Originally Posted by
heirfaus
Hi everyone,
I've made so much progress in my bike setup due to the help of this forum. Thanks to everyone who has contributed.
Today my question is about chainring selection. I just put on a FSA Energy compact with a 50/34 (shimano 9 in the rear). I've noticed now after about 30 miles of commuting I am not using my smaller cogs in the rear. On my small chainring I use the first 5 when taking off and then shift to the large chainring because the chain rubs on the large chain ring if I try to use 34/15(6th rear gear) combination. I find after shifting the front I still never touch the last four rear cogs. In order to make use of the whole range I am going to get a smaller large chain ring.
Is a 48 sufficient to move my cog use or do I need to use a 46?
Thanks,
Chris
You should not be having issues with chain rub if your bike is set up properly although it is always more efficient to maintain the straightest chain line possible for a specific gear.
By swapping to a 48 your top gear will still be 115 gear inches which is something the average rider is not going to push anywhere except down a hill for any distance... humans have a narrow power band and fairly fit humans can use gearings between 50-100 gear inches quite efficiently while lower gearing is good for hills and taller gears are best used in a paceline or on descents.
When you watch a guy like Contador doing a time trial he does not have his bike maxed out at 53:11 as that is 126 gear inches and you will see that he is most often running down a few steps in his range and probably living in that 90-100 gear inch range and spinning at a higher rpm which is far more efficient than trying to hammer a big gear.
46:11 is still 110 gear inches... if you can spin that gearing out you will have to be in great shape but it will be a nice gear for coming down those hills you have in Portland... which I have ridden up and down to excess.