Just a couple of nits to pick...

Not entirely true. Bigger rotors will decrease brake fade because of increased heat-absorbing rotor mass. However, they will NOT make any difference in stopping distance, and the increased mass can have a negative effect on acceleration and ride quality. I will agree that most people buy them for styling.

Drilled and/or slotted rotors do NOT have a noticeable effect on braking performance unless you are using lousy brake pads. They also don't dissipate heat any faster than regular rotors. I have explained this several times in past threads. Baer used to have a disclaimer about this in the FAQ section of their website, but they removed it; I think they caved in to market pressure.

Yes, they help pedal feel, but they won't have any effect on brake fade. How could they? All they do is hold fluid.

FWIW.

 

ss brake lines help brake fade, because as you push the pedal harder, regular brake lines can expand due to heat and the brake line material. ss brake lines don't expand, and therefore reduce brake fade. (at least this is how it has been explained to me).

As far as slots/cross drilling - Marketing material from companies like PowerSlot say that they will improve braking (of course they have to have some reason for slotting them). Usually the reason given has to do with channeling away superheated brake gases, or keeping brake pads clean. I've heard feedback from customers that say that slotted rotors do help braking, but I don't use them myself and a guy who just dropped a couple hundred bucks on new rotors is more likely to say they work better anyway. I will submit to your superior knowledge on this one!

As far as your first point goes (larger rotors = increased heat-absorbing rotor mass) I hadn't really thought of that. When I last talked to the guy from SSBC, I was under the impression that BAER big brake kits (marketed under Eradispeed) would improve braking performance, and the SSBC guy gave me a bunch of reasons why they won't. I'll have to hit him up with that one just to see what he says!

 

I've never heard that, but it kinda makes sense. However, I suspect that the difference isn't nearly as significant as better pads, larger rotors, or better calipers.

Just to rehash (what the heck)... Emitting superheated gas is called "outgassing", and it was a big problem with 20-30 year old performance pads or present-day organic $9.95 specials from Pep Boys. However, modern carbon pads (you name the brand) do not outgas at temperatures lower than what you will see in a blast furnace. The rotors will melt before the pads outgas. Therefore, you do not need slots or holes for this reason.

The slots or holes "keep the pads clean" by continually scraping away pad material, which keeps the pads from glazing; however, modern carbon pads don't glaze very easily, and the constant scraping WILL wear the pads out faster. Basically, they will waste your brake pads for no real benefit.

There's actually a psychological term for this. It's called "cognitive dissonance." It's quite a frequent problem among the import racer and SUV crowds.

 

Hey pollax, are you enjoying your drums in the back? I really like your new rims...they almost look like stock steelies... j/k dude!

Hey, as for your theory...there are several parts to stopping power.

1. clamping force...has to do with master cylinder abilities, size of caliper piston, caliper flex, line buldge, etc.

2. heat absorption...reduces brake fade...bigger rotors absorb more heat and have more area to cool with.

3. leverage of stopping force...bigger rotor with caliper placed farther out has more leverage. Like it's harder to turn a 30 lbs 20" rim, it's also harder to stop since the weight is so far away from the axle. So in order to stop the axle, it is best to apply force as far away from it as possible.

Remember...it really comes down to tire grip - best modification ever is tires!!! From there, better pads...then higher temp fluid (Some of that blue Smurf Blood is cool), then try a bigger master cylinder, then steel braided brake lines from Goodridge or Earl's, then when you are out of other options, use bigger rotors. Use the smalles rotors you can to effectively stop you...bigger rotors mean more unsprung AND rotational weight. Another possibility is air ducting and removal of dust shields from the back.

 

The problem with your CD player example, is that in the case of a larger brake rotor, the outside edge is spinning Faster (not slower, like your CD) than a smaller brake rotor would spin at the same speed.

An 11" rotor has a circumference of 34.54" so the outer edge travels at a speed of 34.54"/wheel revolution vs. a 13" rotor has a circumference of 40.82" so the outer edge travels at a speed of 40.82"/wheel revolution. This is an approximate 15% increase in outer edge speed to offset the approximate 15% increase in rotor size.

The increased speed (and mass) of the larger rotor tends to negate the benefits of increased braking area.

Sometimes I think that PseudoRealityX actually lives in a Pseudo Reality

 

This is the reason I have in my latest mod : a pair of 4-piston RX-7 FC model caliper with custom slotted Honda Odyssey rotors up front.
Anyway, with any kind of performance mod or brake mod, the improvement is minimal if one changes 1 element of the braking system. Same goes for exhaust system; one has to change to performance headers, larger diameter piping, and use a straight thru muffler to see a big gain in hp. Now I know that companies have tested their mufflers and showed increase in hp to defend their products. It's all in a marketing gimmick. The true gain is when the whole system is changed.
Same goes for the brake system; good brake fluid, SS brake lines, bigger rotors, 4-piston calipers (at least) will only see a big improvement felt by the feet. Please bear in mind that I am just expressing my experience here speaking from my setup. Just my 2 cents.

 

I guess what I meant by that was that you can upgrade everything else, but if you don't get better calipers, you won't notice a big improvement in your braking.

 

Correct!

 

Maybe I do struggle with your analogies, but you don't seem to address my points very effectively

I agree "that a larger rotor DOES IN FACT INCREASE the amount of kinetic energy that the pad can take in a given amount of time." This in no way refutes my point that larger rotors are traveling at a faster speed on the outer edge, and have more rotational mass, thereby negating the increase in kinetic energy absorption.

