Manual Brake System Trouble Shooting: Expected Line Pressure?

[Ron Sutton]

Originally Posted by FETorino

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.