I made mention earlier [1] of how the brake rotors from different vendors / product tiers can weigh MUCH differently, but I didn't have my notes handy write I wrote that post. I couldn't quote my findings.
Today I found my notes. This topic is worth a new thread IMHO.
Background: I had had a pulsation-while-hot front brake situation on my Suburban. Upon inspecting the rotors, I noticed that one was noticeably less massive (bigger vent gap) then the other.
I figured it was time to get replacements and shopped for some of the more expensive rotors I could find [2], figuring one can't buy quality without spending money.
While replacing the rotors, I pulled out my refrigerant scale and weighted the old and the new. These measurements were made on Jun30, 2017 @ 231,950mi on the Sub. Here are the numbers:
15.4# OLD Front Left
12.1# OLD Front Right
16.5# NEW Front Left
16.5# NEW Front Right
Look at the differences above in their weights [3]. Why the disparity?
First, I learned that one of the Suburban's OE rotors had been replaced by the Chevrolet garage years prior (when my father owned the vehicle). The service ticket showed a GM replacement rotor (8-digit p/n), but of course GM makes a lot of "serviceable" replacements and perhaps this replacement was a cheapie.
In addition, I know that both rotors had been turned at least once.
The OLD rotors' difference of about 27% (15.4# / 12.1#) is quite marked. It means, in any braking scenario, the lighter rotor's temp rise would be 27% greater than the temp rise of the heavier.
Notice the NEW rotors are 7% and 35% heavier respectively than those they replaced, and in total there's 20% more iron to soak up the heat from braking [4].
FWIW
Notes:
[1] Brake Vibration @ https://www.gmt400.com/threads/brake-vibration.58230/post-1242928
[2] Raybestos p/n 580438PER, $83/ea on RockAuto as of this writing. These also appear to be marketed as ACDELCO p/n 18A258SD $76/ea. These rotors have some funky design etched into them which, according to the inventors' patent, is simply a design with no claims of utility, see https://patents.google.com/patent/USD640620S1 and then take the option to download the .pdf Otherwise, the Raybestos p/n 580438 might the same rotor w/o the funky design and at lower cost, $42/ea RockAuto.
[3] Mass, and not weight, is what really matters, but I'll use weight (lbs) because it's a common term... and anyway, weight and mass are simple multiples of each other when measured at a specific elevation (e.g., sea level).
[4] This is a bit of an mis-statement because some of the total mass is in the hat.
Today I found my notes. This topic is worth a new thread IMHO.
Background: I had had a pulsation-while-hot front brake situation on my Suburban. Upon inspecting the rotors, I noticed that one was noticeably less massive (bigger vent gap) then the other.
I figured it was time to get replacements and shopped for some of the more expensive rotors I could find [2], figuring one can't buy quality without spending money.
While replacing the rotors, I pulled out my refrigerant scale and weighted the old and the new. These measurements were made on Jun30, 2017 @ 231,950mi on the Sub. Here are the numbers:
15.4# OLD Front Left
12.1# OLD Front Right
16.5# NEW Front Left
16.5# NEW Front Right
Look at the differences above in their weights [3]. Why the disparity?
First, I learned that one of the Suburban's OE rotors had been replaced by the Chevrolet garage years prior (when my father owned the vehicle). The service ticket showed a GM replacement rotor (8-digit p/n), but of course GM makes a lot of "serviceable" replacements and perhaps this replacement was a cheapie.
In addition, I know that both rotors had been turned at least once.
The OLD rotors' difference of about 27% (15.4# / 12.1#) is quite marked. It means, in any braking scenario, the lighter rotor's temp rise would be 27% greater than the temp rise of the heavier.
Notice the NEW rotors are 7% and 35% heavier respectively than those they replaced, and in total there's 20% more iron to soak up the heat from braking [4].
FWIW
Notes:
[1] Brake Vibration @ https://www.gmt400.com/threads/brake-vibration.58230/post-1242928
[2] Raybestos p/n 580438PER, $83/ea on RockAuto as of this writing. These also appear to be marketed as ACDELCO p/n 18A258SD $76/ea. These rotors have some funky design etched into them which, according to the inventors' patent, is simply a design with no claims of utility, see https://patents.google.com/patent/USD640620S1 and then take the option to download the .pdf Otherwise, the Raybestos p/n 580438 might the same rotor w/o the funky design and at lower cost, $42/ea RockAuto.
[3] Mass, and not weight, is what really matters, but I'll use weight (lbs) because it's a common term... and anyway, weight and mass are simple multiples of each other when measured at a specific elevation (e.g., sea level).
[4] This is a bit of an mis-statement because some of the total mass is in the hat.
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