Pad size...

[andrewb70]

I am wondering if anyone can explain to me the effect of pad size. Take for instance two brake systems. Both have the same diameter rotors, calipers with the same number and total piston area. Same master cylinder. The only difference is that one system uses a pad that has substantially more area.



Andrew

[MrQuick]

More friction to rotor contact surface. Like opening a jar with larger hands. But more heat can be generated and not dispersed as fast as a smaller pad.

Some cars go the other way. Smaller pad surface but larger rotors.

..wait,this is a trick question right?

[andrewb70]

More friction to rotor contact surface. Like opening a jar with larger hands. But more heat can be generated and not dispersed as fast as a smaller pad.

Some cars go the other way. Smaller pad surface but larger rotors.

..wait,this is a trick question right?

Not a trick question at all. I was just looking at some OEM calipers that use a very large pad. About twice the size of the pad as on my Wilwood billet superlite 6 calipers. However the total piston area of these calipers is about the same as the Wilwoods. So I am trying to gauge the overall effect of using these calipers.

Andrew

[MrQuick]

oh, ok. Just checking! LOL

The Wilwoods will dissipate heat faster.

[andrewb70]

oh, ok. Just checking! LOL

The Wilwoods will dissipate heat faster.

Is that because the smaller pad generated less heat?

What about the actual braking force that is applied to the rotor? Does it change with pad size?

Andrew

[MrQuick]

Is that because the smaller pad generated less heat?

What about the actual braking force that is applied to the rotor? Does it change with pad size?

Andrew

Theoretically the pad will not generate more heat as compared to a larger pad plus more exposed rotor surface area will carry the heat away from the pad surface.

As far as braking force, with the same caliper and piston size. Applied force should remain the same regardless of pad size.

I wonder if there is a calculation for stopping distance/time change

[andrewb70]

As far as braking force, with the same caliper and piston size. Applied force should remain the same regardless of pad size.

Is this because of the difference in the unit loading?

Small pad, force/unit area > large pad, force/unit area

Andrew

[Apogee]

Clamping force doesn't change as that's a function of caliper piston diameters, although applied pressure will vary based on area as stated above. Small pads have higher contact pressures whereas large pads have lower contact pressures given the same hydraulic force.

The brake torque however will vary primarily based on the friction coefficient of the pads since the normal force applied by the calipers is equal. Pad area and correspondingly volume can be used to increase pad life for the reasons above. You'll typically see larger pads used in endurance applications and wide annullus rotors to match for the same reasons.

Tobin

[andrewb70]

Clamping force doesn't change as that's a function of caliper piston diameters, although applied pressure will vary based on area as stated above. Small pads have higher contact pressures whereas large pads have lower contact pressures given the same hydraulic force.

The brake torque however will vary primarily based on the friction coefficient of the pads since the normal force applied by the calipers is equal. Pad area and correspondingly volume can be used to increase pad life for the reasons above. You'll typically see larger pads used in endurance applications and wide annullus rotors to match for the same reasons.

Tobin

Aha! So let me rephrase please, just so I understand this correctly. Take two setups. Each having the same caliper piston area, same diameter rotors, same MC, and the same compound of brake pad, but one having a much larger pad. So the end result is that the braking performance, as measured by a 60-0 test for example, would not change. What would change is the life of the pads. So bigger pads offer greater pad life, all else being equal.

Is that correct?

Andrew

[Skip Fix]

From my understanding the larger pad has more surface area so more friction surface (like the jar comparison) as well as more area to absorb heat from -why they use them in endurance situations, so probably more resistance to fade with long frequent braking like track times. remember also the circle track Late Models even on asphalt circle and road course often use a GM style caliper as class specs, although a 1.25 thickeness rotor. They weigh in at a little over 3000lbs

A recent example- the guy I bought my 05 brake system for my 04 GTO just upgraded to Harrop BIG 6 piston clipers up front and multiple piston rear caliper(I think 4 piston). Had a empty road he did a 60-0 stop with the factory system, painted a mark on the road. CAme bake similar road conditions with the Harrops same distance within several feet. Even he was suprised. Tire width and diameter and weight of the vehicle probably limit 0-60 more than specific brake components if they are all adequate.

And I agree the dynalite pad is tiny.Superlite and GNIII as well as factory calipers have much larger pads.

[Vegas69]

One thing that needs to be considered in brake pad material. A smaller more agressive pad may have the same stopping power as a larger pad. This is all pure speculation since I am no expert. In a street applicatoin where high heat situations usually aren't a factor a smaller pad makes more sense. I would imagine it would produce less brake dust as well.

[Apogee]

Aha! So let me rephrase please, just so I understand this correctly. Take two setups. Each having the same caliper piston area, same diameter rotors, same MC, and the same compound of brake pad, but one having a much larger pad. So the end result is that the braking performance, as measured by a 60-0 test for example, would not change. What would change is the life of the pads. So bigger pads offer greater pad life, all else being equal.

Is that correct?

Andrew

Yes, that is correct as I understand it. The other thing you'll notice is less temperature rise in the pads, everything else remaining the same relative to smaller area/volume pads.

If you're familiar with the 9C1 Caprice in the mid-nineties, GM shortened the piston on the 9C1 calipers and squeezed in some thicker pads to band-aid the not-so-great brakes and get them to pass the fleet service brake test specifications. Before the additional pad volume, they were cooking the pads during repeated hard use and experiencing rapid fade. IMO they should've fixed the problem and thrown some thicker rotors onto them...but that's just me. Pad volume reduces with wear and puts you right back in the same boat in no time flat.

Also consider that there are more things occurring than just simple dynamic friction because in reality you're actually removing material from the pad and depositing it on the rotor and visa versa. This mechanism of energy transfer (breaking mechanical and molecular bonds) is harder to quantify and much more a function of friction compound and presumably area I would think, since area affects contact pressure. I was speaking with one of the guys at Satisfied Brakes, a major brake pad manufacturer in Canada, and the science in a simple brake pad nowadays is nothing short of amazing. He mentioned many of their pads have upwards of dozens of compounding items in various quantities to achieve the desired performance characteristics along with NVH concerns.

Tobin

[andrewb70]

So let me put it yet another way. If my current setup does not have fade issues, has good piston area, and pad wear is not a concern, than going to a setup with the same piston area, but a larger pad is not going to get me any advantages in terms of braking performance. Right?

Andrew

[Apogee]

That would be a true statement...but they sure do look good.

Tobin