just installed a adustable brake bias

to start,, what would be a starting point/ initial set up  50/50 front to rear or 60/ 40 front to rear.. i will be counting the clicks  or turns,    thank you

Does your master cylinder have a proportioning valve, or is there one in the brake system otherwise?

On an autocross car with a gutted proportioning valve, I made adjustments until I liked the results.  Mine didn't have clicks, but you'll likely have to do the same thing.  For motorsports you typically apply more pressure to the rear than for daily driving.

Here are some generic instructions from Tilton; Tilton Proportioning valve instructions

What I like to do for setting up a proportioning valve:

• Get the tires you plan to use on the car at the correct pressure
• Find a representative stretch of pavement
• Get the brakes warmed up
• Brake really hard like you would entering a corner at race pace, but in a straight line.  Start with too much front bias and adjust until you get rear lockup at the same time or slightly earlier than front lockup
• Dial it towards front bias ever so slightly from there

And you're done until you encounter different conditions or change tires!  Some vehicles (mostly street use) I basically set and forget, for example I haven't touched the bias on my MR2 since setting it up but it has also been on the same set of Azenis the whole time.  Others, like the rally car, get fiddled with constantly.

In reply to djsilver (Forum Supporter) :

there was on i the rear of the car , this was removed

Unless the calipers and master cylinders are all the same size 50% on the bias bar is not going to be 50% biased on the brakes so. With a full on, engineered race car I calculate what I'm going to want for nominal final balance and set it there.  On a everything else I set the bias bar at roughly 75% front and sneak up on the final adjustment.  Where I do it depends on the car but the technique is always a variation of starting in a straight line at lower speeds and increasing speed and cornering until it's where I want it.

As far as how much it gets adjusted after the initial setting is concerned it very much depends on the car and the venue.  Circle track cars, particularly on dirt get adjusted a lot during a race.  Mid engine road race cars with the fuel tank near the middle of the car like my Formula Ford rarely get touched.  My Camaro with it's large rear mounted fuel tank and low single digit fuel consumption gets adjusted as fuel burns of every race.

I have mine adjustable from the driver's set so I can fine-tune at the beginning of a session. But for the initial setup, same as mister squiggle. Start with too much front, adjust until no longer too much front. 

I've got a unit to throw into my Challenge car. It has NB Miata front brakes and Fox Mustang rear drums. I've been assuming this will allow me to balance the brakes because I suspect the rear drums are too much brake without out one and I can force more front bias. Is that a correct assumption?

What you're really doing is removing hydraulic pressure from one end. So it might be better to think of it as less rear bias, although technically it is the same thing :)

In reply to APEowner :

i am using calipers of a 2000 porsche boxster.. the rear calipers are smaller than the fronts... not useing a bias bar.. but a dial adjuster

Setup for max braking is the same. The difference is that the ratio is fixed on a bias bar where a valve more closely approximates the correct bias across a range of levels of decel.

Bias bar and prop valve - you can read the answers in this thread the same way with the exception of my previous one :)

You don't want the rears locking up first!  

I was surprised at what role the rears play - basically a bit of added braking and a way to keep the car in line and balanced. I popped a pinhole in a rear brake hose during a practice session and didn't have a spare. I needed the race credit so I just quietly took the rear circuit off line with  couple of bleed screws and went out and ran with front brakes only. Only cost me a second a lap and part of that was probably because I was going a bit less aggressively than usual.

One of the race associations I ran with banned the use of cockpit adjustable limiting valves for the rear circuit, like Keith mentioned, I assume because they didn't want people fiddling with stuff inside the car instead of paying attention to where they were going.

I will admit it does freak out the passenger when you start messing with brake bias between corners - but that's what straights are for!

I've got my Miata's brake adjustment valve in reach of the driver as well for the same reasons Keith does.

I set mine up initially like everyone else, and I don't count clicks from my "happy place" at all.  On the Miata, it's generally only two clicks one way or the other to account for conditions (heat up, fuel load, etc.) since I've gotten it dialed in.

I have nothing to add

Although I have one on my Formula 500 (it came with it) I'm not a fan of them, especially in cars that do 10-12 lap sprint races. If the car is going to change much I'd much prefer a cockpit adjustable bias bar. They change the brake pedal feel ever so slightly and I don't like that.

I autocross the F500 as well as vintage race it; for autocross I run a lot of rear brake bias, to a degree that is really sketchy for a road course. For road racing the fronts lock a hair before the rears. While I get slightly more out of the brakes, the car does start to ever so slightly snake around under the brakes.

Due to my motorcycle racing background it's not an issue for me but I'm pretty sure most drivers would do better with a little more front bias. Also note we seldom race in the rain.