Manual Brake System Trouble Shooting: Expected Line Pressure?

[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]

Ron,

Do you happen to have the piston size numbers for the Baer 6P caliper? My guess is that it's very similar to or the same as the 6S. I'm running the 6P front and rear on my car with 14" rotors.

Given your definitions, I would consider my setup to be more conventional, not a high-travel setup. So I would be leaning towards the 65/35 setup. I'm using the DSE booster and master cylinder, which is obviously a power brake setup instead of a manual setup...

[Ron Sutton]

Oops! I had the Baer caliper model listed as 6S ... but those specs are for the 6P ... as Ron in SoCal's post reminded me. I have updated the two charts to properly reflect the caliper model. No details change.

Originally Posted by carbuff

Ron,

Do you happen to have the piston size numbers for the Baer 6P caliper? My guess is that it's very similar to or the same as the 6S. I'm running the 6P front and rear on my car with 14" rotors.

Given your definitions, I would consider my setup to be more conventional, not a high-travel setup. So I would be leaning towards the 65/35 setup. I'm using the DSE booster and master cylinder, which is obviously a power brake setup instead of a manual setup...

So the specs in the charts ARE of your 6P. But I need the rest of your system specs to calculate braking force & bias.

If you will provide me with front & rear:
Brake piston sizes (all)
Rotor diameters
pedal ratio
Master cylinder bores
Brake pad brand & compound name

I'd be happy to calculate your braking system bias & total braking force.

BUT ... I do not have experience factoring in the hydraulic booster. So the bias will be accurate, but the total braking force will be lower than you actually have, as long as you have booster assist.

Maybe Baer or Tobin can provide us with a correction factor based on the amount of assist from your specific booster ... or at a minimum, a guideline.

[Ron in SoCal]

Originally Posted by carbuff

Ron,

Do you happen to have the piston size numbers for the Baer 6P caliper? My guess is that it's very similar to or the same as the 6S. I'm running the 6P front and rear on my car with 14" rotors.

Given your definitions, I would consider my setup to be more conventional, not a high-travel setup. So I would be leaning towards the 65/35 setup. I'm using the DSE booster and master cylinder, which is obviously a power brake setup instead of a manual setup...

Bryan - I've given RS the 6P piston bores w 14" rotors so I'm sure he'll post as soon as he wakes up . Post up your MC size? IMHO I also think you could achieve a high travel set up with the proper springs/sway bars.

[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!

[Ron Sutton]

Hi Josh,

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.
Just to be clear ... I did not input that line pressure. That is an actual calculation of the line pressure with 100# of force from the driver's braking foot ... into a 6-1 pedal ... with those specific master cylinders.

I don't ever manually input line pressures into my calcs. I always calculate them. I use 100# of force from the driver's braking foot "most of the time" ... because for most adult males I have found that number to be representative of the driver pressing hard ... without tiring his leg out over the course of a race.

I have not performed calc's with "panic stop" level of pressures. But I know it can easily be double & more, because I see it when we're testing pressure at the calipers.

Using 100# is a good baseline starting point, but in the real world of racing, if I'm working with a driver long term, we're tailoring the brake system to him or her.

I've had 12 year old phenoms that weigh 74# body weight, so I had to "up" the brake system for them with more pedal ratio, smaller master cylinders and/or more aggressive brake pads.

Same with some bad ass female drivers I've had. Jessica Clark won two USAC Midget Championships & a NASCAR Modified race with us. She weighed 115 pounds. You don't want the driver to have to overexert themselves to achieve optimum braking force. Tiring them out over a race doesn't make sense.

On the other hand, you you don't want it too sensitive for them either. I had this crazy strong driver that could ... and did ... dead lift the front of a Midget (over 400#). We had to reduce the braking force for him, by switching to larger M/C's.

Make sense?


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.
Yes.

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).
Refer to my comments above.

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

No worries.

[Ron Sutton]

Originally Posted by Ron in SoCal

Bryan - I've given RS the 6P piston bores w 14" rotors so I'm sure he'll post as soon as he wakes up . Post up your MC size? IMHO I also think you could achieve a high travel set up with the proper springs/sway bars.

Thanks for catching that Ron. I mistakenly put the caliper as a 6S in my charts.

I have corrected the charts in this thread to read "6P" ... and corrected my comments in my post to Bryan.

[BANKO]

Ron, thanks for the charts! I've been studying and pondering many questions. It is great to see a line up of all the calipers. Interesting that the GM single piston on and 11.88" rotors have almost as much clamping force as the Wilwood massive TC6R. Can this TC6R caliper be used on a 13" rotor, the smallest size rotor i saw offered is 16", reading the caliper drawing shows it may accomodate a 14" rotor. With a 16" shouldn't this lead to a dramatic brake torque increase? This got me thinking it might be an alternative to the W6A (5.4) on a 14" rotor since it provides 6.9 piston area!!! Key downside is the availability for more tack oriented pads, looks like the highest CoF is .40, comparable to the HP+ pads.

I was also thinking of the benefits of adapting the GM single piston caliper to a larger rotor. Not very sexy, but effective. Quite disappointing to see the Z06 6 pistons have such low clamping force.