My 98 GT MTB converted to a cargo bike with 2.15 Schwalbe Big Apples. I like the lower gearing when I have a load on the bike although that isn't as much of an issue now that its converted to e-assist. But I've not had any issues with tire clearance and it rolls pretty well (for a 100lb bike anyways). I currently commute 4 miles each way and it's 6 miles to the grocery store each week.