Front and rear brake press. Ratio

[jimj11]

Anyone have an psi numbers on front and rear brake press.

[romoman]

Anyone have an psi numbers on front and rear brake press.

What kind of car? Do you want a starting bias? Exact pressures in the system depend on M/C sizes and caliper piston number/size.

[mark elder]

Are you after absolute pressures or the percentage bias?

Bias depends on so many things; wet/dry, front/rear tyre size, front/rear aero, corner type (fast/slow) and the list goes on.

Some F1 guys change the bias for almost every corner (and the % of diff lock); busy guys.......

[jimj11]

Are you after absolute pressures or the percentage bias?

Bias depends on so many things; wet/dry, front/rear tyre size, front/rear aero, corner type (fast/slow) and the list goes on.

Some F1 guys change the bias for almost every corner (and the % of diff lock); busy guys.......

percentage bias

[Rick Iverson]

I start at 55% front, 45% rear

[mark elder]

Agreed. And up to 58% front dry and 52% front wet. And it all depends on a 100 variables. And the driver. Lots depends on the driver and how they initally apply the brakes and then modulate it and then release it (think 3 stages). The shape of the curve is very important.

[DaveW]

And all of this assumes the same caliper piston size F & R. With my Citation Zetec F2000 I am using 1.75" dia caliper pistons front and 1.375" dia caliper pistons rear (same pad compound & size). That with 0.625" dia MC pistons F & R, gives an almost equal balance (pedal force and fluid pressure) F to R, i.e., balance bar almost perfectly centered (dry conditions).

This gives caliper clamping force bias of 62% front and 38% rear assuming the balance bar is centered.

Having more bias to the front than the 55% suggested above and later may relate to having relatively narrow rear radial tires on the back compared to what might be optimum for my weight distribution and suspension geometry, plus my desire to trail-brake, as I mention later.

And, of course, the more G's you pull braking, the more weight you transfer to the front, thus needing more front bias, especially if you're not running a lot of downforce.

[Rick Iverson]

Gents;

I use a Craftsman torsion bar torque wrench I bought on eBay for $5.00 to set my bias.

• I fabricated a pedal press using a shortened round suspension rod (surplus from my Lola FF), L & R threaded ends;
• one end has a 3” a piece of mild steel tubing slightly larger ID than my chassis OD tubing, cut in half lengthwise, bolt head welded to the OD centered both Lat and Long;
• the other end has a rectangular 2.5” x 1.5” plate 0.75” longer than my break pedal pad, top and bottom 0.25” ends bent 90 degrees to “capture” the pedal pad. Bolt head welded to the backside center;
• one end on the brake pedal, other on a chassis cross-bar, and expand until the wheels can no longer be rotated by hand;
• torque wrench to the front wheel nut, apply pressure until it wheel breaks free, and take highest reading.

Although everyone knows I suck at math, but a direct proportional equation even works, then solve for x: 55/120 = 45/x.

Note: 120 is a notional torque to rotate the front wheel.

Do the same in the rear, then move the bias to correct. Recheck, then recheck, then recheck.

[DaveW]

I've never set my bias that way because as Mark Elder said, there are just too many variables that affect what is needed for brake bias. Chassis setup, tire type, tire pressures, spring rates, damper curves, track grip level, corner configurations, driving style, etc. all factor in. I go by previous experience and get it reasonably close to what worked before, then fine tune it at the track. You'll wind up adjusting it at the track anyway.

[Mike B]

I don't remember where I got this and I don't know how accurate it is but I have a bias calculator spreadsheet that also shows caliper force, psi, and a few other things. Just input the specs of your brakes in the yellow cells:

http://www.gyrodynamics.net/brake-bias-calculator/

[Rick Iverson]

Dave, my bad. I was describing the initial setup from a chassis rebuild. I have swapped ends deep breaking, only to realize there must be a starting point.

Again, what we have is my failure to communicate. Sorry.

