Rim width, tyre width and overall diameter
Wheel Size Chart
Rim width decides which tyre widths fit. Overall diameter decides whether the speedometer still reads true. This chart covers 5.0J to 12.0J and the diameter maths for 13 to 22 inch wheels.
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What tyre width fits a 9.5J rim?
The number before the J is the rim width in inches, measured between the flanges. Tyre makers publish a measuring rim and a permitted rim width range for every size; the table below is the common range for passenger car tyres.
Read the middle column first. It is the range most tyres are designed around for that rim width.
| Rim width | Common tyre widths (mm) | Typical fitment |
|---|---|---|
| 5.0J | 155 - 185 | 165 |
| 5.5J | 165 - 195 | 175 |
| 6.0J | 175 - 205 | 185 |
| 6.5J | 185 - 215 | 195 |
| 7.0J | 195 - 225 | 205 |
| 7.5J | 205 - 235 | 215 |
| 8.0J | 215 - 245 | 225 |
| 8.5J | 225 - 255 | 235 |
| 9.0J | 235 - 265 | 245 |
| 9.5J | 245 - 275 | 255 |
| 10.0J | 255 - 285 | 265 |
| 10.5J | 265 - 295 | 275 |
| 11.0J | 275 - 305 | 285 |
| 11.5J | 285 - 315 | 295 |
| 12.0J | 295 - 325 | 305 |
Ranges differ slightly between tyre models. Check the tyre maker data sheet for the size you plan to buy.
How to read a size like 18 x 8.5J ET45
The size on the box is four pieces of information in one line, and only one of them is the width the tyre cares about.
- 18 is the diameter in inches.
- 8.5J is the rim width in inches. J is the flange profile.
- ET45 is the offset: 45 mm from the mounting face to the wheel centre line.
- PCD and centre bore are not in this number and must be checked separately.
Does a bigger wheel change the overall diameter?
Yes, unless the aspect ratio changes too. Overall diameter in mm is rim diameter x 25.4 + 2 x (tyre width x aspect ratio / 100).
Going up one inch usually means dropping about five points of aspect ratio to stay near the original diameter.
| Size | Overall diameter | Change vs 225/45R17 |
|---|---|---|
| 225/45R17 | 634 mm | baseline |
| 235/40R18 | 645 mm | +11 mm |
| 255/35R19 | 661 mm | +27 mm |
| 205/55R16 | 632 mm | -2 mm |
What this chart cannot tell you
A chart matches tyre width to rim width. It says nothing about the car.
- Whether the wheel clears the brake caliper.
- Whether the tyre rubs the arch at full lock or under load.
- Whether the offset keeps the wheel inside the bodywork.
- Whether the load rating suits the car.
A chart and a preview both stop short of a physical test fit.
Frequently asked questions
What tyre width fits a 9.5J wheel?
255 mm is the typical width for a 9.5J rim. 245 mm and 275 mm are usually inside the permitted range, depending on the tyre model.
Can I fit a 225 tyre on an 8.5J rim?
Yes. 225 mm is the lower end of the common range for 8.5J and gives a slightly stretched sidewall. Check the tyre maker permitted rim width first.
Does a bigger wheel change the speedometer?
Only if the overall diameter changes. 235/40R18 is about 11 mm larger than 225/45R17, roughly 1.7 percent, so the speedometer reads slightly low.
Is a wider rim always better?
No. A wider rim needs a wider tyre, adds unsprung weight and can move the tyre into the arch. Match the width to the tyre and the clearance you have.
Does this chart guarantee the wheel will fit my car?
No. It only matches tyre width to rim width. Offset, PCD, centre bore, brake clearance and arch clearance need a separate check.
Standards and sources
This guide uses the wheel and rim vocabulary from ISO 3911 and the passenger-car tyre dimensions in ISO 4000-1. Fitment guidance also draws on ETRTO and TRA references.
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