225/40R18 Tire Size Specifications
Complete dimensional breakdown in inches and millimeters, approved wheel rim widths, vehicle fitments, speedometer error tables, and safe plus-sizing alternatives.
225/40R18 Technical Dimension Table
Standardized measurements computed according to ETRTO & ISO 4000-1 passenger and commercial tire design formulas.
| Specification Property | Imperial (Inches / Miles) | Metric (Millimeters / Kilometers) |
|---|---|---|
| Overall Rolling Diameter | 25.09 in | 637.3 mm |
| Section Width (Cross-section) | 8.86 in | 225 mm |
| Sidewall Cushion Height | 3.54 in | 89.9 mm |
| Circumference (Rolling Distance) | 78.81 in | 2001.8 mm |
| Revolutions per Distance | 829 revs/mile | 515 revs/km |
| Wheel Rim Diameter | 18 in | 457.2 mm |
| Approved Rim Width Range | 6.1" – 7.9" | 155 – 201 mm |
| Measuring / Ideal Rim Width | 7.0 in | 178 mm |
| Aspect Ratio (Profile %) | 40% of section width | |
What 225/40R18 Is Typically Used For
A low aspect ratio puts less rubber between rim and road. That sharpens steering response at the cost of ride comfort and rim protection.
To find the size your specific vehicle takes, check the placard on the driver-side door jamb or your owner's manual. Fitment depends on model year, trim, brake caliper clearance, wheel offset and suspension setup, so the correct size for your car is the one the manufacturer specifies.
Safe Alternative Sizes for 225/40R18 (±3% Rule)
These tire sizes stay within 3% of the 25.09" original diameter, keeping speedometer error minimal and preventing ABS/traction control faults.
Popular Comparisons with 225/40R18
Frequently Asked Questions about 225/40R18
What size is 225/40R18 in inches?
The 225/40R18 tire measures approximately 25.09" in overall diameter, 8.86" in section width (tread/sidewall cross-section), and is mounted on a 18" diameter wheel rim.
What rim width is recommended for 225/40R18?
The approved rim width range for 225/40R18 is 6.1" to 7.9" wide, with an ideal measuring rim width of 7.0" for optimal tread contact and even wear.
What are the closest safe alternative sizes for 225/40R18?
The closest safe tire sizes within the industry standard ±3% diameter limit include 225/45R17. These sizes maintain accurate speedometer calibration and clearance.
How many revolutions per mile does 225/40R18 make?
A standard 225/40R18 tire rotates approximately 829 revolutions per mile (515 revs per kilometer) at normal inflation pressure and rolling radius.