I leave it all the way open on the big pulley and I find that is pretty accurate for speed if you are sitting upright (not in the drops). I think the other day I was averaging about 22mph at 300 watts which seems pretty reasonable to me (maybe 300 would be 1mph faster outside??). Of course for some of you smaller guys, that may not be the case, but I catch a lot of wind when I am upright.