isthereabestwaytofigurewhatsizestemyouwillneedforaroadpositioniknowabout
theputyouhandsandthehoodsandnotbeingabletooseethefrontaxle
butisthereabetterway
.
my experience:
Step 1) Ride a lot - until it hurts.
Step 2) Change something (saddle height or fore/aft position, handlebars, stem, etc.)
Step 3) Repeat steps 1&2 until no more pain.
Sucks, but it’s worked up 'til now! 
-J