225/40R18 vs 225/45R18: Tire Size Comparison
225/45R18 is 0.89 inches taller than 225/40R18 (25.97″ vs 25.09″, +3.53%) and 0 inches wider. The difference is outside the common ±3% guideline. At an indicated 60 mph you would be doing 62.1 mph.
| 225/40R18 | 225/45R18 | Difference | |
|---|---|---|---|
| Overall diameter | 25.09 in | 25.97 in | +0.89 |
| Section width | 8.86 in | 8.86 in | +0 |
| Sidewall height | 3.54 in | 3.99 in | +0.44 |
| Circumference | 78.8 in | 81.6 in | +2.78 |
| Revolutions per mile | 804 | 777 | −27 |
225/40R18 vs 225/45R18 dimensions
| 225/40R18 | 225/45R18 | Difference | |
|---|---|---|---|
| Overall diameter | 25.09 in (637 mm) | 25.97 in (660 mm) | +0.89 in (+3.53%) |
| Section width | 8.86 in | 8.86 in | +0 in |
| Sidewall height | 3.54 in | 3.99 in | +0.44 in |
| Wheel diameter | 18 in | 18 in | same wheel |
| Circumference | 78.8 in | 81.6 in | +2.78 in |
| Revolutions per mile | 804 | 777 | -27 |
Nominal dimensions calculated from the size code. Real tires vary slightly by brand, tread depth and inflation.
Speedometer difference with 225/45R18
| Speedometer shows | Actual speed on 225/45R18 | Difference |
|---|---|---|
| 30 mph | 31.1 mph | +1.1 mph |
| 45 mph | 46.6 mph | +1.6 mph |
| 60 mph | 62.1 mph | +2.1 mph |
| 70 mph | 72.5 mph | +2.5 mph |
| 80 mph | 82.8 mph | +2.8 mph |
Assumes your speedometer is accurate on 225/40R18. Because 225/45R18 is taller, you travel slightly faster than indicated and the odometer under-counts: 10,000 miles on the odometer is about 10,353 real miles.
What changes if you switch
- Ride height: up about 0.44 in (half the diameter change).
- Wheels: both fit a 18-inch wheel; check the tire's approved rim width range.
- Sidewall: a taller sidewall usually rides softer and resists pothole damage, with a little less steering sharpness.
- Effective gearing: slightly taller, so marginally lower engine rpm at speed and slightly slower acceleration.
- Match the original load index and speed rating or higher, and check for rubbing at full steering lock and full suspension compression.
Related tire size comparisons
Frequently asked questions
Can I use 225/45R18 instead of 225/40R18?
225/45R18 is +3.53% in overall diameter compared with 225/40R18 (25.97″ vs 25.09″). That is outside the common ±3% guideline, so it is a bigger change that may affect the speedometer, ABS and clearance. Check your vehicle placard, load index, speed rating and clearance before switching.
How much taller is 225/45R18 than 225/40R18?
225/45R18 is 0.89 inches taller overall, which raises ride height by about 0.44 inches. Sidewall height changes from 3.54″ to 3.99″.
How much wider is 225/45R18 than 225/40R18?
Section width goes from 8.86″ (225 mm) to 8.86″ (225 mm), a difference of +0 in. Actual width also depends on the rim width it is mounted on.
How does 225/45R18 affect my speedometer?
With 225/45R18 fitted in place of 225/40R18, when the speedometer shows 60 mph you are actually going about 62.1 mph. The odometer will record 10,000 miles when you have driven about 10,353.