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 5.7% unless it can be recalibrated for the new size.
Want to try other sizes against these? Open this comparison in the interactive tool.
This swap changes the wheel as well as the tire
35X12.50R20 and 37X12.50R17 sit on different rims — 20 inches against 17. That makes this a wheel purchase rather than a tire purchase, and the cost difference between the two is substantial.
Because the aspect ratio has not dropped to compensate, the overall diameter moves by +5.7%. Check that figure against the 3% guidance before treating this as a straight swap.
Also confirm the new wheel's offset and width suit the vehicle. A different rim diameter says nothing about where the wheel sits laterally, and that is decided separately by offset and width.
35X12.50R20 and 37X12.50R17 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 | 35X12.50R20 | 37X12.50R17 | Difference |
|---|---|---|---|
| Overall diameter | 35" | 37" | +2" (+5.7%) |
| Section width | 12.5" (318 mm) | 12.5" (318 mm) | +0" |
| Sidewall height | 7.5" | 10" | +2.5" |
| Rim diameter | 20" | 17" | −3" |
| Circumference | 109.96" | 116.24" | +6.28" |
| Revolutions per mile | 576 | 545 | −31 |
| Ride height at axle | Baseline | +1" | +1" |
What the dial shows against how fast you are going
Your speedometer was calibrated to 35X12.50R20, which turns about 576 times per mile. Fit 37X12.50R17 at about 545 revolutions per mile and the same wheel speed now represents a greater road speed than the instrument assumes. The error is 5.7% at every speed, so it grows in absolute terms the faster you go.
| Speedometer reads | You are actually doing | Difference |
|---|---|---|
| 30 mph | 31.7 mph | +1.7 mph |
| 45 mph | 47.6 mph | +2.6 mph |
| 60 mph | 63.4 mph | +3.4 mph |
| 75 mph | 79.3 mph | +4.3 mph |
Over distance the same proportion applies to the odometer. Every indicated 1,000 miles on 37X12.50R17 is really about 1057 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 grows by 0 inches, so the tire sits closer to the strut and the inner liner on both sides.
- Overall height grows by 2 inches, of which 1 inches goes upward into the arch — check at full lock and full compression.
- The rim diameter changes from 20 inches to 17 inches, so this swap needs different wheels as well as different tires.
- Speedometer error of 5.7% — check whether your vehicle supports recalibrating for a new tire size.
- Confirm the load index on 37X12.50R17meets 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.
35X12.50R20 vs 37X12.50R17 FAQ
Is 37X12.50R17 bigger than 35X12.50R20?+
37X12.50R17 measures 37 inches in overall diameter against 35 inches for 35X12.50R20. That makes it 2 inches taller, a change of +5.7%. It is also 0 inches wider in section width.
Will 37X12.50R17 fit in place of 35X12.50R20?+
The diameter change is +5.7%, 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 37X12.50R17 give over 35X12.50R20?+
1 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 5.7%. At an indicated 60 mph you would actually be travelling about 63.4 mph, and every indicated 1,000 miles would really be about 1057.
Do I need to regear for 37X12.50R17?+
A +5.7% change shifts the effective gearing noticeably. To restore the original engine speed you would multiply the current axle ratio by 1.057. 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?+
35X12.50R20 turns about 576 times per mile and 37X12.50R17 about 545 — a difference of −31 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.