I've never set my bias that way because as Mark Elder said, there are just too many variables that affect what is needed for brake bias. Chassis setup, tire type, tire pressures, spring rates, damper curves, track grip level, corner configurations, driving style, etc. all factor in. I go by previous experience and get it reasonably close to what worked before, then fine tune it at the track. You'll wind up adjusting it at the track anyway.

[DaveW]

Dave, my bad. I was describing the initial setup from a chassis rebuild. I have swapped ends deep breaking, only to realize there must be a starting point.

Again, what we have is my failure to communicate. Sorry.

Well, my fault, also. It's been so long since I started from scratch on a brake setup that I didn't consider why you were doing that.

[Stan Clayton]

I agree with those recommending about 55% front static brake bias as a starting point, and that ratio has been very well received by owners and drivers of Stohr DSRs, WF1s, and F1000s. To understand why, and just as importantly how to get there, irrespective of your car marque or model, I recommend you start by reading Master Cylinder Math. Using the tools in the article you can build an economical and highly effective brake system that is inherently balanced, and which will require minimal adjustment at the track.

And since this table showing the history and development of Stohr braking packages is already out on the internet, I'll share it with you here.

[mark elder]

I think a static 'apply the brake a little and hug and twist a front and rear wheel' is a reasonable starting point for a new build or you are completely lost (more common than we care to admit...).

My only comment is do NOT try and get a helpful driver to push on the pedal while you run between the ends of the car twisting wheels maddly. A G clamp or a large cable tie or a specially made clamp are your only options.

And, for fear of stating the obvious, do not try to change the bias while there is significant pressure on the brake pedal. The adjuster will not turn due to the pressure. This applies while racing or doing a static set up. Having said that, for a static set up, you might get away with it if the brake pressure is lowish; just look at the adjuster shaft while you turn the dashboard knob.

[Jon Jeffords]

You'll wind up adjusting it at the track anyway.

Dave, what’s your process for setting the brake bias at the track? Do you heat up the brakes and tires to race temp, then brake hard enough to momentarily lock up one end at the most strategic corner(s)?

[DaveW]

Dave, what’s your process for setting the brake bias at the track? Do you heat up the brakes and tires to race temp, then brake hard enough to momentarily lock up one end at the most strategic corner(s)?

Basically, that's it, but with a few refinements. I usually start out where I was the last race or session. Then I look for front grip and/or rear grip on entry - I trail-brake for most medium to slow corners, so those are the most critical things.

If I have too much understeer or front lockup on entry, I adjust more braking to the rear, continuing until the car becomes too over-steering on corner entry, and adjust a little towards the front. Minor lockup on the inside rear wheel on corner entry is not a reason to adjust unless it makes the car unstable.

If the car is unstable on corner entry to start with, I adjust in more front bias until it is stable. Sometimes brake oversteer can be cured with more rear rebound damping or stiffer rear springs to minimize rear ride-height increase with weight transfer.

There are more things that affect brake balance, like downforce F vs R, but that's mostly a separate issue.

[problemchild]

While you do need a reference point to start, do not be afraid to keep moving it until you find it where you like it. Over the past 3 years, I have had a revolving door of world class young drivers through my team. Most will drive the same car with the same basic setup, often identical setup. But the first thing they do, is start adjusting the bias knob. Massive differences in what is otherwise the same setup. One will have it maxed out one way, the other the other way, and both bewildered how the other could even drive the car. When I put an older but good club racer in the car, they rarely touch the bias knob, usually commenting it is "fine where it is".

Me thinks this might be a significant observation.

[stonebridge20]

While you do need a reference point to start, do not be afraid to keep moving it until you find it where you like it. Over the past 3 years, I have had a revolving door of world class young drivers through my team. Most will drive the same car with the same basic setup, often identical setup. But the first thing they do, is start adjusting the bias knob. Massive differences in what is otherwise the same setup. One will have it maxed out one way, the other the other way, and both bewildered how the other could even drive the car. When I put an older but good club racer in the car, they rarely touch the bias knob, usually commenting it is "fine where it is".

Me thinks this might be a significant observation.

Go Kart kids.

Bias knob and mixture screw.

