Brake Rotors

[xkenx1995]

looks like base rear rotor size, not premium.

Premium rears: 345mm
Base rears: 330mm

Figured that was the case. I returned them to FCP, but haven't ordered the correct size yet.

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[Bigboss]

Anyone running drilled &slotted rotors (like both in one rotor)?

 

[FLtrackdays]

Anyone running drilled &slotted rotors (like both in one rotor)?

They’re pretty & I used to on other cars. Until I realized (found out) they crack much easier and burn through pads much quicker. At least on track. If going for looks, go for it!

 

[Bigboss]

They’re pretty & I used to on other cars. Until I realized (found out) they crack much easier and burn through pads much quicker. At least on track. If going for looks, go for it!

Well supposedly having drills and slots together in a rotor gives you the ultimate brake performance of both advantages in one. Untop they look really cool and aggressive perfect for this car. But your saying its not worth it? I dont go on track persay the highways of mexico are my track i push my cars hard everytime, you think id get the same affect with the pads wearing quicker?

 

[kaj]

Well supposedly having drills and slots together in a rotor gives you the ultimate brake performance of both advantages in one. Untop they look really cool and aggressive perfect for this car. But your saying its not worth it? I dont go on track persay the highways of mexico are my track i push my cars hard everytime, you think id get the same affect with the pads wearing quicker?

That was true a few decades ago. With current pad technology, that is no longer the case. These days it's for looks only.
If tracking the car, Most rotors that you can get now, that are crossed drilled, have the holes drilled after the rotor is cast. That is even worse. Guaranteed to crack. Still fine for daily driving.
I know what you're thinking, race car parts are boring. It's true. There's nothing fancy about them

 

[tomfree]

^^^This^^^
I'm not a materials engineer, but I stayed at a Holiday Inn last night.
Brake rotors are heat sinks - they transfer energy from a process into heat. The more mass you have in a heat sink, the better it does it's job. Material and design also factor in, but the easy part to understand is more mass=better. Slotting and cross-drilling remove mass.

Slotting and cross drilling also create stress risers/stress concentrations in a rotor. That makes the metal at that point MUCH more likely to fatigue and fail around those risers - first little hairline cracks like you see in all heavily used rotors, but they expand much more quickly into big structural cracks.

Older brake pad materials, when really hot, created an "off gas" situation where it literally put a layer of gas between the pad and the rotor. Cross-drilling and slotting was created to give the gas a path to evacuate and allow the pad to contact the rotor again. A side effect...it looked pretty cool. It also made them weigh less. Modern brake pads don't off gas.

Now...some of you who ride motorcycles are thinking "OK smarty pants, why are all bike rotors cross drilled?" Weight and rotating mass makes more of a difference on a 500# motorcycle with a 15# rotating wheel assembly than it does on a 3000# with a 50# rotating assembly.

Again...not an engineer. Just a guy who has spent about 20 years in amateur motorsports trying to learn what works and what doesn't so he can keep his cars on track.

 

[Bigboss]

^^^This^^^
I'm not a materials engineer, but I stayed at a Holiday Inn last night.
Brake rotors are heat sinks - they transfer energy from a process into heat. The more mass you have in a heat sink, the better it does it's job. Material and design also factor in, but the easy part to understand is more mass=better. Slotting and cross-drilling remove mass.

Slotting and cross drilling also create stress risers/stress concentrations in a rotor. That makes the metal at that point MUCH more likely to fatigue and fail around those risers - first little hairline cracks like you see in all heavily used rotors, but they expand much more quickly into big structural cracks.

Older brake pad materials, when really hot, created an "off gas" situation where it literally put a layer of gas between the pad and the rotor. Cross-drilling and slotting was created to give the gas a path to evacuate and allow the pad to contact the rotor again. A side effect...it looked pretty cool. It also made them weigh less. Modern brake pads don't off gas.

Now...some of you who ride motorcycles are thinking "OK smarty pants, why are all bike rotors cross drilled?" Weight and rotating mass makes more of a difference on a 500# motorcycle with a 15# rotating wheel assembly than it does on a 3000# with a 50# rotating assembly.

Again...not an engineer. Just a guy who has spent about 20 years in amateur motorsports trying to learn what works and what doesn't so he can keep his cars on track.

So final answer for performance benefits cross drilled rotors are not worth it compared to plain faced ones?

 

[nibble]

So final answer for performance benefits cross drilled rotors are not worth it compared to plain faced ones?

almost correct.

 

[kaj]

^^^This^^^
I'm not a materials engineer, but I stayed at a Holiday Inn last night.
Brake rotors are heat sinks - they transfer energy from a process into heat. The more mass you have in a heat sink, the better it does it's job. Material and design also factor in, but the easy part to understand is more mass=better. Slotting and cross-drilling remove mass.

Slotting and cross drilling also create stress risers/stress concentrations in a rotor. That makes the metal at that point MUCH more likely to fatigue and fail around those risers - first little hairline cracks like you see in all heavily used rotors, but they expand much more quickly into big structural cracks.

Older brake pad materials, when really hot, created an "off gas" situation where it literally put a layer of gas between the pad and the rotor. Cross-drilling and slotting was created to give the gas a path to evacuate and allow the pad to contact the rotor again. A side effect...it looked pretty cool. It also made them weigh less. Modern brake pads don't off gas.

