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      05-07-2020, 06:37 PM   #1
OldenburgerM3
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Stoptech BBK odd rotor groove / uneven wear

Hi all,
Has anybody seen this before? This rotor groove is the worst (driver-side, outboard), but I have it on both front, inboard and outboard disc faces. All four brake pads have a corresponding bump on them.

What would cause a groove like this???? Very confused.
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      05-07-2020, 09:38 PM   #2
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The IMSA pad shape is DR11 for the new ST60 kits. Other pad shapes don't quite fit right so you'll either have a groove like this or you'll have a groove in the brake pad. Having a slightly smaller brake pad is normal even on the OEM kit as that's why you get that lip around the outside of a well worn stock rotor.

Which brake pads are you using?
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      05-08-2020, 07:12 PM   #3
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Quote:
Originally Posted by OldenburgerM3 View Post
Hi all,
Has anybody seen this before? This rotor groove is the worst (driver-side, outboard), but I have it on both front, inboard and outboard disc faces. All four brake pads have a corresponding bump on them.

What would cause a groove like this???? Very confused.
Looks like you have stop tech. Mine does that as well I concluded it's the dust particles pool at the bottom of the grove and it's a abrasive that affect the rotor wear. It does no harm to the brake system. I just ignore after all the years.
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      05-14-2020, 06:47 AM   #4
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Quote:
Originally Posted by tlrid3r View Post
Looks like you have stop tech. Mine does that as well I concluded it's the dust particles pool at the bottom of the grove and it's a abrasive that affect the rotor wear. It does no harm to the brake system. I just ignore after all the years.
I believe tlrid3r is correct. The pad particles travel down the length of the slot as the disc is spinning, and deposit at the end of the slot. That buildup of pad then digs into both the pad and the disc. If you look at your pads, you likely have some grooving or a clump there as well. We see this on our AP Racing J Hook discs. The two edges of the J Hooks converge about half way up the disc face, with both dumping material into the same spot. It forms a harmless groove. It shouldn't have any impact on performance or longevity. If you haven't read our article, "When is it time to replace my iron brake discs", you should check it out. It talks about this phenomena, as well as many others. You may find it helpful. Thanks.

Here's what this type of grooving looks like on our AP J Hooks:
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      05-14-2020, 09:54 AM   #5
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Quote:
Originally Posted by jritt@essex View Post
Quote:
Originally Posted by tlrid3r View Post
Looks like you have stop tech. Mine does that as well I concluded it's the dust particles pool at the bottom of the grove and it's a abrasive that affect the rotor wear. It does no harm to the brake system. I just ignore after all the years.
I believe tlrid3r is correct. The pad particles travel down the length of the slot as the disc is spinning, and deposit at the end of the slot. That buildup of pad then digs into both the pad and the disc. If you look at your pads, you likely have some grooving or a clump there as well. We see this on our AP Racing J Hook discs. The two edges of the J Hooks converge about half way up the disc face, with both dumping material into the same spot. It forms a harmless groove. It shouldn't have any impact on performance or longevity. If you haven't read our article, "When is it time to replace my iron brake discs", you should check it out. It talks about this phenomena, as well as many others. You may find it helpful. Thanks.

Here's what this type of grooving looks like on our AP J Hooks:
Yeah I think J hook rotor are better to handle this. I really want to upgrade to an AP system but waiting till money is right and I feel I need to replace my stoptech. I got the stoptech before I knew of AP. Far more superior.
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      05-14-2020, 10:01 PM   #6
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I'm having a similar issue with my Brembos GTs.
Hope its just something to do with the brakes not being used and sitting around for a long time. Going to give it a good break-in sometime this week and see what happens.
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      05-24-2020, 06:05 PM   #7
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Very interesting, thanks for the replies. I've talked with Stoptech and their best theory was hub flex or radial temperature gradient. Hmmmm.

I think I like your answer best. I didn't notice the groove at the track, but I checked the track pads (Hawk DTC70, COTA, one weekend) and they have a bump in the corresponding location. Brand new setup, one track weekend.

Currently running Stoptech Street that came with the BBK. In other news, I like the Hawk Street 5.0 better than these but not enough to swap until they're dead.
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      05-25-2020, 01:08 AM   #8
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Quote:
Originally Posted by OldenburgerM3 View Post
Very interesting, thanks for the replies. I've talked with Stoptech and their best theory was hub flex or radial temperature gradient. Hmmmm.

I think I like your answer best. I didn't notice the groove at the track, but I checked the track pads (Hawk DTC70, COTA, one weekend) and they have a bump in the corresponding location. Brand new setup, one track weekend.

Currently running Stoptech Street that came with the BBK. In other news, I like the Hawk Street 5.0 better than these but not enough to swap until they're dead.
The DTC70 is a HB122 pad shape which seems to be exactly the same as the DR11/1247 pad shape as the Street pads that come with the ST60 kit, not including the piece on top with the hole in it. When you compare the DRC70 and the Street pads, was the braking material surface pretty much the same dimensions?

They should be so if that's the case, it looks like your pad isn't making contact evenly against the rotor or it's moving around. Do the pads feel loose when the caliper bridge is installed? Is the grove on the other side of the rotor as well?
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      06-07-2020, 07:42 AM   #9
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I have that same groove with the ST40s on my E46. Hasn't caused an issue over the 60 days these rotors have been on track.
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      06-08-2020, 08:57 AM   #10
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Same grooves on my ST60's here too. No issues
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