BIKE: Commuting calculator - assistance needed

[Mike Dahmus]

I'm learning PHP, and wrote a commuting calculator as a proof of concept 
(I intend to use it next to finally do what I've promised Tommy for 
months - that being a user-changeable weighted matrix for bicycle 
facility priorities).

http://www.io.com/~mdahmus/biking/bikecommutecalc.php

If anybody has any educated opinions about the defaults I've used here 
(for tire and tube life), please email me offline.

Thanks,
Mike