What changes between these markings
The wider marking has a lower aspect ratio, and its sidewall is actually 5.75 mm shorter. Since the rim stays at 17 inches, the whole 11.5 mm diameter reduction comes from those two sidewalls. Width alone would predict the wrong direction.
With 215/55R17 as original and 225/50R17 as new, nominal diameter changes from 668.3 to 656.8 mm: −11.5 mm (−1.72%). Nominal section width changes by +10 mm and sidewall height by −5.75 mm per side.
Circumference and theoretical speed
Calculated circumference changes from 2099.53 to 2063.4 mm. Revolutions per kilometer change from 476.3 to 484.64, a +1.75% change. Circumference follows diameter in this circular model; revolution counts move in the opposite direction.
At an indicated 100 km/h, the size-ratio calculation gives 98.28 km/h for the new size. At an indicated 60 mph it gives 58.97 mph. Both examples assume calibration corresponds to the original nominal circumference and ignore existing instrument bias and real rolling deformation.
Keep the comparison direction explicit
The published URL keeps one stable order for this pair. Here 215/55R17 is the original denominator. Reversing the inputs gives a +1.75% diameter change and 101.75 km/h at an indicated 100 km/h. Use Swap in the editable tool to inspect that direction; changing only the sign would be inaccurate.
Half of the diameter difference is −5.75 mm of nominal radius change. It is not a measured ride-height change, and the width difference does not locate the installed sidewall without wheel and product information.
Why this pair has a reference page
A Singapore Honda Club question directly compares 215/55R17 with 225/50R17. Its vehicle context explains the original question, but does not become a vehicle recommendation on this page.
The linked manufacturer entries establish the individual size markings. The public discussion establishes an editorial reason to compare them. Neither source role supplies a fitment approval, search-volume estimate, purchase recommendation or universal acceptable percentage. Check complete vehicle and product requirements separately.
Sources and further reading
- AltiMAX RT45 — General Tire
- 2007 Odyssey: 215/55R17 or 225/50R17 — Singapore Honda Club
- Tire glossary — Michelin