What changes between these markings
The 17-inch rim adds 25.4 mm to the diameter calculation, but each sidewall loses 11.5 mm. The net outside-diameter increase is only 2.4 mm. The tires still require different nominal rim diameters, so the close outside diameter is not interchangeability on one wheel.
With 205/55R16 as original and 225/45R17 as new, nominal diameter changes from 631.9 to 634.3 mm: +2.4 mm (+0.38%). Nominal section width changes by +20 mm and sidewall height by −11.5 mm per side.
Circumference and theoretical speed
Calculated circumference changes from 1985.17 to 1992.71 mm. Revolutions per kilometer change from 503.73 to 501.83, a −0.38% 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 100.38 km/h for the new size. At an indicated 60 mph it gives 60.23 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 205/55R16 is the original denominator. Reversing the inputs gives a −0.38% diameter change and 99.62 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 +1.2 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
An original Stack Exchange question asks about these two markings as a replacement pair. It is evidence that the comparison is useful, rather than evidence that either assembly suits a particular vehicle.
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
- Will a 205/55R16 replace a 225/45R17 tire? — Motor Vehicle Maintenance & Repair Stack Exchange
- Tire glossary — Michelin