21-inch vs 22-inch rims · tyre size comparison
285/30 R21 vs 285/25 R22
285/25 R22 is 3.1 mm (0.12 in) shorter than 285/30 R21, a -0.44% difference in overall diameter. 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
- -3.1 mm
- -0.12 in · -0.44%
- Indicated 70 mph
- 69.7 mph
- Actual speed on 285/25 R22, if the speedometer was accurate on 285/30 R21.
- Sidewall height
- -14.25 mm
- 85.5 mm to 71.25 mm.
Dimensions side by side
| Measurement | 285/30 R21 | 285/25 R22 | Difference |
|---|---|---|---|
| Overall diameter | 704.4 mm27.73 in | 701.3 mm27.61 in | -3.1 mm (-0.44%)-0.12 in |
| Section width | 285 mm11.22 in | 285 mm11.22 in | 0 mm0 in |
| Sidewall height | 85.5 mm3.37 in | 71.25 mm2.81 in | -14.25 mm-0.56 in |
| Circumference | 2,212.94 mm87.12 in | 2,203.2 mm86.74 in | -9.74 mm-0.38 in |
| Rim diameter | 533.4 mm21 in | 558.8 mm22 in | +25.4 mm+1 in |
| Revolutions per mile | 727.24 | 730.46 | +3.21 |
| Revolutions per km | 451.89 | 453.89 | +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 285/25 R22
If the speedometer was accurate on 285/30 R21, fitting 285/25 R22 means the car is travelling 0.44% slower than it shows, and the odometer over-records distance by about the same amount.
| Speedometer shows | Actual on 285/25 R22 | Difference |
|---|---|---|
| 30 mph | 29.87 mph | -0.13 mph |
| 50 mph | 49.78 mph | -0.22 mph |
| 60 mph | 59.74 mph | -0.26 mph |
| 70 mph | 69.69 mph | -0.31 mph |
| 50 km/h | 49.78 km/h | -0.22 km/h |
| 100 km/h | 99.56 km/h | -0.44 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 shorter tyre adds to it. Calibration varies by car; these figures are the tyre-size effect only.
What changes from 285/30 R21 to 285/25 R22
Wheels
These sizes need different wheels: 21-inch for 285/30 R21 and 22-inch for 285/25 R22. 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
285/25 R22 has 14.25 mm less sidewall (71.25 vs 85.5 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
Both are 285 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 -1.6 mm, and the top of the tyre moves the same distance away from the arch. On the same wheel, the sidewalls stay in roughly the same place side to side. A smaller tyre rarely creates new rubbing.
Gearing
Effective gearing changes by +0.44%, 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.
285/30 R21
- Audi RS6 Avant C7 (2013–2018)Factory and popular setup
285/25 R22
- Audi RS6 Avant C7 (2013–2018)Popular setup
More comparisons
285/30 R21 compared
Questions
Can I use 285/25 R22 instead of 285/30 R21?
Only on 22-inch wheels, not the 21-inch wheels that take 285/30 R21. The diameter difference is -0.44%, 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 285/25 R22 than 285/30 R21?
Overall diameter is 3.1 mm (0.12 in) smaller: 701.3 vs 704.4 mm. Section width is the same, and the sidewall is 14.25 mm shorter. These are nominal figures; real tyres vary by model and rim width.
Will 285/25 R22 change my speedometer reading?
Yes, by 0.44%. If the speedometer was accurate on 285/30 R21, an indicated 60 mph would be about 59.7 mph on 285/25 R22, and an indicated 100 km/h about 99.6 km/h. You would be going slower than the speedometer shows.
Which is better, 285/30 R21 or 285/25 R22?
Neither in general. 285/30 R21 has the taller sidewall, which usually rides more comfortably; 285/25 R22 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.