You need to lift your heel directly verticle so you are not over lapping you leg muscles. You are basically kicking yourself in the but. Not out in front of you. You also need to be comfortable in that position not with your leg muscles in tension. I will measure myself and see what I get. At 6' 0" and doing as i said I measured a touch over 340mm. Divided by two that is 170mm which is what I use on most bikes. Roger