As far as the caliper situation, I think you will find (in magazine articles, brake manufacturer web sites, etc...) that larger calipers can significantly change braking distances, whereas other brake upgrades don't have nearly as noticeable an effect on stopping distances. SSBC has a Saturn that does 60-0 in 90ft! This would not be possible w/o 4-piston calipers.

Feel free to post test results that prove me wrong!

 

That's great and all but what does that have to do with my post? I was calling bunk on the fact that increasing torque relative to the axle will do nothing to decrease the stopping distance of a car.

 

It won't decrease the stopping distance of the car necessairaly. If you are on ice with r compound tires...pleezebelieve that your car won't stop any faster. Be precise when speaking technology. One of the benefits of a larger caliper is that it will allow more torque to be transferred in reducing the speed of the axle. So, given enough grip, your car will stop in less distance. Otherwise, your brakes will just lock up sooner. Picture one of those small electric motors that you can get for like $0.99 at Radio Shack, the small one with a 3mm shaft...now imagine hooking up a 1.5V battery (for low torque). Now, try to stop the shaft by gripping it with your fingers...pretty tough right? Ok, now, say you mount a 10mm disk on top of the shaft, and try to stop it from spinning with your fingers...now it's actually possible. One step further, try mounting a 50mm disk on the same motor...it'll be pretty easy to grip it with your fingers and stop it from spinning. To summarize; The same concepts apply to brakes: increased friction area, increased leverage on the rotational axis, and greater cooling area. Thanks for being a part of Applied Physics 101. Have a great day pollax, I need to see you after class, you've been a bad, bad student

 

Wow. I guess I am confused. So are you saying that a faster outer edge helps braking?

Actually, the Saturn in the example stops 60-0 in 90ft on street tires. My point is that no matter what you do to your braking system, you will NEVER get this level of performance out of stock calipers.

All I'm trying to say is that getting larger rotors won't really change the way you brake, whereas getting a stoptech front disc brake upgrade complete package with 4-piston calipers will dramatically improve your ability to brake (assuming that you use good tires, brake fluid, etc...).

I don't know why people keep bringing tires back into the equation. I'M AWARE THAT TIRES MAKE A BIG DIFFERENCE IN BRAKING. But for the sake of comparing specific brake system components (calipers, rotors, etc...), it makes sense to remove other variables from the equation (at least in a hypothetical example).

 

Again I have to ask what relevance does "More work = more heat" have to do with torque acting on the axle?

Can you explain to me how increasing the torque acting on the axis of the axle can possibly produce more heat at the edge of the rotor?

Looking at some back issues, Car and Driver did some tests on a Subaru Impreza with a bunch of big brake kits. Here are the results:

70-0 mph ABS off
Stock - 192 feet
Brembo F50 - 195 feet
Brembo Lotus - 191 feet
Prodrive - 198 feet
Stoptech - 189 feet


The worst was 3% worse than stock and the best 1.5% better than stock. All of these differences are of course are statistically insignificant. Basically you can sum it up by saying big brake kits don't really affect stopping ditance at all.

So what's the big advantage of big brake kits? Less fade!

Average of 25 90-0 mph stops
Stock - Did not complete 25 runs. Stopped after 4 runs because braking distance already exceeded 360 feet
Brembo F50 - 299 feet
Brembo Lotus - 305 feet
Prodrive - 308 feet
Stoptech - 297 feet

The article even quotes Eric Dahl a brake engineer from Brembo: "Don't expect the brake kits to stop you sooner, but expect the 20th lap to feel like the first."

 

Alright check out this link:

http://www.ssbrakes.com/vehicles/project/saturn/

this is the car with complete specs. In their catalog - page number 24 - SSBC claims that this kit allows a vehicle to stop in less than 90ft from 60 - 0. I agree that this is probably bs, but I was simply going off their numbers - I did not witness this test. If you can't find the page I'm referring to, I'd be happy to scan it and email it to you. This number didn't seem so unreasonable to me as some vehicles stop in less than 110ft 60-0 from the factory. I suppose that their comes a point where every foot of reduced stopping distance becomes proportionally harder to achieve.

I agree that a proportioning valve is helpful, but it is also helpful to have a stiff suspension when braking. This reduces (a little) the force on the front brakes and allows the rear brakes to help out a bit more.

I've never locked up my brakes/wheels as I have ABS.

I once saw a car go from 40mph to 0mph in practically 0 feet. I don't think that the driver hit the brakes at all.

 

Actually, that's not the reason. The amount of weight transfer onto the front tires is purely a function of the car's weight, the vertical and horizontal location of its center of gravity, its wheelbase, and its rate of deceleration. The stiffness of the suspension has nothing to do with it.

The suspension stiffness determines one of the *effects* of weight transfer- the compression of the front suspension. All modern cars with IFS are built to increase negative camber as the suspension compresses to counteract body roll when cornering. Therefore, when you brake, the front suspension compresses and the wheels tilt inwards, reducing the size of the tires' contact patches. Stiffer suspension= less traction-reducing compression. If a vehicle has solid axles front and rear (like a typical heavy truck) the suspension has no effect on braking whatsoever. (This is the same reason why a RWD car with a solid rear axle will always be superior at the dragstrip.)

Yeah, I'm nitpicking.