Rim Size Calculator
Enter your current rim width and offset, then the new wheel you are looking at. The calculator shows the tire widths that suit the new rim and how far each edge of the wheel moves.
- Tire width range
- Offset and poke
- Inner clearance check
Tire width ranges are typical guidance. Each tire maker publishes an approved rim range for every size.
A wheel size like 18x8 ET35 tells you three things. 18 is the diameter in inches, 8 is the width between the bead seats in inches, and ET35 is the offset: the distance in millimetres from the wheel's centre line to the face that bolts to the hub. Change the width or offset and the wheel moves closer to the suspension or further out towards the arch.
Rim width and tire width guide
Approved tire widths for common rim widths. Search for your rim or tire width.
| Rim width (in) | Rim width (mm) | Narrowest tire | Best match | Widest tire |
|---|---|---|---|---|
| 5.5 | 140 | 155 | 170 | 200 |
| 6.0 | 152 | 165 | 185 | 215 |
| 6.5 | 165 | 175 | 200 | 235 |
| 7.0 | 178 | 190 | 215 | 255 |
| 7.5 | 191 | 205 | 235 | 270 |
| 8.0 | 203 | 215 | 250 | 290 |
| 8.5 | 216 | 230 | 265 | 310 |
| 9.0 | 229 | 245 | 280 | 325 |
| 9.5 | 241 | 255 | 295 | 345 |
| 10.0 | 254 | 270 | 310 | 365 |
Ranges follow ETRTO and Tire and Rim Association guidance for passenger tires. Low profile tires often have a narrower approved range than the figures here.
Rim width and tire choice
Wider rims need wider tires. Slide the rim width to see the tire range move.
A tire on a rim near the narrow end of its range has a rounded sidewall and softer steering. Near the wide end the sidewall is stretched straight, which sharpens steering but exposes the rim to kerbs.
How to read a wheel size
The numbers are cast on the back of the spokes. Step through a code like 18x8J ET35 5x112.
Diameter
18 is the diameter of the bead seat in inches. It must match your tire.
Centre bore matters too. If the new wheel's bore is larger than your hub, fit spigot rings so the wheel centres properly and does not vibrate.
Higher or lower offset
Offset decides where the wheel sits. Pick a direction to see the effect.
The wheel moves outward. More track width and a flusher look, but closer to the arch lip.
The wheel moves inward towards the suspension and brakes.
Half the extra width goes in and half goes out if the offset stays the same.
Changing width and offset together is how you fit a wider wheel without rubbing. A wheel 1 inch wider with an offset 12.7 mm lower keeps the inner edge in the same place.
Before you buy new wheels
Fitment is more than diameter. Check each point.
Tick each item as you go.
Ask the seller whether the wheel has a TÜV, JWL or VIA certificate. These show the wheel was tested for load and impact.
What the result tells you
Every fitment number in one place. Each tile explains one result.
Narrowest to widest tire for the new rim.
The width that gives a straight, supported sidewall.
How much closer to the suspension the wheel sits.
How much further the wheel pokes out.
A warning when either edge moves more than 10 mm.
Most fitment problems come from the inner edge. If the inner edge moves more than about 5 mm closer to the suspension, check the gap to the strut before ordering.
Frequently Asked Questions
No question matches that search.
What does ET mean on a wheel?
ET is the offset in millimetres, from the German einpresstiefe. It is the distance from the wheel's centre line to the hub mounting face.
What tire size fits an 8 inch rim?
Usually 215 to 255 mm on a passenger car, with 225 to 245 being the most common.
How much does offset change wheel position?
Millimetre for millimetre. Lowering the offset by 10 mm moves the whole wheel 10 mm outward.
What happens if I fit a wider rim with the same offset?
Half of the extra width goes inward and half outward. One inch wider means 12.7 mm each side.
Can I put a 225 tire on a 7 inch rim?
Yes. A 225 tire is normally approved on rims from 6 to 8 inches wide.
Does rim diameter affect tire width?
No. Width and diameter are separate. Diameter must match the tire; width decides the tire width range.
Do I need hub-centric rings?
Yes, if the wheel's centre bore is larger than your car's hub. They stop vibration and take load off the studs.
Fit wheels that look right and clear everything
Match bolt pattern and centre bore first, then use the calculator to keep the edges within about 10 mm and choose a tire in the right width range for the rim. That combination gives good looks without rubbing or unsafe stretch.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.