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  #11  
Old 07-27-2013, 04:16 PM
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I found the HP Plus to be the best all around pad for a pro-touring car and manual brakes. All out road course performance would be their weakness.
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  #12  
Old 07-27-2013, 06:42 PM
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I find the challenge is ... when someone goes to one of the aftermarket 6-piston caliper brake set-ups looking for bad ass brakes ... they are occasionally disappointed with the braking result ... because the pistons are so small, the total piston "area" is insufficient ... and they didn't account for that in the total system

Most car guys don't know the piston area formulas ... so when you glance at the piston sizes written on paper ... and there are 6 of them ... it seems they should add up to more brake caliper clamping force ... but often they do not.

The problem is compounded if we make any one (or more) of these changes:
A. Utilize brake calipers designed to have a strong power booster ... now running without one.

B. Utilize brake calipers designed to run .50 to .65 CoF racing brake pads ... and now have street pads in the .35-.42 CoF Range.

C. Utilize brake calipers designed around systems typically with a 6-1 or higher pedal ... but some factory pedals have less.

D. Utilize brake calipers designed for a 2700# car ... now on a 3500# car.

The charts below, use the standard brake formulas all brake engineers use for manual brake systems. It accounts for every aspect of braking except the tire. This graph shows several front brake calipers ... ALL using the same pedal ratio, same brake pads & same master cylinder size.
*The pedal ratio, brake pads & master cylinder size do not represent what comes from the factory. I made these 3 items a constant only for comparison.

The rotor sizes are different ... to better represent how they're being sold & used. Regardless ... look at the braking force numbers at the bottom. The 3 common GM factory brake calipers are for Gen 2 F-body, G-Body & Impalas are highlighted with blue columns.

Go down to the 2nd line from the bottom ... marked "Brake Torque" ... and compare the factory numbers with aftermarket options. When you wonder why some don't stop stronger ... simply go to the line marked "Caliper Piston Area x2" ... and you'll see important differences.

There is nothing wrong with any of these brake calipers. But if we are building a better brake system for our PT cars ... we need to better understand the total picture. We can't put a caliper on our cars with significantly less piston area ... without running the proper:
1. Pedal ratio
2. Master cylinder size
3. Brake pad CoF
4. Rotor Size
Even then ... we still can't run too small of piston area for our weight of car & expect it to work well.

The numbers can be kind of confusing. All most of us want to know is how much do I need?
In my experience, for 3500# cars, here's a GUIDELINE that is based on total braking force including the front & rear brake systems.

GUIDELINE:
2500# = Average passenger car
3000# = Performance production car
3500# = Good street & track braking system
4000# = Track braking system with good tires
4500-5500# = Full race brake systems

The very bottom line of the chart shows total braking force with that combination if you were looking for 70% front braking, as I often do in race cars.

If anyone is putting together a system & has questions on one part or another, I'll be happy to calculate things and/or advise you. I have spread sheets to work out front & rear systems & compare options. I can also change inputs in this chart to show you how they all look with a different brake pad, pedal ratio, master cylinder, etc.


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Last edited by Ron Sutton; 07-28-2013 at 01:09 PM.
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  #13  
Old 07-27-2013, 09:11 PM
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Quote:
Originally Posted by Ron Sutton View Post

In my experience, for 3500# cars, here's a GUIDELINE that is based on total braking force including the front & rear brake systems.

GUIDELINE:
2500# = Average passenger car
3000# = Performance production car
3500# = Good street & track braking system
4000# = Track braking system with good tires
4500-5500# = Full race brake systems

The very bottom line of the chart shows total braking force with that combination if you were looking for 70% front braking, as I often do in race cars.

If anyone is putting together a system & has questions on one part or another, I'll be happy to calculate things and/or advise you. I have spread sheets to work out front & rear systems & compare options. I can also change inputs in this chart to show you how they all look with a different brake pad, pedal ratio, master cylinder, etc.


Ron

I have a dumb question.

The figure at the bottom is total braking force of the front brakes when they are doing 70% of the work or is it an estimation of the total including the 30% contributed from the rear brakes?

I have W6A front calipers with a 7/8" master cylinder and I have a 6 to 1 pedal ratio. So I read 3141 lbs of force with this set up. Is that 3141 for the front and 4487 total or 3141 total?
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  #14  
Old 07-27-2013, 10:57 PM
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Rob,

Looking at the math, I think the answer is that the Brake Torque line represents the amount of work that the front brakes on an application would be doing while the Total Braking Torque if 70% line means that if 70% of your total car braking is done in the front, and 30% in the back, then you have a combined braking torque equal to that last line. Thus, if you multiply the value in the bottom line by 70%, you get the number in the Brake Torque line (at least for your W6A caliper):

3141 * 0.7 = 2198.7 (2199 rounded)

Now, exactly what the Total Braking Torque number actually means, I'm not sure. I think it refers back to Ron's Guideline, meaning that the 3141 total would fall between the 3000# (Performance Production Car) and the 3500# (Good street & track braking system) areas. Ron, could you please confirm that I'm understanding what that row of the table is referring to?

(I've said it before, and I'm saying it again... I love all this tech you are providing!!! THANX! )
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  #15  
Old 07-28-2013, 02:21 AM
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Originally Posted by FETorino View Post
Ron

I have a dumb question.

The figure at the bottom is total braking force of the front brakes when they are doing 70% of the work or is it an estimation of the total including the 30% contributed from the rear brakes?