Now...some of you who ride motorcycles are thinking "OK smarty pants, why are all bike rotors cross drilled?" Weight and rotating mass makes more of a difference on a 500# motorcycle with a 15# rotating wheel assembly than it does on a 3000# with a 50# rotating assembly.

Again...not an engineer. Just a guy who has spent about 20 years in amateur motorsports trying to learn what works and what doesn't so he can keep his cars on track.

I didn't want to type all that, so thank you.

So final answer for performance benefits cross drilled rotors are not worth it compared to plain faced ones?

Correct. Cross-drilled rotors are also a step down in reliability/longevity.

 

[J29DB03]

Big fan of slotted and dimpled. Had them on my Abarth, currently have them on my wife’s Crosstrek.

 

[tomfree]

Dimpling is better than cross drilling, but it still introduces stress risers to the material.

BUT...it's all about your use case. If you're using them on street cars, in normal street driving, you're probably fine. The difference in longevity between a plain rotor blank and a "modified" one is negligible if you don't stress it to within an inch of it's life. If you like 'em, and you understand your use case, enjoy.

A common response you'll see is when someone does a wholesale "brake job" on their vehicle - fresh fluid, pads, and rotors. "Since I put these cross-drilled rotors on the car, it stops so much better." Well, yes and no...your improvement is likely from the pads and the fresh fluid, and ANY fresh rotor. If you did a blind, back to back test with a blank rotor and a slottted/dimpled one, just about the only way you'd be able to tell the difference is noise, as the slots/dimples act somewhat as an abrasive to the pad material...and a teeny little extra noise under braking.

 

[tomfree]

EDIT!!!!!!!!!

Fixed the FCP Euro Link for the 345mm rear disc for the premium cars. Any quotes of this post before 4/18/23 will have the link to the rear rotors for the base/4cyl cars (330 mm)
*******************************************************************************************

I just had this conversation with Jackie from PhD. My car is a '22, but I don't think there were any changes to the 3.0 brakes between 21 and 22. Here are the URLs for each rotor from FCP Euro...and if you know FCP Euro, they have an insane warranty that covers consumables like this. One of my friends has used this on pads, rotors, and even brake fluid with FCP.

Fronts (There is a right and a left rotor because of the directional vanes)
https://www.fcpeuro.com/products/bmw-brake-disc-zimmermann-34116860911-zim-150293632
https://www.fcpeuro.com/products/bmw-brake-disc-zimmermann-34116860912-zim-150293732

Rears (Non-directional vanes, so right and left are the same p/n from Zimmermann)
https://www.fcpeuro.com/products/bmw-brake-disc-zimmermann-34206880079

Digging this one back up...fixed it. Above is the FCP Euro link to the correct 345mm rear rotor for the premium cars - I verified against Zimmermann's website. This is a cheaper 1-piece rotor, non-directional vanes. There appears to be a 2-piece rear available from Zimm as well. It is $190 vs $120, still non-directional vanes.
https://www.fcpeuro.com/products/bmw-brake-disc-zimmermann-34216860925

 

[kaj]

Digging this one back up...fixed it. Above is the FCP Euro link to the correct 345mm rear rotor for the premium cars - I verified against Zimmermann's website. This is a cheaper 1-piece rotor, non-directional vanes. There appears to be a 2-piece rear available from Zimm as well. It is $190 vs $120, still non-directional vanes.
https://www.fcpeuro.com/products/bmw-brake-disc-zimmermann-34216860925

The link in your quote is for the smaller rotors and the link above is the larger/premium rotors?

 

[tomfree]

The link in your quote is for the smaller rotors and the link above is the larger/premium rotors?

Not exactly. On the first page of this thread, I posted links to the front and rear rotors at FCP Euro. In that original post, the link for the rears was for the smaller 330mm rotors from the base/4cyl car

I fixed the original post on page one (quoted) so it now has the correct 345mm rear rotors.

I realize now this is confusing in the previous post...but for clarity...Zimmerman makes (2) 345mm rear rotors for the car. A less expensive 1-piece rotor and a more expensive (and lighter) 2-piece rotor, similar to the factory rotors.

My intention - when someone searches and finds this thread...they won't have to go past my initial post to find the correct info. It sucks to find the post/thread you want, but sift through all the subsequent posts to find out the original post was incorrect.

 

[kaj]

Not exactly. On the first page of this thread, I posted links to the front and rear rotors at FCP Euro. In that original post, the link for the rears was for the smaller 330mm rotors from the base/4cyl car

I fixed the original post on page one (quoted) so it now has the correct 345mm rear rotors.

I realize now this is confusing in the previous post...but for clarity...Zimmerman makes (2) 345mm rear rotors for the car. A less expensive 1-piece rotor and a more expensive (and lighter) 2-piece rotor, similar to the factory rotors.

My intention - when someone searches and finds this thread...they won't have to go past my initial post to find the correct info. It sucks to find the post/thread you want, but sift through all the subsequent posts to find out the original post was incorrect.

Right on, I hear that. For those still running base model/4cyl rear brakes and those running Premium brakes, that's great info to have.

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