General Discussion Triathlon Talk » Compact Cranks - Yay or Nay? Rss Feed  
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2008-02-08 4:40 PM

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Subject: Compact Cranks - Yay or Nay?

Im looking to get an Ergomo PM, but it turns out that my FSA SL-K cranks are not compatible with the unit. So, I need new cranks to get the Ergomo Pro. Anyways, since I need new cranks I started researching compact cranks o see if they would benefit me.  On my current setup of 53/39 front, 12/25 rear I find that there is always this "dead zone" where one gear is too easy, the other is too hard.  So I find myself shifting to the other ring in the front and dropping or raising 3 gears in the rear to get that next gear that I need. Really annoying when going back and forth through rolling hills.  I only ride a 12/25 because I got it for IMWI last year.  Im doing IMWI (which is my main focus of the season) again this year and am thinking of going with some compact cranks and a 11/23 rear cassette.  Looking at stuff online, it looks like Ill get the better or both worlds (top end speed and low end climbing) with it.  Also talked to a couple of peeps and they said that that "dead zone" would be eliminated since the gears are closer in the rear.  So, what Id like to know is do you ride CCs?  How do you like them?  Are there any downsides to them?  I feel Im a decent rider (avg'd 20.1 at IMWI last year), but am looking for better options in gearing, if they exist, to reduce the amount of shifting back and forth

Also, please keep this to compact cranks as the topic.  I dont want this to go into a which-PM-is-better war.

 Thanks!

-Rob 



2008-02-08 4:45 PM
in reply to: #1202104

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Subject: RE: Compact Cranks - Yay or Nay?
Use this link to check gear ratio's of what ever you decide.  I don't know hardly anything about CC or what their advantages are but am pretty sure you can get the same gear ratios you need in a standard crank.
2008-02-08 5:16 PM
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Master
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Subject: RE: Compact Cranks - Yay or Nay?
I have a set on one of my road bikes and I like them.
2008-02-08 5:17 PM
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Subject: RE: Compact Cranks - Yay or Nay?
I was wanting to try out a compact as well. My idea is a straighter chainline in the big ring with less shift to the small ring. Would like to try a 50/39 as I am more than happy with the small ring at 39.
John.
2008-02-08 6:26 PM
in reply to: #1202104

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Subject: RE: Compact Cranks - Yay or Nay?

I love my compacts and have one on all three of the last bikes I've purchased.

Big question is do you use your top gear currently and very often? How does the new set up compare you are considering via gear inches? 

Only a couple times last season could I have used another gear to go faster but having more low end really helps me keep my power/hr in right zones when climbing hills. I know that keeping power lower getting up the hills at Lake Placid will be a benefit for me later.

I have noticed more and more new bikes are coming with compacts.  

2008-02-08 6:54 PM
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Subject: RE: Compact Cranks - Yay or Nay?
I have compacts.  Like them.  It's the tighter cassette gearing that will probably make a bigger difference in your shifting (fewer 2 teeth jumps in an 11-23).  I went to the compact but ALSO moved from an 11-23 to a 12-25.  I was more interested in getting some more climbing gears (mostly for LP last year).


2008-02-08 7:26 PM
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Subject: RE: Compact Cranks - Yay or Nay?

Rob,

   Your " dead-spot is probably created by the "missing" 18 tooth gear in the 12-25 cassette.  This is the first two tooth jump in the cassette.  The smaller gears have jumps of 6-7% when you shift from 17 to the 19 that's a 12% jump.  With your current 53 the "deadspot" occurs at 20.7 mph @ 90 cadence.  Switching to a 50 big chainring and a 11-23 cassette still leaves you without an 18 cog but shifts the deadspot to 19.5 mph 

The way to completely rid yourself of the "deadspot" would be to use a tighter cassette like an 11-21, this will give you an slightly better top end, an 18 cog to fill your deadspot, but you'll be giving up some low end with a 34x21 verse the 39x25 you have now.  THis raises you lowest gear-inches from 41.0 to 42.5.  Less climbing power but not as bad as if you stuck with a regular crank and just replaced your cassette with a 12-23 to gain an 18 cog.  This would leave you with a low end of 44.6 gear inches.

 

Ray
 

2008-02-08 7:44 PM
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Subject: RE: Compact Cranks - Yay or Nay?
Based on your intial post I would say that compact cranks are not appropriate for you. The main advantage of compact cranks is that they allow an increase in range on the low end of the gearing spectrum, almost to what you get with a triple. So if you need lower gears then go for it. I have a compact and love it, but I need those gears. But you obviously don't need low gears if you are doing the relatively hilly IMWI with a 12/25 cassette in the back.

It is not correct that a 11/23 cassette is spaced closer than a 12/25. They both will have cogs spaced one apart on the 5 small cogs and probably spaced two apart on the larger cogs. If it is spaced any differently at all it is only between two if the cogs in the whole cassette. The difference in the shifting is definatley not in the spacing of the cassette.

The "space" between gears on on a compact crank is actually greater than a standard crank, not less, because the range from high to low is greater (i.e. the difference between chain rings is greater). Instead of switching the back cog three spaces you would have to switch 4 or 5.

But it is true that less shifting in the back is usually required on a compact, and that is because the large difference between the gearing ratio of the large chainring and the small chainring means that there is less overlap in gearing rations between the two chainrings. So instead of shifting to the small chainring you would just leave it in the big ring and only shift the back. In fact the difference between the large and small chainrings is so great that often people with compacts don't use the small chain ring at all except for extended climbs. Because it appears that you are pretty fit and don't need the low gearing you may never need the small chainring if you had a compact. But what you give up is the higher number of gears and the ability to get just the right gear.

If you do get a compact then definately get a casset with an 11 cog as you will not want to give up the high end of the gearing.
2008-02-09 8:31 AM
in reply to: #1202104

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Subject: RE: Compact Cranks - Yay or Nay?

You already know my position....

Yay......all the way!

IMO an 11-23t and 34-50 is the perfect combo for most riding.



Edited by oipolloi 2008-02-09 8:38 AM
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