I have W6A front calipers with a 7/8" master cylinder and I have a 6 to 1 pedal ratio. So I read 3141 lbs of force with this set up. Is that 3141 for the front and 4487 total or 3141 total?

Hey Rob,

A quick brake bias primer ...
For track performance ... "high travel/low roll suspensions" need a brake system with approximately 70% front braking & 30% rear. Conventional "low travel/high roll suspensions work better around 65/35.

The W6A front calipers you have with a 7/8" master cylinder, 6-1 pedal ratio, 14" rotors & Hawk HP Plus brake pads would make 2199# of braking force from the front brakes.

Since you will be running a high travel/low roll suspension, if you decide to target a 70/30 brake bias, you would be shooting for 3141# of total braking force. Meaning you would want your rear system to produce 942# of braking force to go along with your fronts making 2199#.

If you'll let me know what your rear brake specs are, I can calculate what they are & you can evaluate it as a system.

Frankly, knowing what you're looking to do with your Torino, I do not feel 3141# is enough total braking force for your goals. I suspect you would be happiest with 3500-4000# for track days on slicks. That will require a higher CoF pad.

I tend to agree with Todd that the HP Plus makes a good street brake pad, if you have enough clamping force & you do. I think the HP Plus pads ... making 3141# total braking force in your system ... would be good for the street on street tires.

But when you're running track days on Hoosier R6's, you would need to swap in a more aggressive pad, in the .50 to .55 CoF range. Each pad compound has their own unique "personality" ... so there is more to it than just a "number". I would need to discuss pads with you some to help you narrow it down to 2-4 compounds that "sound right" ... then you need to test them on the track & see what you like in the "feel".

Once you have a pad you really like, that can be your "track pad." A lot of guys have track pads & street pads, and just swap them as part of their routine.

For conversation sake, let's use the Wilwood BP-20 pad & say you're working it in the 700 degree range on track on the front brakes. That puts that pad at .50 CoF.
* If you ran the same pad in the rear, it will operate at 150-200 degrees less temp in the rear & have a lower effective CoF number for the rear.

I attached the Wilwood brake pad compound graph for your review & a new chart showing all the brake calipers using a brake pad compound with a .50 CoF.

With the BP-20 pads, you'll notice your front brake caliper, using the same M/C, pedal & rotor would make 2556# of front braking torque. Assuming that is 70% of your braking, the total system would make 3652# of braking torque.

I'd like to see it closer to 4000# for your track days with slicks, but we'll need to find a pad with a relatively predictable torque curve in the .52-.55 range to achieve that. Once I know your rear system, I'll reach out to my guy at PFC.

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Last edited by Ron Sutton; 07-28-2013 at 01:10 PM.
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  #16  
Old 07-28-2013, 02:23 AM
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Quote:
Originally Posted by carbuff View Post
Rob,

Looking at the math, I think the answer is that the Brake Torque line represents the amount of work that the front brakes on an application would be doing while the Total Braking Torque if 70% line means that if 70% of your total car braking is done in the front, and 30% in the back, then you have a combined braking torque equal to that last line. Thus, if you multiply the value in the bottom line by 70%, you get the number in the Brake Torque line (at least for your W6A caliper):

3141 * 0.7 = 2198.7 (2199 rounded)

Now, exactly what the Total Braking Torque number actually means, I'm not sure. I think it refers back to Ron's Guideline, meaning that the 3141 total would fall between the 3000# (Performance Production Car) and the 3500# (Good street & track braking system) areas. Ron, could you please confirm that I'm understanding what that row of the table is referring to?

(I've said it before, and I'm saying it again... I love all this tech you are providing!!! THANX! )
Bryan,

You have it correct. You can look at my post answering Rob for more detail.


.
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Old 07-28-2013, 02:55 AM
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Ron

As always thanks for the detailed explanation. Looking at Brian's math I see it is obvious.

Brian you obviously have a better skill set with calculations than as a food critic.

On my set up in the rear I have a 14" rotor and a Wilwood FNSL 4 piston caliper 120-11782-BK.

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Last edited by FETorino; 07-28-2013 at 03:05 AM.
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  #18  
Old 07-28-2013, 03:36 AM
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Originally Posted by FETorino View Post
Ron

As always thanks for the detailed explanation. Looking at Brian's math I see it is obvious.

Brian you obviously have a better skill set with calculations than as a food critic.

On my set up in the rear I have a 14" rotor and a Wilwood FNSL 4 piston caliper 120-11782-BK.


Hey Rob ! What are we both doing up so late ?!?!

Here are the calcs for your brake system with Wilwood BP-20 brake pads & two different M/C sizes for the rear. The BP-20's CoF curve climbs pretty rapidly, hence the difference in CoF numbers for front & rear.

I'm going to suggest we find brake pads that have a flatter CoF curve but in the .50-.55 range. Once we land on brake pads, then I'll recalculate this so we can see which rear M/C is best.

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Old 07-28-2013, 03:50 AM
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Hey Rob ! What are we both doing up so late ?!?!


Checking brake specs after a night out with friends. What else?

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  #20  
Old 07-28-2013, 10:49 AM
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Checking brake specs after a night out with friends. What else?


Me too ... sorta. We were at a family get together for a birthday party. I couldn't resist checking stuff on here when I got home.

Did the brake calcs make sense with your system?

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