This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
Following are various myths about cycling and why they are/aren't true.
Myth: Wearing a helmet makes your head hotter than if you didn't wear one.
Actual measurements under hard riding conditions with ANSI standard
helmets show no consistent temperature difference from helmetless
riders. Part of the reason is that helmets provide insulated
protection from the sun as well as some airflow around the head.
(Les Earnest Les@cs.Stanford.edu)
Myth: You need to let the air out of your tires before shipping your bike
on an airplane - if you don't, the tires will explode.
Assume your tire at sea level, pumped to 100 psi. Air pressure at sea
level is (about) 15psi. Therefore, the highest pressure which can be
reached in the tire is 100+15=115psi. Ergo: There is no need to
deflate bicycle tires prior to flight to avoid explosions.
(Giles Morris firstname.lastname@example.org)
Addendum: The cargo hold is pressurized to the same pressure as the
(Tom ? email@example.com)
Myth: You can break a bike lock with liquid nitrogen or other liquified gases
Freon cannot cool the lock sufficiently to do any good. Steel
conducts heat into the cooling zone faster than it can be removed by a
freeze bomb at the temperatures of interest. Liquid nitrogen or other
gasses are so cumbersome to handle that a lock on a bike cannot be
immersed as it must be to be effective. The most common and
inconspicuous way to break these locks is by using a 4 inch long 1
inch diameter commercial hydraulic jack attached to a hose and pump
(Jobst Brandt firstname.lastname@example.org)
[More myths welcome!]