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Car math, worked out for you
Free tire and wheel calculators that show the working. Type a size, see every dimension, the effect on your speedometer, and whether a swap actually fits — no account, no upsell.
Calculators
Each one uses the same geometric engine and cites its formulas.
Tire Size Calculator
Compare two tire sizes to scale — diameter, sidewall, circumference, speedometer error, ground clearance, and every alternative size that fits inside the 3% rule.
Open →Side by sideTire Size Comparison
Two sizes, every dimension, the exact percentage difference and a to-scale drawing — plus a chart of the comparisons people run most often.
Open →Wheel Offset Calculator
Offset, backspacing and poke — see how a wheel sits in the arch before you buy, with a to-scale drawing.
SoonTire Diameter Calculator
Overall height from any size code, in inches or millimetres, with the revs-per-mile that follow from it.
SoonBolt Pattern Calculator
Bolt-circle diameter from a stud measurement, and whether one pattern (5x100, 5x114.3) will bolt to another.
SoonHow these are built
The working is on the page
Every result comes with the formula it used and a link to the standard behind it — not a number from a black box.
Metric or inches
One toggle switches every figure — millimetres and km/h, or inches and mph — on all of it, including the diagrams.
No account, no upsell
It is a tool, not a funnel. Nothing to sign up for, nothing pushed at you, no tire shop attached.