225/55 R18
What size is 225/55 R18?
225/55 R18 has an overall diameter of about 27.74 in, a section width of 8.86 in and a sidewall height of 4.87 in. It turns roughly 727 times per mile. Below are the exact figures plus in-tolerance plus/minus sizes you can switch to safely.
- Overall diameter: 27.74 in.
- Section width: 8.86 in.
- Sidewall height: 4.87 in.
- Revolutions: 452 /km · 727 /mi.
- In-tolerance sizes: 245/45 R19 (-0.2%).
Fitment verdict
245/45 R19 stays within the configured tolerance for 225/55 R18: -0.2% diameter and -0.2% speedometer effect.
| Metric | This size: 225/55 R18 | Alternative: 245/45 R19 | Difference | Verdict |
|---|---|---|---|---|
| Overall diameter | 27.74 in | 27.68 in | -0.2% | Within tolerance |
| Section width | 8.86 in | 9.65 in | +0.79 in | Computed difference |
| Sidewall height | 4.87 in | 4.34 in | -0.53 in | Computed difference |
| Circumference | 87.16 in | 86.96 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 | 27.74 in |
|---|---|
| Section width | 8.86 in |
| Sidewall height | 4.87 in |
| Circumference | 87.16 in |
| Revolutions | 452 /km · 727 /mi |
In-tolerance sizes
Alternative sizes that stay within the safe diameter tolerance:
| Size | Diameter | Speedo | Verdict |
|---|---|---|---|
| 245/45 R19 | -0.2% | -0.2% | ✓ OK |
| 275/40 R19 | -0.3% | -0.3% | ✓ OK |
| 225/60 R17 | -0.4% | -0.4% | ✓ OK |
| 225/65 R16 | -0.8% | -0.8% | ✓ OK |
| 215/65 R17 | +0.9% | +0.9% | ✓ OK |
| 235/65 R16 | +1.0% | +1.0% | ✓ OK |
| 255/35 R21 | +1.0% | +1.0% | ✓ OK |
| 255/45 R19 | +1.1% | +1.1% | ✓ OK |
| 225/70 R15 | -1.2% | -1.2% | ✓ OK |
| 235/60 R17 | +1.3% | +1.3% | ✓ OK |
| 235/55 R18 | +1.6% | +1.6% | ✓ OK |
| 235/50 R18 | -1.8% | -1.8% | ✓ OK |
Compare sizes
- Within tolerance · Diameter -0.2%.
- Speedo @ 60: 60 mph → 59.9 mph.
- Sidewall -0.53 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
- 27.74 in 27.68 in-0.06 in
- Sidewall
- 4.87 in 4.34 in-0.53 in
- Width
- 8.86 in 9.65 in+0.79 in
- Circumference
- 87.16 in 86.96 in-0.2%
- Revs / mile
- 727 729
- Speedo @ 60
- 60 mph 59.9 mph-0.2%
- Current —
225/55 R18 - New —
245/45 R19 - Grounded to the road: the axle rises -0.03 in.
Result report
225/55 R18 245/45 R19 · Within tolerance
Use this size when shopping: 245/45 R19
Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.
Safe alternative sizes
| Size | Diameter | Speedo @ 100 | Use this |
|---|---|---|---|
−1″ 195/70R17 | +0.0% | +0.0% | |
OE 225/55R18 | +0.0% | +0.0% | |
+1″ 185/60R19 | -0.0% | -0.0% | |
+2″ 245/40R20 | -0.1% | -0.1% |
More tools
- How to read a tire size
- Plus sizing guide
- Speedometer error guide
- 225mm Section width guide
- /55 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.