GRAN TOCINO
Fitment Bench · measuring guide

Measure your car

Real measurements replace the amber estimates in Fitment Bench. They take about 30 minutes a corner with basic tools. Do one front and one rear corner; the other side is usually within a millimetre or two.

What you need

  • Floor jack and two jack stands, plus wheel chocks
  • A straightedge at least 600 mm (24 in) long: a level or a long steel rule
  • A steel rule or tape measure marked in mm
  • A plumb bob, or a small level held against a straightedge
  • Digital calipers with a depth rod, for studs and lug holes
  • A magnetic digital angle gauge, if you don't have a recent alignment sheet
  • A torque wrench to put the wheels back on

Before you start

  • Park on the flattest floor you have, wheels straight, with your usual fuel load.
  • Measure in millimetres if you can. Fitment Bench takes inches too (the mm / in switch in Hub measurements).
  • All distances start at the hub face, where the studs come through the rotor hat. Outboard is toward the fender, inboard is toward the engine.
  • The drawings are a front view of the passenger side, same as the calculator: outboard on the left.

Safety: the car's weight sits on jack stands under solid jacking points. The floor jack only lifts the suspension back to ride height in step 2. Never put any part of yourself under the car while it is on a jack.

1

Arch height

Do this first, with the car on the ground and the wheel on. It is your ride height, and step 2 uses it to put the suspension back where it sits when driving.

  1. Find the center of the hub (the center cap, or the middle of the lug pattern).
  2. Measure straight up from there to the underside of the fender lip, directly above the hub.
Enter as Arch in Hub measurements, Front or Rear row
Wheel on, car on the ground. Hub center to the fender lip, measured vertically.
2

Wheel off, back to ride height

Without the wheel, the suspension hangs at full droop. The hub drops and usually gains camber, so the other measurements would be off by 10–30 mm.

  1. Loosen the lug nuts, lift the corner and set a jack stand under the body's jacking point. Take the wheel off.
  2. Put the floor jack under the lower control arm or the knuckle, as close to the hub as is solid.
  3. Raise it until the hub-center-to-lip distance matches your step 1 number. The suspension is now loaded the way it is on the road.
  4. Leave the stand in place. If the body starts to lift off it, stop and raise the stand slightly.
Body on a jack stand (not shown). Floor jack under the lower arm until the arch number matches step 1.
3

Find zero: the hub face

The hub face is the flat surface the wheel bolts against: the face of the rotor hat, where the studs come through. Every side-to-side number is measured from this plane.

  1. Clean any rust ridge off the hat face so the straightedge sits flat.
  2. Hold the straightedge vertical, flat across the hat face and between the studs, so it sticks up well past the top of where the wheel would be.
  3. Steps 4 and 5 measure sideways from that straightedge.

The hub face is also where wheel offset is measured from, which is why the calculator can place any wheel once you've measured to it.

Straightedge flat on the hub face. That plane is zero.
4

Inboard clearance

Measure inward from the hub face to the first thing the inner barrel or the tire could touch: the strut body, spring perch, upper arm, or a brake-line bracket.

  1. Measure at the height of the rim's edge and above it: about half the wheel diameter up from the hub center (table below).
  2. Check from there up to the top of the tire, and use the smallest number you find.
  3. Lower down, the wheel's spokes and center are dished outboard and won't reach anything beside the hub, so they don't count here.
WheelRim edge above hub center
15"191 mm · 7.5 in
16"203 mm · 8.0 in
17"216 mm · 8.5 in
18"229 mm · 9.0 in
19"241 mm · 9.5 in
Enter as Inboard
Hub face to the strut, at rim-edge height.
5

Fender lip

How far outboard of the hub face the fender lip sits. This decides how much poke the car can take.

