Please explain this to Tristan

[scottzg]

Big brakes are good.

think of a suv with 22" rims. the stock brakes are only ment for 15" rims.... so the added weight would kill the stock brakes faster than it would if u upgraded to bigger ones.. and the stoping distance goes longer .. so big brakes are good.. thank you haha

this is a joke, right?

[jamal]

Big brakes are good.

think of a suv with 22" rims. the stock brakes are only ment for 15" rims.... so the added weight would kill the stock brakes faster than it would if u upgraded to bigger ones.. and the stoping distance goes longer .. so big brakes are good.. thank you haha

this is a joke, right?

ummm....



But, yeah. Stock brakes would proabably have no problem locking up/ stopping a 3/4 ton Suburban on 22" rims. The first time.

I've faded my brakes, and while good pads and fresh fluid will help with that, I still want to go bigger, because it's not that expensive when you pull the parts used off other Subarus. I'm shopping for some "H6" rears to go with the WRX fronts sitting on my floor, which will give me nice big 11.5" rotors all around and stock bias.

[THAWA]

So, to reiterate. He's right. The stock brakes are more than enough for a stock car. Adding brembos wouldn't necessarily make you stop any faster.

[Subaru_Nation555]

The stock brakes are more than enough for a stock car. Adding brembos wouldn't necessarily make you stop any faster.

Yeah unless you track your car and brake fade is a problem. Other then that BBK are just for bling IMO. Good fluid/pads/lines are all a street car really needs.

[LaureltheQueen]

The point that I believe Tristan was trying to make was that it's stupid to put bigger brakes on a car with a stock engine. I don't believe that's the case.

If you have tires capable of not losing traction(ie:amazing tires) then with brakes with more pistons, you'll be able to clamp down harder on the rotor, thus decreasing stopping distance.

The two main things limiting your stopping distance are your brakes and your tires. If your tires are oh, say re-92's, then you are currently limited by your tires. Upgrade your tires to great tires, then you'll be limited by your brakes.

[THAWA]

Well if you track your car why is your car stock?

[scottzg]

If you have tires capable of not losing traction(ie:amazing tires) then with brakes with more pistons, you'll be able to clamp down harder on the rotor, thus decreasing stopping distance.

The two main things limiting your stopping distance are your brakes and your tires.

If your tires are oh, say re-92's, then you are currently limited by your tires. Upgrade your tires to great tires, then you'll be limited by your brakes.

Wrong

Wrong

Not with currently available technology.

[BAC5.2]

I am in the same boat as Steve. Tons of left-foot, heel-toe, trail braking, and deep braking when tires and surface conditions allow. I spanked a set of pads in, what, 10k?

Big brakes don't necessarily make a car stop in a shorter distance. If the stock brakes can lock the tires, then the stock brakes can threshold the tires to an acceptable stopping distance. Bigger brakes do not allow you to threshold any more or less, though they can help you modulate that line.

HOWEVER, stock brakes are NOT adequate in the cooling necessary to time attack a car. Take a car on a track with stock brakes, and there's a good chance you can overheat them. I know I overheated my stock brakes on a regular basis, and that was on backroads, not on a track.

THAT is the benefit of superhuge brakes. Superior resistance to fade, giving more consistant performance, which lead to more confident performance of your car.

Stock power or 1000whp, stock brakes can safely reduce the vehicles speed from it's maximum attainable speed. Just like cars are not allowed to be spec'd with tires incapable of reaching the maximum speed of the vehicle, they cannot be spec'd with brakes incapable of slowing the car from that speed. Brake size is not a function of power, but rather a function of intended useage. A track bred car, likely won't have drums at all 4 corners. Cars designed to go to the store and get some milk and eggs, can come with smaller brakes without sacrifice in performance.

Big brakes simply make the endeavor of stopping from 150+ a much less hair-raising experience. Plus, they win car shows.

