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Slotted/"J Hook" Brake Rotors - Any benefit?

Brake System Design and Optimization

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Discussion and questions related to the course Brake System Design and Optimization

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I see a lot of artermarket rotors offering a slotted, or J Hook type slotted, design. The claims appear to be: better 'initial bite' compared to plain rotors; a cleaning function for the pads; off gassing relief (although this is also claimed to no longer be an issue for modern pads). This claimed benefit comes at the expense of more pad wear. The other factor is the that they look cool and this look is synonymous with 'high performance', and offers a point of difference for some brands for what otherwise appears to be another iron rotor.

The question is, is there any perceptible difference from slotted rotors over plain rotors?

I could understand if the slotted rotors help with bedding in of the pads and an even transfer of pad material onto the rotors, but would that be better than a properly bedded in plain rotor in the long term?

I don't thing the questions is application specific, however I did find some examples where high performance road car might have slotted rotors (think Porsche or Ferrari) and then the LMP version uses plain rotors (though usually with a different caliper packages as well). On the contrary some of the BMW and Prosche road car examples have people complaining about uneven rotor wear which appears to be caused by a buildup of pad material in the slots. It seems like, all things considered a properly bedded in plain rotor would be best for most street or race use.

Does anyone have any specific experience?

I ran a slotted rotor on one front wheel and a plain rotor on the other side after damaging a rotor during a race weekend and not being able to source either two plain rotors or a matching slotted rotor. In initial braking and retardation, there was no difference in the braking or steering behavior, where it became noticeable was later in the race when the rotors had heat soaked, with the slotted rotors running slightly cooler, and having less pad fade.

I have run plain, slotted and J hook rotors on various cars, but never with the same brake pads or timeframe. The feel that I have is that the plain rotors tend to have a lower initial bite and suffer from pad fade earlier than the slotted or J hooked.

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