  1. Hang a plumb line from the outer edge of the fender lip, directly above the hub. A level held against the lip works too.
  2. Measure straight out from the hub face straightedge to the line, at about hub height.
  3. If the lip has a rolled or pulled edge, hang the line from its outermost point.
Enter as Fender lip
Plumb line from the lip, measured out from the hub face.
6

Camber when measured

The calculator leans the baseline wheel to this angle and starts its camber sliders from it. 0° is true vertical; top of the wheel leaning inboard is negative.

  1. Best: use the camber from your most recent alignment sheet, if nothing has changed since.
  2. Otherwise: zero a magnetic angle gauge on the floor where the car sits, then stick it flat on the hub face between the studs, still at ride height. It reads the hub's lean from vertical, which is the camber.
  3. Top of the hub leaning toward the engine means negative camber.
Enter as Camber °
Angle gauge on the hub face reads the hub's lean from vertical. Lean exaggerated.
7

Stud length

How far the studs stick out past the hub face. Fitment Bench uses it to check how much thread the lug nuts get once you add a spacer or a wheel with a thicker mounting pad.

  1. Lay the calipers' body flat across the hub face beside a stud.
  2. Measure from the hub face to the very tip of the stud.
  3. Check two or three studs. Aftermarket or replaced studs are sometimes longer.
Enter as Front stud length / Rear stud length in Spacers & studs
Hub face to stud tip.
8

Wheel pad depth

Measured on the new wheel, on the bench. It is how much stud the wheel itself uses up before the lug nut's seat. Thick aftermarket mounting pads can use 5–10 mm more than factory wheels.

  1. Lay the wheel face-down on something soft.
  2. Drop a lug nut, seat first, into a lug hole from the front so it rests on the seat.
  3. From the back, measure with the calipers' depth rod from the back face (the side that touches the hub) down to where the nut's threads start.

Thread engagement is then stud length − spacer − pad depth. It should be at least one stud diameter: 12 mm on M12 studs, 14 mm on M14.

Enter as New wheel pad depth in Spacers & studs
Cross-section through one lug hole. Back face to where the nut's threads start.
Optional, for specific checks

Caliper radius and barrel

Only needed for brakes that aren't in the calculator's list (pick "Custom caliper" under Brakes).

  1. Caliper radius: with the wheel off, measure from the center of the hub to the caliper's outermost point, the corner that sticks furthest out from the center.
  2. Barrel inner diameter: on the new wheel, measure straight across the inside of the barrel at the depth where the caliper will sit. It goes in the wheel's spec sheet section and replaces the 14 mm barrel-wall assumption.

Spoke-to-caliper clearance can't be calculated: it depends on the spoke shape. Use the wheel maker's brake fitment template or a test fit for that.

Enter as Front / Rear caliper radius and Barrel inner dia.
Side view. Hub center to the caliper's furthest point, against the inside of the barrel.

KPI and stock scrub radius

Both live under Suspension & alignment and come off an alignment sheet, not a tape measure. Many alignment machines report KPI (also called SAI, steering axis inclination) if the shop runs a caster sweep; ask for it. Without it, 13° is a reasonable default for cars like these. Stock scrub radius is rarely published; leave it blank unless you find a factory number, and the calculator shows the change in scrub instead of the total.

Common mistakes

Measuring at full droopSkipping step 2 drops the hub and adds camber. Inboard and fender numbers come out 10–30 mm off.
Measuring from the rotor's braking surfaceZero is the hat face where the wheel bolts on, not the rotor's friction surface behind it.
Inboard at hub heightBeside the hub the wheel's center is dished away from the strut. Measure at rim-edge height and above.
Fender measured to the paint, not the edgeHang the line from the outermost edge of the lip, including any roll or flare.
Steering not straightTurned wheels move the hub face. Check the steering wheel is centered before measuring the front.
Mixing unitsSet the mm / in switch in Hub measurements before typing. An inch number typed into mm boxes is 25 times too small.

Enter your numbers

Type them into Hub measurements. Each one replaces the estimate and turns from amber to normal. They're saved per car in your browser.

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