18-inch rim · tyre size comparison
255/70 R18 vs 275/65 R18
275/65 R18 and 255/70 R18 are effectively the same height: 275/65 R18 is 0.5 mm taller in overall diameter, a +0.06% difference. That is well inside the ±3% limit commonly used to screen a tire size change; it is a nominal calculation, not a fitment approval.
- Diameter difference
- +0.5 mm
- +0.02 in · +0.06%
- Indicated 70 mph
- 70 mph
- Actual speed on 275/65 R18, if the speedometer was accurate on 255/70 R18.
- Sidewall height
- +0.25 mm
- 178.5 mm to 178.75 mm.
Dimensions side by side
| Measurement | 255/70 R18 | 275/65 R18 | Difference |
|---|---|---|---|
| Overall diameter | 814.2 mm32.06 in | 814.7 mm32.07 in | +0.5 mm (+0.06%)+0.02 in |
| Section width | 255 mm10.04 in | 275 mm10.83 in | +20 mm+0.79 in |
| Sidewall height | 178.5 mm7.03 in | 178.75 mm7.04 in | +0.25 mm+0.01 in |
| Circumference | 2,557.88 mm100.7 in | 2,559.46 mm100.77 in | +1.57 mm+0.06 in |
| Rim diameter | 457.2 mm18 in | 457.2 mm18 in | 0 mm0 in |
| Revolutions per mile | 629.17 | 628.78 | -0.39 |
| Revolutions per km | 390.95 | 390.71 | -0.24 |
Calculated from the nominal size codes, without load or tread wear. Real tyres vary by model, rim width and pressure, so the exact tyre's published dimensions take priority.
Speedometer with 275/65 R18
If the speedometer was accurate on 255/70 R18, fitting 275/65 R18 means the car is travelling 0.06% faster than it shows, and the odometer under-records distance by about the same amount.
| Speedometer shows | Actual on 275/65 R18 | Difference |
|---|---|---|
| 30 mph | 30.02 mph | +0.02 mph |
| 50 mph | 50.03 mph | +0.03 mph |
| 60 mph | 60.04 mph | +0.04 mph |
| 70 mph | 70.04 mph | +0.04 mph |
| 50 km/h | 50.03 km/h | +0.03 km/h |
| 100 km/h | 100.06 km/h | +0.06 km/h |
UN ECE Regulation 39, used in the UK and EU, does not allow a speedometer to show less than the true speed, so many read slightly high from the factory. A taller tyre uses up some of that margin. Calibration varies by car; these figures are the tyre-size effect only.
What changes from 255/70 R18 to 275/65 R18
Wheels
Both fit 18-inch wheels. Our rim-width starting estimate is 7 to 8 inches for 255/70 R18 and 7.5 to 8.5 inches for 275/65 R18, so a 7.5 to 8-inch wheel sits in both ranges. The exact tyre's approved rim range takes priority.
Sidewall and ride comfort
Sidewall height differs by only 0.25 mm (178.5 vs 178.75 mm), so ride comfort and steering feel will depend more on the tyre model and pressures than on the size.
Contact width
275/65 R18 is 20 mm wider in nominal section width (7.8%). A wider tyre usually puts a wider, shorter contact patch on the road, which can help dry grip, but it may follow ruts more, clear standing water less readily and add some rolling resistance.
Wheel well clearance
Ride height is effectively unchanged. On the same wheel width and offset, each sidewall moves about 10 mm further out towards the arch lip and further in towards the suspension. Check clearance at full steering lock and full suspension compression, especially on a lowered car.
Gearing
Effective gearing changes by -0.06%, too little to notice from the driver's seat.
ABS, stability control and AWD
These systems compare wheel speeds. Fit the same size on both ends of an axle, and follow the car maker's rolling-circumference limits, which can be much tighter than 3%.
General tendencies from the nominal numbers, not a test of any tyre. Load index, speed rating, tyre construction and the car's approved sizes matter more than these rules of thumb.
Explained in our guides
- Plus-sizing wheels: tyre diameter and speedometer changesWork through a 17 to 18 inch wheel change, compare tyre diameters and speedometer effects, and understand why a 3% rule cannot approve fitment.
- Staggered vs square wheels: tyres, rotation and AWDCompare square and staggered wheel setups, calculate front-to-rear tyre diameter, and understand rotation limits and all-wheel-drive requirements.
- How to read a tyre size, load index and sidewall markingsDecode tyre width, aspect ratio, rim diameter, load and speed markings, then calculate sidewall height and diameter using a 225/45 R17 example.
Cars in our guides using these sizes
Factory trims and popular community setups from our fitment guides. A popular setup is not a factory approval; each guide explains its trims, axles and clearance limits.
255/70 R18
- Ford Bronco 6th gen, non-Raptor (2021–present)Factory trim
- Jeep Wrangler JK (2007–2018)Factory trim
- Jeep Wrangler JL (2018–present)Factory trim
- Land Rover Defender L663, non-OCTA (2020–present)Factory trim
275/65 R18
- Chevrolet Silverado 1500 4th gen / T1 (2019–present)Factory trim
- Ford F-150 12th generation (2009–2014)Factory and popular setup
- Ford F-150 13th gen (2015–2020)Factory trim
- Ford F-150 14th gen (2021–present)Factory trim
- Ram 1500 DT / 5th gen (2019–present)Factory trim
More comparisons
255/70 R18 compared
275/65 R18 compared
Questions
Can I use 275/65 R18 instead of 255/70 R18?
Both fit 18-inch wheels. The diameter difference is +0.06%, well inside the ±3% screening limit. That does not approve fitment: check the car maker's approved sizes, load index, speed rating, rim width and clearance first.
How much bigger is 275/65 R18 than 255/70 R18?
Overall diameter is 0.5 mm (0.02 in) larger: 814.7 vs 814.2 mm. Section width is 20 mm wider, and the sidewall is 0.25 mm taller. These are nominal figures; real tyres vary by model and rim width.
Will 275/65 R18 change my speedometer reading?
Yes, by 0.06%. If the speedometer was accurate on 255/70 R18, an indicated 60 mph would be about 60 mph on 275/65 R18, and an indicated 100 km/h about 100.1 km/h. You would be going faster than the speedometer shows.
Which is better, 255/70 R18 or 275/65 R18?
Neither in general. 275/65 R18 is wider, which can help dry grip; the narrower size is usually better in standing water and snow. The size listed for your car's trim, on its placard or in the handbook, is the safe default.
Check the exact tyre
Size codes give nominal dimensions. Before buying, confirm the size is approved for your car and check the exact tyre's load and speed ratings and published dimensions.