Phase 7 · Asset & Tech Architecture
Wheel Offset & Tire Fitment Calculator
Before you drop $3,000 on wheels, know if they'll clear. Pit a new setup against stock and watch poke, inner clearance and speedometer error solve in real time.
Estimate — verify physically. Real clearance depends on suspension, ride height, camber, brake size and bodywork this model can't see. Use these numbers to screen a setup, then confirm fitment with a test fit or a trusted shop before buying.
Under the hood
The math, fully exposed
Wheel widths convert to millimetres (×25.4), then we compare the two setups edge to edge:
Poke (outer edge) = (wheel width ÷ 2) − offset
Inset (inner edge) = (wheel width ÷ 2) + offset
Tire diameter = wheel diameter × 25.4 + 2 × (tire width × aspect%)
Speedometer error = (new diameter − stock diameter) ÷ stock diameter
- Poke vs inset: a lower offset moves the outer edge toward the fender; a wider wheel or higher offset moves the inner edge toward the strut and caliper. Both are clearances you can run out of.
- Diameter drives the speedo: keep the new tire's overall diameter close to stock and your speedometer and gearing stay honest. Big jumps throw both off.
- Edges, not guarantees: this compares geometry only. Suspension travel, camber and bodywork decide the final millimetres — always test fit.
Your directives
What to do next, based on your numbers
Adjust the sliders to generate tailored recommendations.
Answers
Frequently asked questions
What is wheel offset (ET) and "poke"?
Offset (ET, in millimetres) is the distance from the wheel's mounting face to its centreline. A lower offset pushes the wheel outward toward the fender ("poke"); a higher offset tucks it inward. Poke is how far the outer edge sticks out compared to stock: (wheel width ÷ 2) − offset. More poke means a more aggressive stance — and a higher chance of rubbing the fender.
Will a wider wheel or tire rub?
It depends on which way the extra width goes. A lower offset moves the outer edge toward the fender (watch for fender rubbing, especially on bumps or full lock); a higher offset or wider wheel can move the inner edge toward the strut, spring or brake caliper. This tool shows both the outer (poke) and inner (inset) change so you can see which clearance is at risk.
How does changing tire size affect my speedometer?
Your speedometer is calibrated to the stock tire's rolling diameter. A taller overall tire travels further per revolution, so you're actually going faster than the dial reads (and your odometer under-counts); a shorter tire does the opposite. We compute the exact percentage error and what your true speed is when the dash shows 60.
Do I need spacers or hubcentric rings?
Spacers push the wheel outward to fine-tune clearance or stance, and any aftermarket wheel that isn't a perfect hub match needs hubcentric rings so the wheel centres on the hub rather than the bolts — this prevents vibration. If your setup adds significant poke, plan for fender work and proper hubcentric hardware rather than forcing the fit.