[jamal]

My brakes are so huge I need 20" wheels to clear them. The discs are vented, drilled, chromed, and have free-spinning centers with leds. There are two calipers on each disc with 8 pistons each. I need them because I live my life 1/4 mile at the time and have to stop every 1/4 mile to pick up the pink slips to the cars I beat. My rear drums are painted red.

Well, I'd say that about wraps things up. Time for bed.

[LaureltheQueen]

If you have tires capable of not losing traction(ie:amazing tires) then with brakes with more pistons, you'll be able to clamp down harder on the rotor, thus decreasing stopping distance.

The two main things limiting your stopping distance are your brakes and your tires.

If your tires are oh, say re-92's, then you are currently limited by your tires. Upgrade your tires to great tires, then you'll be limited by your brakes.

Wrong

Wrong

Not with currently available technology.

care to explain?

[BAC5.2]

More pistons decreases the pressure from the master cylinder across a larger surface area, effectively reducing clamping force. You need an acompanying, smaller bore mastercylinder to gain back the pressure dispersed across a larger piston surface area. I think that's how it works.

Stopping distance has other factors, namely including suspension. To stiff a suspension, and you'll lose a ton of braking traction from high speed over bumpy terrain.

Momentum conquers all, even stock brakes can overcome sticky tires given proper momentum. With future technology in anti-lock-brakes, then it would simply be a matter of brakes and tires, and you could just drop the pedal to the floor and let the computer worry about stopping you to the best of your hardwear's ability.

At least that's what I think Scott would say...

[jamal]

actually, more pistons and more piston area will increase the pressure. Say the line pressure is 100 psi and you have a one sq. in. piston. The pressure on the piston is going to be 100 psi x 1 sq in = 100 lbs. If the piston area is, say 4 in. sq., the force will be 400 lbs with the same 100psi pressure.

[BAC5.2]

Incorrect. Pressure is dispersed across surface area.

Get a scale, and press down 20 pounds with your index finger. Kinda hard, huh? Now use your whole hand. Makes it easier, doesn't it? It's not excruciatingly painful to stand up, but according to your logic, while wearing a pair of shoes with a perfectly distributed 80 sq. in. of surface area contacting the ground, then a 200 pound man would be putting 16,000 pounds of pressure on the ground. That wouldn't be to good.

Pressure is not multiplied across surface area.

[scottzg]

jamal and bac, the difference lies in if you are accounting for the pedal travel or not. I don't feel like going into detail.


And for laurel, i will repeat what i said earlier, but in an easy to swallow format.

Any brake can provide enough clamping power to stop any tire you throw on it. You dont need more pistons or other crap. stock line pressure over stock area is the same as half the line pressure to double the area.

Your brakes provide more than enough clamping force, and before you start thinking that you're gonna fade them quicker because you're stopping faster, consider that theres only a given amount of kinetic energy in a car moving x mph.

There are no tires that grip better than stock brakes.

I agree with everything phil said, except that big brakes make stopping from 150 less scary. If my car is going 150, i have driven off a cliff.

[BAC5.2]

HAHAHA, let me rephrase then.... In a car capable of traveling 150mph, big brakes make stopping less scary.

Better?

I barred pedal travel, simply because that doesn't matter. Ultimately, a brake can only apply so much force that can be used. And as long as the master cylinder can provide that amount of force in the total pedal travel, then pedal travel is just a matter of feel, right? You could use a smaller bore master cylinder, and reduce pedal travel required to acheive the maximum usable brake force, but as long as you can muster that same force with a larger master cylinder, it doesn't effect brake force that the pedal now travels further down. So it's just a matter of feel as long as the master cylinder is capable of producing adequate pressure, right? And brake feel is all subjective.

[jamal]

Pounds per Square Inch.

It does multiply. Force = pressure x Area.

so take a 200 lb guy with 80 in^2 of shoe area:

200 = p x 80
80/200 = 0.4

so by my math the pressure is 0.4 psi. 0.4 psi over 80 in. sq. will create 200 lbs of force. You're multiplying force by area, not pressure by area.

