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I need to repair my car in order to get a safety check certificate.

The rotor that the workshop would be getting for it is 2x RAYBESTOS 780541R for the rear wheels. According to the rockauto website, these rotors are 302 mm (or 11.890 in). However, this same website shows other types or Rotors that would be compatible with my car, such as some of 262 mm (or 10.31 in) of diameter.

I already check the owner's user guide and manual to confirm these numbers but I can't find any reference.

This other website says that the Rear Brake Rotor Diameter is 10.3 in (or 261.62 mm).

Apparently, according to the physics (posted in this forum) the bigger the rotor the more braking power there is. If that is the case, wouldn't a bigger size be preferable?

Where I can find the "official" size of Rotor I should pick?

Also, I am in Canada, meaning, tons of salt on the roads during the winter. Plus a little bit of snow. Shouldn't this body shop be ordering/recommending coated rotors (as well as callipers)?

Is coated rotors always preferable for places that use salt on the roads?

Thank you for your time.

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    Measure the ones on your car as the calipers and mounting are matched to that diameter. If you want to change then all 3 bits need changing.
    – Solar Mike
    Jun 14, 2021 at 5:00
  • The brake pads generally sit very close to the outside edge of the rotor so you definitely don't want to undersize since part of the brake pad would make no contact with the rotor. Your best bet is to measure your existing rotor. FWIW, your car's details matter in regards to trim and engine size so if you're not entering those into the website then expect poor results. Even if you do enter that info into their search then just assume the search is not perfect. Once again, just measure the darn things.
    – MonkeyZeus
    Jun 14, 2021 at 18:53

2 Answers 2

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As Solar Mike explained in his comment you need to measure the existing rotors on your car as the rest of the system is matched to them.

Certain cars even have the rims matched to accomodate the brake.

Coated rotors, in a rough sketch, are just rotors that get shipped with some coating instead of protective oil. A mechanic needs to remove the oil before mounting, but can install the coated ones without further preparation. The rust, without regular driving, will always attack the rotors as they, inclusive the coating, get worn by braking. The caliper itself is mostly cast iron or aluminum and relatively resistant to rust, so no coating is required. Most of the time it is the sliding mechanism thats get blocked by rust and grime, cleaning and lubricating this is part of regular brake maintenance.

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  • Would it be ok changing the size of both Rear Rotors, while keeping the Front ones smaller?
    – Eduardo Reis
    Aug 16, 2021 at 18:14
  • Some cars need a reprogramming of some ECU. I have no idea if that is necessary on your car. What is definitely needed is to match pads, rotors, calipers and bracket to the new diameter. Rear brakes shouldn't be oversized. In my book it doesn't make sense to put larger rotors to the rear
    – Martin
    Aug 16, 2021 at 19:19
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To your first question: the only reasons larger rotors would effect braking is because that they allow larger pad sizes or the caliper would bring the pads higher on the rotors. So "braking power" would not be improved in your situation because you are presumably not changing pad size or calipers.

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    This is not accurate. Larger diameter rotors provide greater stopping power because they can provide more torque. The further the friction material is from the center, the more torque can be generated through the rotor, which means more stopping power. This can be seen even if you have the same sized pads one to the other. Manufacturers are limited by the internal diameter of wheels as to the size of rotors which can be used. Not the only limiting factor, but a major concern why they don't automatically use 20" rotors (or something else as silly).
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jun 14, 2021 at 11:47
  • @Paulster I agree with the physics you describe, but in order to move the pads up or make them bigger, you would have to change the caliper. If you don't change the caliper or pad location on the rotor the braking remains the same.
    – Jupiter
    Jun 14, 2021 at 13:08
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    Agreed, but that's not what you're saying in your answer. What you've stated is incorrect as disk diameter DEFINITELY plays a role in stopping power. Pad size is secondary to this. Yes, a larger pad will make a difference in stopping power, but mostly it causes the frictional area to be spread further across the rotor. A larger pad will last longer (more material), but realistically the size doesn't matter as much as location in reference to the center of the rotor and friction material used.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jun 14, 2021 at 13:22
  • Edited my answer to include both scenarios.
    – Jupiter
    Jun 14, 2021 at 15:52

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