Originally Posted by
StanSeven
Yep, do a search on specs for your bike. The limiting road bike factor for tire width is usually fork clearance.
Also thinner isn't necessarily faster. Speed is dependent on rolling resistance and the ability of the tire to maintain smooth contact with road surface is affected by tire width, construction, and air pressure. So a wider tire that maintains contact might be faster than hold that bounces.
This. "Thinner is faster" is largely a myth, and fatter is certainly more comfortable and secure.
As others have said, your wheels should be fine with 28s. I've run tires from 19 to 41mm on the same wheels with no problems. But you'll be limited by fork clearance or (maybe) the brake arch. The figures are probably published somewhere, but it might be more accurate to go to a bike shop and tell them you need to try some tires and you'll buy them if they fit. But then if they fit, you have to buy them. No ordering off the net.