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StormRune, are you sure the grooves in your pic aren't reliefs cut at the factory to balance the rotors? My non-S rotors have the depth indicator dimples as shown in gota911's pics. Plus, if you wore the rotors down to the grooves in your photo, I think the rotor would frag.
My Porsche rotors have the dimples. At 44k miles, my rotors were down almost to the point where the last of the dimples were almost worn away. When I mic'd them, the fronts were down to 26mm, which confirms that the deepest of the dimples are drilled down to this point, making them a good indicator of rotor wear.
That could certainly be the case. Maybe I made a very bad assumption in that photo I found online. I'm away on a business trip but I'll check my own rotors out of curiosity this weekend. I'll assume you are right and that I'll find the same dimples on my own rotors. I'm surprised I've never noticed this.
Newbies Hospitality Director Lifetime Rennlist Member
Joined: Apr 2005
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From: Winston-Salem, NC
Storm,
I never noticed the dimples on my original discs either, probably because brake dust settles in the dimples, which makes them look like the drilled holes.
I never noticed the dimples on my original discs either, probably because brake dust settles in the dimples, which makes them look like the drilled holes.
This. I didn't notice them until I pulled the new ones out of the box. Then I went back to the original ones and saw the dimples. After driving and from a few feet away, the dimples are just as black as the holes that are through-drilled.
They are different depths, so I assume that the more shallow dimples are an early warning system to let you know you can still turn them and the deeper ones are to let you know that rotor needs to be replaced.
A few weeks back I cleaned out the brake dust in every hole on the front disks. Some were packed really tight. I used the opposite end of a detailing stick cut at a 45 for sharpness. Might have been a waste of time, but if those holes have a real purpose, then it was worth the trouble. Sorry OT a bit.
Newbies Hospitality Director Lifetime Rennlist Member
Joined: Apr 2005
Posts: 18,084
Likes: 34
From: Winston-Salem, NC
Chrono,
The holes allow air to flow from the surfaces of the disc (both sides) to the ribbed center of the disc where the air gets expelled. This airflow aids in cooling the discs, so you efforts were not in vane.
This. I didn't notice them until I pulled the new ones out of the box. Then I went back to the original ones and saw the dimples. After driving and from a few feet away, the dimples are just as black as the holes that are through-drilled.
They are different depths, so I assume that the more shallow dimples are an early warning system to let you know you can still turn them and the deeper ones are to let you know that rotor needs to be replaced.
It's elegantly simple, actually.
To be clear, I'm not degrading the usefulness as I find it a great feature for a quick look and to ensure yourself your are not in the danger zone **yet**. But I still rely on the micrometer at various points of contact. I measure inside and outside. I may be a bit **** on this but since I do a fair amount of tracking, I want to know with a higher level of certainty how my safety margin is holding up.
To me it is sort of like the brake pad wear sensors, if you are at the wear limit, you are too far for my safety tolerance (again, track safety). In fact our group and most others I have run with require no less than 1/2 of original pad thickness to pass inspection. We also have a brake disc requirement.
Leftmost dots are the wear bars holes on my 2009 with 19k miles.
Thanks for this great post. I've been wondering when to change my rotors. The front left rotor on my 2009 997.2 shows the wear dots after 19k and some track events.
I know this is an older thread, but I am wondering the exact same thing on my 2009 base 997.2. The pads have about 30% left as of a month ago when I purchased it. I see the wear indicators on the front rotors, but there are no indicators on the back. I used my micrometer and the rotor thickness is about 1.075”. Not sure if that is good or bad.
I found my own answer at least for the 2009 MY. Having issues uploading pictures for some reason so I will try again later. Front thickness must be above 26mm and 26mm for the rear too.
I believe 2mm below the starting specification is the wear limit for most if not all Porsche rotors. For example if the new thickness is 34mm, the minimum thickness is 32mm.
I believe 2mm below the starting specification is the wear limit for most if not all Porsche rotors. For example if the new thickness is 34mm, the minimum thickness is 32mm.
You are correct sir. Front new-34mm and Rear new-28mm. They do say that if you resurface the rotor to add .6mm to the 26mm & 32mm to the discard limit. This is for S cars and not the base 997.2.
These dimples as wear indicators seemed logical to me. However, I called Porsche dealer and a 20 year service veteran said this is not what they are for. That they are just for air and water movement. That being said, I would take with a grain of salt this idea unless some kind of Porsche or rotor manufacturer proof becomes available. I would love for this to be proven, as would make awesome indicators. If anyone can find proof, please post it.
The holes allow air to flow from the surfaces of the disc (both sides) to the ribbed center of the disc where the air gets expelled. This airflow aids in cooling the discs, so you efforts were not in vane.
It took me four years, but I see what you did there.
03-12-2015 | 01:25 AM
