19-inch vs 20-inch rims · tyre size comparison
235/65 R19 vs 255/55 R20
255/55 R20 and 235/65 R19 are effectively the same height: 255/55 R20 is 0.4 mm taller in overall diameter, a +0.05% 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
- +0.4 mm
- +0.02 in · +0.05%
- Indicated 70 mph
- 70 mph
- Actual speed on 255/55 R20, if the speedometer was accurate on 235/65 R19.
- Sidewall height
- -12.5 mm
- 152.75 mm to 140.25 mm.
Dimensions side by side
| Measurement | 235/65 R19 | 255/55 R20 | Difference |
|---|---|---|---|
| Overall diameter | 788.1 mm31.03 in | 788.5 mm31.04 in | +0.4 mm (+0.05%)+0.02 in |
| Section width | 235 mm9.25 in | 255 mm10.04 in | +20 mm+0.79 in |
| Sidewall height | 152.75 mm6.01 in | 140.25 mm5.52 in | -12.5 mm-0.49 in |
| Circumference | 2,475.89 mm97.48 in | 2,477.15 mm97.53 in | +1.26 mm+0.05 in |
| Rim diameter | 482.6 mm19 in | 508 mm20 in | +25.4 mm+1 in |
| Revolutions per mile | 650.01 | 649.68 | -0.33 |
| Revolutions per km | 403.9 | 403.69 | -0.2 |
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 255/55 R20
If the speedometer was accurate on 235/65 R19, fitting 255/55 R20 means the car is travelling 0.05% faster than it shows, and the odometer under-records distance by about the same amount.
| Speedometer shows | Actual on 255/55 R20 | Difference |
|---|---|---|
| 30 mph | 30.02 mph | +0.02 mph |
| 50 mph | 50.03 mph | +0.03 mph |
| 60 mph | 60.03 mph | +0.03 mph |
| 70 mph | 70.04 mph | +0.04 mph |
| 50 km/h | 50.03 km/h | +0.03 km/h |
| 100 km/h | 100.05 km/h | +0.05 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 235/65 R19 to 255/55 R20
Wheels
These sizes need different wheels: 19-inch for 235/65 R19 and 20-inch for 255/55 R20. The larger wheel usually weighs a little more; the smaller one must still clear the brake calipers. Check rim width, offset and load rating for whichever wheel you fit.
Sidewall and ride comfort
255/55 R20 has 12.5 mm less sidewall (140.25 vs 152.75 mm). A shorter sidewall usually sharpens steering response, but rides a little firmer and leaves the rim more exposed to potholes and kerbs.
Contact width
255/55 R20 is 20 mm wider in nominal section width (8.5%). 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 -0.05%, 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.
235/65 R19
- Land Rover Range Rover L405 (2012–2021)Factory trim
- Land Rover Range Rover Sport L494 (2013–2022)Factory trim
255/55 R20
- Land Rover Range Rover L405 (2012–2021)Factory trim
- Land Rover Range Rover Sport L494 (2013–2022)Factory trim
More comparisons
Questions
Can I use 255/55 R20 instead of 235/65 R19?
Only on 20-inch wheels, not the 19-inch wheels that take 235/65 R19. The diameter difference is +0.05%, 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 255/55 R20 than 235/65 R19?
Overall diameter is 0.4 mm (0.02 in) larger: 788.5 vs 788.1 mm. Section width is 20 mm wider, and the sidewall is 12.5 mm shorter. These are nominal figures; real tyres vary by model and rim width.
Will 255/55 R20 change my speedometer reading?
Yes, by 0.05%. If the speedometer was accurate on 235/65 R19, an indicated 60 mph would be about 60 mph on 255/55 R20, and an indicated 100 km/h about 100.1 km/h. You would be going faster than the speedometer shows.
Which is better, 235/65 R19 or 255/55 R20?
Neither in general. 235/65 R19 has the taller sidewall, which usually rides more comfortably; 255/55 R20 usually steers more sharply. 255/55 R20 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.