17-inch rim · tyre size comparison
205/40 R17 vs 205/45 R17
205/45 R17 is 20.5 mm (0.81 in) taller than 205/40 R17, a +3.44% 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
- +20.5 mm
- +0.81 in · +3.44%
- Indicated 70 mph
- 72.4 mph
- Actual speed on 205/45 R17, if the speedometer was accurate on 205/40 R17.
- Sidewall height
- +10.25 mm
- 82 mm to 92.25 mm.
Dimensions side by side
| Measurement | 205/40 R17 | 205/45 R17 | Difference |
|---|---|---|---|
| Overall diameter | 595.8 mm23.46 in | 616.3 mm24.26 in | +20.5 mm (+3.44%)+0.81 in |
| Section width | 205 mm8.07 in | 205 mm8.07 in | 0 mm0 in |
| Sidewall height | 82 mm3.23 in | 92.25 mm3.63 in | +10.25 mm+0.4 in |
| Circumference | 1,871.76 mm73.69 in | 1,936.16 mm76.23 in | +64.4 mm+2.54 in |
| Rim diameter | 431.8 mm17 in | 431.8 mm17 in | 0 mm0 in |
| Revolutions per mile | 859.8 | 831.2 | -28.6 |
| Revolutions per km | 534.26 | 516.49 | -17.77 |
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 205/45 R17
If the speedometer was accurate on 205/40 R17, fitting 205/45 R17 means the car is travelling 3.44% faster than it shows, and the odometer under-records distance by about the same amount.
| Speedometer shows | Actual on 205/45 R17 | Difference |
|---|---|---|
| 30 mph | 31.03 mph | +1.03 mph |
| 50 mph | 51.72 mph | +1.72 mph |
| 60 mph | 62.06 mph | +2.06 mph |
| 70 mph | 72.41 mph | +2.41 mph |
| 50 km/h | 51.72 km/h | +1.72 km/h |
| 100 km/h | 103.44 km/h | +3.44 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 taller tyre uses up some of that margin. Calibration varies by car; these figures are the tyre-size effect only.
What changes from 205/40 R17 to 205/45 R17
Wheels
Both fit 17-inch wheels. Our rim-width starting estimate is 6.5 to 7.5 inches for 205/40 R17 and 6.5 to 7.5 inches for 205/45 R17, so a 6.5 to 7.5-inch wheel sits in both ranges. The exact tyre's approved rim range takes priority.
Sidewall and ride comfort
205/45 R17 has 10.25 mm more sidewall (92.25 vs 82 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 205 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 +10.3 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 -3.33%: 3,000 rpm at a given road speed becomes about 2,900 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 3.4% diameter gap, never mix 205/40 R17 and 205/45 R17 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.
205/40 R17
- Ford Fiesta ST Mk7 (2013–2017)Factory trim
- Mazda MX-5 Miata NB (1998–2005)Factory trim
- Volkswagen Golf / GTI / VR6 Mk3 (1991–1997)Popular setup
205/45 R17
- Ford Fiesta ST Mk8 (2018–2022)Factory and popular setup
- Honda Civic Type R EP3 (2001–2005)Factory trim
- Mazda MX-5 Miata ND (2015–present)Factory trim
- MINI Cooper S / JCW R53 (2002–2006)Factory and popular setup
- MINI Cooper S / John Cooper Works F56 (2014–2024)Factory trim
- MINI Cooper S / John Cooper Works R56 (2006–2013)Factory and popular setup
- Toyota GR Yaris GXPA16 (2020–present)Factory trim
More comparisons
205/40 R17 compared
205/45 R17 compared
Questions
Can I use 205/45 R17 instead of 205/40 R17?
Both fit 17-inch wheels. The diameter difference is +3.44%, 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 205/45 R17 than 205/40 R17?
Overall diameter is 20.5 mm (0.81 in) larger: 616.3 vs 595.8 mm. Section width is the same, and the sidewall is 10.25 mm taller. These are nominal figures; real tyres vary by model and rim width.
Will 205/45 R17 change my speedometer reading?
Yes, by 3.44%. If the speedometer was accurate on 205/40 R17, an indicated 60 mph would be about 62.1 mph on 205/45 R17, and an indicated 100 km/h about 103.4 km/h. You would be going faster than the speedometer shows.
Which is better, 205/40 R17 or 205/45 R17?
Neither in general. 205/45 R17 has the taller sidewall, which usually rides more comfortably; 205/40 R17 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.