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I noticed when looking at a Porsche 918 the other day that the brake calipers are not the same position on the front wheels as the rear ones. I then noticed that they are laid out the same on a BMW M3.

I thought that potentially this was something that all cars did, however I saw that a Mercedes-Benz C63 AMG has them all mounted at the rear of the wheel (which seems more "normal" to me, for some reason).

What's the reason that Porsche and BMW have chosen to place the calipers at a different location on the different wheels?

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    I don't know for sure and have often wondered. The only reason I can come up with is the geometry of the suspension. I keep thinking depending on the placement of the caliper, it could torque the suspension differently, causing it to lift or plant the wheel in the braking process. This is just a theory and probably wildly wrong. – Pᴀᴜʟsᴛᴇʀ2 Nov 11 '16 at 14:43
  • Good idea @Pᴀᴜʟsᴛᴇʀ2, I thought something similar: when the calipers are both at the front, the centre of mass is shifted forwards, both at the back and its shifted backwards, but if the back caliper is forwards and the front caliper is backwards, the centre of mass remains central (as they cancel eachother) - but of course this is dependent on the wheels being the same size! – James Monger Nov 11 '16 at 14:45
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    I wasn't talking about the weight or center of mass, I'm talking about how during the braking process the caliper gripping the rotor might have an effect on how the suspension pieces would react. Talking about the torque being produced on the suspension components. Different locations might produce different results. – Pᴀᴜʟsᴛᴇʀ2 Nov 11 '16 at 15:03
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    @Pᴀᴜʟsᴛᴇʀ2 With the caliper and rotor both attached to the knuckle, the only forces would be isolated to the mounting hardware, and would not effect the suspension. The rotor would want to push the caliper in a direction, the caliper would want to push the mounting hardware, and the mounting hardware would push back, cancelling all loads from the disc. – MooseLucifer Nov 11 '16 at 17:39
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I don't believe there is a special placement in consumer vehicles. Most are designed with space in mind and ease of servicing. With the energy being transferred from the spinning rotor to the stationary brake system, the force would likely be the same from any clock position the caliper is in. Therefore, position probably isn't as critical.

Things manufacturers consider when choosing mounting location;

  1. Available space around suspension
  2. Adequate mounting area
  3. Ease of servicing/bleeding
  4. Cooling and heat dissipation
  5. Damage/debris avoidance
  6. Vehicle purpose

This is a great video that explains it - Brake Caliper Location - Explained from Engineering Explained.

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