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Old 02-01-2002, 01:59 PM   #1
V6
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Default rear brake upgrade?

Just curious, most people concern about upgrading the front brakes but not many people concern about upgrading the rear brakes.

Why?

Thanks.
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Old 02-01-2002, 02:10 PM   #2
GTBGUY
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V6 - on an 4wd or AWD vehicle, all four drive wheels are tied together via the drive shaft. Generally when the front wheels slow down, the rears will slow down as well (affected by the fronts). There are a few different routes to upgrading brakes :

1) Pads & Rotors @ all four corners w/ better fluid and lines.

2) 4 pot BBK up front, stock in the rear (or uprated pads and rotors in the rear)

3) Full blown 4pot BBK up front and 2 pot rear.

Generally speaking, methods 1 & 3 allow for brake biasing to be the same as the orginal car, as you keep the braking power even. The most effective upgrade is method 3, however it is also the most expensive.

Depending on rules & budget constraints etc, method 1 may be more cost effective, as well provide equal braking performance as method 2.
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Old 02-01-2002, 04:19 PM   #3
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Also , the fact that the front brakes do the bulk of the braking involved (something like 80-20 or 70-30) - upgrading the fronts make a huge difference.

Going to a 2 pot rear is not exactly an easy proposition either, as you need new hubs and the lot to make it work !!! If you attempt to just do it - you'll lose your e-brake!!

An easier (and cheaper) solution - is to upgrade your rear brakes (This assumes Impreza) from your stock RS/WRX setup, and simply goto Legacy Turbo rears. The rotors are vented, and the brake calipers/pad surface is slightly larger to improve braking ability.

-victor
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Old 02-01-2002, 04:28 PM   #4
FastPorsche
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Default Re: rear brake upgrade?

Quote:
Originally posted by V6
Just curious, most people concern about upgrading the front brakes but not many people concern about upgrading the rear brakes.

Why?

Thanks.
See cobb big brakes for WRX
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Old 02-01-2002, 04:38 PM   #5
FastPorsche
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Default Re: rear brake upgrade?

Quote:
Originally posted by V6
Just curious, most people concern about upgrading the front brakes but not many people concern about upgrading the rear brakes.

Why?

Thanks.
See cobb big brakes for WRX
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Old 02-01-2002, 05:18 PM   #6
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Quote:
Originally posted by GTBGUY
V6 - on an 4wd or AWD vehicle, all four drive wheels are tied together via the drive shaft. Generally when the front wheels slow down, the rears will slow down as well (affected by the fronts).
That is FALSE. You have a center diff. Ever pull your E-brake?

Kevin
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Old 02-01-2002, 06:22 PM   #7
Austin
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You can also buy rear rotors from an H6 legacy outback. They are 11.4 inches (wrx oem 10.3"), and you also need the caliper bracket. You can keep the wrx caliper and pads.
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Old 02-01-2002, 08:43 PM   #8
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I went with 4 pots all the way around. Brake bias!? As far as I am concerned bias in any perfomance application needs to be regulated with an inline brake bias valve.




SLR-
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Old 02-01-2002, 10:16 PM   #9
GTBGUY
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Red Rocket - I was simplifying the process. However, if you don't believe this, there's a simple test. When your car is on a lift w/ the e-brake off, rotate one of the rear wheels, and you'll see the fronts rotate as well.
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Old 02-02-2002, 05:26 PM   #10
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does anybody have info on the wilwood rear brake kit (under 1000) does this include a new caliper.
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Old 02-02-2002, 05:28 PM   #11
FastPorsche
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Default Its long but...

Quote:
Originally posted by V6
Just curious, most people concern about upgrading the front brakes but not many people concern about upgrading the rear brakes.

Why?

Thanks.
I responded to this yesterday but again the post has disapeared so I just pointed you to another thread.

IMO its a huge over sight to not upgrade the rears. I went to Stoptechs webpage the Trey reffered me to and well, IMO its cleaverly worded (I'll just leave it at that). Most cars from the factory dont have enough rear brake (has to do with saftey and profits). Adding more bias to the rear will make the car stop sooner and more stable (I am not talking about normal street use where maybe only using front brakes is acceptable for some). The car with more rear bias will not nose dive so much when you get on the brake hard (As in track use)

Trey said
"We have tested this at track events and measured brake operating temperatures under a variety of conditions. Our findings lead us to the solution we provide. We spent a great deal of time on maintaining a balance in the braking system. "

But did not elaberate about temps.

I think they dont offer it because the people who make there brake kit dont make it. As it turns out Cobb dose not seem to be a parts manufacture but is either puting kit together from manufactures or reselling some elses kit. Thereis nothing wrong with that, and it happens all the time. But they would be at the mercey of the supplier/manufacture.

Because of the design in the rear of these cars it not as easy to make a simple kit to upgrade rears. That IMO is why there is little activity there. Wilwood dose make a kit that is 6 piston front and 4 piston rear if your interested. The kit (4-Pfront and 2P rears) fron Subaru also not alot of money and would work out nice IMO.

