Ground Clearance Change Calculator

This calculator works by halving the overall diameter change between 2 tires. The axle sits at the tire's center, so it rises by half of the extra height.

1. Enter the current size, for example 265/70R17 (31.61 in).
2. Enter the new size, for example 315/70R17 (34.36 in).
3. Read the diameter change: +2.76 in.
4. Read the clearance change: +1.38 in (+35.0 mm).

The result applies to every part hung from the axle or suspension: the differential, the frame, the rocker panels and the bumpers.

The formula is Clearance Change = (New Diameter − Old Diameter) ÷ 2.

Worked example: 235/65R17 (29.03 in) to 245/70R17 (30.50 in) gives (30.50 − 29.03) ÷ 2 = 0.74 in (18.7 mm).

The formula gives the static, unloaded change. A softer sidewall under load gives back a few millimeters.

The conversion table shows the clearance gain for 8 tire changes in inches and millimeters. Gains run from +0.24 in (+6.0 mm) to +1.46 in (+37.1 mm).

A 20 mm wider tire at a 70 series adds 0.55 in (14 mm) of clearance. A move to a 35 in tire from a 32 in tire adds about 1.5 in (37 mm).

The Ground Clearance Change Calculator is a tool that measures how much higher the axle, differential and body sit after a tire size change. Tires are the only lift that raises the differential; suspension lifts raise the body but leave the axle at the same height.

Off-road drivers use the figure to judge rock clearance under the differential housing. Daily drivers use it to check driveway and parking-garage clearance.

This calculator has 4 uses: differential clearance, approach angles, step-height checks and garage checks.

• Raise differential clearance: Measure the gain under the axle housing.
• Improve approach angles: Estimate the bumper height gain.
• Check step height: Know the added step-in height.
• Check garages: Add the gain to total vehicle height.