RE: Notches on brake rotors

[Coelacanth]

I'm sure this has been asked before, but my searches in this section for "rotor notch" or "divot" or just "notch" turned up nothing relevant. What are these notches for? Online searching seems to show a different kind of notch is machined along edges of rotors to balance them, but both my old and new rotors have these notches cut in right in line with a stud, so this doesn't appear to be a balancing mark, but rather positional. What are these notches for?

 

[RemCharger]

I would guess some sort of locating tool when machining commenced.
Slightly different note; how much were they and where did they come from?

 

[kiwigtx]

I would guess some sort of locating tool when machining commenced.

You mean like @Richard Cranium 's cookie cutter meme? Makes it easy to grab?

 

[Coelacanth]

I would guess some sort of locating tool when machining commenced.
Slightly different note; how much were they and where did they come from?

I got the Dynamic Friction rotors on RockAuto, P/N: 60040005. I got them with new SKF inner seals #17110 shipped for about $340 CAD after the dollar conversion.

 

[RemCharger]

I got the Dynamic Friction rotors on RockAuto, P/N: 60040005. I got them with new SKF inner seals #17110 shipped for about $340 CAD after the dollar conversion.

Thanks, that's about what my cousin just paid for his D150

 

[1STMP]

Do they fit, and are they concentric?
I see no reason for hogging out the
holes other than a machining malfunction.
Don't know if I'd trust these mounted and
in use, tbough hub centricity seems to be
correct. I'd take them back to the parts store
and ask to see another set for a side by side
comparison. Looks to me like somdthing that
got past quality control.

 

[1STMP]

I found this and hope it
sheds some light on your
question.

"Some manufacturers, like Brembo, use a notch or a cut along the outer edge of the rotor during production to ensure balance. This notch is not a sign of imbalance but rather a deliberate manufacturing process to achieve perfect balance."

I have to admit I've not seen
this before and had always
assumed normal machining
processes would be enough
to ballance a rotor.
Thanks for posting.

 

[padam]

Do they fit, and are they concentric?
I see no reason for hogging out the
holes other than a machining malfunction.
Don't know if I'd trust these mounted and
in use, tbough hub centricity seems to be
correct. I'd take them back to the parts store
and ask to see another set for a side by side
comparison. Looks to me like somdthing that
got past quality control.

I think that might be an optical illusion.

 

[1STMP]

I'm having a hard time believing that a couple
grams of material removed from a rotor is
detrimental to it's overall performance and
feel. Especially when the magnitude of noticible
vibration occurs typically further from center axis.
A gimmick to charge more? Hey, it's got a notch.
You gotta ask yourself, how many rotors were
manufactured without that notch that have
served their purpose. There are millions of
rotors out there with no notches. Hype and
what's pushed as cool
is more money out of your
wallet.
With typical street driving.m

(granted some butthole
in a Camaro) pushes your
ego to the edge...

 

[Coelacanth]

My original rotors have the same notches in them. This doesn't seem to be the same thing as the balancing machining, which isn't a divot like my image, but a small area ground away. Side-by-side, the new looks identical to the old. I'm guessing it's indeed for balancing. Rotors are an extremely heavy part, relatively speaking, and directly involved with steering and suspension, so if they weren't balanced, you would DEFINITELY notice it. That's why they balance wheels, and a bunch of mud and dirt accumulation inside a wheel can cause vibrations.

EDIT: I believe we now have a definitive answer on why rotors have these notches. I never had a look at both of my old rotors until tonight. The notches are shown on the bottom in this pic, and are different sizes. Clearly this indicates the reason must be for balancing...and that one of them was not machined very precisely, from the looks of the amount of material machined out.

 

[1STMP]

I'm leaning more towards these being a positioning
guide for hole locations. If it were for ballancing,
the size and location of the notch would vary.
Geometric dimensioning and tolerancing would
remove any inballance.
If these notches were used for ballancing,
then why aren't all rotors machined in the
same manner? Lots of rotors out there w/no
notches.

 

[dadsbee]

Factory...

 

[Coelacanth]

If it were for ballancing,
the size and location of the notch would vary.

Which is exactly what I've shown in my image showing my two original rotors. The notches are different sizes.

 

[1STMP]

Which is exactly what I've shown in my image showing my two original rotors. The notches are different sizes.

Please note the location.
All notches shown are either
in line or exactly centered
between two lug holes. If
these notches were for
ballancing, they would be
in different locations around
the circumfrance of the
rim mounting surface.
Also note that rotor wear
is not constant about the
circumferance of pad
contact, so ballancing
would be a wasted effort
as rotors typically warp
and twist do to high heat
cycles.
Different vendors that build
rotors may use different
machining practices that
would explain the difference
in the notches overall depth
and size.
Again, if ballancing were this
critical, you would see
evidence of such on every
rotor produced by any
manufacturer.

 

[Coelacanth]

If you research this, you will see evidence of this on most rotors. It might not be an obvious divot like my examples shown above; on newer rotors, it's more likely that there's a small area on one section that's machined down a bit.

Mill Balancing: Why Is There a Notch in My Brake Rotor? | PowerStop