With out having more equipment like dual master cylinders it would be trick to dial in the bias so its important to optimise braking through your parts choice(calipers and rotors).

Stoptech who make the kit for Cobb says

"February 18, 2001

One of the most common questions received from new owners of our front brake upgrade kits is "Do I now need to upgrade my rear brakes too?" To answer this, we need to look at the role of the rear braking system from a few different perspectives. The answer may surprise you, especially hearing this from a company that sells big brake upgrades!


Rear Brake 101


One of the many design factors that goes into the development of a base braking system is the mysterious "bias" or "balance." Truth be told, it's a pretty simple concept to grasp: for vehicle stability under braking, it is required that the rear brakes do NOT lock before the front brakes. Simple, right? Most of you probably knew that already.

OK, so what governs the 'lock up' point of the rear brakes? Drum roll, please:

1. tire tractive capability (friction)
2. tire normal force (weight on the tire)

This can be proven from looking that the fundamental relationship for maximum sustainable tire force: F=µN, where:

F = the lock up point, or peak force
µ = tire-road coefficient of friction
N = normal load sitting on the tire

So, when the OEM is designing a brake system, they 'size' the system components (calipers, master cylinder, rotor OD, etc.) to generate the proper amount of torque at both ends of the vehicle so that the front brake force ('F' above) exceeds its peak traction first. At this point, the front brakes lock and the car slides in a nice, stable straight line. (Note that at STOPTECH, we design our front brake upgrade kits in the very same fashion for the very same reasons.)


Potential Impacts of Big Front Brakes


Fortunately (from a safety standpoint anyway), when most big-brake suppliers adapt a mondo rotor and caliper package to a vehicle, they end up actually increasing the FRONT bias. How? By increasing the effective caliper piston area and the rotor effective radius, these two factors work together to increase the 'mechanical gain' of the front brakes, building more torque for the same pressure, everything else being equal. So, from a bias perspective we are not pushing the vehicle toward instability, but rather just the opposite - we are underbraking the rear axle! The obvious impact would be an increase in stopping distance - probably the one thing the new owner was actually hoping to reduce. Ironic. So, say you chose to install these big brakes on the front axle but want to maintain the OEM bias. What's the answer? Well, one way would be to invest in big rear brakes too which increase the rear mechanical gain to the point that the system is balanced once again.


So, What's The Harm In Doing That?


Well, let's look at why we upgraded the front brakes in the first place. Contrary to popular belief, the real reason sports- and racing cars use big brakes is to deal with heat. Period. There has been a bunch of stuff published which will disclaim this, but when you look at the braking system from a design standpoint, making them 'bigger' doesn't fundamentally do anything for stopping distance. It's all about the heat. So, you upgraded the front brakes because of thermal concerns but as a hidden surprise got a shift in brake bias. As a band-aid to this condition, you now spend thousands more on a rear brake upgrade because the front system was not sized correctly in the first place. Sure, it looks great, but there is another option...


Which Is?


When upgrading your front brakes, it is possible to size the caliper pistons and rotor effective radius to maintain the original brake system's pressure-torque relationship. Yea, it takes more engineering know-how and you can't sell the same part to everyone anymore, but you are not altering the base brake balance from what the OEM intended. This design philosophy stands behind every brake upgrade kit STOPTECH manufactures. Now, if you sized the front brakes correctly, why would you need to change the rear brakes? Good question. If there are no thermal concerns with the rear brakes (and on a front-engine street car there rarely are) then by installing a rear big-brake kit all you are doing is (a) spending money and (b) adding unsprung weight. This is not usually viewed as favorable, unless you like driving a heavy, expensive car.


Oh Yea - One More Thing…


Finally, under an OEM bias condition, the rear brakes only contribute about 15-20% of all the braking force the vehicle generates, and when you install sticky tires you actually DECREASE the amount of work they need to do. Why? Because at the higher deceleration levels afforded by race tires, there is more weight transfer taking place, reducing the normal force on the rear tires and increasing it on the front (remember F=µN from above?). If anything, we now want to decrease the rear effectiveness. Ironic once again.
Of course, if you decide to upsize your rear brake system components you can also impact the front-rear torque relationship, and consequently you can "bias" the "balance" more toward the rear. Go too far, and the rear brakes could lock before the fronts. Again, not the end result you were expecting, right?
It has been said that "The folks at STOPTECH should consider developing a rear kit to match their front setup. They'll be very happy with the performance improvement if done properly." Well, since our FRONT systems are designed properly, we save you the need to spend your money on the back axle.

Let's reword that quote to reflect the STOPTECH philosophy: "Our competitors should consider developing a FRONT kit to match their stock bias condition. They'll be very happy with the performance improvement if done properly, AND will save their customers the cost of a rear brake upgrade in the process.""



By This I am guessing that there are very small pistons in the calipers or there not being 100% forthcoming.

Last How much brake dose 250HP 2400lbs car need? Probably not as much as is being offered by some companies out there.

Last edited by FastPorsche; 02-02-2002 at 05:35 PM.
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