Wheel offset and inner clearance calculator

Width changes both edges; offset moves the whole wheel

Converting width to millimetres puts it on the same basis as offset.

Half the width difference reaches each edge before the change in mounting position is applied. A negative offset difference shifts both edges outward, but its effect on inner clearance has the opposite sign.

The Tire size and speedometer comparison calculator checks a different part of the proposed change: tire diameter and its nominal rolling effect. Neither calculation by itself establishes fitment.

A geometry result is not a fitment check

The measured width here is between bead seats.

Real flanges extend farther, and a tire can protrude past the wheel. Caliper clearance also depends on spoke shape. A spacer changes effective offset arithmetically without establishing that the hardware or mounting arrangement is approved.

Check spacer direction with unchanged width

Keep both widths and offsets equal, then enter a ten-millimetre spacer for the proposed wheel. The nominal outer edge moves ten millimetres outward, while the inward envelope retreats by ten millimetres. That paired sign check helps catch the common mistake of treating both changes as reduced clearance.

If you already measured a complete wheel-and-spacer effective offset, enter that offset and leave spacer thickness at zero. Adding the spacer a second time would shift the wheel twice. Measure clearances on the actual vehicle; a negative arithmetic change does not resolve spoke shape or fastening questions.

Work through the entered example

Changing from 7 inches ET45 to 8 inches ET35 adds 22.7 mm outward and consumes 2.7 mm of inner clearance.

Start with this case, then change one input and calculate again. Keep the other assumptions fixed so the result has an interpretable cause. The result table exposes intermediate quantities and units rather than hiding them behind a single headline number.

Use the output in a real plan

The measured width here is between bead seats. Real flanges extend farther, and a tire can protrude past the wheel. Caliper clearance also depends on spoke shape. A spacer changes effective offset arithmetically without establishing that the hardware or mounting arrangement is approved.

Before purchasing material or comparing alternatives, check the measurements at the point where they enter the calculation. A mathematically precise answer can still be a poor plan when the measured size, loss allowance or price basis is wrong. Save the input assumptions with any result you intend to reuse.