Surly claims it will take 44's and I don't doubt it. My mechanic friends at a LBS tell me they have set up a lot of CC's for monstercross. However, as long as I'm riding this bike SS, I'll go with narrower tires. I ride at least a third of my yearly mileage SS, and will probably increase that this year. Right now I am using 28 Gators. And, I have a set of 30 Speedmax on another set of wheels ready to go. One thing I've learned about SS is that, when it's between you, one gear and the road, you really feel the slog of fat tires in acceleration and climbing.