This second tuple is intentionally very different from the close plus-size example. It shows why a calculator must display the signed magnitude rather than hide it behind a generic good/bad badge. The original is 235/65 R17, the comparison is 265/70 R17, and the speedometer scenario begins at 60 mph. No vehicle is implied and no fitment claim is made.
Diameters are 737.3 mm and 802.8 mm
For 235/65 R17, one sidewall is 235 × 65 ÷ 100 = 152.75 mm; with the 431.8 mm rim, diameter is 737.3 mm. For 265/70 R17, one sidewall is 185.5 mm; the same rim then gives 802.8 mm. Both are exact nominal values. Their difference is +65.5 mm, and half of that is a nominal radius or ground-clearance change of +32.75 mm.
Nominal diameter rises about 8.8838 percent
Divide the +65.5 mm difference by the original 737.3 mm and multiply by 100. The exact rational result rounds to +8.8838 percent for display. TireCalc shows the number without calling it acceptable, equivalent, legal, or safe. Those words require vehicle-specific specifications, ratings, clearances, and jurisdictional rules that the size formula does not contain.
At 60 mph the theoretical value is about 65.3303 mph
The exact speed model is 60 × 802.8 ÷ 737.3, displayed as approximately 65.3303 mph. The +5.3303 mph difference follows from nominal geometry alone. A real installation can produce another result, and the large width and radius changes demand much more than a speedometer calculation: consult the placard, manual, manufacturers, applicable rules, and a qualified professional.