05-28-2021, 07:32 PM | #1 |
Lieutenant
433
Rep 442
Posts |
Measure the whole disc face!
I swap pads so often for track/summer/winter that I don't have any correlation between pad wear and disc wear. At 50K miles, I knew my discs were getting worn, but the faces still looked good.
Obviously, the way to determine disc wear to is measure the thickness. I've been using my standard digital caliper, and last fall I measured 29.02 and 28.96 on my front discs. That was down from 29.4mm the year before. Definitely some wear, but well above the 28.4mm minimum thickness. Considering the new thickness of 30.1mm, I still had at least a third of the thickness left. Not great for track, but no real worries. The problem is that I was only measuring the outer edge of the disc. (Not the wear ridge, but just inside that on the worn surface.) My standard caliper isn't really the right tool, and since I'm a tool nerd, I decided to buy a cheap digital disc caliper. For $40, I got a tool that isn't super accurate, but easily measures to 0.1 mm accuracy, and more importantly can read multiple places across the disc face. And the longer arms make it WAY easier to use the caliper and read the values. So, measured the discs with my fancy new tool, and I got a 28.9+mm reading on the outer edge. About the same as my good caliper. Than I measured the inner edge of the wear face. 27.9mm. Uh-oh. I just went from having some comfortable meat on the discs, to being WAY under minimum spec. Both discs were about the same, and definitely needed immediate replacement. So, I thought I would post this here to remind everyone that the disc wear may not be even from the inside to outside edge. And that maybe a cheapish tool would be a good investment to learn how much wear your discs really have. Got the new discs in the mail today. On the car, I've never really noticed how big these things are, but handling them as separate pieces, wow, they are MASSIVE. Way bigger and heavier than any other discs I've ever replaced on my family sedans/wagons. They are weighing in at about 22.8 lbs. And these are the original BMW aluminum hat models. Hate to see what the cheaper full iron discs weigh. |
05-28-2021, 10:48 PM | #2 | |
Brigadier General
4413
Rep 3,497
Posts |
Quote:
I bought, but have yet to use, the BMW tool for performing these measurements: The best price I found for the measurement caliper was at Germain BMW Parts: https://parts.germainbmw.com/oem-par...10-83300495451. Rotors for performance cars certainly have quite a bit of mass, don't they! The dimpled and slotted units I got as part of an M Performance Brake Kit came in at: Front: 370X30 26.50# .Rear: 345X45 19.25# vs. 19.50# for the 34206797605 plain rotors
__________________
2017 M240i: 23.8K, 28.9 mpg, MT, Sunroof Delete, 3,432#, EB, Leather, Driving Assistance Package, Heated Front Seats | Sold: E12 530i, E24 M635CSi, E39 520i, E30 325is, E36 M3 (2)
TC Kline Coilovers; H&R Front Bar; Wavetrac; Al Subframe Bushings; 18X9/9½ ARC-8s; 255/35-18 PS4S (4); Dinan Elite V2 & CAI; MPerf Orange BBK; Schroth Quick Fit Pro; GTechniq Crystal Serum Ultra Ceramic; Suntek PPF |
|
Appreciate
0
|
05-29-2021, 09:44 AM | #3 | ||||
Lieutenant
249
Rep 506
Posts |
Quote:
Quote:
__________________
E46 -> E90 -> F30 -> F23
|
||||
Appreciate
0
|
05-29-2021, 10:19 AM | #4 |
Car Geek
3626
Rep 3,594
Posts |
That's due to the fact that dradernh's front rotors are 370mm diameter (3/4-series Mperformance size) vs the standard Mperformance 340mm diameter on the 2-series.
|
Appreciate
0
|
05-29-2021, 01:00 PM | #5 | |
Brigadier General
4413
Rep 3,497
Posts |
Quote:
You can see what they look like here: https://www.realoem.com/bmw/enUS/sho...diagId=03_0104, and here: https://www.realoem.com/bmw/enUS/sho...diagId=03_0103; as well as here: and here: They look to me like they're made of two pieces riveted together, so not really a two-piece arrangement in the manner of race brakes like this AP Racing disc with hat:
__________________
2017 M240i: 23.8K, 28.9 mpg, MT, Sunroof Delete, 3,432#, EB, Leather, Driving Assistance Package, Heated Front Seats | Sold: E12 530i, E24 M635CSi, E39 520i, E30 325is, E36 M3 (2)
TC Kline Coilovers; H&R Front Bar; Wavetrac; Al Subframe Bushings; 18X9/9½ ARC-8s; 255/35-18 PS4S (4); Dinan Elite V2 & CAI; MPerf Orange BBK; Schroth Quick Fit Pro; GTechniq Crystal Serum Ultra Ceramic; Suntek PPF Last edited by dradernh; 05-29-2021 at 01:22 PM.. |
|
Appreciate
1
WolfGTI716.00 |
05-29-2021, 02:47 PM | #6 |
Major General
1403
Rep 5,262
Posts |
28.4mm is the minimum thickness to install new pads....
