Well, from a purely mechanical point of view (pardon pun) leverage would
be one possible factor. Hold your wheel in your hands and spin it. now
try stopping the spin by grabbing the spokes first near the hub, then
again further out.

May you have the wind at your back.
And a really low gear for the hills!
Chris

Chris'Z Corner
"The Website for the Common Bicyclist":
http://www.geocities.com/czcorner