If you're going light, 28's are gonna be OK and I think you'll be happier with them than 23 or 25. I couldn't/wouldn't do it, but I've seen others get along just fine touring on skinny tires, including my wife who rode the transam with me on her bianchi eros. If your bike is a typical road bike, you won't have clearance for all 28's. Eg, panaracers fit the eros just fine, but specialized armadillos were too fat. I've also tried some Huthinson 28's on a road bike and there wasn't enough clearance.