33x12.50R17 vs 315/70R17
315/70R17 is +1.36″ in overall diameter and −3 mm in section width against 33x12.50R17 — a diameter change of +4.13%, which breaks the ±3% substitution rule. An indicated 60 mph would really be 62.5 mph.
Every dimension
| Dimension | 33x12.50R17 → 315/70R17 | Change |
|---|---|---|
| Overall diameter | 33.00″ → 34.36″ | +1.36″ (+4.13%) |
| Section width | 318 mm → 315 mm | −3 mm (−0.79%) |
| Sidewall height | 203.2 mm → 220.5 mm | +17.3 mm |
| Rolling circumference | 103.67″ → 107.95″ | +4.28″ |
| Revolutions per mile | 611.2 → 586.9 | −24.2 |
| Axle height / clearance | 16.50″ → 17.18″ | +0.68″ |
Which is taller, 33x12.50R17 or 315/70R17?
315/70R17 is the taller of the two, at 34.36″ against 33.00″. The gap is 1.36 inches, or 34.6 mm.
One of these is a flotation size, which states its overall diameter on the sidewall, while the metric size only implies one — so the comparison is between a stated height and a derived one. 33x12.50R17 is 317.5 mm wide with a 203.2 mm sidewall on a 17″ wheel; 315/70R17 is 315 mm wide with a 220.5 mm sidewall on a 17″ wheel.
What the speedometer will read
| Speedometer reads | Actual speed | Error |
|---|---|---|
| 25 mph | 26.0 mph | +1.0 mph |
| 40 mph | 41.7 mph | +1.7 mph |
| 55 mph | 57.3 mph | +2.3 mph |
| 60 mph | 62.5 mph | +2.5 mph |
| 70 mph | 72.9 mph | +2.9 mph |
| 80 mph | 83.3 mph | +3.3 mph |
Fitting 315/70R17 in place of 33x12.50R17 multiplies every speed and distance reading by 1.04128. Over 10,000 indicated miles the odometer is out by +413 miles.
Effective gearing moves by the same proportion. A vehicle with 3.73 axles running 33x12.50R17 would need 3.88 to keep the same engine speed on 315/70R17. Work it out for your own axle ratio.
Full specification of each size
33x12.50R17
| Dimension | Metric | Imperial |
|---|---|---|
| Section width | 317.5 mm | 12.50″ |
| Sidewall height | 203.2 mm | 8.00″ |
| Wheel diameter | 431.8 mm | 17.0″ |
| Overall diameter | 838.2 mm | 33.00″ |
| Rolling circumference | 2,633.3 mm | 103.67″ |
| Revolutions per mile | 379.8 / km | 611.2 / mile |
| Measuring rim (estimate) | 254 mm | 10″ |
315/70R17
| Dimension | Metric | Imperial |
|---|---|---|
| Section width | 315.0 mm | 12.40″ |
| Sidewall height | 220.5 mm | 8.68″ |
| Wheel diameter | 431.8 mm | 17.0″ |
| Overall diameter | 872.8 mm | 34.36″ |
| Rolling circumference | 2,742.0 mm | 107.95″ |
| Revolutions per mile | 364.7 / km | 586.9 / mile |
| Measuring rim (estimate) | 241 mm | 9.5″ |
Rim widths differ too: 33x12.50R17 is designed for 9″–11″ and 315/70R17 for 9″–10.5″. Their measuring rims differ, so the same wheel will not be ideal for both.
Can you swap one for the other?
Outside the ±3% rule
The diameter difference of +4.13% exceeds the ±3% rule of thumb. Expect a speedometer error of about 2.5 mph at an indicated 60, and an odometer that is off by the same proportion. It is a common swap even so — it just needs the instruments recalibrated to stay honest.
Neither figure says anything about physical fitment. Whether 315/70R17 clears the strut, the fender liner and the steering stops depends on wheel offset and suspension geometry that a size code does not encode. For maintenance rather than sizing, Car Basics covers tire care.
33x12.50R17 vs 315/70R17: common questions
- Is 315/70R17 bigger than 33x12.50R17?
- 315/70R17 is 1.36 inches taller and 3 mm narrower. In overall diameter that is +4.13%, which exceeds the ±3% rule of thumb for a substitution.
- How much will 315/70R17 throw off my speedometer?
- Every reading scales by 1.04128. An indicated 60 mph becomes 62.5 mph, and every 100 miles on the odometer is really 104.1 miles.
- How much does 315/70R17 change ground clearance over 33x12.50R17?
- The axle centerline moves by 0.68 inches — half the diameter change, because half the extra height sits below the hub and half above it.
- Will 315/70R17 fit where 33x12.50R17 fits?
- Nothing derived from the size code can answer that. Clearance depends on wheel offset, suspension travel and body dimensions that no tire size contains. This page tells you exactly what changes dimensionally, which is the part that can be calculated.
Related comparisons
Other tire maths on this site
- tire size calculatorRead any tire size code and get overall diameter, sidewall height, circumference and revolutions per mile, with the arithmetic shown.
- tire size comparisonPut two sizes side by side and see the difference in diameter, width, sidewall, ground clearance and speedometer reading.
- tire size chartEvery common size sorted by wheel diameter, with overall diameter in inches and millimeters and revolutions per mile.
- tire diameter calculatorOverall diameter, radius and rolling circumference from the size code, and the reverse — the sizes that produce a diameter you want.
- speedometer error calculatorHow far out your speedometer and odometer read after a tire size change, at any indicated speed.
- plus sizing calculatorLarger wheel, same rolling diameter. Plus one and plus two candidates ranked by how close they hold the original diameter.
- gear ratio calculatorThe axle ratio that restores stock engine rpm after a tire diameter change, plus cruising rpm at any speed.
- metric to inch tire conversionConvert a metric size such as 285/70R17 to its inch equivalent, and an inch size such as 33x12.50R17 back to metric.
- rim width rangeThe rim widths a size is designed to mount on, and how section width changes as the rim gets wider.
- tire size meaningWhat every character in 265/70R17 stands for, digit by digit, including the load index and speed rating.