19-inch rim · tyre size comparison
255/40 R19 vs 255/45 R19
255/45 R19 is 25.5 mm (1 in) taller than 255/40 R19, a +3.71% difference in overall diameter. That is just outside the ±3% limit commonly used to screen a tire size change, so expect a noticeable speedometer error; it is a nominal calculation, not a fitment approval.
- Diameter difference
- +25.5 mm
- +1 in · +3.71%
- Indicated 70 mph
- 72.6 mph
- Actual speed on 255/45 R19, if the speedometer was accurate on 255/40 R19.
- Sidewall height
- +12.75 mm
- 102 mm to 114.75 mm.
Dimensions side by side
| Measurement | 255/40 R19 | 255/45 R19 | Difference |
|---|---|---|---|
| Overall diameter | 686.6 mm27.03 in | 712.1 mm28.04 in | +25.5 mm (+3.71%)+1 in |
| Section width | 255 mm10.04 in | 255 mm10.04 in | 0 mm0 in |
| Sidewall height | 102 mm4.02 in | 114.75 mm4.52 in | +12.75 mm+0.5 in |
| Circumference | 2,157.02 mm84.92 in | 2,237.13 mm88.08 in | +80.11 mm+3.15 in |
| Rim diameter | 482.6 mm19 in | 482.6 mm19 in | 0 mm0 in |
| Revolutions per mile | 746.1 | 719.38 | -26.72 |
| Revolutions per km | 463.6 | 447 | -16.6 |
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 255/45 R19
If the speedometer was accurate on 255/40 R19, fitting 255/45 R19 means the car is travelling 3.71% faster than it shows, and the odometer under-records distance by about the same amount.
| Speedometer shows | Actual on 255/45 R19 | Difference |
|---|---|---|
| 30 mph | 31.11 mph | +1.11 mph |
| 50 mph | 51.86 mph | +1.86 mph |
| 60 mph | 62.23 mph | +2.23 mph |
| 70 mph | 72.6 mph | +2.6 mph |
| 50 km/h | 51.86 km/h | +1.86 km/h |
| 100 km/h | 103.71 km/h | +3.71 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 255/40 R19 to 255/45 R19
Wheels
Both fit 19-inch wheels. Our rim-width starting estimate is 8 to 9 inches for 255/40 R19 and 8 to 9 inches for 255/45 R19, so a 8 to 9-inch wheel sits in both ranges. The exact tyre's approved rim range takes priority.
Sidewall and ride comfort
255/45 R19 has 12.75 mm more sidewall (114.75 vs 102 mm). A taller sidewall usually rides a little softer and gives the rim more protection from potholes and kerbs, at the cost of some steering sharpness.
Contact width
Both are 255 mm in nominal section width, so the tread is about as wide. Contact patch area is set mostly by load and pressure, so grip differences come more from the tyre model than this size change.
Wheel well clearance
Ride height changes by about +12.8 mm, and the top of the tyre moves the same distance closer to the arch. On the same wheel, the sidewalls stay in roughly the same place side to side. Check clearance at full steering lock and full suspension compression, especially on a lowered car.
Gearing
The effective final drive changes by -3.58%: 3,000 rpm at a given road speed becomes about 2,890 rpm. Gearing gets noticeably longer, so cruising revs drop and acceleration in each gear softens.
ABS, stability control and AWD
These systems compare wheel speeds. Fit the same size on both ends of an axle; with a 3.7% diameter gap, never mix 255/40 R19 and 255/45 R19 on an AWD car, 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.
255/40 R19
- BMW 5 Series / M5 E60/E61 (2003–2010)Factory trim
- BMW 5 Series F10/F11 (2010–2017)Popular setup
- Ford Mustang S550 (2015–2023)Factory and popular setup
- Ford Mustang S650 (2024–present)Factory and popular setup
- Infiniti Q50 V37 (2014–2024)Popular setup
- Infiniti Q60 CV37 (2017–2022)Factory and popular setup
- Nissan Z RZ34 (2023–present)Factory and popular setup
255/45 R19
- Tesla Model Y 1st gen, pre-Juniper (2020–2025)Factory and popular setup
More comparisons
255/40 R19 compared
255/45 R19 compared
Questions
Can I use 255/45 R19 instead of 255/40 R19?
Both fit 19-inch wheels. The diameter difference is +3.71%, just outside the ±3% screening limit, so most fitters would treat it as a different size class rather than a direct replacement. 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 255/45 R19 than 255/40 R19?
Overall diameter is 25.5 mm (1 in) larger: 712.1 vs 686.6 mm. Section width is the same, and the sidewall is 12.75 mm taller. These are nominal figures; real tyres vary by model and rim width.
Will 255/45 R19 change my speedometer reading?
Yes, by 3.71%. If the speedometer was accurate on 255/40 R19, an indicated 60 mph would be about 62.2 mph on 255/45 R19, and an indicated 100 km/h about 103.7 km/h. You would be going faster than the speedometer shows.
Which is better, 255/40 R19 or 255/45 R19?
Neither in general. 255/45 R19 has the taller sidewall, which usually rides more comfortably; 255/40 R19 usually steers more sharply. 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.