27.6 is the minimum thickness when the rotor must be replaced... "Installation of new brake pads is approved only provided that the brake disc thickness exceeds the specified dimension (see table). Brake discs must be replaced when they reach the nominal thickness (see table) minus 2.4 mm!" Nominal size (diameter x thickness) mm 340x30 Minimum brake disc thickness stamped on brake disc chamber mm 28,4 Yes you need to measure at 3 spots and even even on a few different position on the disc... I got this for $25 https://www.harborfreight.com/6-in-l...per-63714.html |
Appreciate
1
PeterWT253.50 |
05-29-2021, 05:33 PM | #7 | |
Lieutenant
254
Rep 558
Posts |
Quote:
$27 is perfect.
__________________
My 2017 M240i: MHD, xHP, Modded OE Intake, AA GESi 400 CPSI Cat DP, Dinan Mid-pipe, M Performance LSD & Rear Diffuser, BMS Exhaust Tips, Apex EC-7 Wheels, M-Tech Front Lip, iND Painted Mirror Caps, Smoked Reflectors
|
|
Appreciate
0
|
05-29-2021, 05:36 PM | #8 | |
Lieutenant
254
Rep 558
Posts |
Quote:
__________________
My 2017 M240i: MHD, xHP, Modded OE Intake, AA GESi 400 CPSI Cat DP, Dinan Mid-pipe, M Performance LSD & Rear Diffuser, BMS Exhaust Tips, Apex EC-7 Wheels, M-Tech Front Lip, iND Painted Mirror Caps, Smoked Reflectors
|
|
Appreciate
1
dradernh4413.00 |
05-29-2021, 07:02 PM | #9 | ||
Major General
1403
Rep 5,262
Posts |
Quote:
Else EBC yellow stuff are my choice for sport street and even moderate track |
||
Appreciate
1
PeterWT253.50 |
05-30-2021, 07:33 AM | #10 |
Lieutenant
254
Rep 558
Posts |
I already bought the Brembo, but if I don't like them, I'll consider swapping them for the EBC red or yellow. Thanks for the heads up.
__________________
My 2017 M240i: MHD, xHP, Modded OE Intake, AA GESi 400 CPSI Cat DP, Dinan Mid-pipe, M Performance LSD & Rear Diffuser, BMS Exhaust Tips, Apex EC-7 Wheels, M-Tech Front Lip, iND Painted Mirror Caps, Smoked Reflectors
|
Appreciate
0
|
06-01-2021, 10:18 PM | #11 | |
Lieutenant
433
Rep 442
Posts |
Quote:
Measured the rear discs this past weekend while putting the track pads on. (BIR this weekend, yay!) Just as much variance from inside to outside as the fronts. But the inside minimum is still comfortably above the listed 22.4mm minimum. Likely replace them soon. That Harbor Freight unit looks identical to the Vinca unit I bought on Amazon. Not a super high precision tool, but more than accurate enough for this purpose. |
|
Appreciate
0
|
06-01-2021, 10:30 PM | #12 | ||
Major General
1403
Rep 5,262
Posts |
Quote:
|
||
Appreciate
0
|
07-25-2021, 12:03 AM | #13 |
Second Lieutenant
78
Rep 230
Posts |
Anyone know the minimum for the rears? I know they come brand new at 24mm.
__________________
'04 E46, '08 E93, '16 F22 M235i, '17 i01 i3
|
Appreciate
0
|
07-25-2021, 09:53 PM | #14 |
Lieutenant
433
Rep 442
Posts |
|
Appreciate
0
|
07-31-2021, 11:20 AM | #15 |
Second Lieutenant
78
Rep 230
Posts |
__________________
'04 E46, '08 E93, '16 F22 M235i, '17 i01 i3
|
Appreciate
0
|
Post Reply |
Bookmarks |
|
|