225/40 R18
What size is 225/40 R18?
225/40 R18 has an overall diameter of about 25.09 in, a section width of 8.86 in and a sidewall height of 3.54 in. It turns roughly 804 times per mile. Below are the exact figures plus in-tolerance plus/minus sizes you can switch to safely.
- Overall diameter: 25.09 in.
- Section width: 8.86 in.
- Sidewall height: 3.54 in.
- Revolutions: 500 /km · 804 /mi.
- In-tolerance sizes: 255/35 R18 (-0.2%).
Fitment verdict
255/35 R18 stays within the configured tolerance for 225/40 R18: -0.2% diameter and -0.2% speedometer effect.
| Metric | This size: 225/40 R18 | Alternative: 255/35 R18 | Difference | Verdict |
|---|---|---|---|---|
| Overall diameter | 25.09 in | 25.03 in | -0.2% | Within tolerance |
| Section width | 8.86 in | 10.04 in | +1.18 in | Computed difference |
| Sidewall height | 3.54 in | 3.51 in | -0.03 in | Computed difference |
| Circumference | 78.81 in | 78.63 in | -0.2% | Within tolerance |
| Speedo | 0.0% | -0.2% | -0.2% | Within tolerance |
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.
Specification
| Overall diameter | 25.09 in |
|---|---|
| Section width | 8.86 in |
| Sidewall height | 3.54 in |
| Circumference | 78.81 in |
| Revolutions | 500 /km · 804 /mi |
In-tolerance sizes
Alternative sizes that stay within the safe diameter tolerance:
| Size | Diameter | Speedo | Verdict |
|---|---|---|---|
| 255/35 R18 | -0.2% | -0.2% | ✓ OK |
| 195/65 R15 | -0.4% | -0.4% | ✓ OK |
| 225/35 R19 | +0.5% | +0.5% | ✓ OK |
| 225/45 R17 | -0.5% | -0.5% | ✓ OK |
| 195/60 R16 | +0.5% | +0.5% | ✓ OK |
| 205/55 R16 | -0.8% | -0.8% | ✓ OK |
| 215/55 R16 | +0.9% | +0.9% | ✓ OK |
| 225/50 R16 | -0.9% | -0.9% | ✓ OK |
| 235/45 R17 | +1.0% | +1.0% | ✓ OK |
| 235/40 R18 | +1.3% | +1.3% | ✓ OK |
| 195/70 R14 | -1.3% | -1.3% | ✓ OK |
| 215/50 R17 | +1.5% | +1.5% | ✓ OK |
Compare sizes
- Within tolerance · Diameter -0.2%.
- Speedo @ 60: 60 mph → 59.9 mph.
- Sidewall -0.03 in · Width +1.18 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
- 25.09 in 25.03 in-0.06 in
- Sidewall
- 3.54 in 3.51 in-0.03 in
- Width
- 8.86 in 10.04 in+1.18 in
- Circumference
- 78.81 in 78.63 in-0.2%
- Revs / mile
- 804 806
- Speedo @ 60
- 60 mph 59.9 mph-0.2%
- Current —
225/40 R18 - New —
255/35 R18 - Grounded to the road: the axle rises -0.03 in.
Result report
225/40 R18 255/35 R18 · Within tolerance
Use this size when shopping: 255/35 R18
Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.
Safe alternative sizes
| Size | Diameter | Speedo @ 100 | Use this |
|---|---|---|---|
−1″ 205/50R17 | -0.1% | -0.1% | |
OE 225/40R18 | +0.0% | +0.0% | |
+1″ 155/50R19 | +0.1% | +0.1% | |
+2″ 215/30R20 | -0.0% | -0.0% |
More tools
- How to read a tire size
- Plus sizing guide
- Speedometer error guide
- 225mm Section width guide
- /40 Aspect ratio guide
- Rim diameter 18"
- Load index chart
- Speed rating chart
- Rim width and tyre fitment guide
- Wheel offset guide
- Wheel spacers guide
- Tyre pressure for heavy loads and towing
What changed
- Reviewed deterministic geometry, load/speed references, sitemap inclusion and localized page shell.