285/65R18 vs 275/70R18
275/70R18 is +0.57 in (+1.8%) in diameter and 0.39 in narrower than 285/65R18.
Size comparison285/65R18
| Dimension | 285/65R18 | 275/70R18 | Difference |
|---|---|---|---|
| Overall diameter UN R30 §6.1.2.1 | 32.59 in 827.7 mm | 33.16 in 842.2 mm | +0.57 in |
| Section width UN R30 §6.1.2.1 | 11.22 in 285.0 mm | 10.83 in 275.0 mm | −0.39 in |
| Sidewall height UN R30 §6.1.2.1 | 7.29 in 185.3 mm | 7.58 in 192.5 mm | +0.29 in |
| Rim diameter Marked on the tire | 18 in | 18 in | 0 in |
| Circumference From diameter | 102.37 in | 104.17 in | +1.80 in |
| Revolutions per mile From diameter | 619 | 608 | −11 |
| Allowed real diameter UN R30 §6.1.5 | 32.15–33.17 in | 32.70–33.76 in |
Nominal, not measuredReal tires vary by brand and load range.
- 285/65R18 32.59 in
- 275/70R18 33.16 in
Speedometer change
mph
If your speedometer is calibrated for 285/65R18 and you fit 275/70R18, the tire is +1.8% in diameter, so your true speed differs from the reading as shown below.
| Reading | True speed | Difference |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 mph |
| 45 mph | 45.8 mph | +0.8 mph |
| 55 mph | 56.0 mph | +1.0 mph |
| 60 mph | 61.1 mph | +1.1 mph |
| 70 mph | 71.2 mph | +1.2 mph |
| 80 mph | 81.4 mph | +1.4 mph |
What changes
- Ride height changes by +0.29 in at the axle (half the diameter change).
- 275/70R18 is the taller tire.
- Revolutions per mile change by -11.
Nominal dimensions from the official sizing formula (sources below). This comparison doesn't check fit: wheel width, offset and clearance decide that. See changing tire size.
Each size
Printed from https://tiresizecalc.net/compare/285-65r18-vs-275-70r18/. Figures as published on 2026-11-01. The full working and the official sources are on that page.
Sources
- UN Regulation No. 30 - Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and their trailers (Revision 3). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.29/Rev.3. 2007-03-29. Para 2.15 and 6.1.2.1: aspect ratio and outer diameter, D = d + 2H. Retrieved 2026-11-01.
- UN Regulation No. 54 - Uniform provisions concerning the approval of pneumatic tyres for commercial vehicles and their trailers (Revision 2). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.53/Rev.2. 2004-04-16. Para 6.1.2.1: the same formula for light truck tires. Retrieved 2026-11-01.
- UN Regulation No. 30 - Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and their trailers (Revision 3). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.29/Rev.3. 2007-03-29. Para 6.1.5: allowed outer diameter, Dmin = d + 2H x 0.97, Dmax = d + 2H x 1.04. Retrieved 2026-11-01.
- Computed by tiresizecalc.net from the cited formula. Sri Murugan Systems. Circumference = pi x diameter; revolutions per mile = 63,360 / circumference; 1 in = 25.4 mm exactly. Retrieved 2026-11-01.
- Computed by tiresizecalc.net from the cited formula. Sri Murugan Systems. Speedometer: true speed = indicated speed x new diameter / old diameter. Retrieved 2026-11-01.
Last reviewed 2026-11-01. The full source list, with dates and file checksums, is in How the numbers are calculated. To report an error, email contactus@tiresizecalc.net.