TreadSize

Computed tire swap

245/60R15 vs 255/60R15

Diameter +1.78% · Speedo at 60 mph reads 61.1 mph actual · Ground clearance +6.0 mm

Methodology: this page compares ETRTO-derived tire dimensions, circumference, speedometer error, and the TreadSize 3% diameter rule. Last reviewed June 2026 by the TreadSize editorial team.

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.

Physical fitment still needs inspection: this comparison checks diameter, circumference, speedometer error, and ground clearance. It does not verify fender clearance, brake clearance, rim width compatibility, load index, or speed rating.

Visual diameter overlay

245/60R15 width245 mm
255/60R15 width255 mm

Fitment risk beyond diameter

Low fitment risk

  • Diameter is within the common ±3% first-gate tolerance.
  • New tire is 10 mm wider; check inner strut clearance, fender clearance, and wheel offset.
  • Always compare against the vehicle door-placard OE size, load index, and speed rating before buying.

Speedometer effect

When the vehicle's speedometer (calibrated to 245/60R15) reads 60 mph, the actual speed with 255/60R15 mounted is:

Indicated
60 mph
Actual
61.1 mph

Speedometer error: +1.78%  ·  Odometer reads high by 1.78%

Full comparison

Measurement 245/60R15 255/60R15 Delta
Overall diameter 26.57" 27.05" +1.78%
Section width 245 mm 255 mm +10 mm
Sidewall height 147 mm 153 mm +6.00 mm
Rim diameter 15" 15" +0"
Circumference 2121 mm 2158 mm +38 mm
Revs / mile 759 746 -13
Ground clearance change +6.0 mm

Questions about this swap

What is the diameter difference between 245/60R15 and 255/60R15?

255/60R15 is 1.78% larger in overall diameter than 245/60R15 — a difference of 12.0 mm (0.47 inches).

How does 255/60R15 affect the speedometer if the car was calibrated for 245/60R15?

When the speedometer reads 60 mph (calibrated for 245/60R15), the actual speed with 255/60R15 is 61.1 mph — an error of +1.78%.

Is it safe to replace 245/60R15 with 255/60R15?

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.