225/45R18 vs 235/45R18

What changes between these markings

Both aspect ratios read 45, but their sidewalls are not the same height. A 10 mm wider marking adds 4.5 mm to each sidewall because 45 is a percentage of width. The resulting diameter increase is 9 mm.

With 225/45R18 as original and 235/45R18 as new, nominal diameter changes from 659.7 to 668.7 mm: +9 mm (+1.36%). Nominal section width changes by +10 mm and sidewall height by +4.5 mm per side.

Circumference and theoretical speed

Calculated circumference changes from 2072.51 to 2100.78 mm. Revolutions per kilometer change from 482.51 to 476.01, a −1.35% 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 101.36 km/h for the new size. At an indicated 60 mph it gives 60.82 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 225/45R18 is the original denominator. Reversing the inputs gives a −1.35% diameter change and 98.65 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 +4.5 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 Kia Stinger Forum topic explicitly groups 225/45R18 and 235/45R18 with another option. The topic supplies evidence for comparing the markings, not evidence that dimensions alone settle load ratings or vehicle suitability.

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.

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