[QUOTE=Motorad;6321679Anyway, here are two questions to begin the OP:
* Is there a website that lists tires not only by their advertised widths, but their measured widths?

* What risks are there to riding a tire that is very snug within the forks, say only 0.25 or 0.5 inch of clearance on either side of the tire ... and do you ride with tires that are this snug within the forks?[/QUOTE]

1. I've got identical 28mm tires (Continental Gatorskins) mounted on two different bikes. On my tandem, with Velocity Dyad rims, they measure 28mm when inflated. On another road bike, with Velocity AeroHead rims, they measure 26.5mm. 1 1/2 millimeters isn't much but it does show that rim width matters.

2. I would guess that 1/4 inch would be plenty of tire clearance. The problem is making sure you have 1/4 inch clearance everywhere. Most of the time I encounter problems squeezing a tire past the brakes before I have frame clearance problems. Another point of interference is the front derailleur when it's in an extreme gear position.