it seems like the 12" is a good length, but what about the longer ones? does it matter really? is it preference? would I benefit from the 14"? or would i not utilize all the travel?
most likely you'd never use those extra 2 inches. I had 14's on my rear for a while and I later fell into some 12's and thought i'd see how they did, I really liked the 12's better and plan on keeping them.
