I got a bit of a problem. I had a good design of a 24 x 1.75 pair of wheels on a current little knock around I had designed. Then my computer got sick. Unfortunately I lost that design and I am subsequently forgotten how to change the tire/wheel size from my standard 700 C down to that little science wheel.
any clues?
I assume your Wheels dialog box is set to Standard. You can switch that to Custom as shown below and set Tire diameter and width to whatever you like.