Tire Stretch Calculator
The verdict is the published rim-width table. A percentage is just how the picture looks.
- Minimum, measuring and maximum are published rim widths for that section.
- A rim past maximum is stretch. We describe it in millimetres; we do not grade 4/8/12%.
- Below minimum the bead may not seat. The tire maker’s spec wins over this table.
What it does
Looks up the ETRTO/TRA min–measuring–max rim for that section width and tells you if the rim you typed is inside, too narrow, or too wide. Also reports rim millimetres minus section width as a description, not a grade.
How to use it
Enter the tire size and the advertised rim width (the stamped J-width).
How to read the result
Inside the table is the only line we will call acceptable. Community charts that color 0–4–8–12% as “safe / aggressive” are not a standard — they contradict each other, so we do not use them as a verdict. A tire on a rim below minimum may not bead safely.
What this does not calculate
Passenger/LT ETRTO series, same table as Recommended rim width. Flotation and some Load Range E tires publish different charts. The tire maker’s spec wins.
Does not simulate inner-fender rub of a squared-off sidewall, and does not grade stance.
Questions
- Why no green/yellow/red percent bands?
- Those bands are forum convention, not ETRTO. We already have a real table. Using both as if they were law would mix a standard with a vibe.
- Is stretching illegal?
- We are not a lawyer. It can void a warranty and it can unseat a bead. Stay inside the published rim range unless you know why you are leaving it.
Related tools
- Rim Width Calculator by Tire SizeMeasuring width is where the tire is spec’d. Acceptable is the full range. Optimal is near measuring.
- Free Tire Size CalculatorPaste a size. See the real dimensions — not just the numbers on the sidewall.
- Free Wheel Offset CalculatorMore positive offset tucks the wheel in. More width with the same offset pokes both ways.
Estimate — not a fitment approval.
