07 / FITMENT TOOLS
Wheel & Tire Fitment Change
Compare two complete setups.
What changes
GEOMETRY ESTIMATEExample calculation. Replace these values with your setup.
The new tire envelope reaches farther toward the suspension.
Tire envelope sourceCurrent: Nominal section width · New: Nominal section width
- Tire envelope inner clearance change
- -12.0 mm
- Tire envelope outer extension change
- -2.0 mm
Less space toward the car
Farther inward
Where your new setup moves
Inner clearance change
- Change
- -12 mm
Compare the inside edge of each tire against the same mounting face. A negative clearance change means less space toward the car. Enter a measured gap to see the remaining space.
ACurrent / A
View from above · tire envelope.
BNew / B
View from above · tire envelope.
| Measurement | Current | New | Change |
|---|---|---|---|
| Nominal wheel inner clearance change | — | — | -13.3 mm |
| Nominal wheel outer extension change | — | — | -0.7 mm |
| Tire envelope inner clearance change | — | — | -12.0 mm |
| Tire envelope outer extension change | — | — | -2.0 mm |
| 225.0 mm | 235.0 mm | +10.0 mm | |
| Tire free diameter | 634.3 mm | 645.2 mm | +10.9 mm |
| Change in unloaded radius | — | — | +5.5 mm |
| Estimated speed change | — | — | +1.72% |
| 35.0 mm | 42.0 mm | +7.0 mm |
Assumptions & limits
- Tire envelopes are symmetric about the wheel center plane. Nominal section width does not include every sidewall protrusion.
- Projected clearances are static lateral estimates for the selected surface and unchanged hub, alignment, and obstacle geometry.
- Brake clearance, rim-width approval, steering, suspension travel, tire deflection, load, and vehicle geometry are not evaluated.
- Positive clearance does not guarantee fit. Verify the complete installation physically.
- At least one tire envelope uses nominal section width; this is not a measured physical tire envelope.
Compare a complete wheel and tire setup
Compare wheel planes and tire envelopes separately. Add a measured current gap to estimate static clearance at the same tire or wheel-lip surface.
Example · 225/45R17, 17x8 ET35 → 235/40R18, 18x8.5 ET42
The nominal tire envelope moves 12 mm closer on the inner side and 2 mm inward on the outer side. Current tire gaps of 20 mm inside and 15 mm outside project to 8 mm and 17 mm respectively.
These are static estimates at the same obstruction references. Positive values do not establish fitment through steering, suspension travel or load.
Fitment questions
Does this tell me whether the setup will fit my vehicle?
It compares geometry and can project a supplied static gap; it does not certify fitment. Actual tire dimensions, approved rim widths, brake clearance, steering, suspension travel, load and vehicle requirements need separate verification.
Why must each tire diameter match its wheel?
A tire marked R17 requires a matching 17-inch wheel rim, and R18 requires 18 inches. The current and new setups may use different diameters, but each tire-and-wheel pair must match.
Can I use measured dimensions instead of the size marking?
Yes. Optional inputs accept manufacturer-specified or measured tire diameter and envelope width. Wheel-lip clearance projections also require overall wheel widths and the symmetric-flange assumption for both setups. Select the surface that your current gaps were measured from.
Methodology & limits
How this tool works
Tire inner reach = envelope width / 2 + offset. Tire outer reach = envelope width / 2 − offset. Projected clearance = measured current clearance plus the signed clearance change.