Plus sizing guide
What is plus sizing?
Plus sizing fits a larger rim while keeping the overall tire diameter nearly the same by using a lower-profile tire. Plus one (+1) means a 1-inch larger rim with a proportionally reduced aspect ratio; plus two (+2) means 2 inches larger. Benefits: sharper handling and appearance. Drawbacks: reduced ride comfort due to the shorter sidewall.
- Plus sizing fits a larger rim while keeping the overall tire diameter nearly the same by using a lower-profile tire.
- Plus one (+1) means a 1-inch larger rim with a proportionally reduced aspect ratio; plus two (+2) means 2 inches larger.
- Benefits: sharper handling and appearance.
FAQ
- What is plus sizing?
- Plus sizing fits a larger rim while keeping the overall tire diameter nearly the same by using a lower-profile tire. Plus one (+1) means a 1-inch larger rim with a proportionally reduced aspect ratio; plus two (+2) means 2 inches larger. Benefits: sharper handling and appearance. Drawbacks: reduced ride comfort due to the shorter sidewall.
- What should I verify before using this information?
- Use TireFitLab values as a sizing reference, then verify the vehicle handbook, tire placard, rim compatibility, load rating, and physical clearance before fitting.
Worked examples
These rows use the same geometry engine as the calculator, so the numbers match the interactive result above.
| Current size | Candidate size | Diameter delta | Speedometer at 60 mph | Tolerance |
|---|---|---|---|---|
| 225/45R17 | 235/40R18 | +1.7% (+10.9 mm) | 60 mph → 61.0 mph | within |
| 205/55R16 | 225/45R17 | +0.4% (+2.4 mm) | 60 mph → 60.2 mph | within |
| 215/65R16 | 225/60R17 | +2.3% (+15.9 mm) | 60 mph → 61.4 mph | within |
What to do with it: Use the exact vehicle placard size before buying.
| Size | Specification |
|---|---|
| Plus 0 (stock) | Keep the original rim diameter. Replace with a tire of the same size. |
| Plus 1 (+1") | One inch larger rim. Reduce the aspect ratio to maintain the same overall diameter. |
| Plus 2 (+2") | Two inches larger rim. Further reduce the aspect ratio. Requires precise fitment check. |
Tire size calculator
- Within tolerance · Diameter +1.7%.
- Speedo @ 60: 60 mph → 61.0 mph.
- Sidewall -0.29 in · Width +0.39 in.
How this result is calculated
Computed from nominal tire-size geometry: diameter, circumference and speedometer error. It does not check wheel-arch, suspension or brake clearance.
Methodology- Diameter
- 24.97 in 25.40 in+0.43 in
- Sidewall
- 3.99 in 3.70 in-0.29 in
- Width
- 8.86 in 9.25 in+0.39 in
- Circumference
- 78.45 in 79.80 in+1.7%
- Revs / mile
- 808 794
- Speedo @ 60
- 60 mph 61.0 mph+1.7%
- Current —
225/45R17 - New —
235/40R18 - Grounded to the road: the axle rises +0.21 in.
Result report
225/45 R17 235/40 R18 · Within tolerance
Use this size when shopping: 235/40 R18
Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.
Safe alternative sizes
| Size | Diameter | Speedo @ 100 | Use this |
|---|---|---|---|
−1″ 285/40R16 | +0.0% | +0.0% | |
OE 225/45R17 | +0.0% | +0.0% | |
+1″ 295/30R18 | -0.0% | -0.0% | |
+2″ 305/25R19 | +0.1% | +0.1% |
Tire & wheel reference guides · Rim diameter guide
Seasonal check
Planning a long summer drive?
Use the budget and running-cost tools before a trip, especially if the current tyres are worn or the replacement size changes diameter.
What changed
- Reviewed deterministic geometry, load/speed references, sitemap inclusion and localized page shell.