According to the chart I just googled, a G60 15 has a diameter of 26.46" and a G70 15 has a diameter of 27.46". Different letter sizes have different height differences, and then you need to take in the wheel diameter that also changes the differences. As I remember from back in the day, an F70 14 had about the same height as a G60 15, but that was a long time ago. Gene