Here's the Math
C-40 said:
If you're using the standard 53/39 now, then the 50/34 lops 6% off the top end makes the low end 13% lower with the same cassette.
If you happen to be using a 12-25 now, changing to a 50/34 and an 11-23 does not accomplish much. The low gear is equivalent to a 39/26 and the top gear is a slight bit more than a 53/12.
This has been discussed extensively in other posts. here are the numbers
Regular 53/12=116.7
FSA 50/11=120
Regular 39/25=41.2
FSA 34/23=39.1
In other words, you have just gained on both ends. You certainly have not lost. You have a gear thats a bit easier and one that is a bit harder by adjusting the spacings between gears. If you enter all values in a spreadheet you will also find that you only have one duplicate gear ration instead of two in other words you have 17 gears you can actually use.
Now if you use a 25 cog on the rear, you actually have a 35.9 ratio which equivalent to almost a 29 cog with regular gearing.
I found for example that it is a huge benefit to be able to ride a 12/23 with the compact which gives me finer gearing in the middle with a 12.13.14.15.16.17.19.21.23....love that 16 in there! That's were you spend most of your time in the 14..17 range with a 85..100cadence.
You still have a 110.1 ratio in your 12 which is still a bit harder than you normal 53/12 combination. Unless you go downhill you really don't need the 50/11 combination.
In order to play with these gearing, I got one of the cycle dynamics Titanium cog sets with all available gears from 11..25. That allows me to mix and match and have a 11..21 for flat rides, 12..25s for hills, 11..20 for time trials. Highly recommended. They hold up very well.
Anyway, it's fun to play with the numbers, even more fun to ride. Believe me, the compacts are here to stay, not only because of Tyler.