Tire Stretch Calculator
Check a tire width against a wheel width using a published rim width chart, and see how stretched or bulged it will be.
Enter your numbers and press Calculate.
The chart behind it
Performance Plus Tire publishes a general tire-width-for-wheel-width chart from 5.0 to 10.0 inches. It calls the chart a general guide and says it is not a substitute for the individual tire's published specs.
| Wheel width | Minimum | Ideal | Maximum |
|---|---|---|---|
| 5 in | 155 mm | 165–175 mm | 185 mm |
| 5.5 in | 165 mm | 175–185 mm | 195 mm |
| 6 in | 175 mm | 185–195 mm | 205 mm |
| 6.5 in | 185 mm | 195–205 mm | 215 mm |
| 7 in | 195 mm | 205–215 mm | 225 mm |
| 7.5 in | 205 mm | 215–225 mm | 235 mm |
| 8 in | 215 mm | 225–235 mm | 245 mm |
| 8.5 in | 225 mm | 235–245 mm | 255 mm |
| 9 in | 235 mm | 245–255 mm | 265 mm |
| 9.5 in | 245 mm | 255–265 mm | 275 mm |
| 10 in | 255 mm | 265–275 mm | 285 mm |
Tire widths on a 9.5-inch wheel
| Section width | Inches | On the chart |
|---|---|---|
| 225 mm | 8.9 in | Outside chart |
| 235 mm | 9.3 in | Outside chart |
| 245 mm | 9.6 in | Within limits |
| 255 mm | 10.0 in | Ideal |
| 265 mm | 10.4 in | Ideal |
| 275 mm | 10.8 in | Within limits |
| 285 mm | 11.2 in | Outside chart |
| 295 mm | 11.6 in | Outside chart |
Performance Plus Tire general chart. The tire's own approved range decides.
Stretch and bulge
A tire narrower than the chart's minimum is stretched: the sidewalls angle outward from the bead to the tread. One wider than the maximum bulges past the rim. Both move the tire away from the shape it was designed to hold. Tire Rack notes that each tire size has an approved rim width range and a measuring rim, the width at which its listed dimensions are taken.
Offset on a 9.5-inch wheel
| Offset | Backspacing | Front spacing |
|---|---|---|
| −12 | 4.78 in | 5.72 in |
| 0 | 5.25 in | 5.25 in |
| +20 | 6.04 in | 4.46 in |
| +35 | 6.63 in | 3.87 in |
| +45 | 7.02 in | 3.48 in |
Check clearance before you buy
Offset and width tell you where the wheel's lips end up; they do not tell you what is in the way. Before ordering, measure your current setup:
- Inner clearance. With the wheels straight, measure from the inner lip of the current wheel to the nearest suspension part: strut body, spring perch, upper control arm or sway bar link. If the new wheel's inner lip moves in by more than that gap, it will hit.
- Brake clearance. Big calipers sit inside the barrel. The spoke face, not just the lip, has to clear them, which is why a wheel's spoke design matters as much as its offset.
- Outer clearance. Hang a plumb line or hold a level against the fender lip and measure in to the tire's sidewall. A new wheel that moves out more than that gap will stick past the fender.
- Steering and suspension travel. Turn to full lock and check the fender liner, then remember the suspension compresses over bumps. Static clearance is the best case.
Enter both wheels in the calculator above: the outer-lip number is the extra space you need at the fender, and the inner-lip number is the extra space you need at the suspension.
Common questions
What is the ideal tire width for a 9.5 inch rim?
255 to 265 mm on the Performance Plus Tire chart.
Is a 235 tire on a 9.5 inch rim stretched?
Yes by the chart: it is below the 245 mm minimum.
Sources
- https://mickeythompsontires.com/tech-bulletins/backspacing-and-offset
- https://speedwaymotors.com/the-toolbox/wheel-offset-vs-backspacing-explained/30059
- https://www.tirerack.com/wheels/tech/techpage.jsp?techid=101
- https://www.performanceplustire.com/Blog/tire-size-for-wheel-width
- https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=200