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Old 12-09-2006, 12:19 PM   #2
ButtDyno
Street's closed, pizza boy
 
Member#: 17301
Join Date: Apr 2002
Chapter/Region: MAIC
Location: Why do they always say the Evo
Vehicle:
is the "dark side"
06 Evo #7 STU, 03 IS300

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Part 2: Big brake kits and other meta-issues.

Do I need to upgrade my brakes?

In general - your stock brakes are probably pretty good (depending on which car you start with). I quote Gary Sheehan a lot in this FAQ. He RACED, yes RACED, a WRX on the stock calipers in NASA's US Touring Car Challenge - basically NASA's equivalent of SCCA's World Challenge. Serious touring car racing. He ran on the stock calipers for an entire season. And did well. Consider this when you are thinking about whether or not you need to upgrade your brakes. (More info: http://forums.nasioc.com/forums/showthread.php?t=197590)

Ultimately he and his team went with Stoptechs - not because they were seeing fade on that setup, but because the heat generated from it was causing unnecessary wear elsewhere. (And again... they were RACING... not doing track days, not autocrossing, and not doing "spirited driving".)

If you are doing anything other than tracking the car, or driving like an asshat on public roads, you likely do not need a big brake kit or anything close to it. If you are fading your brakes driving on the street, slow the **** down.

What are some reasons people upgrade their brakes?

1. They want to decrease stopping distance.
2. They want their brakes to handle heat well and not fade (i.e. track use)
3. They want their car to brake "flatter"
4. They want their brakes to look cool
5. They want to reduce unsprung weight.

Let's look at those reasons.

1. Decreasing stopping distance

How can I shorten stopping distance? What's the best bang for buck way?

This one is easy - TIRES! As Stoptech so elegantly says:
http://www.stoptech.com/tech_info/wp...lections.shtml
Quote:
1) The brakes don't stop the vehicle - the tires do. The brakes slow the rotation of the wheels and tires. This means that braking distance measured on a single stop from a highway legal speed or higher is almost totally dependent upon the stopping ability of the tires in use - which, in the case of aftermarket advertising, may or may not be the ones originally fitted to the car by the OE manufacturer.
If you are dropping big $$ on brakes while running all season tires, you are wasting your money!

"I don't believe you... I installed cross drilled rotors and my car stops on a DIME now!"

Your butt dyno may be tricking you.

http://forums.nasioc.com/forums/show...6&postcount=39
Quote:
Originally Posted by GarySheehan
If you added front bias because the pistons are too big, it will definitely FEEL like it's braking harder, because the nose will dive down more. If the pistons are sized correctly, the simple fact that you've got much better pedal feel can make it feel like you're stopping considerably harder.

Consider this. Decreasing stopping distance from 60-0mph by 6-10 feet with a brake upgrade is considered a MAJOR improvement over stock in the braking industry. I'm not sure that anyone can feel that difference. So when people say their brakes stop so much harder than stock and they haven't upgraded tires, the first thing I think of is too much front bias.

The only way to significantly decrease your stopping distance is to put stickier tires on the car or drastically increase downforce. Period. Anyone that tells you otherwise is is lying to you or doesn't know what they are talking about.

Gary
Sheehan Motor Racing
www.teamSMR.com
Size changed for emphasis

I don't believe you... I have a BBK not just pads... I swear I stop like 50 feet sooner!

http://forums.nasioc.com/forums/show...7&postcount=26
Quote:
Originally Posted by GarySheehan
Sdecker,

I'm inclined to think that your 50 foot drop in braking distance is more a factor of driver improvement or driver confidence rather than the actual effectiveness of the brakes. As long as the brakes are within the temp range of the pad, they will both stop the car very similarly.

I raced for a full year on the stock rotors and calipers. We had them set up where they would not fade. Switching to Stoptech's made my life easier because they are more consistent, have a better feel and run at lower temps, thus not ruining everything around the braking system. But they did not drastically decrease my stopping distance. Probably a few feet.

I could see you losing 50 feet of stopping distance if you were experiencing pad fade with the stock system, but you can't compare the two. If you used a hot pad and a hot fluid in the stock system, they wouldn't fade and then you could make that comparison.
How ELSE can I decrease stopping distance?

Here is a pretty good thread:
http://forums.nasioc.com/forums/show...hreadid=351743

2. Reducing brake fade

What is brake fade?

Brake fade occurs when your brake system is put into a temperature range that it was not designed for. This can happen if you take your car to a track event without upgrading the brake pads and brake fluid. The result is that you will push the brake pedal, but the car won’t slow down, which is quite unpleasant

There are three types of brake fade:
http://www.se-r.net/car_info/brake_p...l#Brake%20Fade

Pad fade: your pads are designed to work inside of a certain temperature range. If you get them too hot you can get them outside of that range, especially if they are near the end of their life. You resolve this in two ways: 1) driving within the limits of your pads (duh) or 2) installing pads with a higher temperature range.

Green fade: If you do not bed your pads in, they will not grip like you expect them to. This is easily fixed. Bed in your pads!

Fluid fade: Like pads, brake fluid has a temperature range it is comfortable operating in. If your fluid is not up to the task, it can boil, which introduces air bubbles into the brake system. This results in a soft pedal and can also be quite scary. Fortunately, better fluid is cheap.

"I'm not an asshat, I track my car, but I see fade. What should I do?"

