Originally Posted by MichaelW
Are you sure that the frame and brakes can accept a tyre that wide?
Many road bikes have quite narrow clearance and can barely take 28mm.
The bad news is that road bike brakes are usually the factor that limits how wide a tire you can use. 28mm is about it for most road brakes. You might be able to cheat a little bit on that if you wait to inflate the tire until after you install the wheel in the frame.
The good news is that I wouldn't worry excessively about riding a 28mm tire on a crushed limestone rail-trail conversion. My wife and I do it regularly with our tandem.