General question: Why are bigger brakes better?
 

I understand that bigger breaks (rotors and pads) stop a given car better than smaller breaks. What I don't understand is why. It seems to me that breaking is more about friction between the tire and the road. As long as a small break setup can squeeze the rotor hard enough to stop the wheel rotating (causing the tire to skid) then it seems that should be good enough. A bigger break gains no advantage from being able to squeeze harder.

I do think that larger breaks might give you more control of how hard the breaks squeeze allowing you better control over breaking force without locking up the wheels. Is this the difference?

My thoughts above don't take into account heat build-up during breaking or ABS. I realize bigger breaks would spread the heat out more and fade less and I don't really know what effects ABS might have.

http://www.memedepot.com/uploads/0/2...if_serious.jpg

First off, it's "brakes," not "breaks."

"It seems to me that breaking is more about friction between the tire and the road" That's not correct. Braking is about the friction between the brake pad and rotor. Therefore, bigger brakes -> more surface area -> more friction = better stopping ability

Damn, frost beat me to it.

More surface area = more friction and better stopping.

higher capacity, improved consistency.

like playing a 1000watt stereo but only at 5-10% of its power.

:facepalm:


Thats the kind of question someone asks when they don't show up to auto mechanics class?

^^agree.

Bigger brakes also allow for less pressure for the same amount of torque given the same conditions as a standard brake set. For the most part, the increase surface area allows for a larger pad which results in more bite. The tires play a big part in stopping distance, but the brakes are doing most of the work. Bigger brakes, with the right material, also spread heat better and can withstand higher cycles before failing/fading.

Also, it would actually be easier to lock-up the brakes (tire looses traction) with bigger brakes, but thats a whole other topic.

Friction Lesson:

*Friction is a measure of how hard it is to slide one object over another. Take a look at the figure below. Both of the blocks are made from the same material, but one is heavier. I think we all know which one will be harder for the bulldozer to push.

http://static.howstuffworks.com/gif/brake-friction1.gif

To understand why this is, let's take a close look at one of the blocks and the table:

http://static.howstuffworks.com/gif/brake-friction2.gif

Because friction exists at the microscopic level, the amount of force it takes to move a given block is proportional to that block's weight.

Even though the blocks look smooth to the naked eye, they are actually quite rough at the microscopic level. When you set the block down on the table, the little peaks and valleys get squished together, and some of them may actually weld together. The weight of the heavier block causes it to squish together more, so it is even harder to slide.

Different materials have different microscopic structures; for instance, it is harder to slide rubber against rubber than it is to slide steel against steel. The type of material determines the coefficient of friction, the ratio of the force required to slide the block to the block's weight. If the coefficient were 1.0 in our example, then it would take 100 pounds of force to slide the 100-pound (45 kg) block, or 400 pounds (180 kg) of force to slide the 400-pound block. If the coefficient were 0.1, then it would take 10 pounds of force to slide to the 100-pound block or 40 pounds of force to slide the 400-pound block.

So the amount of force it takes to move a given block is proportional to that block's weight. The more weight, the more force required. This concept applies for devices like brakes and clutches, where a pad is pressed against a spinning disc. The more force that presses on the pad, the greater the stopping force.

howstuffworks.com

Actually... he is more right than you guys are. Braking is 100% limited by the grip of your tires. He is also right that the pressure is spread over a larger surface which makes braking modulation easier as well as heat dissipation. The materials used are also part of the mix, sport brakes tend to have less flex to them and are designed to transfer more of that pressure to the rotor.

Another thing to keep in mind axeman71 is that you're making an assumption that bigger = better and thats not true. AP Racing 6-pot brakes are better than a lot of those 8 pot show brakes that take up half the rotor.

Also, I dont want to repeat what everyone else already said, but more surface area to create friction with..

Who invited the rocket scientist? :D

:bowrofl:

Brakes? We don't need no stinking Brakes!!!

That's kind of an obvious statement, it's like saying braking is 100% affected by the speed you are going. But we wouldn't attribute good braking to slow speed, nor should we attribute good braking to contact between the tire and the road. If we hydroplane and can't stop, we don't blame the brakes themselves, right?

I'm convinced. I'm gonna put Shimano brakes on my Z.

LMAO poor guy

Nope, brakes too big are going to lock the tires.

