So I have been riding a 2003 Hardrock Comp mainly for commuting/fitness for the last couple of months. My daily commute is 34 miles round trip (I do it about 2-3x a week). I'm ready to upgrade to something faster and easier to ride. The mountain bike is a difficult ride to justify riding into work much more than I have been and would like to start riding a bit more. Ideally, I'd like to get a road bike. Main reason is the speed and options for hand positions. Also, I feel like I can get more bang for my buck in terms of a used road bike vs. a newer hybrid.

My main concern with going to a road bike is that about 1/2 of my commute is usually done on a well maintained limestone path, the Illinois Prairie Path. I see a few road bikes on there, but have been told by my LBS owner that a road bike is not a good idea on crushed limestone. I carry almost nothing to work so bags and storage is not an issue.

Basically my question is, will I regret purchasing a road bike and doing 16 miles a day on a limestone path? What's the widest tire most road bikes will accept?

Thanks for any help steering me in the right direction.