I have a Spec Tarmac E5 that has a small indent in it, but doesn't look like it is going to catastrophically fail anytime soon. I want to retire it from racing, but I was wondering about turning it into a training bike with fire road capability. I can actually ride fire roads with 23mm tires if they aren't too rocky, but I was wondering if any manufacturers make a small enough treaded, cyclocross style tire that I might be able to slide in there. I would anticipate riding dusty roads, not mud, so as long as the tire fits, mud clearance shouldn't be an issue.