There is no spec given for this. There are minimum dimensions that must be
observed, and the M3 (E36) rotors have a specific admonition against turning
the rotors -- because the M3 has the specific admonition and the other
models do not, it seems to me that it might be appropriate is some cases to
turn rotors on the other E36 models beside the M3, but one must remain with
a minimum thickness that exceeds the number stamped on the rotor. So,
turning a rotor might be okay IF the result is a rotor that is thicker than
the min. specification -- as a practical matter, I don't see how a rotor can
be turned AND retain a thickness that is greater than the minumum.
The life of the brake pads is a matter of driving habits/environment, and
the life of the rotors is a matter of the life of the pads. Again, as a
practical matter, most rotors will last through two sets of brakes. Rear
pads will last through two sets of front pads, so rear rotors need to be
replaced every fourth brake job, and front rotors need to be replaced every
other brake job.
Obviously, your mileage may vary, but as a general guideline, I think these
numbers should work out pretty well.
I'd like to say a big thanks to everyone that responded to my original
post. I'm still a little amazed that BMW use rotor materials that wear
out so quickly and (even more amazingly) that owners appear to accept that.
Guess I'm just going to have to come to terms with it as a consequence
of driving an otherwise wonderful car ... or just brake less :-)
I think you missed the point Steve. It is not a design flaw (bad thing)
that the rotors wear relatively fast. It is a fact of life if you want
good brakes. Cars with brake rotors that last over 100k miles also
can't brake worth a damn.
It's not that I think this is a design fault - believe me I know all
about them, I own a Land Rover - just an outdated way of looking at
things. I also don't think it's a fact of life either, not these days
I feel a bit of empirical experimentation coming on tomorrow. Let's see
just how much better the 730 can stop compared to the Disco, remembering
that the Landie is considerably heavier than the Bimmer. Maybe I'll see
if my son will lend me his Focus too - that's nice and light.
Watch this space ...
Not only are you comparing apples and oranges, you're throwing bananas into
the basket as well. If you are going to select or reject a car because of
how often the brake rotors have to be replaced, I'll not be watching this
cars with rotors that last 100K miles can't brake worth a damn. I would
never reject a car simply on the basis that something like the brake
rotors (a wearing part) have to be replaced more often that I think they
should be - I never suggested that at all - I'm just curious to see
their respective braking abilities at first hand.
Whether you'll be watching this space or not won't have any influence on
whether I carry out the experiment, or not, either. But I bet someone
You'd need to compare two cars with the same size (diameter) rotors and
wheels, one with hard rotors and one (BMW) with the softer variety. I'm
guessing the big Land Rover would have larger discs, no?
I'll be interested to hear how fast you can haul down the 2 cars from
the same speed, even with their obvious differences. If you can't stop
your BMW faster than a Land Rover, there's something seriously wrong.
They don't wear out quickly. I didn't put rotors on my E36 until it hit
about 150,000 miles, and when it got slammed at 215,000, the brakes were
going strong. But, I drive 40 miles to work on a mostly wide open freeway
and seldom need the brakes, and when I see others slamming the brakes on in
front of me, I lift off the gas and lightly apply my brakes and avoid the
need to apply them with the gusto needed by many of those around me.
If people drive the way I drive, it is reasonable that the rotors would last
3 or 4 pad changes, but it is reasonable that the rotors last 2 changes
before you even have to look at them.
Yes, there are times that rotors need to be replaced with each pad-change,
but this should be the exception rather than the rule, and indicates
aggressive driving -- aggressive stopping to be precise. If the shop is
telling you that you have the rotors replaced, ask for the numbers. If you
wear the brakes down to the backing plate and damage the rotors, expect to
replace the rotors. But if you have the pads replaced before they get to the
backing plates, then there is no reason the new pads can simply jump right
on the car. If the old pads made small ridges, then it is common that the
ridges can be removed when the pads are changed the first time, then the
rotors should be replaced the next time pads are changed. Removing these
ridges is called "turning the rotors," depending on how deep the ridges are,
the rotors might not be able to be turned. I think the common position
around here is that the rotors can never be turned, but I am not certain
this is true all of the time; it matters on how much material needs to be
removed to make the rotors flat again. I think the idea is that if so little
material needs to be removed to make the rotors flat, then there's no point
in turning them, and if they are worn so badly that they need to be turned,
then they are beyond hope. I suppose that if this is the way these guys look
at this, then it is true, you do not turn BMW rotors. When I replaced my
rotors (front only) they had small ridges that I wanted to clean up, but
when they were cleaned there wasn't enough material left. With 150k on the
car, I thought I was doing pretty well, so I bought new rotors and went home
and installed them.
Rotors are cheap these days, BMW rotors run to about $50 per corner, and
give superior braking performance.
similar driving styles and you get the sort of lifetime from your rotors
that I would expect - but you're the first person in this thread to
suggest they can get 150k miles from a set.
The cost is not really an issue as far as I'm concerned on safety
critical parts ... if it needs replacing then it needs replacing :-)
Keep driving safely.
Let me clarify that particular point, 150k miles. I bought the car used with
105 already on it. What I do know is that it went from 150 to 215, 65k, and
I was not even thinking of doing brake work, at least not work that included
I think it is reasonable to suggest that rotors will last through two sets
of pads, but careful drivers can get three sets of pads past a set of rotors
if they try. I don't think it is right to suggest that one will get this
sort of wear, because if they don't they they think something is wrong. One
should plan on two sets of pads for a set of rotors, then be thrilled if he
can get three sets of pads per set of rotors.
I guess in the grand scheme of things, it's not that big a deal to replace
your brakes every couple years instead of every 5 years. (or whatever the
numbers work out to for various people in various cars).
I certainly wouldn't give up any driving pleasure for longer-lived brakes.
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