Is there 'really' a difference between (standard) E39 rotors of various brands?

Serious question:

Is there 'really' a difference between E39 rotors of various brands?
ASSUMPTION: OEM size & fitment (i.e., nothing fancy ... apples to apples comparison).

Over in this thread today, the rotor-quality question came up:
- E39 (1997 - 2003) > Ever hear of Winhere brake rotors??

Personally, I'm leaning toward "a rotor is a rotor" ... as I have no anecdotal or personal experience otherwise ... but ... that's why I ask the question.

To be clear, I'm sure there 'can' be (perhaps huge) differences between rotors, mostly on the quality side ... but ... the question is whether ... in reality ... there is a meaningful difference between rotors of the most-recommended brands for our E39?

Given the following OEM-fitment replacement rotors:
- What rotors are recommended for street use on the E39

QUESTION: Is there really a 'meaningful' difference between these rotors?

Most often recommended replacement rotors:
- ATE solid (Premium One brand is OEM?)
- Balo (which model?)
- Brembo solid (which model?)
- Centric Premium ?model
- Zimmermann ?model

When you say "meaningful difference", I am assuming that you are referring to braking distance since that is the primary metric to measure braking performance. Since the brake rotor simply acts as a surface for the brake pad to grip onto to slow down a moving vehicle, I would agree that there should be no performance difference (e.g. stopping distance) between rotors that are made of the same material, assuming the same brake pads, equal quality of construction and street use. While most rotors are constructed of steel, I do not think the coefficient of friction varies significantly between the various grades of steel used. Any performance differences in fade, cooling, etc. would be due to design, mass, etc. Things like brake warping, out of round, etc. are quality issues outside the scope of this discussion. Other issues like brake squeal are probably more dependent upon the brake pad used, vice the rotor.

Originally Posted by bluebee

Serious question:

Is there 'really' a difference between E39 rotors of various brands?


Personally, I'm leaning toward "a rotor is a rotor".

Probably correct...unless the rotors are manufactured with inferior raw materials or quality control isn't real a priority. The only difference I could discern was coated rotors don't corrode as quickly as non-coated. Other than that, as long the steel is of the highest quality obtainable and the rotors balance well, a rotor is probably a rotor.

A rotor by any other name will still stop your car.

a little poetic flourish there

The quality of steel and manufacturing process is why I wouldn't order a Chinese brand. I'd be worried about what happens the first time I go down a mountain and the brakes get hot. Ever see a Chery crash test video? They're probably out of round, unbalanced, and brittle.

Originally Posted by Fudman

When you say "meaningful difference", I am assuming that you are referring to braking distance

Good point!

I left 'meaningful' undefined because I wasn't sure what was meaningful.

I do agree, probably the 'most meaningful' metric is stopping feel & distance.

Originally Posted by Fudman

Any performance differences in fade, cooling, etc. would be due to design, mass, etc.

Sounds reasonable that an OEM-shaped rotor would perform as OEM shaped-rotors do.

Originally Posted by Fudman

Things like brake warping, out of round, etc. are quality issues outside the scope of this discussion.

I'm not so sure that's out of scope.

When I chose my first E39 replacement rotors, I simply researched the brands that you guys recommended - and simply selected the least expensive (taxed and shipped to my door) of those.

If it had been 'warped' (in quotes because what I think you meant was the faces were not parallel due to lousy manufacturing tolerances), or out of round (I'm not sure what that means), I would not have been happy.

So, I would disagree here and say that meeting the OEM specs would be as important a criteria as performance (i.e., stopping ability).

Originally Posted by Fudman

Other issues like brake squeal are probably more dependent upon the brake pad used, vice the rotor

Agreed.

Originally Posted by AnotherGeezer

coated rotors don't corrode as quickly as non-coated

I'd lump that under cosmetics and not 'meaningful' in a performance sense.

Originally Posted by AnotherGeezer

the rotors balance well

Presumably you mean even distribution of weight.

Is weight imbalance (as opposed to size tolerance) a common problem?

How would we know if a rotor is not weight 'balanced'?

For example, following your recommendations, I noticed, in post 91 of the brake thread, that my new and old rotors had a weight-balancing slice taken out of the edge:
- What is this slice taken out of my rotor (1)

Note: Ignore the text on the picture - we found the answer (it was for weight distribution):

Originally Posted by AnotherGeezer

a rotor is probably a rotor

Intuition says the more the marketing guys try to tell us otherwise, the more the case is that, yes, a (recommended brand) rotor of the OEM fitment will perform like any other (recommended brand) rotor of OEM fitment.

Originally Posted by AnotherGeezer

A rotor by any other name will still stop your car.

Nice!

A rotor, by any other name, will stop just the same!

Originally Posted by bmw_n00b13

I wouldn't order a Chinese brand

Seems reasonable.

