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Old 05-25-2002, 07:13 AM   #1
romanom
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Lightbulb Brake Performance Vs. Brake Feel

I think too many are mixing these two up from reading some posts. Especially about the 4 piston Subaru fixed calipers. Just to clarify, in brief, the differences.

Brake feel: pedal effort and pedal travel for any given desired deceleration. Ease of brake pressure modulation, accuracy and precision of modulation. Feedback through the pedal "describing" pad rotor contact dynamics and pressure fluctuations.

Brake Performance: Level of brake torque produced and the resistance to brake torque loss, better known as fade.

For performance I do not use the term stopping distance because that involves more than just the brakes.

Benefits of "better" feel:

Brake feel is just like steering feel. The better the feel/feedback is the more of the inherent performance you will actually be able to use.

Imagine a car that has 1.0g of lateral grip, but has lousy steering. Too light, completely dead, nothing happens just off-center, poor linear response and too much or too little ratio. Like a Mercedes AMG

How much of that great 1.0g are you ever going to be actually using with poor steering?

Same with brakes. Improving feel will allow you to better use what you have.

However, it will not objectively increase brake performance. If you are already getting the max out of you system then better feel will not get you more.


I will not go into how to improve performance as this has already been posted mulitple times. Sorry, but do a search
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Old 05-25-2002, 11:03 AM   #2
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Old 05-25-2002, 11:25 AM   #3
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I never posted this before, because to be honest to me it's obvious. But to others it might not be.

The formula below is a decent way to estimate what, if any, increase you have in brake torque after an upgrade:


Brake Torque Increase %=

[(caliper piston area new/old) * (effective radius new/old)* (brake pad friction coefficient new/old)]

*effective radius is the distance from the center of the hub to the center of the brake pad

*For sliding calipers multiply the areas by 2

Any answer equal to 1 means no increase. Any answer less than 1 means you've gone backwards. Any answer greater than 1 means a torque increase.


This will NOT give you the actual brake torque, just the difference.


Now things like steel lines, stiffer calipers effect feel not performance. Only force applied, torque arm and friction do that. You can change things like lines, calipers, pedals and boosters to change the characteristics. Such as, initial bite point and initial deceleration level, pedal travel and effort, pedal force mulitiplication. However, these do not actually produce more brake torque.
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Old 05-25-2002, 11:35 AM   #4
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Good post...I would differ slightly that things that effect feel can effect performance over time. In other words, less fad due to stainless lines or better pads for example, can deliver more consistent performance lap after lap..long after stock stuff gives up. So in that way, you get better feel and performance

Oh...and check your packages next week Mike!
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Old 05-25-2002, 11:37 AM   #5
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Quote:
Originally posted by adam99rs
Good post...I would differ slightly that things that effect feel can effect performance over time. In other words, less fad due to stainless lines or better pads for example, can deliver more consistent performance lap after lap..long after stock stuff gives up. So in that way, you get better feel and performance

Oh...and check your packages next week Mike!
Yeah, you make a point about fade. The stuff above is for torque only not torque loss! Excellent point!



Packages huh? WoooooHOOOOO! Cool thanks!
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Old 05-25-2002, 01:04 PM   #6
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This begs the question then- will Subaru 4 pots increase brake torque? Are they increasing effective area or piston area (twice as many pistons)?

Or do the 4pots simply provide better feel/feedback? Or both?

Curious as I have toyed w/ this upgrade.

Thanks,

Big Sky
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Old 05-25-2002, 01:18 PM   #7
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Quote:
Originally posted by BIGSKYWRX
This begs the question then- will Subaru 4 pots increase brake torque? Are they increasing effective area or piston area (twice as many pistons)?

Or do the 4pots simply provide better feel/feedback? Or both?

Curious as I have toyed w/ this upgrade.

Thanks,

Big Sky

Having 4 pistons on a fixed is the same as having 2 on a slider. Becuase the force of the pistons on a slider are applied on both pads equally.

That is why you need to double the piston area on a slider in the equation above.

If the piston area of one side on the 4-pot is larger than the stock 2 piston slider then it will increase brake torque.

