Rim & Tire Fitment Calculator
Enter your wheel width and see exactly which tire section widths fit — and which are ideal versus just acceptable.
How wheel width and tire width relate
Every wheel width is designed for a band of tire section widths, not a single one. The accepted industry guideline — the same one wheel shops and tire retailers use — gives roughly a 30mm-wide window for each wheel size. The linear relationship works out to:
| Wheel width | Minimum | Recommended | Maximum |
|---|---|---|---|
| 7.0" | 195mm | 200–220mm | 225mm |
| 8.0" | 215mm | 220–240mm | 245mm |
| 9.0" | 235mm | 240–260mm | 265mm |
| 10.0" | 255mm | 260–280mm | 285mm |
Each half-inch of wheel width corresponds to about 5mm of tire section width. Staying in the recommended band keeps the tread flat on the road, which is what gives you even wear, predictable grip, and a properly seated bead.
Why the rounded-profile problem matters
When a tire is mounted on a rim narrower than its design range, the casing pulls the tread into a dome. Only the center of the tread fully contacts the road, so you lose grip exactly when you need it — under braking and cornering — and the center wears out early. Mount it too wide and the opposite happens: the shoulders dig in, the center lifts, and the bead is more likely to unseat in a hard corner. The window exists to keep the contact patch flat.
Frequently asked questions
- How do I know what tire width fits my wheel?
- Each wheel width has a section-width window roughly 30mm wide. As a rule of thumb, the minimum tire width in mm is about 20 times the wheel width in inches plus 55, and the maximum is that plus 30. An 8-inch wheel, for example, comfortably takes 215–245mm tires, with 225–235mm being ideal. The calculator on this page shows the exact window for your wheel.
- What happens if a tire is too wide for the wheel?
- A tire that is too wide for the rim takes on a rounded, light-bulb profile. The tread edges lift slightly off the road, which reduces grip and even tread wear, makes the sidewall more vulnerable to pinch damage, and can cause unpredictable handling. Too narrow and the tread pinches inward, increasing center wear and the chance of the bead unseating under hard cornering.
- Does wheel offset affect tire fitment?
- Yes, but separately from width. Offset determines how far the tire/wheel sits in or out relative to the suspension and fender. A width can be mechanically fine for the rim yet still rub the fender or strut because the offset pushes it too far in or out. Check width first with this tool, then confirm offset clearance for your specific vehicle.
- Can I run a wider tire on my stock wheels?
- Often yes, within the window. Most factory wheels can accept one step wider than stock (for example 235 instead of 225 on the same rim) while staying in the acceptable range. Going beyond the window means changing wheels too. Use the calculator to see how many steps of width your current wheel allows.