How is sampled disc thickness variation calculated?

For thickness readings taken according to the applicable service procedure, the sampled range is maximum reading minus minimum reading.

Does this page supply universal brake-disc limits?

No. Enter the minimum thickness, permitted sampled variation and permitted installed-disc lateral total indicator reading from the exact vehicle or component service information.

Does an arithmetic comparison diagnose brake judder?

No. Thickness variation and runout can contribute, but diagnosis also requires the applicable inspection procedure and checks of the hub, bearing, mounting, friction surfaces and other brake components.

Measurement arithmetic

Brake Disc Thickness & Runout Comparator

Calculate the range of thickness samples and compare measurements only with limits copied from the exact vehicle or brake-component service information.

No universal limitUser-supplied specificationsNot a diagnosis

Arithmetic comparison

Sampled thickness range (max − min)

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Minimum measured thickness

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Maximum measured thickness

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Entered lateral TIR

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Comparison with entered limits

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Calculation

sampled thickness range = max(tᵢ) − min(tᵢ)

This is arithmetic on the submitted samples. It is meaningful only when every reading follows the same applicable service procedure, including measuring radius, surface preparation and instrument use. “DTV” terminology and sampling procedures can vary between manufacturers.

Limits are component-specific

This page does not identify a single ISO pass/fail limit for all road-vehicle brake discs. Enter limits from current service information for the exact vehicle and component. A result “within entered limits” is not permission to return a brake system to service.

Brembo minimum-thickness guidance says to measure at least four points, use the lowest reading and compare it with the MIN TH marking. Its disc installation instructions specify installed-disc runout setup and also direct users to vehicle-manufacturer instructions.

A 2018 MINI service bulletin even notes a change where an eight-point measurement was no longer required. This is why the calculator does not invent a universal number of points or limit.

Not a fault diagnosis

Infiniti service information discusses both thickness variation and runout in brake judder and also identifies other contributors. Follow the vehicle diagnostic tree before machining or replacing parts.

Safety boundary: brake-system inspection and repair require the vehicle maker’s procedure, suitable metrology and competent personnel. This page performs no hub, bearing, crack, friction-surface, heat-damage, pad, caliper or hydraulic checks.