I understand in concept the DOT codes for brakes indicating some coeff of friction when cold and hot (relatively).

What makes a brake pad good for initial bite? For fade resistance?

Why are some pads good for initial bite but not for fade resistance? Good for fade resistance but not great for initial bite? Good for both?

Why are there FG, GF and GG pads and what makes them so?

The composition of the brake material changes the way they work, drastically.
Having a face type brake in a passenger car, you’ll never get them hot enough to bite.
Most brake fade comes from overheating the fluid in the calipers. When that happens you lose braking. Combine that with rubber brake lines and it gets really bad.
For a passenger car, that you want to drive the shutout if, and not worry about brake fade, look at Hawk HPS pads. Replace the rubber brake lines with stainless lines. It’ll feel like your brakes work a lot better just off that.
If you’re worried about temp, you can get DOT4 fluid, but at that point, you should have really researched and studied braking and the effects. DOT4 fluid and DOT3 don’t work together. You have to really flush the lines, and if you’re really not driving hard, it’s an unnecessary step.

Back to your question, OEM pads have great bite initially, but survey heat, they lose bite.
Race pads don’t bite until they get hot.

As I said a while ago, check the Hawk HPS pads, and get some braided stainless hoses. It’ll make all the difference in the world.

Initial brake bite is a function of brake compound and temperature.
Brake fade is a function of brake fluid properties (Boiling Point) and temperature.

DOT 3 and DOT 4 are compatible. DOT 4 has higher dry and wet boiling points than DOT 3, so if your car calls for DOT 4, use it. If you want to switch from DOT 3 to DOT 4, you don't have to do anything fancy, just a normal brake fluid change.

Speaking of dry and wet boiling points, DOT 3 and DOT 4 brake fluids are hydroscopic: they will absorb water. This lowers their boiling points. The Motorcraft fluid I use in my F350 has a minimum dry boiling point of 509 degrees, but a minimum wet boiling point of 338 degrees. Don't ask me how the sealed braking system gets water in it, but it does and over time the boiling point will continue to be degraded. It's important to change your fluid every few years, whatever the manufacturer recommends, for that reason. Even if you aren't pushing your brakes to the boiling point, water in the fluid will corrode the calipers and pistons which will cause the seals to fail.

quote:

Originally posted by Lunasee:
Initial brake bite is a function of brake compound and temperature.
Brake fade is a function of brake fluid properties (Boiling Point) and temperature.

Pads will also effect brake fade. Even more so of most non-tracked cars then fluid.

quote:

Originally posted by Beancooker: As I said a while ago, check the Hawk HPS pads, and get some braided stainless hoses. It’ll make all the difference in the world.

Agree about Hark HPS pads. I've been using them on cars for almost 20 years and they offer a huge improvement over OEM pads. You would be hard pressed to make these pads fade on the street.

quote:

Originally posted by Beancooker:
As I said a while ago, check the Hawk HPS pads, and get some braided stainless hoses. It’ll make all the difference in the world.

I guess your mileage may vary on Hawk pads. I installed a set of Hawk HPS pads on my truck a number of years ago, and to date, they've been the worst pads I've ever dealt with. Whether they stopped well became a non-issue given they were so incredibly noisy, I couldn't get them off my truck fast enough. Hawk sent me a second set, and they were no different than the first. In the end I simply went with a set of Wagner ThermoQuiet Ceramic pads that have proven to be long wearing, quiet, low dusting, and good stopping. And they cost significantly less than the Hawks.

quote:

Originally posted by Lunasee:
Brake fade is a function of brake fluid properties (Boiling Point) and temperature.

How does that work in an air brake system?

Brake fade has everything to do with heat. The ability of the components to dissipate heat, mass of the vehicle and speed. Lining compounds will need to be different for driving conditions, i.e. flat roads compared to hilly roads. Ambient temperatures play too. If I remember correctly, the first letter is for temperatures, and the second letter is for driving conditions.

quote:

Originally posted by bigdeal:

quote:

Originally posted by Beancooker:
As I said a while ago, check the Hawk HPS pads, and get some braided stainless hoses. It’ll make all the difference in the world.

I guess your mileage may vary on Hawk pads. I installed a set of Hawk HPS pads on my truck a number of years ago, and to date, they've been the worst pads I've ever dealt with. Whether they stopped well became a non-issue given they were so incredibly noisy, I couldn't get them off my truck fast enough. Hawk sent me a second set, and they were no different than the first. In the end I simply went with a set of Wagner ThermoQuiet Ceramic pads that have proven to be long wearing, quiet, low dusting, and good stopping. And they cost significantly less than the Hawks.

That sucks. I have only put them on cars so no experience with trucks. Hawk is a motorsports company that started with products for the racing and street car markets. Wonder if they just used their designs to make their truck pads without any real R&D for that market.

quote:

Originally posted by trapper189:
DOT 3 and DOT 4 are compatible.

No, they are not. Plain and simple.
DOT4 can replace DOT3, but if you have DOT4, and try to replace with DOT3, you’re in for failure.

Rule of thumb (refer to The Boondock Saints) is don’t mix the two in either fashion. I’ve raced cars for over 20 years (amateur, autocross, and lots of different street racing, and replaced more brakes than most people would in 10 lifetimes.
I’m not an expert, but don’t mix the damn fluids of you’re really looking to cause issues.

Yes, I am passionate about this, for reasons I don’t care to get into.
I don’t want to see that happen to one of my SigForum Brothers.

quote:

Originally posted by Beancooker:

quote:

Originally posted by trapper189:
DOT 3 and DOT 4 are compatible.

No, they are not. Plain and simple.
DOT4 can replace DOT3, but if you have DOT4, and try to replace with DOT3, you’re in for failure.

Would you care to read the next two sentences I wrote? Don't post what I write out of context.

quote:

Originally posted by trapper189:
DOT 3 and DOT 4 are compatible. DOT 4 has higher dry and wet boiling points than DOT 3, so if your car calls for DOT 4, use it. If you want to switch from DOT 3 to DOT 4, you don't have to do anything fancy, just a normal brake fluid change.

quote:

Originally posted by Beancooker:
DOT4 fluid and DOT3 don’t work together. You have to really flush the lines, and if you’re really not driving hard, it’s an unnecessary step.

This is wrong. DOT 4 works fine with DOT 3.