[Rick Iverson]

While you do need a reference point to start, do not be afraid to keep moving it until you find it where you like it. Over the past 3 years, I have had a revolving door of world class young drivers through my team. Most will drive the same car with the same basic setup, often identical setup. But the first thing they do, is start adjusting the bias knob. Massive differences in what is otherwise the same setup. One will have it maxed out one way, the other the other way, and both bewildered how the other could even drive the car. When I put an older but good club racer in the car, they rarely touch the bias knob, usually commenting it is "fine where it is".

Me thinks this might be a significant observation.

Good stuff to here, Man.

[billtebbutt]

For a starting point, I do it the way it was done in the dark ages. I get Steve to hold the pedal down (with his hand) until I can just not turn a front wheel anymore. Then I adjust the rears so that they just barely turn when the front is just barely locked. As taught to me 35 years ago by Ollie Clubine.....

And to Greg's point (he characterizes me well as the aged club racer, NOT the young world-class hotshoe), I almost never adjust the bias after that. So, there is some lap time reduction to be had here, in an area where I never really gave it much thought.

cheers,
BT

[lance3556]

Years ago I went thru the process of changing brake set up, master cylinder size and piston diameter, went thru several iterations before I was happy. I had a spread sheet that you can plug into all the variables and it calculates force and pedal travel. It was pretty good for baseline. Then I did purchase a "disk Brake Analyzer" that you install pressure plates in place of the pads and can take a real measurement to compare the force on front and rear pads, this gives you a measurement that you can redo if you make any changes, but you have to have drivable set up to baseline. I can not seem to attach the spread sheet, so if you would like it, PM me and I can Email you. I generally run a little more rear in the F500 so i can get a better rotation on turn in with the solid axle, but generally close to 52-48 and usually as fuel burns during a run I will shift to the rear several clicks during a race. but one has to be careful, an emergency ah S!!! stop with a sharp jab can really loosen the rear end

[chrisw52]

Gents;

I use a Craftsman torsion bar torque wrench I bought on eBay for $5.00 to set my bias.

• I fabricated a pedal press using a shortened round suspension rod (surplus from my Lola FF), L & R threaded ends;
• one end has a 3” a piece of mild steel tubing slightly larger ID than my chassis OD tubing, cut in half lengthwise, bolt head welded to the OD centered both Lat and Long;
• the other end has a rectangular 2.5” x 1.5” plate 0.75” longer than my break pedal pad, top and bottom 0.25” ends bent 90 degrees to “capture” the pedal pad. Bolt head welded to the backside center;
• one end on the brake pedal, other on a chassis cross-bar, and expand until the wheels can no longer be rotated by hand;
• torque wrench to the front wheel nut, apply pressure until it wheel breaks free, and take highest reading.

Although everyone knows I suck at math, but a direct proportional equation even works, then solve for x: 55/120 = 45/x.

Note: 120 is a notional torque to rotate the front wheel.

Do the same in the rear, then move the bias to correct. Recheck, then recheck, then recheck.

Interesting, I am going to try this over the winter.

[alangbaker]

For a starting point, I do it the way it was done in the dark ages. I get Steve to hold the pedal down (with his hand) until I can just not turn a front wheel anymore. Then I adjust the rears so that they just barely turn when the front is just barely locked. As taught to me 35 years ago by Ollie Clubine.....

And to Greg's point (he characterizes me well as the aged club racer, NOT the young world-class hotshoe), I almost never adjust the bias after that. So, there is some lap time reduction to be had here, in an area where I never really gave it much thought.

I use a hardware store pistol grip clamp to hold down the pedal. This style:


With the shock cover off, it's easy to turn the clamp over and adjust pressure on the pedal until the front wheels are just locked.

[racpercival]

Hi Dave or anyone. On the USF cars, do you know whether they use the .70 MC for the front brakes, and .75 for the rears, or the other way around? I know that the calipers are pfc 44mm in the fronts and 41mm in the rears. I’ll also check out the calculator discussion and run some of the math, but wanted to see if someone know how they typically run in these cars.