235/40 R18
What size is 235/40 R18?
235/40 R18 has an overall diameter of about 25.40 in, a section width of 9.25 in and a sidewall height of 3.70 in. It turns roughly 794 times per mile. Below are the exact figures plus in-tolerance plus/minus sizes you can switch to safely.
- Overall diameter: 25.40 in.
- Section width: 9.25 in.
- Sidewall height: 3.70 in.
- Revolutions: 493 /km · 794 /mi.
- In-tolerance sizes: 215/50 R17 (+0.2%).
Fitment verdict
215/50 R17 stays within the configured tolerance for 235/40 R18: +0.2% diameter and +0.2% speedometer effect.
| Metric | This size: 235/40 R18 | Alternative: 215/50 R17 | Difference | Verdict |
|---|---|---|---|---|
| Overall diameter | 25.40 in | 25.46 in | +0.2% | Within tolerance |
| Section width | 9.25 in | 8.46 in | -0.79 in | Computed difference |
| Sidewall height | 3.70 in | 4.23 in | +0.53 in | Computed difference |
| Circumference | 79.80 in | 80.00 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 | 25.40 in |
|---|---|
| Section width | 9.25 in |
| Sidewall height | 3.70 in |
| Circumference | 79.80 in |
| Revolutions | 493 /km · 794 /mi |
In-tolerance sizes
Alternative sizes that stay within the safe diameter tolerance:
| Size | Diameter | Speedo | Verdict |
|---|---|---|---|
| 215/50 R17 | +0.2% | +0.2% | ✓ OK |
| 235/35 R19 | +0.3% | +0.3% | ✓ OK |
| 235/45 R17 | -0.3% | -0.3% | ✓ OK |
| 205/65 R15 | +0.4% | +0.4% | ✓ OK |
| 215/55 R16 | -0.4% | -0.4% | ✓ OK |
| 195/60 R16 | -0.7% | -0.7% | ✓ OK |
| 225/35 R19 | -0.8% | -0.8% | ✓ OK |
| 245/45 R17 | +1.1% | +1.1% | ✓ OK |
| 205/60 R16 | +1.1% | +1.1% | ✓ OK |
| 225/40 R18 | -1.2% | -1.2% | ✓ OK |
| 245/40 R18 | +1.2% | +1.2% | ✓ OK |
| 225/55 R16 | +1.3% | +1.3% | ✓ OK |
Compare sizes
- Within tolerance · Diameter +0.2%.
- Speedo @ 60: 60 mph → 60.1 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
- 25.40 in 25.46 in+0.06 in
- Sidewall
- 3.70 in 4.23 in+0.53 in
- Width
- 9.25 in 8.46 in-0.79 in
- Circumference
- 79.80 in 80.00 in+0.2%
- Revs / mile
- 794 792
- Speedo @ 60
- 60 mph 60.1 mph+0.2%
- Current —
235/40 R18 - New —
215/50 R17 - Grounded to the road: the axle rises +0.03 in.
Result report
235/40 R18 215/50 R17 · Within tolerance
Use this size when shopping: 215/50 R17
Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.
Safe alternative sizes
| Size | Diameter | Speedo @ 100 | Use this |
|---|---|---|---|
−1″ 305/35R17 | +0.0% | +0.0% | |
OE 235/40R18 | +0.0% | +0.0% | |
+1″ 125/65R19 | -0.0% | -0.0% | |
+2″ 125/55R20 | +0.0% | +0.0% |
More tools
- How to read a tire size
- Plus sizing guide
- Speedometer error guide
- 235mm 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.