Bicycle Mechanics - Tire Question-Help Please?

Just started riding my new(vintage)Trek 520, built in 1985... very sweet and smooth ride.

However I noticed some rot on my back tire and some wear on my front and was thinking I would treat the Ol' Guy(the bike not me!)to some new rubbers.

Speed isn't important(I am slower on it than a turtle)nor is fashion(she's vintage after all)BUT I do want something dependable, long lasting and beefy.

I'm a heavy guy-Clydsdale-and wanted to know how I can get the most beefyness that's out there in relation to tires. They are 700c's and I guess I am curious about the differences between something like a 700x32 and a 700x40... would the 40 be more stable for a bigger guy like me? And also, is there any connection between my size and a tires Max. PSI... for instance I found a 700x37 tire that can inflate to 90 PSI and another tire, 700x40, that only has a 50 max PSI... what gives?

Last question... for any particular tire size what size tube do you need-the exact same size or one that falls in that size variance ex. 700x32-40 versus 700x32?

Oh, almost forgot to mention... currently my Trek has Presta valves... when I buy some new tires and tubes, any advantages/disadvantages to Presta versus Shrader? Either is fine by me as my pump can accept both but I was curious as to their differences.

Sorry for any moronic questions here... but I'm trying to learn! :)

the larger the tire, the lesser the (rated)max psi... It is because volume and cross section of the larger tire is larger.. Anyway, it doesn't matter.. Larger tires can absorb more vibrations, bumps, etc. because of the lower pressure, safely without pinch flats (so they say).

The down side is, they are heavier and has greater rolling resistance than the smaller ones..

Regarding presta and shrader.. It depends on what your rim will accomodate... most narrow rims use presta because using shrader would mean a larger hole on the rim which may decrease, to some amount, its strength..

See if a shrader valve would fit into the rim(hole).. If not, you have to use presta..

Hope it helps.

I'm not about to get in a religious war over schraeder/presta. I keep all my bikes presta, but that's as much so I don't have to constantly re-adjust my floor pump as anything else. As for tire sizes, you might check to see what will fit on your rim. If you go to this link and scroll down, you'll find a handy chart on tire to rim width:
http://www.sheldonbrown.com/tire-sizing.html

In some frames, clearance can also be an issue. The larger the tire width, the higer the tire stands off the rim, and some racing/road frames won't take tires much larger than 28c.

Most tubes fall within a variance. At least most of the ones I buy, anyway. As to the recomended hi inflation, that's determined by some arcane mix of TPI (threads per inch) in the tire casing, tire width, rider weight, eye of newt and bat tounges, with a few other things I don't understand thrown into the mix.