245/40 R18
What size is 245/40 R18?
245/40 R18 has an overall diameter of about 25.72 in, a section width of 9.65 in and a sidewall height of 3.86 in. It turns roughly 784 times per mile. Below are the exact figures plus in-tolerance plus/minus sizes you can switch to safely.
- Overall diameter: 25.72 in.
- Section width: 9.65 in.
- Sidewall height: 3.86 in.
- Revolutions: 487 /km · 784 /mi.
- In-tolerance sizes: 225/55 R16 (+0.1%).
Fitment verdict
225/55 R16 stays within the configured tolerance for 245/40 R18: +0.1% diameter and +0.1% speedometer effect.
| Metric | This size: 245/40 R18 | Alternative: 225/55 R16 | Difference | Verdict |
|---|---|---|---|---|
| Overall diameter | 25.72 in | 25.74 in | +0.1% | Within tolerance |
| Section width | 9.65 in | 8.86 in | -0.79 in | Computed difference |
| Sidewall height | 3.86 in | 4.87 in | +1.01 in | Computed difference |
| Circumference | 80.79 in | 80.88 in | +0.1% | Within tolerance |
| Speedo | 0.0% | +0.1% | +0.1% | 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 | 25.72 in |
|---|---|
| Section width | 9.65 in |
| Sidewall height | 3.86 in |
| Circumference | 80.79 in |
| Revolutions | 487 /km · 784 /mi |
In-tolerance sizes
Alternative sizes that stay within the safe diameter tolerance:
| Size | Diameter | Speedo | Verdict |
|---|---|---|---|
| 225/55 R16 | +0.1% | +0.1% | ✓ OK |
| 205/60 R16 | -0.1% | -0.1% | ✓ OK |
| 245/35 R19 | +0.1% | +0.1% | ✓ OK |
| 245/45 R17 | -0.1% | -0.1% | ✓ OK |
| 225/50 R17 | +0.6% | +0.6% | ✓ OK |
| 205/55 R17 | +0.6% | +0.6% | ✓ OK |
| 205/65 R15 | -0.9% | -0.9% | ✓ OK |
| 235/35 R19 | -0.9% | -0.9% | ✓ OK |
| 215/50 R17 | -1.0% | -1.0% | ✓ OK |
| 225/45 R18 | +1.0% | +1.0% | ✓ OK |
| 255/35 R19 | +1.2% | +1.2% | ✓ OK |
| 235/40 R18 | -1.2% | -1.2% | ✓ OK |
Compare sizes
- Within tolerance · Diameter +0.1%.
- Speedo @ 60: 60 mph → 60.1 mph.
- Sidewall +1.01 in · Width -0.79 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
- 25.72 in 25.74 in+0.03 in
- Sidewall
- 3.86 in 4.87 in+1.01 in
- Width
- 9.65 in 8.86 in-0.79 in
- Circumference
- 80.79 in 80.88 in+0.1%
- Revs / mile
- 784 783
- Speedo @ 60
- 60 mph 60.1 mph+0.1%
- Current —
245/40 R18 - New —
225/55 R16 - Grounded to the road: the axle rises +0.01 in.
Result report
245/40 R18 225/55 R16 · Within tolerance
Use this size when shopping: 225/55 R16
Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.
Safe alternative sizes
| Size | Diameter | Speedo @ 100 | Use this |
|---|---|---|---|
−1″ 185/60R17 | +0.1% | +0.1% | |
OE 245/40R18 | +0.0% | +0.0% | |
+1″ 155/55R19 | -0.0% | -0.0% | |
+2″ 145/50R20 | -0.0% | -0.0% |
More tools
- How to read a tire size
- Plus sizing guide
- Speedometer error guide
- 245mm 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.