18-inch rim · tyre size comparison
275/35 R18 vs 275/40 R18
275/40 R18 is 27.5 mm (1.08 in) taller than 275/35 R18, a +4.23% difference in overall diameter. That is 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
- +27.5 mm
- +1.08 in · +4.23%
- Indicated 70 mph
- 73 mph
- Actual speed on 275/40 R18, if the speedometer was accurate on 275/35 R18.
- Sidewall height
- +13.75 mm
- 96.25 mm to 110 mm.
Dimensions side by side
| Measurement | 275/35 R18 | 275/40 R18 | Difference |
|---|---|---|---|
| Overall diameter | 649.7 mm25.58 in | 677.2 mm26.66 in | +27.5 mm (+4.23%)+1.08 in |
| Section width | 275 mm10.83 in | 275 mm10.83 in | 0 mm0 in |
| Sidewall height | 96.25 mm3.79 in | 110 mm4.33 in | +13.75 mm+0.54 in |
| Circumference | 2,041.09 mm80.36 in | 2,127.49 mm83.76 in | +86.39 mm+3.4 in |
| Rim diameter | 457.2 mm18 in | 457.2 mm18 in | 0 mm0 in |
| Revolutions per mile | 788.47 | 756.45 | -32.02 |
| Revolutions per km | 489.93 | 470.04 | -19.9 |
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 275/40 R18
If the speedometer was accurate on 275/35 R18, fitting 275/40 R18 means the car is travelling 4.23% faster than it shows, and the odometer under-records distance by about the same amount.
| Speedometer shows | Actual on 275/40 R18 | Difference |
|---|---|---|
| 30 mph | 31.27 mph | +1.27 mph |
| 50 mph | 52.12 mph | +2.12 mph |
| 60 mph | 62.54 mph | +2.54 mph |
| 70 mph | 72.96 mph | +2.96 mph |
| 50 km/h | 52.12 km/h | +2.12 km/h |
| 100 km/h | 104.23 km/h | +4.23 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 275/35 R18 to 275/40 R18
Wheels
Both fit 18-inch wheels. Our rim-width starting estimate is 8.5 to 9.5 inches for 275/35 R18 and 8.5 to 9.5 inches for 275/40 R18, so a 8.5 to 9.5-inch wheel sits in both ranges. The exact tyre's approved rim range takes priority.
Sidewall and ride comfort
275/40 R18 has 13.75 mm more sidewall (110 vs 96.25 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 275 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 +13.8 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 -4.06%: 3,000 rpm at a given road speed becomes about 2,880 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 4.2% diameter gap, never mix 275/35 R18 and 275/40 R18 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.
275/35 R18
- Audi RS3 8Y (2021–present)Popular setup
- BMW 5 Series / M5 E39 (1995–2003)Factory and popular setup
- BMW 5 Series / M5 E60/E61 (2003–2010)Factory trim
- BMW M2 F87 (2016–2021)Popular setup
- BMW M3 E46 (2000–2006)Popular setup
- BMW M3 E92 (2007–2013)Popular setup
- BMW M3 F80 (2014–2018)Popular setup
- BMW M4 F82 (2014–2020)Popular setup
- Chevrolet Corvette C5 (1997–2004)Popular setup
- Chevrolet Corvette C7 (2014–2019)Popular setup
- Ford Mustang SN95 / New Edge (1994–2004)Popular setup
- Honda Civic Type R FL5 (2023–present)Popular setup
- Mitsubishi Lancer Evolution X CZ4A (2007–2016)Popular setup
- Nissan 370Z Z34 (2009–2020)Popular setup
- Toyota GR Supra A90 / A91 (2019–present)Popular setup
- Toyota Supra A70 (Mk3) (1986–1993)Popular setup
275/40 R18
- BMW 5 Series F10/F11 (2010–2017)Factory trim
- BMW M3 F80 (2014–2018)Factory trim
- BMW M3 G80 (2021–present)Factory trim
- BMW M4 F82 (2014–2020)Factory trim
- BMW M4 G82 (2021–present)Factory trim
- Chevrolet Corvette C5 (1997–2004)Factory trim
- Nissan 350Z Z33 (2002–2009)Popular setup
- Toyota GR Supra A90 / A91 (2019–present)Factory trim
More comparisons
275/40 R18 compared
Questions
Can I use 275/40 R18 instead of 275/35 R18?
Both fit 18-inch wheels. The diameter difference is +4.23%, 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 275/40 R18 than 275/35 R18?
Overall diameter is 27.5 mm (1.08 in) larger: 677.2 vs 649.7 mm. Section width is the same, and the sidewall is 13.75 mm taller. These are nominal figures; real tyres vary by model and rim width.
Will 275/40 R18 change my speedometer reading?
Yes, by 4.23%. If the speedometer was accurate on 275/35 R18, an indicated 60 mph would be about 62.5 mph on 275/40 R18, and an indicated 100 km/h about 104.2 km/h. You would be going faster than the speedometer shows.
Which is better, 275/35 R18 or 275/40 R18?
Neither in general. 275/40 R18 has the taller sidewall, which usually rides more comfortably; 275/35 R18 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.