All of what you cite - disc, pad and caliper materials/engineering, cooling ability. Stuff like machined vs cast parts, stainless lines etc.

Also, for aftermarket outfits like Brembo who sell significantly less units than the OEM guys, their R&D and marketing costs (do OEMs even do marketing outside of selling direct to auto mfg's?) are spread over a much smaller customer base.

And probably not an insignificant amount of "because we can" thrown in.

Larger disc rotors give more surface area to “grab” and stop the car. Brake calipers can have pistons on both sides of the caliper and can also have dual pistons on each side. More power to stop.

The weight of the car also dictates how much braking power is necessary. Light car doesn’t need much to stop.

Ok, so brakes.

Brakes convert the cars kinetic energy (speed) into heat.

So first, on a high performance car those brakes need to take the heat of braking. On a high performance car, you will be braking from higher speed than a normal car. Kinetic energy is 1/2*mass*Velocity^2, so for a two cars with equal mass, the one braking from 120 mph will have 4 times the energy than a car going 60 mph. So even if a high performance car is lighter than other cars, it easily needs brakes that can absorb much more energy. Also if they are on a race track, they need to be able to brake from high speed multiple times, with little time to cool off between. So this drives large disks. This also drives things like drilled or vented rotors, that allow airflow in the disc, so that they can get rid of that heat as fast as possible.

Second, material. So a standard brake pad and a steel rotor, the friction between the pad and rotor is pretty much constant as the rotor temperature, until the rotor starts to get too hot, then friction starts dropping quickly. This leads to brake fade, where the driver needs to apply more force to the rotor, since the friction is less. If it gets bad enough, the brakes become useless. So high performance cars may have different pad material that works better at high temperature, so you can run hotter rotors and still have similar brake pressures. The issue with some of these pads is that they create more brake dust and also may not work as well at low temperatures as standard pads. There are also ceramic discs, these have less friction at low temperature, but can get very hot before the friction starts going down. So these are great on a track, because once they get warm, they just keep working. So temperature has a couple aspects, the first is the brakes working at all once they get hot and the other is giving the driver a consistent pedal pressure for a certain stopping power. This is important on a track, because you want to brake as late as possible and as hard as possible. If you get to the braking point and suddenly you need to brake much harder, you can go into the corner too fast, because you did not start braking hard enough soon enough.

Third is stiffness. This gets trickier. This goes back to brake feel. If you want good brake control, where you can control the amount of braking exactly, you need a stiff system. So this drives to nice big calipers. You don't want them bending and twisting as you apply a bunch of brake pressure on the disc. So fancy calipers are actually machined from a single piece of metal. Cheaper ones are two parts bolted together. Also, you go with stainless steel brake lines, compared to simple rubber ones on normal cars. This makes the lines stiffer, so as the pressure of brake fluid increases, the lines expand less. So, the more movement of the brake pedal results in pushing on the brake disc, not simply expanding the brake lines.

So that gets you 95 percent of it. There are bunch of other details, like how the rotor is mounted so that it stays constant and does not change as temperature increase, which will affect feel. There is also how pistons are arranged and the size the pistons, which affect feel, especially when the pad first contacts the disc.

Really, from a single stop from 60 mph to 0, for equal weight/tire size/etc, a car with small brake will stop just as fast as car with these high performance brakes. The real reason is for multiple high speed braking events in close succession and very precises brake control on the limit.

Size is one of the single biggest factors that determines braking efficiency. Good summary here:

"The braking torque is the result of the product of three factors: the effective radius of the disc, the clamping force of the caliper and the friction coefficient. The larger the disc diameter, the greater the braking torque. Increasing the diameter of the disc, in fact, increases the effective radius and thus, keeping the other variables unaltered, the braking torque increases. The dimensions of the brake pad also count. The reason is found in the heat exchange: a wider pad facilitates the disposal of heat and reduces the inclination of the braking system to fade and therefore makes it possible to apply the brakes often in quick succession compared to a smaller pad. Also, the number and diameter of the caliper pistons is directly proportional to the braking torque. Both act on the clamping force and hence the greater the clamping force of the caliper the greater the capacity of the caliper will be to exert a force on the pads and the more effective the braking will be."

Then factor in friction material and braking distribution.

The stock brakes on the Golf R are very nice. But, once you start to modify the car, the brakes REALLY need to be upgraded. Once I went to Stage 2, my stock brakes were not enough to give me confidence on the track. At stage 3, I went to the Porsche big brake kit and felt infinitely better. I went to ceramic racing pads and finally felt I could control the power in the vehicle. Like night and day.

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If there are no dogs in Heaven, then when I die I want to go where they went. - Will Rogers

Emery's Third Coast Triathlon | Tri Wisconsin Triathlon Team | Push Endurance | GLWR

I know a lot about brakes, and I really enjoyed reading your post.

Good stuff

So why are calipers machined not cast?

