Depends, I have like four stages of tuck. One is just full upright normal, one is with arms bent resting my lower torso on the tank a little sort of in a half-tuck, one is a 'full tuck' where I tuck far enough that if I crane my neck back and look up I can just see the horizon out of the top of the helmet...and the fourth is a long-haul tuck where I'll scoot my ass all the way back and put my torso almost fully flat on the tank to support the weight more evenly...I pull my elbows in all the way against the bike and almost rest my chin on the tank. Both the 'full tuck' and the long-haul tuck require looking through the windscreen (which is why it's so damn stupid to have anything darker than a normal tint).