Plus-sizing 225/40R18 to 22″ wheels on 225 mm tires
| Sidewall height available(25.09″ diameter − 22″ rim) ÷ 2 | 1.54in |
|---|---|
| Aspect ratio that would needbelow anything made — the rim is too big for this diameter | 17.4 |
Notes
- This combination does not exist. Holding 225/40R18's 25.09″ overall diameter on a 22″ rim leaves 1.54″ of sidewall, which on a 225 mm tyre is an aspect ratio of 17.4 — outside the 25–75 range anything is made in.
- Either step to a smaller rim, or change the section width. Wider tyres need a lower aspect ratio for the same sidewall height, so going wider is usually what makes a large rim step work.
The whole point is that diameter does not change
Plus-sizing means a bigger wheel and a shorter sidewall, adding up to the same rolling diameter. Go up 4″ of rim and the sidewall has to lose exactly half of that on each side.
Holding 225/40R18's 25.09″ overall diameter on a 22″ wheel with a 225 mm tire needs an aspect ratio of 17.4. Tires are not made in continuous aspect ratios — the nearest is 25, which lands the new diameter at 26.43″, or 5.35% from stock.
The target here is ±1%, not ±3%
The general limit for tire changes is 3%, because that is where speedometers, ABS and stability control start reading meaningfully wrong. Plus-sizing is held to about 1%, and the reason is simple: this is a change you chose to make. There is no reason to accept an error you introduced for looks.
What you are trading away
Sidewall goes from 3.54″ to 2.21″. That is sharper steering response and a firmer ride, and it is also a much higher chance of bending a wheel on a pothole. Below about 4 inches of sidewall, potholes start costing wheels rather than tires.
The wheel also gets heavier as the tire gets lighter — and the wheel is unsprung, rotating mass, which is the worst possible place to add weight for acceleration, braking and ride. Check the actual wheel weight before assuming bigger looks better and drives better.
Section width is not tread width
225 mm is the widest point of the sidewall. Check it at full steering lock and full suspension compression, not sitting still in the driveway.
Nearby sizes
- Plus-sizing 245/65R17 to 22″ wheels on 225 mm tires
- Plus-sizing 235/40R18 to 22″ wheels on 225 mm tires
- Plus-sizing 245/45R17 to 22″ wheels on 225 mm tires
- Plus-sizing 235/60R18 to 22″ wheels on 225 mm tires
- Plus-sizing 225/40R18 to 21″ wheels on 225 mm tires
- Plus-sizing 225/40R18 to 20″ wheels on 225 mm tires
Read more
- Load Index and Speed Rating — The Two Codes at the End of the SizeEveryone reads the size and stops. The two characters after it are the ones with a safety consequence.
- Speedometer Error From Tire Size — One Ratio, and It Runs Both WaysA one-inch increase in diameter on a 30-inch tire is a 3.3% error. At an indicated 70 you are doing a bit over 72.
- Recalibrating a Speedometer After a Tire Change: Four Routes, and How to Verify It WorkedOn most modern vehicles the tire size is a stored number, not a mechanical ratio. Where that is true, correcting it takes minutes; where it is not, the options get physical.
- Plus Sizing Chart: Wider Tire, Shorter Sidewall, Same Rolling DiameterPlus sizing trades sidewall for wheel and keeps the overall diameter where it was. Done properly nothing on the vehicle notices — which is the entire point.