E92 M3 Minimum Brake Disc Thickness

[John Laverick]

At the risk of being flamed for stupidity ..... my M3 has just been into BMW and they reported the front discs as urgent replacement as they're below minimum thickness but the pads still have 4mm useable wear.

What do you reckon? Should I change them now or are they safe until the pads are finished? I'm a little sceptical of BMW recommendations for replacement and would have thought the discs still have some usable meat under min. thickness?

I don't track the car by the way.

Pad thickness
New= 14mm
Actual = 7mm
Minimum = 3mm

Disc minimum thickness= 28.4mm
Actual = 28.0mm

[PetrolBreakfast]

I'm not the flaming type but I would recommend you get them changed, no point messing around trying to eek out the last (and least performant) few mm of pad and disc.

What if you really need to lean on them, someone jumps out, avoid an accident etc? You'll be livid if in the pursuit of getting the last bit of 'value' out of them you actually don't stop in the shortest distance you could have. Nice car, nice new brakes, enjoy winter safely, job done.

[John Laverick]

PetrolBreakfast said:

I'm not the flaming type but I would recommend you get them changed, no point messing around trying to eek out the last (and least performant) few mm of pad and disc.

What if you really need to lean on them, someone jumps out, avoid an accident etc? You'll be livid if in the pursuit of getting the last bit of 'value' out of them you actually don't stop in the shortest distance you could have. Nice car, nice new brakes, enjoy winter safely, job done.

I know what you're saying but on the other hand there is also no point in changing them unnecessarily early either ... the pads are 65% worn and the discs only just under minimum thickness. Might give them a quick measure myself to double check come to think of it.

Braking performance is currently uneffected .... ok for full on track use the last 5% of performance might be missing but on the road they're more than powerful enough.

Just after people's thoughts, I'll change them if people think the recommended minimum thickness is really the point at which the must be changed.

My thought process was that it's a bit like BMW recommending tyres are changed at 3mm whereas in my personal view I'd run a tyre right down to 2mm in the summer before changing.

[Welshbeef]

You shouldn't put used pads onto different discs.

Discs can last 120k on BMWs for sensible use - though I know someone who has worn a set of discs out in 20k in the current shape 320d...
Pads can last 60k on BMWs


However you have stated the disc actual thickness is below the minimum useful serviceable life of he disc. What happens when it gets thin?dosc get hot quicker meaning it's ability to effectively stop decreases. I guess you are looking at a £2k discand pad change on an older E92 M3 which is hard to swallow

[John Laverick]

Nearer £850 so not too bad .... just had the rear discs and pads done and had four new Michelins so was trying to stave off another big bill!

Anyhooo ... I had in my mind that minimum thickness might be the minimum thickness could fit a new set of pads. Seems not.

Did a bit more reading, it's pretty clear here:

http://textar-professional.com/minimum-brake-disc-...

Will get it booked in!

[NelsonM3]

Your minimum pad wear indicator will come on at 3mil anyway. So you may as well wait until then.