Originally Posted by rowebr

After you install the larger tires, but before you go on a long ride, take the bike on a test ride and ride uphill out of the saddle. With very tight clearance between the chainstays, it is possible that the tire will rub under hard pedaling. Hopefully the test ride will provide a good indication of whether that is a problem.

If you don't already have one, a FiberFix spoke is a good insurance policy to take with you on long rides. It lets you replace a broken spoke without removing the freewheel/cassette. When only a small wobble would cause the rear tire to rub, its an even better idea to bring one along.

Changing from 25mm to 28mm tires actually does make a noticeable difference in comfort so I think this is an experiment worth trying. I hope it works!