Question: what size mountain bike tires should i use?
Answer: Mountain Bike Tire Size and Width Once you've identified your tire diameter (29”, 27.5” or 26”), you'll want to dial in your width: A cross-country bike will have tires in the 1.9" to 2.25" width range. Trail and all-mountain bikes will have tires in the 2.25" to 2.4" width range.