255/45 R18
What size is 255/45 R18?
255/45 R18 has an overall diameter of about 27.04 in, a section width of 10.04 in and a sidewall height of 4.52 in. It turns roughly 746 times per mile. Below are the exact figures plus in-tolerance plus/minus sizes you can switch to safely.
- Overall diameter: 27.04 in.
- Section width: 10.04 in.
- Sidewall height: 4.52 in.
- Revolutions: 464 /km · 746 /mi.
- In-tolerance sizes: 255/40 R19 (-0.0%).
Fitment verdict
255/40 R19 stays within the configured tolerance for 255/45 R18: 0.0% diameter and 0.0% speedometer effect.
| Metric | This size: 255/45 R18 | Alternative: 255/40 R19 | Difference | Verdict |
|---|---|---|---|---|
| Overall diameter | 27.04 in | 27.03 in | 0.0% | Within tolerance |
| Section width | 10.04 in | 10.04 in | 0.00 in | Computed difference |
| Sidewall height | 4.52 in | 4.02 in | -0.50 in | Computed difference |
| Circumference | 84.93 in | 84.92 in | 0.0% | Within tolerance |
| Speedo | 0.0% | 0.0% | 0.0% | 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 | 27.04 in |
|---|---|
| Section width | 10.04 in |
| Sidewall height | 4.52 in |
| Circumference | 84.93 in |
| Revolutions | 464 /km · 746 /mi |
In-tolerance sizes
Alternative sizes that stay within the safe diameter tolerance:
| Size | Diameter | Speedo | Verdict |
|---|---|---|---|
| 255/40 R19 | -0.0% | -0.0% | ✓ OK |
| 255/35 R20 | -0.0% | -0.0% | ✓ OK |
| 215/65 R16 | -0.1% | -0.1% | ✓ OK |
| 235/60 R16 | +0.2% | +0.2% | ✓ OK |
| 215/60 R17 | +0.5% | +0.5% | ✓ OK |
| 235/55 R17 | +0.5% | +0.5% | ✓ OK |
| 215/70 R15 | -0.7% | -0.7% | ✓ OK |
| 235/50 R18 | +0.8% | +0.8% | ✓ OK |
| 245/35 R20 | -1.0% | -1.0% | ✓ OK |
| 225/55 R17 | -1.1% | -1.1% | ✓ OK |
| 245/40 R19 | -1.2% | -1.2% | ✓ OK |
| 245/45 R18 | -1.3% | -1.3% | ✓ OK |
Compare sizes
- Within tolerance · Diameter -0.0%.
- Speedo @ 60: 60 mph → 60.0 mph.
- Sidewall -0.50 in · Width +0.00 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
- 27.04 in 27.03 in-0.00 in
- Sidewall
- 4.52 in 4.02 in-0.50 in
- Width
- 10.04 in 10.04 in+0.00 in
- Circumference
- 84.93 in 84.92 in-0.0%
- Revs / mile
- 746 746
- Speedo @ 60
- 60 mph 60.0 mph-0.0%
- Current —
255/45 R18 - New —
255/40 R19 - Grounded to the road: the axle rises -0.00 in.
Result report
255/45 R18 255/40 R19 · Within tolerance
Use this size when shopping: 255/40 R19
Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.
Safe alternative sizes
| Size | Diameter | Speedo @ 100 | Use this |
|---|---|---|---|
−1″ 255/50R17 | +0.0% | +0.0% | |
OE 255/45R18 | +0.0% | +0.0% | |
+1″ 255/40R19 | -0.0% | -0.0% | |
+2″ 255/35R20 | -0.0% | -0.0% |
More tools
- How to read a tire size
- Plus sizing guide
- Speedometer error guide
- 255mm Section width guide
- /45 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.