RCZ is right on. Braking is tire limited, the base brakes of any car are capable of locking the tire and hence have a sufficient coefficient of friction. Better brakes (not necessarily bigger) may improve pedal feel, modulation, but most importantly consistency.

one thing to take home from this is that bigger brakes are better, and tires with more grip are better, however the ability of the car to stop is limited whichever is the weak link. all things being equal, same tires, same car, same conditions etc, the car with bigger brakes is going to stop better. The ability of a car to stop is limited by a lot of things, tire compound is just one of them. weight of the car (even number of passengers affects the weight), speed at which it is traveling, road conditions (wet/dry, hot/cold). all things being equal, bigger brakes (assuming kits being compared are of equal quality) are going to stop the car better. end of story. if you want to put those brakes on a minivan going 100mph in the snow down a hill or on grandma's carolla going 20mph down main street, obviously they are going to perform differently, but that is because of other variables, not the brakes themselves.

I came in here to say most of that, except the last part. Friction is independent of surface area, at least with most materials.

Besides the heat dissipation, bigger rotors allow for bigger calipers, with bigger components that are usually more easily modulated.

Wow, big discussion for one evening. I don't understand the sarcasm in the first 3 or 4 posts, I was asking a serious question. Just saying "duh, bigger brakes are better" doesn't tell me why which is what I was asking. The misspelling was just me not paying attention (I am a bad speller though). I maybe didn't ask the question in a clear enough way.

Taking our Z's as an example: I expect the larger sport brakes to stop the car from 60mph to 0mph in a shorter distance than the standard brakes (btw, I have not yet read any reviews testing the standard brakes, they all test sport packages). I know from experience that the standard brakes produce enough friction on the rotor to completely stop the tire from rotating making the tire skid over the pavement (or, well the ABS come on but you know what I mean). So, why do the larger sport brakes stop the car in a shorter distance? Yes, the sport brakes have a larger surface area in contact with the rotor and produce more friction but there is already enough friction with the standard brakes to lock up the wheels. The only answer I can gather (both from this discussion and my own imagination) is the larger brakes allow greater control over the stopping force allowing the driver to push the brakes closer to the point of locking up the wheel without crossing over the point where the tire starts to skid.

The sport package tires are wider than the base model tires, that is the only real difference. Put the sports wheels on the base car and the base wheels on the sports model car and the results should reverse.

I think heat is like 90% of the reason for the move to bigger brakes in most applications. Some people will find examples where that is not true, but the added absorption and dissipation area provides a huge benefit.

I don't think that a comparison in stopping distance between base and sport would do much good, as they sport different size/weight rims, as well as different stock tires in notably different sizes. I believe that the stopping distance would likely be very close.

I know I kept stock size brakes on my s2000, and despite the (relatively ) large rims I had on the thing, the stopping distance was in line with other s2k's sporting BBK's. On a track or in the twisties though, my rotors would heat up to the point where they were glowing red, while the rotors on said BBK's were still much cooler.

Contrary to the belief many will have, for the contact between brake pads and the rotor, surface area is irrelevant. The reason that surface area plays a role in other situations (notably tires) is due to adhesion (pieces of the tire bond to the road).

I'll keep this as brief as I can (despite my reputation...). For a ONE TIME PANIC STOP, the tires are the limitation as long as there is enough braking torque to activate the ABS. Any model currently sold by Nissan (as well as most car manufacturers) makes that grade.

The big difference with a properly designed and built BBK is that you can do high-speed panic stops repeatedly without significant changes in stopping distance or pedal feel. While most people don't drive down the highway doing repeated 80-0mph braking, I've been though many a mountain pass when I didn't have enough brakes to keep them from fading. Some cars give you some warning before the pedal goes to the floor, but a few of them can give the driver quite an unwelcome surprise.

It's not the pad surface area that creates the extra friction. However, a larger pad will run at lower temperatures, which is very good for it and the rotor. Lower pad temperatures mean easier pad selection, better modulation (for many compounds), lower chance of boiling the brake fluid, more consistent and repeatable performance and increased pad and rotor life.

One of the added benefits of a BBK for regular street driving is the fantastic pedal feel. At least when you hit the off-ramp at speed to find that cars are back up around a blind curve, you know that you can bring the car down with confidence and control. Just keep an eye on those mirrors! :driving:

Chris

"Braking is tire limited" is a very misleading statement.

Not really. Chris - AP covered it pretty well. Braking is initially tire limited, as any modern car can exceed tire to road friction with rotor to pad friction. Tire is the weakest link. Once you take repeated stops into consideration then many other factors come into play, and that is where the quality after-market brakes show their strength in resisting fade, consistent pedal feel, and durability.

Not really that misleading. Just saying that the original poster is not as wrong as you guys made it seem.

Now that you guys mentioned it, friction factors are pressure and mu, not SA. Sorry its been a while since highschool haha.

And our Sport Brakes give you very little warning when they go! Before the BBK, I got a soft pedal in one turn and slowed it way down and coasted into the pits, and took about 100 yards to stop from 20mph.

It's pretty difficult to describe that sort of "excitement" without experiencing it yourself!!!