Plus Sizing: Bigger Wheels Without Changing the Overall Size
Updated 8 November 2026. Every figure on this page comes from the same formulas as our calculators.
Plus sizing means fitting a larger wheel with a lower-profile tire so that the overall diameter stays almost the same. The speedometer stays accurate and the car sits at the same height, while the wheel looks bigger and the sidewall gets shorter.
The idea in one example
Start from a common compact-car size, 205/55R16:
| Size | Rim | Sidewall | Diameter | Change |
|---|---|---|---|---|
| 205/55R16 (original) | 16 in | 112.8 mm | 24.88 in | — |
| 225/45R17 (plus one) | 17 in | 101.3 mm | 24.97 in | +0.38 % |
| 225/40R18 (plus two) | 18 in | 90.0 mm | 25.09 in | +0.84 % |
Each inch of extra rim is cancelled by a shorter sidewall, so the overall diameter moves by less than 1 %. With 225/40R18, an indicated 60 mph is 60.5 mph. Compare these two sizes.
The usual pattern
- Rim up by 1 inch.
- Width up by about 10 to 20 mm.
- Aspect ratio down by about 5 to 10 points.
The pattern is only a starting point; the diameter is what has to match. The plus size calculator lists real tire sizes within ±3 % of your original diameter for each rim size.
What changes when you plus size
- Width: going from 205 to 225 mm adds 20 mm, about 10 mm on each side on the same wheel. A new wider wheel also moves in and out; use the offset calculator for that.
- Sidewall: a shorter sidewall usually sharpens steering response but gives a firmer ride and less cushion for the rim on potholes.
- Weight and cost: bigger wheels and low-profile tires are often heavier and more expensive.
- Load index: the new tire must carry at least the load the vehicle requires. Low-profile tires sometimes need an XL (reinforced) version to match the original load index.
Going down: minus sizing
The same idea works the other way. Some drivers fit a smaller wheel with a taller sidewall for winter tires, which are often cheaper in smaller sizes. The limit is the brakes: the wheel must clear the calipers, so check the smallest rim the vehicle allows.
Before you buy
- Check the vehicle placard or handbook for approved sizes and the required load index and speed rating.
- Make sure the new wheel matches the bolt pattern, centre bore and offset range for the car.
- Ask the fitter to check clearance at full lock once the wheels are on.