235/55R18 vs 235/60R18

What changes between these markings

At a width of 235 mm, five aspect-ratio points equal 11.75 mm of sidewall. Doubling that gives a 23.5 mm outside-diameter increase. A taller calculated sidewall alone does not quantify ride comfort or impact behavior.

With 235/55R18 as original and 235/60R18 as new, nominal diameter changes from 715.7 to 739.2 mm: +23.5 mm (+3.28%). Nominal section width changes by 0 mm and sidewall height by +11.75 mm per side.

Circumference and theoretical speed

Calculated circumference changes from 2248.44 to 2322.27 mm. Revolutions per kilometer change from 444.75 to 430.61, a −3.18% 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 103.28 km/h for the new size. At an indicated 60 mph it gives 61.97 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 235/55R18 is the original denominator. Reversing the inputs gives a −3.18% diameter change and 96.82 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 +11.75 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

An AutoUA question discusses these two 18-inch markings alongside a 17-inch option. It asks about comfort; TireSpan isolates the nominal dimensions and does not turn the question’s subjective observations into performance data.

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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