Plus-sizing 255/55R18 to 17″ wheels on 245 mm tires
| Recommended size | 245/60R17 |
|---|---|
| Exact aspect ratio needednearest made is 60 | 62.4 |
| Overall diameter-1.61% | 29.04″ → 28.57″ |
| Within ±1% (plus-size target)try a different width | No |
| Within ±3% (general limit)speedometer, ABS and stability control all read off this | Yes |
| Sidewall height5% — this is what changes the ride | 5.52″ → 5.79″ |
| Section width-10 mm — check clearance at full lock | 255 → 245 mm |
| Rim stepplus -1 | 18″ → 17″ |
- Current size
- 255/55R18
- New wheel
- 17 in
- New width
- 245 mm
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 -1″ of rim and the sidewall has to lose exactly half of that on each side.
Holding 255/55R18's 29.04″ overall diameter on a 17″ wheel with a 245 mm tire needs an aspect ratio of 62.4. Tires are not made in continuous aspect ratios — the nearest is 60, which lands the new diameter at 28.57″, or -1.61% 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 5.52″ to 5.79″. 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
245 mm is the widest point of the sidewall. Check it at full steering lock and full suspension compression, not sitting still in the driveway.
Notes
- Plus-sizing keeps the overall diameter and changes everything else. Going up -1″ of rim means losing -0.27″ of sidewall on each side, which is why the aspect ratio has to come down from 55 to 60.
- 1.61% is inside the general ±3% window but outside the ±1% plus-sizing target. The available aspect ratios do not land closer at 245 mm; a 255 mm tyre may get you nearer.
- Less sidewall is the trade you are making, and it is a real one. 5.79″ of rubber between the rim and the road means sharper steering response, a firmer ride, and a much higher chance of bending a wheel on a pothole. Below about 4″ of sidewall, potholes start costing wheels rather than tyres.
- The wheel gets heavier as the tyre gets lighter, and the wheel is unsprung and rotating. Plus-sizing frequently adds weight where it hurts acceleration, braking and ride quality most — check the actual wheel weight before assuming bigger looks better and drives better.
- Section width is the widest point of the sidewall, not the tread. 245 mm needs checking at full steering lock and full suspension compression, not just sitting still.
Nearby sizes
- Plus-sizing 245/40R18 to 17″ wheels on 245 mm tires
- Plus-sizing 265/60R18 to 17″ wheels on 245 mm tires
- Plus-sizing 235/60R18 to 17″ wheels on 245 mm tires
- Plus-sizing 245/45R19 to 17″ wheels on 245 mm tires
- Plus-sizing 255/55R18 to 18″ wheels on 245 mm tires
- Plus-sizing 255/55R18 to 19″ wheels on 245 mm tires
- Plus-sizing 255/55R18 to 17″ wheels on 235 mm tires
- Plus-sizing 255/55R18 to 17″ wheels on 255 mm tires
- Plus-sizing 255/55R18 to 17″ wheels on 225 mm tires
- Plus-sizing 255/55R18 to 17″ wheels on 265 mm tires
Read more
- What Is a 33-Inch Tire in Metric? Seven Answers, RankedSeven common metric sizes get called 33s. They span half an inch in height and nearly two inches in width, and the width is what decides whether they fit.
- Reading a Tire Sidewall: Every Marking, in OrderThe size is the part everyone reads. The characters after it are the part that decides whether the tire is legal on your vehicle.
- Metric to Inches Tire Size: Both Directions, WorkedMetric to inches is arithmetic with one answer. Inches to metric has many answers, because you are choosing among sizes that happen to land near your target.
- Comparing Two Tire Sizes: The Four Numbers That ChangeComparing sizes by diameter alone hides the change that most often causes the problem. Four numbers move when you change a tire, and they move independently.