The min allowable thickness of a pad is 2mm. On the W210, the rotors are 28 mm new, and I think the min allowable thickess is somewhere around 25mm. This means that each side can have about 1.5mm of material worn away before the rotor reaches min thickness. Thus, a pad worn to the max allowable thickess on a rotor worn to the max allowable thickess would still allow the backing plate to clear the lip of the rotor by .5mm. If the backing plate was contacting the lip of the rotor, I bet they were well beyond min thickess if you were to measure them.

If you use the stock pads and rotors on the W210, the rotors will wear to min thickess with 2 sets of pads.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record