low gear - hardly any of my rides are below 5000 elevation gain - so once the time comes along to purchase a new bike i'll keep the compact crank option in mind.
2006-07-26 6:58 PM
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Subject: RE: what are compact cranks for?
RD condensed version.
2006-07-26 7:00 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?
The other benefit that others haven't pointed to is that an 11-23 gives you much closer gearing than a 12-27 with fewer big drops between cogs - one of the interesting things I've found with a power meter is that on my road bike (compact and played with a range of cassettes from 11-23 to 12-27) is that I can fine tune my power output much more easily...

eg my target for Oly bike is to keep around 200-220 Watts (Threshold is 235) - with the tighly spaced cassette and the compact crankset (I have regulars still at the moment on my Tri bike) I can do that over changing terrain much more easily than with 53/39s and a 12-25 or 12-27 and if I put a 11-23 on with those cranks than I struggle to keep cadence up on relatively hilly terrain (I try not to take power over 300W).

This doesn't just apply to those with Power meters but to everyone as well - you can use RPE and find out the same.
2006-11-24 2:37 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?

If you were doing an extremely hilly course - say either Six Gaps (10,000' climb/multiple ~15% grades) or the Brasstown Bald Buster Century (14,000' climb/up to 20% grade) - could you do a compact crank and a 12/27?  Would the gearing then be anemic on the flats?

Generally speaking, is your rear deraillure still compatible when switching from an 11/23 to a 12/27? (Specifically speaking, will a 10-speed Ultegra make the jump?)

Lastly, what are some of the varieties of compact cranks to choose from?  Outside of weight weenie stuff, what are the variable to consider for each crank?

2006-11-24 2:58 PM
in reply to: #607653

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Subject: RE: what are compact cranks for?
brian - 2006-11-24 2:37 PM

If you were doing an extremely hilly course - say either Six Gaps (10,000' climb/multiple ~15% grades) or the Brasstown Bald Buster Century (14,000' climb/up to 20% grade) - could you do a compact crank and a 12/27?  Would the gearing then be anemic on the flats?

Generally speaking, is your rear deraillure still compatible when switching from an 11/23 to a 12/27? (Specifically speaking, will a 10-speed Ultegra make the jump?)

Lastly, what are some of the varieties of compact cranks to choose from?  Outside of weight weenie stuff, what are the variable to consider for each crank?

Courtesy www.sheldonbrown,com, speed in MPH at 90rpm:

Standard 53/39 with a 11-23:

 5335.9 %39
1133.9 24.9
9.1 %
1231.1 22.9
8.3 %
1328.7 21.1
7.7 %
1426.6 19.6
7.1 %
1524.9 18.3
6.7 %
1623.3 17.2
6.3 %
1721.9 16.1
11.8 %
1919.6 14.4
10.5 %
2117.8 13.1
9.5 %
2316.2 11.9

Compact 34/50 with a 12-25 (12-27 wasn't available in 10-speed):

 5047.1 %34
1229.3 19.9
8.3 %
1327.1 18.4
7.7 %
1425.1 17.1
7.1 %
1523.5 15.9
6.7 %
1622.0 15.0
6.3 %
1720.7 14.1
11.8 %
1918.5 12.6
10.5 %
2116.8 11.4
9.5 %
2315.3 10.4
8.7 %
2514.1 9.6

The "anemia" would come in the upper gear, with top speeds of 34 vs 29. Chances are you can't hold either speed very long on the flats. You may lose something on the downhills, however.

 



2006-11-25 11:28 AM
in reply to: #607662

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Subject: RE: what are compact cranks for?

Okay, that covers the anemia - and, for the record, I cannot maintain 29 mph on a flat - how 'bout the compatability + choices of cranks?

2006-11-26 9:02 AM
in reply to: #607653

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Subject: RE: what are compact cranks for?
brian - 2006-11-24 3:37 PM

If you were doing an extremely hilly course - say either Six Gaps (10,000' climb/multiple ~15% grades) or the Brasstown Bald Buster Century (14,000' climb/up to 20% grade) - could you do a compact crank and a 12/27?  Would the gearing then be anemic on the flats?

Generally speaking, is your rear deraillure still compatible when switching from an 11/23 to a 12/27? (Specifically speaking, will a 10-speed Ultegra make the jump?)

Lastly, what are some of the varieties of compact cranks to choose from?  Outside of weight weenie stuff, what are the variable to consider for each crank?



Brian, I live in the Catskill Mountains and my road bike has a compact with a 12-27. It is not anemic on the flats. But I top out at about 30 mph, downhill, so i get passed by a few of my friends. I love the compact gearing! I was on traditional 53-39 and was having trouble with the very steep sections after a 6 mile climb, and my legs were wrecked for the runs, so i decided to give training a shot, and then a couple of months later bought a compact crankset!

