Nominal tire size versus measured dimensions

What a nominal result means

TireSpan derives a mathematical shape from width, aspect ratio and rim diameter. Two tires carrying the same normalized marking therefore receive the same nominal result here. That consistency is useful when you want to isolate the effect of a label change without mixing in model-specific measurements.

Why a manufacturer’s table can show another number

A manufacturer can publish dimensions for a specific tire model on a stated measuring rim. Its reported diameter, section width or revolutions per mile may differ from a simple label calculation. Preserve that context when comparing figures. A measured specification and a nominal result can both be useful without being interchangeable.

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For 225/45R18, this site calculates 659.7 mm diameter and about 776.52 revolutions per mile from a circular circumference. If a product table gives a different revolution count, do not average the two or replace one field while retaining all the other nominal assumptions. Either compare two nominal models or compare two appropriately documented product specifications.

What the directory source establishes

A source link confirms that the manufacturer published the marking. TireSpan retains the original source notation separately, including designations such as ZR or LT where present. The public page normalizes only the dimensions used by the geometry model. It does not imply that those extra designations have no importance.

Use a question that matches the information

“How does the nominal diameter change?” can be answered from the marking. “What is this exact tire’s published diameter on its measuring rim?” needs the manufacturer’s specification. “Will it clear my vehicle under use?” needs additional vehicle and physical information. Keeping those questions separate prevents a precise-looking number from claiming more than its inputs support.

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