Originally Posted by FarHorizon
My wheels are currently fitted with Vittoria 700c x 23mm tires. I have about 8mm (0.36") clearance between the top of the existing tire and the bottom of the brake caliper. I have about 12mm (0.46") clearance between the sides of the existing tire and the sides of the brake caliper when in the functional (closed and ready for use) position. What is the largest tire that I can hope to fit on this rim without rubbing the brake?
Based on those measurements, you could go up to a 32 mm tire, probably. I say "probably" because not all tires labeled 32 mm are actually 32 mm, the manufacturers play fairly loose with the numbers.
But there are a couple of other things you haven't considered:
1. How much clearance is there where the tire crosses the chainstays? Many modern racing bikes have VERY little clearance at the chainstays, some can't take anything larger than a 25 mm tire...
2. How wide are your rims? If you have very narrow rims, wide tires may feel squirmy on them. (see the chart at the bottom of this page:
http://sheldonbrown.com/tire-sizing.html)
I also desire to run the highest pressure tire possible (125psig +) because I'm riding on rough pavement and don't want to damage my expensive rims.
First of all, high tire pressure will prevent you from bottoming out your rims and denting them, but when you go over bumps the higher pressure will cause more of the force to be transmitted to the rim, spokes, hub, and frame. This puts unnecessary stress on the bike and makes for a very rough ride, and it's part of the reason why mountain bikers on rough terrain use a LOW tire pressure.
Expensive road wheels are usually very light and meant for racing. They're often the weakest part of a bike. I don't know what particular wheels you're using, or what you're using them for, but if you're planning on riding on rough roads, do yourself a favor and get a pair of sturdy 32 or 36 spoke wheels and save the good wheels for racing.