Outer Tire Position Calculator
Estimate how far a tire's outer sidewall moves toward the fender after a width or offset change. Use a measured baseline in mm or inches.
Estimate tire movement toward the fender.
Outer Tire Position Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Outer Tire Position Calculator Works?
The Outer Tire Position Calculator works by adding half of the tire width change to the offset reduction. The result is the outward movement of the outer sidewall. The tool uses 3 steps.
Measure the fender gap
Drop a plumb line from the fender lip and measure to the outer sidewall, for example 12 mm (0.47 in).
Enter changes
Type the tire width change and the offset change.
Read the new position
The calculator subtracts the outward movement from 12 mm and reports any amount the tire sits past the fender.
Outer Tire Position Calculator Formula
The Outer Tire Position Calculator formula is Δouter = (W_new − W_old) ÷ 2 − (ET_new − ET_old), where a positive value moves the sidewall outward.
Δout = ΔW_tire ÷ 2 − ΔETG_new = G_meas − Δout- ΔW_tire
- Tire width change (mm)
- ΔET
- Offset change (mm), a lower ET pushes outward
- G_meas
- Measured inset from fender lip (mm)
Worked example
A tire 20 mm wider on a wheel with 10 mm less offset moves the outer sidewall 20 mm (0.79 in) outward. A 12 mm (0.47 in) inset becomes 8 mm past the fender lip.
Outer Tire Position Calculator Conversion Table
The Outer Tire Position Calculator conversion table shows outer sidewall movement for 7 combinations from a 12 mm (0.47 in) inset.
| Tire width change | Offset change | Outward movement | Result |
|---|---|---|---|
| +10 mm | +0 mm | +5.0 mm (+0.20 in) | 7.0 mm |
| +20 mm | +0 mm | +10.0 mm (+0.39 in) | 2.0 mm |
| +20 mm | -10 mm | +20.0 mm (+0.79 in) | Past fender by 8.0 mm |
| +20 mm | +10 mm | +0.0 mm (+0.00 in) | 12.0 mm |
| +30 mm | -20 mm | +35.0 mm (+1.38 in) | Past fender by 23.0 mm |
| +0 mm | -15 mm | +15.0 mm (+0.59 in) | Past fender by 3.0 mm |
| -10 mm | +5 mm | -10.0 mm (-0.39 in) | 22.0 mm |
What is Outer Tire Position Calculator?
An Outer Tire Position Calculator is a tool that predicts how far a tire's outer sidewall moves toward or past the fender lip. Many road rules require the tread to stay inside the bodywork when viewed from above.
Lower offset and wider tires both push the outer sidewall outward. The 2 effects add together.
Camber changes the result at the top of the tire. Negative camber tucks the top of the tire inward by a few millimeters.
What are the uses of Outer Tire Position Calculator?
There are 4 main uses of the Outer Tire Position Calculator, including flush fitment and legal compliance.
Flush fitment
Set the sidewall flush with the fender lip.
Legal compliance
Keep the tread covered by the body in regions that require coverage.
Fender rolling decisions
Decide whether the lip needs rolling.
Mud flap fitment
Check that flaps still cover the tire.
Related Clearance & Stance Tools
View All 134 Subtools →Estimate clearance changes from tire radius.
Compare manufacturer-specified loaded tire radii.
Estimate static vertical gap changes.
Estimate changes toward suspension components.
Estimate changes at the inner wheel edge.
Estimate changes at the outer wheel edge.