265/65R18 vs 275/65R18
Switching from 265/65R18 to 275/65R18 changes the overall diameter by +13.0 mm (+1.6%) — inside the commonly used ±3% guideline. Every figure below is calculated from the two size codes with the standard formulas.
| Measurement | 265/65R18 | 275/65R18 | Difference |
|---|---|---|---|
| Overall diameter | 801.7 mm | 814.7 mm | +13.0 mm (+1.6%) |
| Overall diameter | 31.56 in | 32.07 in | +0.51 in |
| Tire width | 265 mm (10.43 in) | 275 mm (10.83 in) | +10 mm |
| Sidewall height | 172.3 mm (6.78 in) | 178.8 mm (7.04 in) | +6.5 mm |
| Wheel (rim) diameter | 18.0 in | 18.0 in | 0.0 in |
| Circumference | 2519 mm | 2559 mm | +41 mm |
| Revolutions per mile | 2007 | 1975 | -32 |
| Revolutions per km | 397 | 391 | -6 |
Speedometer error
Calibrated for 265/65R18, the speedometer under-reads or over-reads once 275/65R18 is fitted. This is your real speed at each indicated speed:
| Speedometer shows | Actual speed on 275/65R18 | Error |
|---|---|---|
| 20 mph | 20.3 mph | +0.3 mph |
| 40 mph | 40.6 mph | +0.6 mph |
| 60 mph | 61.0 mph | +1.0 mph |
| 80 mph | 81.3 mph | +1.3 mph |
| 100 mph | 101.6 mph | +1.6 mph |
How these two sizes are worked out
265/65R18 breaks down as a 265 mm tread width with a sidewall of 65% of that width (172.3 mm) on a 18.0-inch wheel, giving an overall diameter of 801.7 mm (31.56 in). 275/65R18 works out to 814.7 mm (32.07 in) the same way. The standard formulas are the same ones used on the tire size calculator page: diameter = rim × 25.4 + 2 × sidewall, circumference = π × diameter, revolutions per mile = 63,360 ÷ diameter in inches.
Nominal sizes vary slightly between brands and models, and tread wear shrinks a tire over its life. These figures follow the size codes exactly; your vehicle manual or a professional tire shop is the authority for what fits your vehicle.
More comparisons
Frequently asked questions
Can I replace 265/65R18 tires with 275/65R18?
The diameter change is +1.6%, which is within the commonly used ±3% guideline. Diameter is only one part of fitment — wheel width range, load index, speed rating and physical clearance all have to check out too, so confirm with your vehicle manual or a professional tire shop before buying.
Will 275/65R18 make my speedometer read wrong?
Yes, by the diameter ratio. When the dial shows 60 mph you are really doing 61.0 mph on 275/65R18. The full table above covers 20 to 100 mph.
Which tire is taller, 265/65R18 or 275/65R18?
275/65R18 is taller — 814.7 mm against 801.7 mm overall diameter, a difference of 13.0 mm.