Manual Brake System Trouble Shooting: Expected Line Pressure?

[FETorino]

Originally Posted by Ron Sutton

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?

[carbuff]

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! )

[Ron Sutton]

Originally Posted by carbuff

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.

.

[FETorino]

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.

[Ron Sutton]

Originally Posted by FETorino

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.

[FETorino]

Originally Posted by Ron Sutton

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

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

[Ron Sutton]

Originally Posted by FETorino

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?

[carbuff]

Originally Posted by FETorino

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

Hmm, 25 years as an engineer vs. 45 years of eating, what's wrong with this picture?

[FETorino]

Originally Posted by Ron Sutton

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?

Yes very clear this am. Something was making them a little fuzzier to review last night Not certain what that was

Originally Posted by carbuff

Hmm, 25 years as an engineer vs. 45 years of eating, what's wrong with this picture?

Formal education has helped you on the engineering front. Your eating habits are Feral.

Originally Posted by BANKO

Another thing I noticed on your charts is an assumed static line pressure of 499psi for 7/8" MC and 679psi for 3/4" MC, can you speak to the what is an expected maximum line pressure in a manual setup. Some guys have mentioned measuring pressures of 800-1000psi. I assume this is primarily achieved by a greater input to the pedal rather than reducing MC size. Do you have numbers for the following driving styles: normal (non fatiguing pedal input), semi-aggressive pedal input (spirited driving / auto cross), aggressive pedal input (high speed track braking and panic stop situations).

As always thanks for your wealth of knowledge and willingness to educate us!

The chart assumes a 100lbs of driver force on the pedal resulting in a 300lb force on the master.

So I guess the question boils down to why the 100 lb number is used and how do we relate the figure to an amount of pedal pressure that is familiar?

[Ron Sutton]

Good morning Rob,

Originally Posted by FETorino

Yes very clear this am. Something was making them a little fuzzier to review last night Not certain what that was
I have a pretty good idea "why".



The chart assumes a 100lbs of driver force on the pedal resulting in a 300lb force on the master.

So I guess the question boils down to why the 100 lb number is used and how do we relate the figure to an amount of pedal pressure that is familiar?

Read my post to Josh & that should provide clarity.