Are any of the recommended rotors Chinese brands?

Originally Posted by bluebee

A rotor, by any other name, will stop just the same!

A better poetic flourish

Balo's don't rust.
Some Zimmermann's are zinc coated.
Not sure about metallurgic composition of "non-brands" - the most important one.

I believe that there is a definite difference between brake rotors. If the foundry does not have good technology and quality control, all sorts of inconsistent grain structure and inter-metallic compounds (hard spots) are probable. Besides, consider that many aftermarket brake manufacturers sell 2 or more grades of rotors with the price ratio approaching 2 to 1. While I doubt the cost ratio is that high, I'm pretty sure that there is a difference between the bottom & premium grades. Unless their product spec sheets and descriptions are pure fairy tales.

I think that many common brake vibration problems are a result of the irregularities throughout the rotor. Further, the temperatures created during braking can be high enough to cause changes in the grain microstructure and growth of inter-metallic compounds that will affect the surface condition of the rotor. Especially if the foundry practices are deficient. A lot of reading and a little personal experience leads me to believe that at the very least, many "warped" rotor are not in fact distorted, but rather have hard spots of intermetallics &/or resultant uneven brake pad deposits on the rotor friction surfaces due to the irregularities. Both will cause braking effect variation as the wheel rotates.

Have you ever had brake shudder/vibration without any pulsing in the pedal? Many of my brake problems over the years have been that way. Friction variation is the most likely explanation. Especially since I could make a good case that a pure warp, i.e. run-out, in a rotor should not pulse the pedal (particularly with single piston floating calipers), would create only insignificant braking variation and would cause only mild steering wheel shake. (Thicknes variation is another matter & would cause both pulsing pedal and brake vibration.)

A prior car (GM), bought brand new, went 100k miles on the original Delco pads & rotors without any vibration ever. No complaints there. I bought brand name premium grade pads and PG grade rotors. "PG" being premium grade, so I was told. After about 10k miles I had a vicious brake vibration, but no pedal pulsing. I had the rotors turned. OK for 10k miles, then vibration back. I checked into the rotor brand & grade. It turned out "PG" was professional grade. In other words, bottom line, enough to pass a safety check - just don't keep the car. A learning experience for me.
I checked run-out and thickness - all in spec. I then tried hand sanding the rotors with good abrasive paper to scuff up and remove any micro irregularities from the surfaces. Good for about 10k miles & then vibration returned. Eventually I put Delco pads & rotors on & problem gone for for another 100k until the car died.

For the extra hundred or so bucks on a brake job, I'm not going to take the chance on no name, unknown quality or low grade rotors. BMW, ATE, Zimmermann, etc. for me.

But I am willing to buy for as much off list price as I can find The adage that "you get what you pay for" needs very careful interpretation in real life.

Regards
RDL

One thing to look for is the size of the cooling vein area. The larger the cooling area the greater chance of warping. Cheap rotors have a larger vein area so they can use less metal.

I found this picture that shows the difference from a Quality to cheap rotor.

Originally Posted by Joe@Bavarian

One thing to look for is the size of the cooling vein area. The larger the cooling area the greater chance of warping. Cheap rotors have a larger vein area so they can use less metal.

Good info. Thanks Joe.

Originally Posted by Joe@Bavarian

One thing to look for is the size of the cooling vein area. The larger the cooling area the greater chance of warping. Cheap rotors have a larger vein area so they can use less metal.

I found this picture that shows the difference from a Quality to cheap rotor.

Cool picture! thanks for sharing! May I ask what brand the one is on the right ?

Originally Posted by Joe@Bavarian

One thing to look for is the size of the cooling vein area. The larger the cooling area the greater chance of warping. Cheap rotors have a larger vein area so they can use less metal.

I found this picture that shows the difference from a Quality to cheap rotor.

hmmm this is really interesting.

Originally Posted by Joe@Bavarian

Cheap rotors have a larger vein area so they can use less metal

Interesting that vein area is something to look for.

So the question would be whether the vane area is similar or not in the most-often-recommended E39 replacement rotors:

Most often recommended replacement rotors:
- ATE solid (Premium One brand is OEM?)
- Balo (which model?)
- Brembo solid (which model?)
- Centric Premium ?model
- Zimmermann ?model

BTW, over in this thread today:
- Yet another rotors/pad question

A reference was made to a nice treatise of drilled vs slotted vs solid rotors (although this thread is only about OEM-equivalent rotors):
- Cross drilled rotor myths dissolved

Originally Posted by bmw_n00b13

The quality of steel and manufacturing process is why I wouldn't order a Chinese brand. I'd be worried about what happens the first time I go down a mountain and the brakes get hot. Ever see a Chery crash test video? They're probably out of round, unbalanced, and brittle.