Fixed calipers require opposing pistons because that is the only way to get a force on both pads. And companies use fixed because they are dramatically stiffer than sliders. Not to mention usually lighter, more reliable and lower height.
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Old 05-25-2002, 02:00 PM   #8
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Default Re: Brake Performance Vs. Brake Feel

Quote:
Originally posted by romanom
I think too many are mixing these two up from reading some go into how to improve performance as this has already been posted mulitple times. Sorry, but do a search

one way you can improve performance on bumpy spots is to PULL THE ABS FUSE

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Old 05-25-2002, 02:11 PM   #9
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Default Re: Re: Brake Performance Vs. Brake Feel

Quote:
Originally posted by jmott



one way you can improve performance on bumpy spots is to PULL THE ABS FUSE

Wise a55!
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Old 05-25-2002, 03:55 PM   #10
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Unhappy Re: Re: Brake Performance Vs. Brake Feel

Quote:
Originally posted by jmott



one way you can improve performance on bumpy spots is to PULL THE ABS FUSE


jmott,

you hate the ABS now what if:

check it out (if you haven't)


For those that like pulling the ABS fuse
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Old 05-03-2003, 02:48 PM   #11
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Quote:
Originally posted by romanom
I never posted this before, because to be honest to me it's obvious. But to others it might not be.

The formula below is a decent way to estimate what, if any, increase you have in brake torque after an upgrade:


Brake Torque Increase %=

[(caliper piston area new/old) * (effective radius new/old)* (brake pad friction coefficient new/old)]

*effective radius is the distance from the center of the hub to the center of the brake pad

*For sliding calipers multiply the areas by 2

Any answer equal to 1 means no increase. Any answer less than 1 means you've gone backwards. Any answer greater than 1 means a torque increase.


This will NOT give you the actual brake torque, just the difference.


Now things like steel lines, stiffer calipers effect feel not performance. Only force applied, torque arm and friction do that. You can change things like lines, calipers, pedals and boosters to change the characteristics. Such as, initial bite point and initial deceleration level, pedal travel and effort, pedal force mulitiplication. However, these do not actually produce more brake torque.
Anyone have the numbers to use in the "old" for the stock USDMY 2003 WRX wagon?
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Old 05-03-2003, 03:59 PM   #12
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Quote:
Originally posted by BIGSKYWRX
This begs the question then- will Subaru 4 pots increase brake torque? Are they increasing effective area or piston area (twice as many pistons)?

Or do the 4pots simply provide better feel/feedback? Or both?

Curious as I have toyed w/ this upgrade.

Thanks,

Big Sky
From what I understand, and it's limited for sure...

The Subaru 4 Pots have the same caliper piston area as the 2 Pots... So it's just a feel thing.
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Old 05-03-2003, 11:22 PM   #13
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One thing to add, improvements of a brake system are variable depending on what the starting setup brought to the table. Sometimes decreasing brake torque selectively can increase chassis braking performance. Sometimes less is more. You have to take a holistic approach to brake system upgrades or they can turn out as downgrades.

ss
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Old 05-03-2003, 11:29 PM   #14
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Quote:
Originally posted by BIGSKYWRX
This begs the question then- will Subaru 4 pots increase brake torque? Are they increasing effective area or piston area (twice as many pistons)?

Or do the 4pots simply provide better feel/feedback? Or both?

Curious as I have toyed w/ this upgrade.

Thanks,

Big Sky
I have examined USDM Legacy GT and WRX and JDM B4/GT-B 2pot front calipers and they all appear identical in every aspect except caliper brackets, which are dependent on year and rotor used.

The Legacy GT calipers use a smaller bracket to use the 277mm rotor. All the others use the 294mm rotor just like the 4pots. The caliper piston sizes in the 4pots apear identical in diameter to the 2pots. So any of the 2pot Subaru front calipers being used with the 294mm rotor should have nearly identical torque output to the 4pots(assuming equal pad coefficient of friction.)

The 4ots vs 2pot WRX calipers bring feel and uptake(and bigger pad choice) to the table.

ss
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Old 12-16-2012, 03:30 PM   #15
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Quote:
Originally Posted by romanom View Post
is this link correct?
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Old 12-16-2012, 05:47 PM   #16
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Quote:
Originally Posted by njdriver04 View Post
is this link correct?
Obviously not. 10 years ago, when this thread was started, NASIOC was the i-club, hence the link from 10 years ago points to the i-club. I'm guessing if you search for threads started by the same guy that started this thread you can find the correct link.
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Old 12-16-2012, 06:31 PM   #17
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Old 12-16-2012, 09:21 PM   #18
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got it thanks

where is the nasioc history thread?
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