How much difference does crank length on the bike make? I am thinknig mine maybe too short, its 172.5mm, maybe i should be going for a longer one, i am 6ft? Will this save much time?
I have 175s and I am 6'1, I would say they have made a bit of difference, turning the heavy gears seems way easier on my race bike compared to my training bike which has 170s on.
You've got to think, are you a spinner (90-110 race cadence), or a masher (70-90 race cadence). If you are a spinner I think 172.5s at 6 foot tall is fine. I like pushing bigger gears, so I suit the 175s better. Its something to do with a longer crank providing more leverage, but its harder to spin at high cadence.
It's a bit of a handful, and it may raise more questions than it answers, but this article
from Slowtwitch might be of interest to you.