Free gearhead tool · no sign-up
New tire size? Check it first.
Compare two tire sizes side by side — the change in overall diameter, how far off your speedometer will read, and the drift on your odometer.
Current tire
/
R
New tire
/
R
mph
Actual speed at 60 mph
0 mph
your speedo vs reality
0"
Current Ø
0"
New Ø
0%
Diameter Δ
…
Overall diameter = wheel + (2 × width × aspect ÷ 100). Speedometer/odometer error assumes your vehicle was calibrated for the current size; actual speed = indicated × (new ÷ current diameter). Real-world rolling diameter varies a little with load, pressure, and brand. A rough fitment guideline is to stay within ±3% of stock — but check clearance, load rating, and your owner's manual. Not a substitute for professional fitment.
GearShift helps shops quote, schedule, and follow up — so the bays stay full and nothing slips.
See how GearShift works →