This is a modification rather than a substitution. Check clearance at full steering lock and full suspension compression, confirm the load rating meets the placard, and expect the speedometer to read low by about 4.1% unless it can be recalibrated for the new size.
Want to try other sizes against these? Open this comparison in the interactive tool.
A step up in height on the same rim
315/70R17 keeps the 17-inch rim but stands 1.36 inches taller than 33X12.50R17. Because the wheel stays the same, this is a tire-only change — the existing wheels carry over provided their width suits the new section.
The extra height splits evenly: 0.68 inches of additional ground clearance at the axle, and 0.68 inches less space above the tire. That second half is where fitment problems appear, and it is the one nobody measures.
Sidewall grows from 8 inches to 8.68, which softens the ride and gives more protection against rim damage on rough surfaces. It also introduces a little more flex under cornering load.
33X12.50R17 and 315/70R17 measured against each other
Both sizes reduced to the same units. The diameter row is the one that drives everything else on this page — ride height, gearing, speedometer accuracy and odometer readings all follow from it.
| Measurement | 33X12.50R17 | 315/70R17 | Difference |
|---|---|---|---|
| Overall diameter | 33" | 34.36" | +1.36" (+4.1%) |
| Section width | 12.5" (318 mm) | 12.4" (315 mm) | −0.1" |
| Sidewall height | 8" | 8.68" | +0.68" |
| Rim diameter | 17" | 17" | +0" |
| Circumference | 103.67" | 107.95" | +4.28" |
| Revolutions per mile | 611 | 587 | −24 |
| Ride height at axle | Baseline | +0.68" | +0.68" |
What the dial shows against how fast you are going
Your speedometer was calibrated to 33X12.50R17, which turns about 611 times per mile. Fit 315/70R17 at about 587 revolutions per mile and the same wheel speed now represents a greater road speed than the instrument assumes. The error is 4.1% at every speed, so it grows in absolute terms the faster you go.
| Speedometer reads | You are actually doing | Difference |
|---|---|---|
| 30 mph | 31.2 mph | +1.2 mph |
| 45 mph | 46.9 mph | +1.9 mph |
| 60 mph | 62.5 mph | +2.5 mph |
| 75 mph | 78.1 mph | +3.1 mph |
Over distance the same proportion applies to the odometer. Every indicated 1,000 miles on 315/70R17 is really about 1041 miles covered — worth knowing on a leased vehicle, where recorded mileage and real mileage drift apart.
What this particular change asks you to check
- Section width drops by 0.1 inches, which gains inboard clearance but reduces contact patch.
- Overall height grows by 1.36 inches, of which 0.68 inches goes upward into the arch — check at full lock and full compression.
- Both sizes use a 17-inch rim, so the existing wheels carry over if their width suits the new section.
- Speedometer error of 4.1% — check whether your vehicle supports recalibrating for a new tire size.
- Confirm the load index on 315/70R17meets or exceeds the figure on the vehicle's tire placard, particularly if the vehicle tows or carries load.
- On all-wheel-drive and four-wheel-drive vehicles, change all four together — mismatched rolling circumferences load the differentials and transfer case continuously.
33X12.50R17 vs 315/70R17 FAQ
Is 315/70R17 bigger than 33X12.50R17?+
315/70R17 measures 34.36 inches in overall diameter against 33 inches for 33X12.50R17. That makes it 1.36 inches taller, a change of +4.1%. It is also 0.1 inches narrower in section width.
Will 315/70R17 fit in place of 33X12.50R17?+
The diameter change is +4.1%, which is outside the 3% envelope usually treated as a routine substitution. Treat this as a modification: verify clearance at full steering lock and full suspension compression, confirm the load rating meets the vehicle placard, and expect the speedometer to read incorrectly unless it can be recalibrated.
How much lift does 315/70R17 give over 33X12.50R17?+
0.68 inches at the axle — half the diameter difference. The other half of the change goes upward into the wheel arch, which is where fitment problems usually appear.
How far off will my speedometer be?+
The speedometer will read low by about 4.1%. At an indicated 60 mph you would actually be travelling about 62.5 mph, and every indicated 1,000 miles would really be about 1041.
Do I need to regear for 315/70R17?+
A +4.1% change shifts the effective gearing noticeably. To restore the original engine speed you would multiply the current axle ratio by 1.041. Whether that is worth doing depends on how the vehicle is used — towing and heavily loaded driving make the case sooner than commuting does.
What is the revolutions-per-mile difference?+
33X12.50R17 turns about 611 times per mile and 315/70R17 about 587 — a difference of −24 revolutions. That figure is what the speedometer and odometer are calibrated against, which is why both readings shift.
These are nominal figures. Every number above is calculated from the marked size. Real tires vary from nominal by a few millimetres between manufacturers, and by more as tread wears or pressure changes. Use this to plan and to check a quote — measure the actual tire before committing to a tight fitment.