[BAC5.2]

I stand corrected then.

So why do the non-USDM 4-piston calipers shift brake bias rearward compared to the USDM 2-piston calipers? Afterall, they do have a larger piston surface area than the USDM 2-pots, right?

Clarify that for me?

[jamal]

The explanation I heard was that the 2-pots exert the force on both sides of the disc, whereas the 4-pots have two pistons exerting the force over each side.

The only reason I can come up with would be due to different pad area.

The 4-pot pads are bigger, right? On the disc side, the area works the other way around, because the disc exerts an opposing normal force on pad, so a larger area means less overall pressure with the same force.

i.e.: that 400lbs exerted by the 4 in^2 pistons under 100psi is distributed back over the area of the pad, so a smaller pad will exert more force.

If the pads were the same area on the 2-pots as the 4-pot, they would exert the same pressure.

[BAC5.2]

So brakes with more pistons (which generally have larger pads) would, then, decrease force on the rotor?

[jamal]

I guess so, assuming the pistons are the same size and all that. From what I hear, the reason for the 4-pots isn't for more "stopping power," it's better brake modulation. Having 2 pistons on each side is supposed to put a more even force on the discs than 2-pistons and slider pins.

[rallysam]

Laurel,

I think what people are saying is this - you are definitely right that this has nothing to do with engine power.

On the issue of having good tires, you are right in theory about needing good brakes if you had the world's most incredible tires. People are just disagreeing because in reality there are no tires that are "THAT GOOD" that the stock braking system wouldn't be able to lock 'em.

And, it sounds like EVERYONE agrees that the reason for an upgrade is to avoid overheating, not to clamp down harder, and overheating is most commonly encountered on tracks (or anywhere else you find that you can really brake like a maniac from high speeds repeatedly).

Sam

[Warp3]

http://www.ffcobra.com/FAQ/brakes3.html
(originally from Grassroots Motorsports magazine)

I was going to post a link to the brake test that GRM did comparing stock brakes vs. upgraded (pads, fluid, etc.) vs. a big brake kit, but I can't seem to find that anywhere and the only similar article I can find is about brake pads (including some testing).

Regardless, "big brakes" have the primary purpose of increasing thermal mass thus making them perform longer without fading when being worked hard. Unless you are overheating your stock brakes currently, upgrading rotor size simply will not help you stop any faster (though upgrading pads, fluid and lines often will). Larger brakes may very well help you modulate the brakes better so you can stay at the limit of lockup more easily, but you are still limited to the adhesion limits of the tire for sheer maximum deceleration.

Sorry, but if you aren't overworking (or at least nearing the workload limits of) what you've got, then you are just adding unsprung weight.

[LaureltheQueen]

Okay, fine, I understand what you guys are saying, you're right.

Now out of curiosity... if the WRX has a stopping distance of 123 feet, how is the STi able to stop at 110 feet?

[Yukonart]

Okay, fine, I understand what you guys are saying, you're right.

Now out of curiosity... if the WRX has a stopping distance of 123 feet, how is the STi able to stop at 110 feet?

Magic.



I'll submit that if anyone locally would like to feel what a stock STi's "big brake" setup can do. . . they're more than welcome to come along for a ride. I think Laurel can already attest to the fact that it DOES, in fact, stop quite a bit quicker than almost any other car you'll encounter on the street.


But I guess since I've yet to track it, none of this information or experience is valid.

[rallysam]

Okay, fine, I understand what you guys are saying, you're right.

Now out of curiosity... if the WRX has a stopping distance of 123 feet, how is the STi able to stop at 110 feet?

Just hazarding a guess here:

Soft rubber compound, wider contact patch due to wider tire, longer contact patch due to larger diameter wheels, practically slick due to having almost no sipes whatsoever.

So tires basically. Now, the brakes are awesome, and they might help control things a bit better, but I think for the most part they do something different than help your braking distance on first application.