235/30R18 tire size
235/30R18 is a metric size: 23.6" tall, 9.3" wide, on a 18" rim — about a 23.5x9.50R18. The sidewall is 2.8" and the tire turns 856 times per mile.
235/30R18 specs
| Overall diameter (height) | 23.55" · 598 mm |
|---|---|
| Section width | 9.25" · 235 mm |
| Sidewall height | 2.78" · 71 mm (30% of width) |
| Rim diameter | 18" |
| Circumference | 73.99" · 1.879 m |
| Revolutions per mile | 856 (532 per km) |
| Inch (flotation) equivalent | 23.5x9.50R18 |
Equivalent sizes on a 18" rim
Sizes within ±5% of the overall diameter. Green rows are inside the usual ±3% limit for keeping the speedometer, ABS and gearing right; red rows are bigger changes that need clearance checks.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 205/40R18 | 24.46" | +3.84% | -30 mm | 62.3 mph | calculate → |
| 215/35R18 | 23.93" | +1.59% | -20 mm | 61.0 mph | calculate → |
| 225/35R18 | 24.20" | +2.76% | -10 mm | 61.7 mph | calculate → |
| 235/35R18 | 24.48" | +3.93% | 0 mm | 62.4 mph | calculate → |
| 205/35R18 | 23.65" | +0.42% | -30 mm | 60.3 mph | calculate → |
Plus / minus sizing: 17" and 19" rims
Same overall height on a different rim. Check wheel width and clearance before switching.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 205/40R17 | 23.46" | -0.40% | -30 mm | 59.8 mph | calculate → |
| 215/40R17 | 23.77" | +0.94% | -20 mm | 60.6 mph | calculate → |
| 245/35R17 | 23.75" | +0.85% | +10 mm | 60.5 mph | calculate → |
Try another size against 235/30R18
Questions
What size is 235/30R18 in inches?
235/30R18 is about 23.6" tall and 9.3" wide on a 18-inch rim — roughly a 23.5x9.50R18 in inch sizing.
What does 235/30R18 mean?
235 mm section width, sidewall 30% of the width (2.78"), radial construction, 18-inch rim.
What tire sizes are equivalent to 235/30R18?
On the same 18" rim, within 3% of the diameter: 205/35R18 (+0.42%), 215/35R18 (+1.59%), 225/35R18 (+2.76%), 205/40R18 (+3.84%), 235/35R18 (+3.93%).
How many revolutions per mile does a 235/30R18 tire make?
About 856 revolutions per mile (circumference 74.0").
How these numbers are computed
Diameter = rim + 2 × sidewall, sidewall = width × aspect ÷ 100, circumference = π × diameter, revolutions per mile = 63,360 ÷ circumference. Real tires differ by brand by a few tenths of an inch. Last reviewed October 14, 2026.