305/70R17 vs 285/75R17
285/75R17 is +0.02 in (+0.1%) in diameter and 0.79 in narrower than 305/70R17.
Size comparison305/70R17
| Dimension | 305/70R17 | 285/75R17 | Difference |
|---|---|---|---|
| Overall diameter UN R30 §6.1.2.1 | 33.81 in 858.8 mm | 33.83 in 859.3 mm | +0.02 in |
| Section width UN R30 §6.1.2.1 | 12.01 in 305.0 mm | 11.22 in 285.0 mm | −0.79 in |
| Sidewall height UN R30 §6.1.2.1 | 8.41 in 213.5 mm | 8.42 in 213.8 mm | +0.01 in |
| Rim diameter Marked on the tire | 17 in | 17 in | 0 in |
| Circumference From diameter | 106.22 in | 106.28 in | +0.06 in |
| Revolutions per mile From diameter | 596 | 596 | 0 |
| Allowed real diameter UN R30 §6.1.5 | 33.31–34.48 in | 33.33–34.50 in |
Nominal, not measuredReal tires vary by brand and load range.
- 305/70R17 33.81 in
- 285/75R17 33.83 in
Speedometer change
mph
If your speedometer is calibrated for 305/70R17 and you fit 285/75R17, the tire is +0.1% in diameter, so your true speed differs from the reading as shown below.
| Reading | True speed | Difference |
|---|---|---|
| 30 mph | 30.0 mph | 0.0 mph |
| 45 mph | 45.0 mph | 0.0 mph |
| 55 mph | 55.0 mph | 0.0 mph |
| 60 mph | 60.0 mph | 0.0 mph |
| 70 mph | 70.0 mph | 0.0 mph |
| 80 mph | 80.0 mph | 0.0 mph |
What changes
- Ride height changes by +0.01 in at the axle (half the diameter change).
- 285/75R17 is the taller tire.
- Revolutions per mile change by +0.
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/305-70r17-vs-285-75r17/. 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.