Tyre Size & Wheel Fitment Calculator
Compare tire dimensions, analyze speedometer variance, and calculate wheel offset & suspension clearance
Tyre 1 — Original / OEM Spec
Tyre 2 — New / Upgraded Spec
Diameter Variance & Fitment Verdict
+0.38% Difference
Safe Fitment (Within ±3% Rule)
+1.2 mm (+0.05″) Ride Height Increase
Overall Rolling Diameter
634.3 mm vs 631.9 mm
+2.4 mm (+0.09″)
Sidewall Cushion Height
101.3 mm vs 112.8 mm
-11.5 mm (-0.45″) lower profile
Rolling Circumference
1,992.7 mm vs 1,985.2 mm
+7.5 mm (+0.30″) per turn
Revolutions per Distance
807.6 vs 810.7 / mi
-3.1 revs/mi (-1.9 revs/km)
mph on dashboard
True Ground Speed at Gauge Reading
60.2 mph
Speedometer reads 0.38% slower than actual vehicle motion
Speedometer Variance Table
Indicated Speed
Actual True Speed
Net Variance
Speedometer Error Behavior
Under-reporting
Traveling faster than dial shows
Distance Error over 1,000 mi / km
+3.8 mi (Actual)
Odometer records less mileage
Calculates wheel position relative to suspension struts and outer fenders based on rim width and offset (ET).
Original Wheel Specs
Positive (+) is inward inset
New Wheel Specs
Lower ET pushes wheel out
Fender Stance & Wheel Poke
+17.7 mm
Pushes outward towards fender by 17.7 mm (0.70″)
Inner Strut Clearance
-7.7 mm
7.7 mm closer to suspension
Total Wheel Width Change
+1.0″ (+25.4 mm)
From 6.5″ to 7.5″ rim width
Track Width Expansion
+10.0 mm (+0.39″)
Across axle (2 × ET reduction)
Fender Rubbing Risk
Moderate / Flush
Check fender liner clearance