Wheel Hub Runout Tolerance: Measurement and Interpretation

Wheel hub runout tolerance is the maximum wobble the vehicle manufacturer allows on the hub's wheel mounting face during one full rotation. It is usually given as lateral runout in millimetres or thousandths of an inch. Technicians measure it with a dial indicator against the hub flange. Many passenger vehicles specify a limit of about 0.05 mm (0.002 in), but the limit varies by model, so the manufacturer specifications for the vehicle always decide whether a hub passes.

Hub runout matters because the wheel and tire bolt to this flange. Any tilt in the mounting face carries outward to the rim and tread, and it grows with distance from the hub centre. To estimate how large that effect becomes, you need the tire's size, which is printed on the sidewall. This article explains those markings first and then covers measurement and interpretation.

What do the numbers on the tire sidewall mean?

The main sidewall code describes the tire's dimensions, construction and performance ratings. In the example 225/45R17 94V, each part tells you something different:

• 225 is the section width in millimetres. It is the nominal width of the inflated tire on a specified measuring rim.
• 45 is the aspect ratio. This is a percentage, not a length: the sidewall height is 45% of the section width.
• R means radial construction. It is not a size value.
• 17 is the rim diameter in inches. It is the diameter of the wheel's bead seat, not of the tire.
• 94 is the load index. It is a code that refers to a maximum load per tire in a standard table, not a weight in any unit.
• V is the speed rating. It is a letter code for the maximum rated speed under specified test conditions.

Other common markings include the DOT or manufacturing code with the week and year of production, the maximum inflation pressure, the maximum load, and in some markets UTQG ratings for treadwear, traction and temperature. None of these markings states the tire's runout or roundness. Some tires carry coloured dots for match-mounting. These usually mark a light point or a high point of radial runout, but the conventions vary between tire makers.

How do you calculate sidewall height, diameter and circumference from tire size?

Calculate tire geometry in four steps. Find the sidewall height from the width and aspect ratio, then add two sidewalls to the rim diameter, then use the result for radius and circumference.

1. Sidewall height = section width × (aspect ratio ÷ 100). For 225/45R17: 225 × 0.45 = 101.25 mm.
2. Rim diameter in millimetres = inches × 25.4. For a 17 in rim: 17 × 25.4 = 431.8 mm.
3. Overall diameter = rim diameter + 2 × sidewall height. For 225/45R17: 431.8 + 202.5 = 634.3 mm. The radius is about 317.2 mm.
4. Circumference = π × overall diameter. For 225/45R17: 3.1416 × 634.3 ≈ 1,992.7 mm.

Example size comparison: 225/45R17 vs. 245/40R18

A wider tire with a lower aspect ratio can still have a similar sidewall height, because the percentage applies to a larger width. The rim diameter then has the largest effect on overall size.

Calculated geometry vs. actual tire dimensions and fitment

These calculations give nominal geometry, not the real size of a specific tire on a specific car. Actual diameter and width vary with:

• the tire manufacturer and model;
• the rim width the tire is mounted on;
• inflation pressure and vehicle load;
• tread wear.

A matching calculated diameter also does not prove that a tire is compatible with a vehicle. Fitment depends on:

• wheel offset and clearance to suspension and bodywork;
• load index and speed rating requirements;
• effects on the speedometer and stability systems;
• the vehicle manufacturer's approved sizes.

How does hub runout relate to tire size?

Lateral runout on the hub flange is magnified at larger radii, because a tilted mounting face tilts the whole wheel and tire. If the flange wobbles by a given amount at a given measuring radius, the wobble at another radius is roughly proportional to the ratio of the two radii. This is a simplified geometric estimate. It assumes the mounting face is flat but tilted, with no other wheel or tire runout added.

Here is an example calculation. Assume a hub reads 0.05 mm total indicator reading at a measuring radius of 70 mm:

The example shows two useful points:

• A hub reading that looks tiny can become several times larger at the rim and tread.
• Changing between tire sizes of similar overall diameter barely changes that amplification.

The overall diameter from the sidewall code matters more than the width or aspect ratio alone. The same proportional logic means a hub tilt also shows up at the outer edge of a brake rotor mounted on the flange.

How do you measure wheel hub runout with a dial indicator?

Measure hub runout by placing a dial indicator against the wheel mounting face and rotating the hub one full turn. The difference between the highest and lowest readings is the total indicator reading.

1. Raise and support the vehicle safely. Remove the wheel.
2. Remove the brake rotor if the manufacturer procedure calls for measuring the bare hub flange.
3. Clean the mounting face thoroughly. Rust, scale or debris can add false runout.
4. Check the wheel bearing for play. Bearing endplay makes the reading move when you push or pull the hub, which corrupts the runout result.
5. Mount the dial indicator on a rigid base, such as a magnetic base on the steering knuckle or another fixed suspension part.
6. Place the plunger perpendicular to the mounting face, near its outer edge, where it will not hit the wheel studs.
7. Preload the indicator slightly and set it to zero.
8. Rotate the hub slowly through one full revolution. Note the maximum and minimum readings.
9. Subtract the minimum from the maximum to get the lateral runout. Repeat to confirm the result is consistent.
10. Compare the result with the manufacturer specifications. Use the measuring radius the procedure defines, if one is stated.

How do you interpret hub runout readings?

A reading at or below the manufacturer's limit means the hub mounting face is acceptable. A reading above the limit means you need to find the cause before replacing parts.

• Within specification: The hub is not the likely source of wheel wobble or rotor runout. If vibration persists, measure wheel and tire runout separately.
• Slightly over specification: Re-clean the face and recheck the setup and bearing play. A small amount of rust or a poorly mounted indicator often explains a marginal reading.
• Clearly over specification with no bearing play: The flange may be bent or distorted. Possible causes include impact damage or improperly pressed studs. Hub replacement is the usual correction. Some shops reduce the effect on the rotor by repositioning it or machining it on the car, but this does not correct the hub itself.
• Reading changes when the hub is rocked: The bearing has play. Treat this as a bearing problem rather than a flange runout value.

Hub runout vs. wheel and tire runout

Hub runout, wheel runout and tire runout are separate measurements with separate tolerances.

• Hub runout is measured on the flange and is usually the tightest tolerance.
• Wheel runout is measured lateral and radial runout at the rim bead seats or flanges.
• Tire runout is usually measured on the tread and sidewall when mounted.

Because hub tilt grows with radius, measure the hub first when you diagnose roundness or wobble problems. That way a hub fault is not mistaken for a bent rim or an out-of-round tire.