Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Uses nominal bead-seat widths. Actual rim lips, tires, suspension clearance and compatibility are not assessed.
Example Calculation
- Old wheel width: 7 in
- Old offset: 40 mm
- New wheel width: 8 in
- New offset: 35 mm
Going from 7 in ET40 to 8 in ET35 adds 17.7 mm outward projection and 7.7 mm inward intrusion.
Frequently asked questions
How do I use this calculator?
Enter old wheel width, old offset, new wheel width, new offset. The result updates automatically. Use Reset to restore the example values.
What method does it use?
extra outer projection=half width change−offset change; extra inner intrusion=half width change+offset change.. Uses nominal bead-seat widths. Actual rim lips, tires, suspension clearance and compatibility are not assessed.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.