Make sure you have pads that are track-worthy. There are basically three categories of brake pads:
-street-only pads: won't hold up to a track day. Either don't try, or drive like a chicken on the straights
-street/track pads: you can track these, but you will have to deal with the tradeoffs - likely noise and dust.
-track-only pads: you don't want to daily drive these, as the noise and dust will likely annoy you. They may also eat your rotors prematurely.

Make sure you also have a brake fluid that won't boil easily.

Finally, if you still see fade, congratulations! You're probably working the car pretty hard. It's time to start looking into vented rotors and big brake kits.

You can also try brake ducts. Some vendors (i.e. RaceComp Engineering) make some, and some people have made their own.

What else should I know about picking pads for track use?

A thread full of good advice, especially Todd TCE's post, is here:
http://forums.nasioc.com/forums/show....php?t=1269968

3. Braking "flatter"

When I hit the brakes, the nose of the car dives down pretty significantly. Can I fix this?

Most Imprezas come with a fairly significant front brake bias from the factory. For a discussion of brake bias, check out this article on StopTech's website:
http://www.stoptech.com/whitepapers/...erformance.htm

There are a few ways to make the car more "flat" while braking:
-Suspension mods. Making your suspension stiffer (i.e. the springs) (and lower - right?) will make the car dive less.
-Reduce front brake torque
-Increase rear brake torque

OK, I've got a stiffer suspension. I'm decreasing weight transfer under braking now, right?

No

http://www.turnfast.com/tech_handlin...eightxfr.shtml
Quote:
... the amount of weight transfer is not altered by springs, shocks, anti-roll bars, etc. Weight transfer is a result of inertia and momentum. These suspension components cannot change that. What these components can do is impact how much the suspension moves in response to the load change, and how quickly the load transfers to the tire contact patches.

The amount of weight transfer is dominated by the vehicle's weight, location of the center of gravity, wheelbase, and track, and the amount of force applied during braking, accelerating, and cornering.
It goes on to say that suspension mods can change the *rate* of weight transfer, and help maintain the appropriate contact patches and all that

How can I change brake torque?

Legacy777 has done a bunch of work on this subject.
http://forums.nasioc.com/forums/show...t=brake+torque

His Excel spreadsheet for calculating brake torque is here:
http://www.main.experiencetherave.co.../brakemath.xls

Some of the variables that you can easily control are:

* Pad coefficient. If you want more rear bias, put a more aggressive pad in the rear than the front, and vice versa.

* Rotor size. This changes the effective diameter of the rotor. Bigger rotors = grab the rotor further out from the center = more effective torque.

* The "H6" upgrade is very popular among Impreza owners because it's so damn cheap and has a noticeable impact on the car's bias. For the 2.5RS's and the 02-05 WRX's, the stock rear calipers can be used with a larger rotor from the H6 Legacy, and a different caliper bracket to move the stock rear caliper further out to accomodate the bigger rotor. You definitely need the OEM caliper bracket, but you can choose from several 290x10 rotors if you want slots or something.

* Unabomber's guide to the H6 upgrade is here: http://forums.nasioc.com/forums/showthread.php?t=522006

* A list of non-Subaru H6 sized rotors is here: http://forums.nasioc.com/forums/showthread.php?t=562057

* Piston area. The visual size of the calipers has NOTHING to do with how much torque they generate. The crappy looking two pots from the 02-05 WRX have more piston area than the 4-pots on the 06 WRX or the StopTech kit for the 02-05 WRX. If the 4-pots are placed on an 02-05 WRX they will reduce the front piston area and thus decrease front brake torque.

4. Making the brakes look cool

I saw this sweet BBK from some cool sounding Japanese company. I want to put it on my car to impress my friends. Should I?

What you should never do is compromise your car's safety for looks. I didn't realize how bad some of the BBK's on the market were until I saw this:
http://www.stoptech.com/company_info...hallenge.shtml

Now - admittedly this is StopTech's website. But StopTech doesn't make any outrageous claims. The stock RSX in that comparison was on Michelin Pilot MXM4's - an all season tire. It did 60-0 in 132 feet. Of the two StopTech shod cars, one was on Hoosiers (very sticky) and one was on Advan A032R's (also very sticky). So you'd expect them to stop noticeably shorter than the stock car on all seasons.

But the terrifying thing about that comparison is how bad some of those high dollar kits are. A Ford Expedition stops 60-0 in 140 feet, 8 feet slower than our stock RSX (see http://autos.yahoo.com/ford_expediti...4-performance/)

-The Brembo kit, on sticky Advan 048's, was a foot slower to stop than the stock RSX.
-The Wilwood kit, on Nitto NT01's (race tires), was 11 feet slower to stop than the stock RSX, and equivalent to the Ford Expedition.
-The Project Mu kit, on the same Hoosiers that the StopTechs stopped in 110 feet with, stopped at 171 feet. To put that into clearer terms, if they were 30 feet behind the Expedition at 60 mph, and both the Expedition and the Project Mu RSX hit their brakes at the same time, the RSX would still rear end the Expedition. That's freaking ridiculous! And how many of you leave 30 feet between you and the car in front of you at 60 mph?

There are other variables - wheel alignment for instance, maybe some of the cars were broken - but it's a pretty scary looking test.

Cliff notes: make sure your bling is well-engineered bling.

5. Reducing unsprung weight

Will my BBK be lighter or heavier than stock?

Here's a list:
http://forums.nasioc.com/forums/showthread.php?t=596404

"what else should I read about brakes"

There are some great articles on stoptech.com: http://www.stoptech.com/technical/




I hope this is helpful!
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Last edited by ButtDyno; 12-21-2008 at 01:02 AM.
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