Wheel Fitment Calculator
Compare a new wheel and tire setup against your current one. See how offset and width change poke and inner clearance, how tire size shifts your overall diameter, and how much your speedometer will read off — instantly.
Poke change
+25.7 mm
further out (toward fender)
Diameter change
+7.9 mm
+1.2% overall
Speedometer
60.7 mph
actual at an indicated 60 mph (+1.2%)
| Spec | Current | New | Δ |
|---|---|---|---|
| Overall diameter (mm) | 653.20 | 661.10 | +7.90 |
| Overall diameter (in) | 25.72 | 26.03 | +0.31 |
| Sidewall height (mm) | 98.00 | 89.25 | -8.75 |
| Backspacing (in) | 6.13 | 6.12 | -0.01 |
| Outer edge (poke) (mm) | 72.95 | 98.65 | +25.70 |
| Inner edge (mm) | 142.95 | 142.65 | -0.30 |
| Revs per mile | 784.20 | 774.90 | -9.30 |
- InfoOverall tire diameter changes 1.2% — within the ~3% rule of thumb.
- InfoThe new setup sits 25.7mm further out (more poke) — check fender-lip clearance.
Estimates only. Real-world clearance depends on suspension, fenders, camber, and tire model. SpeedSpec validates true part fitment against your specific vehicle.
Offset, poke, and backspacing
Offset (ET) is the distance from the wheel’s mounting face to its centerline. A lower offset (or a wider wheel) pushes the outer lip outward — that’s poke — and moves the inner edge toward your suspension. The calculator reports both edges relative to the hub so you can judge fender-lip and strut clearance before you buy.
Tire diameter and the 3% rule
Overall tire diameter is the bead diameter plus two sidewalls. Keeping the new diameter within about 3% of stock preserves your speedometer, ABS, and traction-control calibration and keeps clearance predictable. Beyond that, expect noticeable speedometer error and possible rubbing.
Speedometer error
Your speedometer is calibrated for the factory tire. A larger overall diameter travels farther per revolution, so your true speed is higher than the dash shows; a smaller one does the opposite. The calculator converts the diameter change into your actual speed at an indicated 60 mph.
From calculator to confidence
This tool is a quick geometry check, not a fitment guarantee. SpeedSpec validates true part fitment — wheels, tires, brakes, and more — against your specific year, make, model, and options.