I also put a compact on my race bike, "Zippy" with a 12-25. we will see how that works out.

"Yes" is the answer to your question on the rear derailleur compatibility.
"Don't know" is my answer to options about the cranks. I bought the FSA ones on sale. Not the carbon ones. I know you can get a 50-34 or a 50-36.

Edited by jeanneroth 2006-11-26 9:09 AM
2006-11-26 9:23 AM
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Subject: RE: what are compact cranks for?
brian - 2006-11-24 12:37 PM

 Generally speaking, is your rear deraillure still compatible when switching from an 11/23 to a 12/27? (Specifically speaking, will a 10-speed Ultegra make the jump?)

 

Yes. You can change the cassettes with little or no adjustment necessary, provided you're changing out one 10 speed for another.

2006-11-26 6:49 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?
It's been covered above pretty well.  I've gone with compact and 12/25 on both my road bike and tri bike.  I'll be picking up another cassette (11/23) for my tri bike to use on flat courses like IMFL but otherwise the 12/25 is great, even on relatively flat terrain.  As triathletes we should be concerned primarily with efficiency, spinning a relatively high cadence, and riding in a manner that sets us up for a solid run.  In that respect I can't think of a good reason not to run a compact (again, for a triathlete) unless you are an extremely strong cyclist (elite).  Don't let ego get the better of you...pick the equipment that gets the job done best.  I'm not impressed with the guy that runs the 54 tooth TT ring and 11-21 cassette unless he also turns in the fastest combined bike/run split.
2006-11-26 11:33 PM
in reply to: #493040

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Subject: RE: what are compact cranks for?
Compact Cranks allow you to maintain a relatively constant cadence by keeping the gearing closely meshed. A good analogy is that of a car's transmission. The more gears you have the more easily you can keep the engine's revs in any given range, thus maintaining power or efficiency, depending on the setup. Thus Compact Cranks allow you to maintain a more consistent cadence when working up and down the gears.

As Joel said previsouly, you can mash on the big gears if you are an elite cyclist but for the Triathlete spinning at a higher cadence will preserve your legs for the run.

You can mess around with rear cassettes for specific rides if you like but I personally, would rather *know* my existing setup intimately. Besides it's much cheaper and less prone to error keeping the same configuration.


2006-11-26 11:41 PM
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Subject: RE: what are compact cranks for?

I say if you need to climb a bunch of hills, get a triple.   Everything is covered at the minor expense of a few extra grams. 

 

 

2006-11-27 4:44 AM
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Subject: RE: what are compact cranks for?
tkbslc - 2006-11-26 11:41 PM

I say if you need to climb a bunch of hills, get a triple.   Everything is covered at the minor expense of a few extra grams. 

Going from a double to a triple is more than a "minor expense of a few extra grams." In addition to a new crankset you would need new shifters. LOT cheaper to just get a compact.

2006-11-27 8:31 AM
in reply to: #608618

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Subject: RE: what are compact cranks for?
the bear - 2006-11-27 5:44 AM
tkbslc - 2006-11-26 11:41 PM

I say if you need to climb a bunch of hills, get a triple.   Everything is covered at the minor expense of a few extra grams. 

Going from a double to a triple is more than a "minor expense of a few extra grams." In addition to a new crankset you would need new shifters. LOT cheaper to just get a compact.

See?  Apparently Bear was up all night converting his ride to a triple.  That's an awful lot of effort....

And whether you're putting a bigger casette on, or a compact, make sure you adjust your chain length appropriately.  Here's an article that'll help you figure it out.... sheldonbrown.com/deakins/lowgears.html

2006-11-27 8:48 AM
in reply to: #608618

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Subject: RE: what are compact cranks for?
Well, I'll disagree with Joel here and say that I really don't see any specific need/reason to go with a compact ever ....... at least for me personally. And it doesn't have to do anything with ego and such. As anyone who has ridden with me would tell, I always am in the 100+ cadence range for all my rides and I run a standard 53/39 with an 11-21 for a flat course and 11-23 for a normal or rolling course.

If you are going THAT slow that you would be spinning at 90 rpms in a 34/25 up a hill, then there is a strong argument that you should be riding a triple in the first place. This is not to belittle anyone's efforts, but we're talking 6 - 7 mph here for that type of gearing ......... Standing and slogging through with a 39/23 gets me up at about 9 mph at 65 - 70 cadence. The only time I'm even in that gear is on a 10%+ grade hill. Proponents for compact cranks will say that may not be the most efficient way to transmit power, I understand that, but it is what works the best for me.

If you are concerned about climbing, first thing to do would be to try a 12-25 or 27 and see how that works for you before you go dropping another couple of hundred bucks on a complete new crank and bb. And ride lots ....... it will be what really makes the difference!
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