I would guess you have 2.2 inch tires, probably can go down to 1.5" tires without getting new rims. I would probably just ask at the bike shop to make sure, but you'll probably be able to go down to 1.5" or 1.25". You put some slicks on there and you'll be faster for sure, maybe a couple mph or possible twice that. You can put a rigid fork on it, if it has suspension or lock out the fork. Taking off the suspension fork will probably take off 4 pounds of weight, maybe more depending on how old the bike is or you can lockout the fork to make it roll better when standing or climbing.