I have changed gears & tire diameters several times with great results.
For the ones I have done for myself & others in the last ten years, I have been able to check the speedometer at 55 MPH & my GPS has agreed, every time.
Tire diameter changes with wear. Diameter is also affected by rim width. Wider wheel = smaller diameter. Plus the fact that the op indicated that he was not extremely accurate with his gps or even his gauge readout. I figured a 36 but I'm sure he'll be happy with the 35.
None of that really matters about wear and width that your mentioning. The op said they measure 24 inches. Plug that into the chart, 35. But I agree, 34-36 probably will keep him close enough to right.
