Quote Originally Posted by bouncybouncy
OK...did a little research and have an add on...

my rear is (i guess what you would say) is 11-23
it reads
11-12-13-14-15-16-17-21-23

so what you are saying is that i can get the double up front 34/50 then get a bigger set in the rear, maybe a 13-29 without having to change the derailer?
You'll need to check your rear derailleur and find out the max sprocket size it can handle. Some derailleurs made for 11-23 won't be able to handle a 13-29. You can check the Shimano site, for instance, and for each model it will tell you the min and max sprocket sizes, the max front sprocket difference, and the total capacity in teeth.