The first number in your bottom-bracket size (for example, the number 68 in the size 68 x 113) is the Shell Width, which must match your frame's bottom-bracket shell width. For spindle length, if your seat tube is 1 3/8-inch in diameter, you will probably need the wider length, because your front derailleur will be placed further away from the center of the bottom bracket. If you still have questions or concerns on choosing the right bottom bracket, please contact us!