235/45R18 vs 245/45R18: Tire Size Comparison
245/45R18 is 0.35 inches taller than 235/45R18 (26.68″ vs 26.33″, +1.35%) and 0.39 inches wider. The difference is within the common ±3% guideline. At an indicated 60 mph you would be doing 60.8 mph.
| 235/45R18 | 245/45R18 | Difference | |
|---|---|---|---|
| Overall diameter | 26.33 in | 26.68 in | +0.35 |
| Section width | 9.25 in | 9.65 in | +0.39 |
| Sidewall height | 4.16 in | 4.34 in | +0.18 |
| Circumference | 82.7 in | 83.8 in | +1.11 |
| Revolutions per mile | 766 | 756 | −10 |
235/45R18 vs 245/45R18 dimensions
| 235/45R18 | 245/45R18 | Difference | |
|---|---|---|---|
| Overall diameter | 26.33 in (669 mm) | 26.68 in (678 mm) | +0.35 in (+1.35%) |
| Section width | 9.25 in | 9.65 in | +0.39 in |
| Sidewall height | 4.16 in | 4.34 in | +0.18 in |
| Wheel diameter | 18 in | 18 in | same wheel |
| Circumference | 82.7 in | 83.8 in | +1.11 in |
| Revolutions per mile | 766 | 756 | -10 |
Nominal dimensions calculated from the size code. Real tires vary slightly by brand, tread depth and inflation.
Speedometer difference with 245/45R18
| Speedometer shows | Actual speed on 245/45R18 | Difference |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 mph |
| 45 mph | 45.6 mph | +0.6 mph |
| 60 mph | 60.8 mph | +0.8 mph |
| 70 mph | 70.9 mph | +0.9 mph |
| 80 mph | 81.1 mph | +1.1 mph |
Assumes your speedometer is accurate on 235/45R18. Because 245/45R18 is taller, you travel slightly faster than indicated and the odometer under-counts: 10,000 miles on the odometer is about 10,135 real miles.
What changes if you switch
- Ride height: up about 0.18 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 245/45R18 instead of 235/45R18?
245/45R18 is +1.35% in overall diameter compared with 235/45R18 (26.68″ vs 26.33″). That is inside the common ±3% guideline, so it is often used as an alternative. Check your vehicle placard, load index, speed rating and clearance before switching.
How much taller is 245/45R18 than 235/45R18?
245/45R18 is 0.35 inches taller overall, which raises ride height by about 0.18 inches. Sidewall height changes from 4.16″ to 4.34″.
How much wider is 245/45R18 than 235/45R18?
Section width goes from 9.25″ (235 mm) to 9.65″ (245 mm), a difference of +0.39 in. Actual width also depends on the rim width it is mounted on.
How does 245/45R18 affect my speedometer?
With 245/45R18 fitted in place of 235/45R18, when the speedometer shows 60 mph you are actually going about 60.8 mph. The odometer will record 10,000 miles when you have driven about 10,135.