+1.
Chinese/ Asian metal = junk IMO.

Thanks guys, will reach out. Appreciate it.

Might want to contact 540i M-Sport as he has PSS14s, which I think might be the same adjustments.

I think those are the ones you can adjust with a button inside the car.

Hey Edgy, I haven't forgot you, but I still did not installed mine...

I put Balo's on the front couple month ago. I don't know what to say, they are made in Germany and so far their performance is just what BMW does... Stops you like no other.

Also the pads are important factor in braking and stopping distance (IMO).
But from my experience few days ago when I went and bought lower arms from NAPA which they were the best they can make with life time warranty and they were more expensive than Lomforders, they just didn't fit on the car! The bushing side where there are a lot of teeth, didn't go in the housing where it is supposed to be bolted.

Stick to a German brand because they made the car and they know the sizes and every little spec on the car whereas other companies who try to make parts for those, they are just pathetic.

My point is that there will be small differences and you might not be able to detect them and small details/differences can be hard to detect on rotors but in my case (the control arms) it happened to be easy. They just didn't fit lol. The materials could be better don't get me wrong but if those engineers couldn't make it fit perfectly as it is supposed to, then personally I don't think they are capable of making something they claim to meet or EXCEED OE specs.... Maybe I shouldn't judge on a single experience but it was a very frustrating experience.

Good thread. Just to contribute, how about the Euro floating rotor vs. NA rotors? Any big difference?

My M5 has these, but I haven't pulled the wheels yet for a close look. Will do so when I'm ready to adjust the Bilsteins.

BTW, I'm still trying to connect with someone who has first hand knowledge of adjusting a Bilstein PSS9 coilover kit. If you know anyone, please ping me. I'd appreciate it.

Originally Posted by Edgy36-39

BTW, I'm still trying to connect with someone who has first hand knowledge of adjusting a Bilstein PSS9 coilover kit. If you know anyone, please ping me. I'd appreciate it.

Might want to contact 540i M-Sport as he has PSS14s, which I think might be the same adjustments.

http://www.bimmerfest.com/forums/member.php?u=11820

Originally Posted by dvsgene

Might want to contact 540i M-Sport as he has PSS14s, which I think might be the same adjustments.

http://www.bimmerfest.com/forums/member.php?u=11820

Actually, mine are the Bilstein B14 PSS, which is the same springs, and shocks/struts, but with no damping adjustments, only height adjustable. There is a nut on the struts where the adjustment knob would be.

Originally Posted by Edgy36-39

Good thread. Just to contribute, how about the Euro floating rotor vs. NA rotors? Any big difference?

My M5 has these, but I haven't pulled the wheels yet for a close look. Will do so when I'm ready to adjust the Bilsteins.

BTW, I'm still trying to connect with someone who has first hand knowledge of adjusting a Bilstein PSS9 coilover kit. If you know anyone, please ping me. I'd appreciate it.

Contact MattMartinDrift, TheTinPusher, and Mad Dog 20/20.
They will be able to help!
Also

Threads:
http://forums.bimmerforums.com/forum...=435130&page=2

http://forums.bimmerforums.com/forum....php?t=1423290

Originally Posted by Edgy36-39

Good thread. Just to contribute, how about the Euro floating rotor vs. NA rotors? Any big difference?

My M5 has these, but I haven't pulled the wheels yet for a close look. Will do so when I'm ready to adjust the Bilsteins.

BTW, I'm still trying to connect with someone who has first hand knowledge of adjusting a Bilstein PSS9 coilover kit. If you know anyone, please ping me. I'd appreciate it.

If you need to adjust the height you will need the pair of fixed spanner wrenches they came with. If you don't have them, you can probably buy better quality ones from a race shop, either locally or online. You just need to make sure they fit properly. The Bilstein ones are pretty cheaply made, but work. They are very thin and made from cheap metal. Better quality spanners are a bit thicker, and engage the sprockets at three points, instead of one, preventing slipping off.

So topical.. Im in this same boat too.. Zimmermann or Balo??

Where is zimmermann produced?

Originally Posted by Brandon540/6M

So topical.. Im in this same boat too.. Zimmermann or Balo??

I've got both on the car right now Balo solid front, Zimmerman cross drilled rears. Either is fine. Balo make very good solids, Zimmerman very good cross drills.

Once the Zimmerman wears down, I'll go with Balo Solid rears again.

Originally Posted by dvsgene

I've got both on the car right now Balo solid front, Zimmerman cross drilled rears. Either is fine. Balo make very good solids, Zimmerman very good cross drills.

Once the Zimmerman wears down, I'll go with Balo Solid rears again.

Hmm.. I wonder about just the plain rotors from zimmermann.. i think im putting too much effort into this, I need to just pick something and order it!