265/65R17 vs 275/55R18
Diameter -2.14% · Speedo at 60 mph reads 58.7 mph actual · Ground clearance -8.3 mm
Generally safe — within the 3% tolerance
The diameter difference is ≤3%, which is the widely-accepted fitment tolerance for speedometer accuracy and ABS/traction-control calibration. Verify clearance and load rating with a tire professional before installing.
Speedometer effect
When the vehicle's speedometer (calibrated to 265/65R17) reads 60 mph, the actual speed with 275/55R18 mounted is:
Speedometer error: -2.13% · Odometer reads low by 2.13%
Full comparison
| Measurement | 265/65R17 | 275/55R18 | Delta |
|---|---|---|---|
| Overall diameter | 30.56" | 29.91" | -2.14% |
| Section width | 265 mm | 275 mm | +10 mm |
| Sidewall height | 172.25 mm | 151.25 mm | -21.00 mm |
| Rim diameter | 17" | 18" | +1" |
| Circumference | 2439 mm | 2387 mm | -52 mm |
| Revs / mile | 660 | 674 | 14 |
| Ground clearance change | -8.3 mm | ||
Questions about this swap
What is the diameter difference between 265/65R17 and 275/55R18?
275/55R18 is 2.14% smaller in overall diameter than 265/65R17 — a difference of 16.6 mm (0.65 inches).
How does 275/55R18 affect the speedometer if the car was calibrated for 265/65R17?
When the speedometer reads 60 mph (calibrated for 265/65R17), the actual speed with 275/55R18 is 58.7 mph — an error of -2.13%.
Is it safe to replace 265/65R17 with 275/55R18?
Generally safe — within the 3% tolerance. The diameter difference is ≤3%, which is the widely-accepted fitment tolerance for speedometer accuracy and ABS/traction-control calibration. Verify clearance and load rating with a tire professional before installing.
All calculations use standard ETRTO formulas. Confirm fitment with a qualified tire professional and your vehicle's door-placard before purchasing.