When initial measurements of the fitted disc and successive observation do not give clear answers, it may be useful to analyse disc dimensions further.

Placing the disc on a bench as seen in the illustration, it is possible to measure its dimensions without these being affected by other brake components.

- After cleaning the surface coming into contact with the hub using sandpaper, the disc must be able to rest on the bench bearing without run out. This is done by holding the disc at the extremities of a diameter with the fingers and checking its vertical movement. If the disc is unstable this indicates distortion due to incorrect or excessive tightening.

- With the aid of a DTI Gauge mounted on a fixed base it is possible to measure the disc's production run out, provided that it has not been rectified by the mechanic at the time of fitting. This measurement is carried out by resting the DTI Gauge against the external or internal edge of the disc where the pads have not worn the braking surfaces. If the run out value measured is greater than 0.05 mm it means that the disc originally had a marked run out, a certain cause of vibration. If the value is less, then the acquired run out is measured by placing the point of the DTI Gauge at the centre of the braking surface: if it is beyond the tolerance this indicates incorrect installation that causes vibrations after a few thousand kilometres (cold judder due to a DTV increase).

- Lastly, when travelling, it is possible to determine if vibrations are caused by the front discs or the rear drums. Proceeding at low speed, pull lightly on the handbrake: if there are vibrations the problem concerns the rear drums (check and, if necessary, replace them).