recommendations for brake pad replacement

[JCL]

Originally Posted by The Cleaner

This is true, OEM pads have a very specific rockwell hardness to wear WITH the rotor. Most dustless pads are much harder and not carbon based and tear rotors faster. They don’t transfer heat to the caliper and fluid like OEM pads and have a higher rotor temps during braking.

There is really nothing positive about dustless pads when comparing to OEM spec TUV approved pads other than less dust.

Agree completely with the hardness comments. I don't understand the heat comments however. Carbon is an insulator, and would not promote heat transfer. Apart from that, however, why would it be a good idea to transfer heat to the caliper and then the fluid? That is what causes boiling of the brake fluid, and thus loss of braking when the brake pedal sinks to the floor. The pads need to insulate, it is part of the design function.

The amount of heat that goes into the rotor is directly related to the energy absorbed by the brake. The brake can only get hotter if it is absorbing more kinetic energy, the same energy absorbtion rate will produce the same heat in the rotor. So, if the rotor is in fact hotter with aftermarket pads it is because the vehicle is stopping more quickly.

All that aside, I do agree that the OEM pads are a good all around balance, with the sole exception of the dust factor.

[Tomaz]

I've been running the Axxis Deluxe for the last 45K miles. No problems, no squeaking, abnormal rotor wear, or noticeable braking difference. I never bedded them except to use them normally. I completely recommend them.

[The Cleaner]

Originally Posted by JCL

The amount of heat that goes into the rotor is directly related to the energy absorbed by the brake. The brake can only get hotter if it is absorbing more kinetic energy, the same energy absorbtion rate will produce the same heat in the rotor. So, if the rotor is in fact hotter with aftermarket pads it is because the vehicle is stopping more quickly.

All that aside, I do agree that the OEM pads are a good all around balance, with the sole exception of the dust factor.

Your comments are accurate, however material density both rotor and pad will have a significant impact on heat dissipation. The energy that is changing to heat needs to move, not just insulated, the rotor, caliper and fluid all play parts in moving that heat/energy away from the friction surface. If it was insulated a brake system would quickly lose efficiently. The more surface area heat can be transfered to the cooler the brake surface stays. Brake fluid is used for heat exchange as is the caliper pads and rotor.

TMD Friction produced a video illustrating various material failures (pads, fluid and rotors) due to single components being out of specification. They have a machine that will progressively build up heat in a brake system until failure. It decelerates a given mass from 200 KPH to 50 KPH by applying the brakes for 10 seconds every 30 seconds.

[JCL]

Originally Posted by The Cleaner

Your comments are accurate, however material density both rotor and pad will have a significant impact on heat dissipation. The energy that is changing to heat needs to move, not just insulated, the rotor, caliper and fluid all play parts in moving that heat/energy away from the friction surface. If it was insulated a brake system would quickly lose efficiently. The more surface area heat can be transfered to the cooler the brake surface stays. Brake fluid is used for heat exchange as is the caliper pads and rotor.

TMD Friction produced a video illustrating various material failures (pads, fluid and rotors) due to single components being out of specification. They have a machine that will progressively build up heat in a brake system until failure. It decelerates a given mass from 200 KPH to 50 KPH by applying the brakes for 10 seconds every 30 seconds.

I don't understand the material density impact, it seems to me that pad composition matters more than density, particularly for insulators. The rotor densities don't change much for the slight material differences between rotors. I would agree that heat dissipation is impacted by the overall rotor mass, not density, but that factor only impacts the speed of the heating/cooling cycles, ie it doesn't affect the overall thermal capacity. It does affect the speed at which the brake rotor gets there. It is the cooling fin arrangement and resultant airflow that affects the stead-state heat capacity.

I had figured the heat went to the rotor, and was radiated/convected from there. I don't have any data on how much is distributed by the various paths. I can see that heat goes to the fluid, but the fluid doesn't have a way of getting rid of it quickly, so that is a byproduct rather than a cooling mechanism, ie it heats up but then the heat tends to stay there. I wasn't suggesting that the brake was insulated, just the conduction path from the rotor surface back to the piston, which heats the brake fluid.

The TMD video sounds interesting. It doesn't sound like a real world test but rather a destructive test to analyze failure modes.

Cheers

Jeff

[The Cleaner]

Originally Posted by JCL

I don't understand the material density impact, it seems to me that pad composition matters more than density, particularly for insulators.
Jeff

I think composition determins density but I might need to go back to school at this point.

I am unfortunately not a scientist so I can’t get much more technical. My stance on sticking to OEM components for predictability in everything from temperature, stopping distance and ABS dependence are illustrated in this document comparing many brake pads on Police vehicles. There are significant changes in many of the tests based on material. What’s interesting in the study is that even in police applications the OEM pad seems to have some of the best performance. I thinks this is due to testing that aftermarket pad makers simply don’t have.

I truly believe that OEM pads are better tested and more predictable than aftermarket pads, especially aftermarket pads that deviate from the basic materials used for OEM fitment. If they were really better the car manufacturer would be using them. Buying a pad based on the dust it may produce on wheels just seems to be to insignificant IMO.

The test is a few years old, but still a good comparison
http://www.nlectc.org/pdffiles/Evalu...kePads2000.pdf