Tires and Wheels
Scrub Radius Change Calculator
Estimate the lateral tire-center shift that contributes to scrub-radius change. True scrub radius also requires suspension steering-axis geometry and tire radius.
Inputs for approximate lateral contact shift
The loaded values demonstrate the calculation. Replace them with measurements for one vehicle and operating condition.
Recording the operating setup
Measure the installed component and the vehicle reference points rather than relying only on a catalog dimension — this workflow must also account for the fact that true scrub radius also requires suspension steering-axis geometry and tire radius.
- Record Original wheel offset as factory or current wheel offset — measure from the stated reference points and note whether the vehicle or component is loaded.
- Record New wheel offset as proposed wheel offset — measure from the stated reference points and note whether the vehicle or component is loaded.
- Record Additional spacer as spacer thickness installed with the new wheel — use a measurement or specification from the exact component and operating condition being evaluated.
Building one consistent data set
Original wheel offset. Factory or current wheel offset — for this measurement, measure from the stated reference points and note whether the vehicle or component is loaded.
Document New wheel offset as proposed wheel offset — this means you should measure from the stated reference points and note whether the vehicle or component is loaded.
For Additional spacer, use the quantity described as spacer thickness installed with the new wheel — in the vehicle record, use a measurement or specification from the exact component and operating condition being evaluated.
The mathematical relationship
Estimate the lateral tire-center shift that contributes to scrub-radius change — nominal dimensions and installed measurements can produce different fitment conclusions.
True scrub radius also requires suspension steering-axis geometry and tire radius — that condition defines when approximate lateral contact shift is comparable with another result.
In “approximate lateral shift = original offset − effective new offset,” the calculation does not infer a missing vehicle measurement.
No term beyond original wheel offset, new wheel offset, and additional spacer is introduced in “approximate lateral shift = original offset − effective new offset.”
What remains a separate check
Suspension travel, steering angle, tire growth, body tolerances, and alignment can reveal interference that a static dimension misses — for additional spacer, the page specifically expects spacer thickness installed with the new wheel.
Loaded values as a demonstration
One reproducible example uses Original wheel offset = 45 mm, New wheel offset = 30 mm, and Additional spacer = 0 mm.
The resulting values are Approximate lateral contact shift = 15.0 mm.
The Hot Tire Pressure is the appropriate follow-up when the vehicle review also needs to estimate tire pressure after internal air temperature rises.
Meaning of the calculated value
Approximate lateral contact shift answers “Estimate the lateral tire-center shift that contributes to scrub-radius change.”
Large changes can alter steering feel, bearing loads, and clearance — when that condition changes, compare separate calculator runs instead of blending the inputs.
Interpreting this calculator
What measurement source fits Original wheel offset when it represents factory or current wheel offset?
Because original wheel offset represents factory or current wheel offset, use a source tied to the exact vehicle, component, and operating period described by the other fields.
How does the warning “True scrub radius also requires suspension steering-axis geometry and tire radius” affect Approximate lateral contact shift?
The condition “True scrub radius also requires suspension steering-axis geometry and tire radius” is not corrected automatically by the numeric inputs, so create a separate scrub radius change case when it changes.