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I have changed front brake rotors and noticed two extra holes in the hub and in the brake rotor. The holes are matching with each other. The purpose of them are unclear for me.

The car: Astra H 2012 model year.

The brake rotor: ATE 24.0125-0131.1

Then I have searched for similar (with extra holes) brake rotor and hub examples and found enough, see pictures in the bottom of the question. There are the cases with non-matching hub/brake rotor holes - 9 in the brake rotor and only 5 in the hub...

The question: what is the point of this extra holes and why in one case them matches (my Astra H) and in another case them doesn't match (Volkswagen Golf, Skoda Octavia)?


Pictures:

The Astra H's hub

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The Astra H's separate brake rotor

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The Astra H's hub and the brake rotor assembled

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EDIT start

The Astra H's brake rotor back side. It is not having drum inside, so it can't be used with brake shoes, thus, these holes can't be designed for hand brake adjustment.

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EDIT end


Non matching holes examples:

The Skoda Octavia's hub and brake rotor

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The Volkswagen Golf's brake rotor

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The Volkswagen Golf's hub

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  • 2
    A possible unverified use I can think of is to position the rotor for finish machining. The rotor slips on to a fixture the two extra holes fit over a pin to locate and hold the rotor in position while the bolt pattern is drilled. – mikes Aug 4 at 20:16
  • @mikes It is legitimate version, I thought the same firstly, but: 1) why the hub also have the same holes pattern? There must be some reason for this. 2) What about cases with 4-5 extra holes? For example here: matching 10 holes in the brake rotor and hub – MiniMax Aug 4 at 20:26
  • @mikes Can the 4-5 hole cases serve for the weight reducing or the metal economy? Like lightweight hub or brake discs. Maybe this holes have added for right balancing/weight distribution (when there are symmetric pattern)? Doesn't explain my Astra H 2 non symmetric holes, though... – MiniMax Aug 4 at 20:30
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    When there is a complete set of extra holes the likely use is multiple fitment with 2 distinct bolt patterns. In the case of 5 bolt holes there is no way to add 2 holes and make it symmetric. Balancing is a possibility, but not to save material as the cost of removing the material likely exceeds the material cost. Unless someone in the community actually makes rotors all we have is speculation at this point. – mikes Aug 4 at 21:14
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    youtu.be/MAzbbID6BZ0 @ around 3:47 – hello moto Aug 5 at 11:51
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Some rotors have an M8 threaded hole to use for helping to remove the rotor from the hub (and brake drums sometimes had one or two threaded holes for the same purpose, but not M8...), but most just seem to belt 9 bells of s**t out of it with a hammer until it comes off.

The larger holes you indicate may well be for the original machining process or as a "pass through" hole to allow a screwdriver to adjust a handbrake mechanism for example. Don't forget that a rotor that you think may only fit on a golf, may well fit on 20 or 30 other makes & models... Some brake drums had holes positioned so that the brake shoe clearance could be easily adjusted (either it was the back plate or the drum depending on the design.

  • I have found the example of matching 10 holes in the brake rotor and hub, but only 5 of them are working. Which of your variants fits in there? It isn't for handbrake adjustment, isn't for removing the rotor from the hub. Also, they are symmetric unlike to my hub/rotor holes. – MiniMax Aug 4 at 20:18
  • I have thought and understood, that the rotor in the video has inner drum and was designed for brake shoes in it. Just used with the outer caliper in this particular case, right? Thus, can this holes serve for ventilation brake shoes? Also, I have understood, that my rotor doesn't have inner drum, so it can't be used with brake shoes. I have added its back side photo in the question. – MiniMax Aug 5 at 9:29
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    Some cars have shoes inside the rotor for the handbrake, but not all. The holes will probably be for adjustment as expalined previously. I doubt for cooling as a handbrake does not get hot in use - it is designed (mostly) for stationary application. – Solar Mike Aug 5 at 9:34
  • But my rotor (and golf version too) doesn't have a drum and thus, doesn't have space for shoes and handbrake mechanism. If these holes for adjustment - that they supposed to adjust? If I understand right - the lack of drum assumes the outer handbrake mechanism only, combined with the caliper, like in my Astra H. Or I don't know something? – MiniMax Aug 5 at 9:43
  • The manufacturers will make a rotor with holes to make it fit as many applications as possible, because it is the cheapest option for them. They do not care whether you will use all the holes or not or even understand what all the holes are for.... As long as you have the correct rotor for your car and it is correctly fitted you will be fine. – Solar Mike Aug 5 at 9:53

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