# 11/25 vs 12/27 for 34/50 compact



## shadowpl (Apr 23, 2010)

My new bike came with an FSA Gossamer compact 34/50 crank and Shimano 105 12/27 rear cassette. I don't feel like I get the power I got on my old bike with 39/53. Am I better off changing to a 39/53 in the front (if possible) or changing the rear to a 11/25? Or is there a better option. I ride in a fairly hilly area, but feel I don't get the speed I want in the flats and slight downhills. Thanks


----------



## Bridgey (Mar 26, 2003)

I just bought a compact crankset. If you have an 11/25 it is actually a heavier gear 50 x 11 a 53 x 12, so your top range wouldn't be different. A 34 x 25 is probably much the same as a 39 x 27. Being a 34/50 up front produces less gaps in between gears which can be helpful, but when you change between big and small, you need to go about 3 to 4 cogs up or down on the rear sprokets vs 2 up or down on the rear for the 39/53. I prefer the compact as it lighter and is almost like having a triple combination without the weight. 

In short, by getting a 11/25, you save money vs buying a whole new crankset. Just depends on whether you can handle a little extra shifting when going up and down the front change ring.


----------



## Mtn2RoadConvert (Aug 28, 2006)

Depends on how strong of a rider you are. I live in a fairly hilly area as well and found my old bike with Shimano Ultegra 53/39 and 12/25 was good on the flats but tough on some of the bigger climbs, so I switched to a compact crank (50/34), but as you say lost a little bit of top end speed. My new bike with Sram Force has a compact crank and 11/28 that seems to cover the me on the hills and got the top end speed back that I was lacking with my other bike. So, I would try changing the cassette before the crank in your case. I believe Ultegra 6700 has a 11/27 cassette that would work with your 105 rear derailleur.


----------



## golfernut78 (Mar 19, 2009)

i switched to a compact this off season from a 53/38 with 12-26 setup. i originally switched to a 50/34 with an 11-23 setup. in theory this was to be a good setup looking at the high end and low end of it, but it was an absolute mess for my working gears. made the change to an 11-25 and i am pretty happy.

i spend a lot of time in the 50/17, 50/19 and 50/21. with the 11-23 i didn't like the the chain line in the 50/21. with the 11-25 i can still hit the 50/23 (not a combo i like to use because of chain line) if i need something a little easier for a moment or at stop lights without stretching the rear deraileur.

i did consider a 12-25 instead of an 11-25 because the a 50/12 is more than enough for me, but the problem is the 12-25 would have created issues for me in the 34. in the small ring i find myself using the 34/13 and 34/14 combos often. with the 11-25 i don't have a bad chain line with the 34/13, but with the 12-25 its not a chain line i like to be using.

i am still considering changes. i made the change to a compact to get a tighter cassatte and i really haven't done that (although in my change i went from 9 speed to 10 speed). i am now considering two options: change the 50 to 48 and go back to the 11-23 or change the 34 to a 36 and go to a 12-25. seeing that i already have the 11-23 i am leaning more towards getting the 48. i know a 48 sounds small, but i am not a racer or a fast rider. i typically average 16-18 mph in my rides. i am looking for comfort in my gears. a 48/11 is still a gear i am only going to use either downhill or down wind.


----------



## C-40 (Feb 4, 2004)

*simple math...*

A 50/11 is just a little bigger gear than a 53/12 and a 34/25 is almost as low as a 39/29, so you'll get the best of both with the switch to an 11-25. That's what I use for the Colorado mountains.

To figure the equivalent low gear ratio: (25/34) x 39 = 28.7. That proves that the 34/25 is nearly as low as a 39/29.


----------



## Hank Stamper (Sep 9, 2009)

shadowpl said:


> My new bike came with an FSA Gossamer compact 34/50 crank and Shimano 105 12/27 rear cassette. I don't feel like I get the power I got on my old bike with 39/53.


It's either in your head or the reason you feel that way is because your fit on the new bike is different. Assuming you're not spinning out 50/12 and the arms are the same lengh your feeling that you're getting less power could not be related to the new crankset's gears.
My guess would be it's the new fit.


----------



## fallzboater (Feb 16, 2003)

You probably can't correct your chainrings without swapping cranks, but you can easily correct your cassette. My vote is to put on a men's crank.


----------



## shadowpl (Apr 23, 2010)

*Thanks*

Thanks all for your suggestions. I think I'll definately just change the rear. Probably just to the 11-25. But that 11-27 you suggested "MTN" sounded interesting. I looked up the 6700 and in comes in an 11-28, same rings as the 11-25 but the last jump is from 24 to 28 rather than from 23 to 25. I only have a few hills here in CT that I have to go down to 34/27 and can still stay in the saddle. Most of the time I only have to go 34/24. I think 34/25 should be fine. And I normally ave 19-20 MPH on my rides, so I think I'll like the 11-25. I also found on the FSA website that they recommend the 11-25 with the compacts. Will the same chain work or will I need to adjust/change it?


----------



## ukbloke (Sep 1, 2007)

shadowpl said:


> I looked up the 6700 and in comes in an 11-28


If you pair 50-34 with 11-28 you need to consider RD chain capacity. My experience is that 50-34 with 12-27 is right at the safe limit for the 6600 or 7800 short-cage RD capacity. It is already a few teeth beyond the Shimano spec. It slightly depends on your chain-stay length too. To go beyond this you will need the slightly expanded capacity of the 6700 RD, or equivalent.

One could set it up with a chain that is too short for the "never-used" big/big cross-chained combination, but I like to play it safe so that my drive train will not self-destruct in any available gear!

I tried 11-28 on an SRAM Red bike demo, and didn't like the jumps. I typically pair my 50-34 compact with 12-25, occasionally use 12-27 for outrageously steep stuff, and have an unused 11-25 on the shelf as a spare.


----------



## SystemShock (Jun 14, 2008)

golfernut78 said:


> i switched to a compact this off season from a 53/38 with 12-26 setup. i originally switched to a 50/34 with an 11-23 setup. in theory this was to be a good setup looking at the high end and low end of it, but it was an absolute mess for my working gears. made the change to an 11-25 and i am pretty happy.
> 
> i spend a lot of time in the 50/17, 50/19 and 50/21. with the 11-23 i didn't like the the chain line in the 50/21. with the 11-25 i can still hit the 50/23 (not a combo i like to use because of chain line) if i need something a little easier for a moment or at stop lights without stretching the rear deraileur.
> 
> i did consider a 12-25 instead of an 11-25 because the a 50/12 is more than enough for me, but the problem is the 12-25 would have created issues for me in the 34. in the small ring i find myself using the 34/13 and 34/14 combos often. with the 11-25 i don't have a bad chain line with the 34/13, but with the 12-25 its not a chain line i like to be using.


Why do you even have to be in the 34/13 and 34/14 that often?

Those gears pretty much duplicate your 50/19 and 50/21.
.


----------



## orangeclymer (Aug 18, 2009)

compact W 11/27 and it rocks da house..


----------

