When I cleaned up my 30 year old Shogun Primo Sport, there was a tire size stamped on the wheel, it was small but I found it. The other option is to take it into a bike shop and have them put tires on it. You could look at the cost in this fashion; 1. you get the correct size tires the first time, 2. the additional cost is for their expertise, and 3. you pick the tread for how you are going to use it. I did it that way for two bikes and after paying the bill didn't, think about it again. I'm too old to fall off my bike because of some mechanical error I could have avoided. Hope this is helpful.