> There is no reason to believe that OEM brake rotors are any better than
> those made by a reputable after market manufacturer.
Actually - there is. And it's not OEM vs the others, it OE vs OEM (as in
Original Equipment from BMW and Original Equipment Manufacturer - where
they can use the term because at one time they may have manufactured one
little part for BMW.)
> Indeed it's not unknown for pattern parts to be made by the same Co that supplies the motor Co,
> but being 'pattern parts' they are usually cheaper.
And it's also known that BMW rotors are fully balanced. If you look at
the newer ones you'll see little circular grind marks on the cooling
fins between the two rotor surfaces. Older ones used balance clips that
clipped onto the fins. ATE makes BMW rotors, ATE also makes "OEM" rotors
that fit the same BMWs. The ATE OE rotors are balanced. The ATE "OEM"
rotors are not. Same deal with brake pads.. ATE OE pads have chamfered
edges. ATE "OEM" pads do not. Does it make a difference? Sure does - I
found this out when I had to redo a job I did with ATE "OEM" stuff due
to shudder and vibration. With the BMW parts installed - the brakes felt
just like they did from the factory.
> Bearings are a classic example. A std bearing bought from a bearing
> supplier might cost £3-4. Put in a box with a car makers logo on it, and the price
> can more than double. For exactly the same spec bearing, from the same
> manufacturer.
You're on solider ground with this statement on bearings, although BMW
may specify closer than standard tolerances on bearings then the
tolerances of an "off the shelf bearing". If the PN is identical - then
the bearing is likely identical, but I've seen BMW specific bearings
with a manufacturer's part number on them that can't be located in the
manufacturer's catalog. Same dimensions as a stock bearing - different
tolerances.
> Mike.
OE = Original Equipment - from BMW
OEM = Original Equipment Manufacturer - which doesn't mean they
manufacture THIS part for the manufacturer, or that this part meets the
OE specifications.
Dan Buchan - 17 Jan 2007 20:53 GMT
> And it's also known that BMW rotors are fully balanced. If you look at
> the newer ones you'll see little circular grind marks on the cooling
[quoted text clipped - 6 lines]
> to shudder and vibration. With the BMW parts installed - the brakes felt
> just like they did from the factory.
Whenever I used ATE OEM pads they were chamfered. Used ATE discs too
and never had a problem. Do discs really need balancing?
> OEM = Original Equipment Manufacturer - which doesn't mean they
> manufacture THIS part for the manufacturer, or that this part meets the
> OE specifications.
Obviously that's true, but conversely you can't say the OEM part is NOT
the same, either.
Dave Plowman (News) - 18 Jan 2007 00:29 GMT
> Whenever I used ATE OEM pads they were chamfered. Used ATE discs too
> and never had a problem. Do discs really need balancing?
I always fit ATE and have since my first BMW and never had a problem
either.
I can't see why a well made disc should need balancing - it would have to
start out as a very poor casting if it was significantly out of balance
after machineing. Perhaps the ones Mr Admin saw with signs of balancing
started off as poor castings.
It's rather the same as with tyres. The pick of the bunch don't need
balancing either when new. They usually go to the makers to be fitted to
new cars.

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Richard Sexton - 18 Jan 2007 01:43 GMT
>> Whenever I used ATE OEM pads they were chamfered. Used ATE discs too
>> and never had a problem. Do discs really need balancing?
>
>I always fit ATE and have since my first BMW and never had a problem
>either.
I just get an or car balance which takwes care of any sligh imbalance in the
wheel, tire, hub, rotors, half shafts etc.
I resist the urge to get factory parts. 10 years later, so far so good.

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admin - 18 Jan 2007 14:41 GMT
>> Whenever I used ATE OEM pads they were chamfered. Used ATE discs too
>> and never had a problem. Do discs really need balancing?
I think the difference is the amount of chamfer. BMW pads have a deep
chamfer that goes at least 1" or so into the pad. Aftermarket pads
typically have a small edge chamfer. The deep chamfer stays in place for
a long time as the pad wears, and puts more braking force on a smaller
area to begin with - which may help with pad-bedding-in.
> I always fit ATE and have since my first BMW and never had a problem
> either.
[quoted text clipped - 3 lines]
> after machineing. Perhaps the ones Mr Admin saw with signs of balancing
> started off as poor castings.
Think about the casting with ventilated rotors - there is no way to
machine the interior fin area, and this is a rough sand casting
(probably done via lost-wax). There is obviously some need for balancing
or BMW wouldn't bother doing it. Considering how fussy BMW front ends
are for balance, it seems to be a GOOD THING to have the rotors balanced.
> It's rather the same as with tyres. The pick of the bunch don't need
> balancing either when new. They usually go to the makers to be fitted to
> new cars.
It we take this analogy further - then the pick of the bunch of rotors
are sent to BMW who finds they still need balancing. Look at a factory
rotor - on the E39 ones you'll see circular grinding marks at points
along the fins where material was removed (undoubtably by an automated
machine) to balance them.
I'm not one to waste money - but the work required to redo this job when
it goes bad is enough to keep me using OE parts. Redid it once and that
was enough aggravation that I don't want to redo it again.
Dave Plowman (News) - 18 Jan 2007 17:46 GMT
> I'm not one to waste money - but the work required to redo this job when
> it goes bad is enough to keep me using OE parts. Redid it once and that
> was enough aggravation that I don't want to redo it again.
I'd not like to guess how many discs my brother and myself have replaced
on our BMWs over the years, but they've all been ATE and all fine. Perhaps
they come from more than one factory depending on the country they're
supplying.

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Mike G - 18 Jan 2007 02:16 GMT
>> There is no reason to believe that OEM brake rotors are any better than
>> those made by a reputable after market manufacturer.
[quoted text clipped - 18 lines]
> vibration. With the BMW parts installed - the brakes felt just like they
> did from the factory.
I think you were just unfortunate. I've fitted many pattern discs and pads
to my cars over the years without any problems concerning balance or
efficiency.
I don't believe in trying to save money on safety related items, if it means
the parts are sub standard. If I believed that were the case I wouldn't use
them.
A few weeks ago I had pattern rear discs, pads and brake shoes fitted to my
E39.
Total cost for the parts, under £100. No complaints so far.
I don't know what BMW charge for the same parts, but I imagine it to be
considerably more.
>> Bearings are a classic example. A std bearing bought from a bearing
>> supplier might cost £3-4. Put in a box with a car makers logo on it, and
[quoted text clipped - 9 lines]
> manufacturer's catalog. Same dimensions as a stock bearing - different
> tolerances.
Somehow I doubt that. An off the shelf stock bearings is built to what might
be called a std commercial tolerance, but by selective assy, and at added
cost, a more precise bearing can be supplied. AFAIK designated by 'o', 'oo'
and 'ooo' with 'ooo' bearings being the most precise.
> OE = Original Equipment - from BMW
Which is what I meant. OK a mistake on my part, but the context in which I
used the term should have made that fairly obvious.
Mike