Are bigger stock brakes on higher performance cars e.g. I guess prosche, q7 etc just bigger cheaper two piece systems as opposed to, I'm guessing, a gt3 rs which would be a real sports car?

You step on the horizontal pedal to the left and the car slows down or stops.

That's it in a nutshell.

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Favorite Gear: Dimond | Cadex | Desoto Sport | Hoka One One

Nice summary, I was to lazy to type all that up.

But you skipped the big controversial DYI / aftermarket upgrade -- Brake Fluid (dot 3,4,5.1 vs 5 - Glycol vs Silicone)

The other thing to remember, you as a customer have one set of preferences, the OEM has another. So just cause the OEM did it one way doesn't mean its the best way for you. Of course just cause a sports car does it doesn't mean its best for your commuter car. -- DONT GET DRILLED and SLOTTED rotors.

On brake pads, there are several factors (noise / fade/ dust / wear) you may have different priority than the OEM and different than the race car. A race car doesn't care about wear they will replace every race, but fade is huge, Dust and noise no concern either. You on the other hand may not like brake squeel and dirty wheels, and may not do many back to back 100mph to 30 decel's.

Personally, I buy cheap rotors, and replace every or every other pad change. Pad's Im a bit all over the place on depending on whats available, which car and how I am feeling that day.

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Just Triing
Triathlete since 9:56:39 AM EST Aug 20, 2006.
Be kind English is my 2nd language. My primary language is Dave it's a unique evolution of English.

I tried the Wearever platinum at about $50 for my 97 Suburban. They were noisy and after driven through some mud puddles started grinding and wore out quickly. They sucked. The cheaper Wearever pads for about $20 (Gold or Silver) work much better for me. Quieter, longer lasting, and I don't notice any difference in stopping power.

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It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev

High end calipers are usually forged aluminum. Basic calipers are cast iron. Aluminum cuts the unsprung weight by a factor of three over iron or steel, and forging results in the highest possible stiffness and best grain orientation for the shape of the part.

The larger calipers will use four, six (or even eight?) pistons to more evenly apply the braking force to the pads, where basic calipers use two pistons (or even just one, in a sliding caliper) and depend on the stiffness of the brake pad to spread the load over the friction surface.

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Less is more.

Thanks, been awhile since I needed any of the knowledge, so I wrote the aspects that I still have some sort of handle on.

I did skip the fluid question, because I vaguely believed it is over hyped aspect of brake fade. But, didn't feel like researching anything.

Well, cheaper ones are cast. But cast materials just do not have as good of material properties as forged block machined. The cast material just is not as strong, so you have to make parts of it thicker, which adds weights. Also, the cast part may not be able to do some of the geometries as the machined part (on the other hand the cast part can do some of the internal features better). But it is also the fact that machining of aluminum is just so fast now, it is really not much more expensive than a casting for low volume parts.

Yes, the GT3 does use a single piece (or monoblock) caliper. I don't know about the SUVs, but I think some of the high performance ones may use monoblocks, I mean they need some serious brakes because they are fast and heavy.

Thanks

2 factors, that racers use Silicone - Higher boiling point, and incompressible (or less so then Glycol). If the caliper gets to hot, the brake fluid can boil (which introduces air bubbles which are very compressible) and causes loss of brake feel, the other side is as push on the brake the fluid compresses some (silicone less so -- personally think the difference is so small not really an effect). Other think if you have Glycol, or Silicone you can't just switch to the other, they are incompatible and you need to replace all the lines and the caliper.

Ok there is one other argument on the fluid (Glycol can hold water) so some say that makes rust in your lines, and that silicone fluid will delay the onset of lines rusting.

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Just Triing
Triathlete since 9:56:39 AM EST Aug 20, 2006.
Be kind English is my 2nd language. My primary language is Dave it's a unique evolution of English.

Yea, I was just trying to remember if dot 5.1 was good enough for the vast majority of brake systems, because the something else will start to go because of the heat before the fluid starts boiling.

Well the water also lowers the boiling temperature of the brake fluid, so that is another strike to glycol.

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They're up to ten pot brakes, heck 4 piston brakes are common in the MTB stuff. Carbon fiber is also used at the highest end of auto, and even a couple folks offering CF disks for bicycles now.

 
For us regular car drivers the pad material can make a big difference in feel but like DavHamm said you have to decide what is important to you. I owned a BMW 330 that had huge brakes on it for the size of car it is, same as the M3. It stopped great and the feel through the pedal was really good, but lord almighty the brake dust was insane! It was my wife's daily commuter, so very little spirited driving. I would wash her wheels on a weekend and by Wednesday they were nasty again. I switched her over to ceramic pads and the brake dust went away, the wheels could go 2 weeks without cleaning, but the pedal feel was not near as good, stopping was still good once you got a firm mash on the pedal, but feel and modulation was not as good.

I have a BMW 530i as well that I daily drive, same issue with brake dust, I will likely change that to ceramic pads here soon as well. It is a commuter for me and I don't drive like a moron anymore so I'd rather have clean wheels than performance brakes.