Brake bias valve

[ChrisL]

I am assuming that screwing inwards adjusts the brake bias toward the front. Can someone confirm this please?

Also, has anyone tried to fine tune the bias of the brakes? If so, what have you found to be the best setting. Also, how much effect on the bias does, say, a full turn have?

I recently braked hard in front of an observer and discovered that the back brakes locked up well before the front.

Just one more thing. I have an earlyish car (chassis 18) so can anyone tell me if the bias control has changed since I built mine?

[Ron Earp]

On the valves I use on cars screwing it clockwise shuts off braking to the rear. It doesn't increase the front, just reduces rear braking. So, if you are locking up in the rear turn the valve in a bit until that rear lock up just quits. Be aware that under track work as the fluid gets warm and the pads/rotors gets warm the adjustment will change slightly.

R

[ChrisL]

Thanks Ron. I guess that’s what I was trying to say by “front bias” but you put it much more concisely [img]/ubbthreads/images/graemlins/smile.gif[/img]

Do you find that small turns have a significant effect or small effect on the bias? I ask because I want to minimize the number of test runs that I have to do. (I expect that the neighbors and the local constabulary would frown upon this type of test work on public roads). The car will actually be on the track very soon so I will be fine tuning it when I get there, but track time is limited so I’d like to have a better start point before I go racing.

[Ron Earp]

I have found that with the valves are sort of useless throughout the entire range except a certain point, where they are incredibly sensitive. This is from Wilwood and a few others that we've used, they all seem about the same. At that point a 1/2 turn makes a difference. There is one on our Z car, don't know who makes it, but I had to secure it because it was near my leg and if my leg touched it and rotated it 1/2 turn it'd mess the balance up. So, yes, it is sensitive but only around the region where the needle in the valve is close to the seat, which is what you'd expect.

[Tony Hunt]

Chris,
One way of testing brake bias, without flatting your tyres or frightening the neighbourhood dogs and cats, is to do the testing on grass. An outside observer will tell you whether the backs or fronts locked up first in the same way, but you can do the whole thing at much lower speeds and in a more controlled environment.
One thought - you DO have grass in Oz? [img]/ubbthreads/images/graemlins/cool.gif[/img]
For grass, perhaps read dust!

[Hershal Byrd]

Chris,
If it's any help...I went through the testing ordeal and forund that if you have 3 and a quarter turns out (counter clockwise) works best for my car. I assume you have the PBR's and the same proportioning valve I do. I have a knurled knob on mine and this makes it easy to adjust during hot laps. I have to screw it out a half turn after the brakes get hot. I'm not all that good but I can sure see why they call this cheating with it inside the cockpit.. [img]/ubbthreads/images/graemlins/grin.gif[/img]

Hersh [img]/ubbthreads/images/graemlins/smile.gif[/img]

[Robert Logan]

Chris, Hershal,

It is very good to see that Hershal came up with more or less exactly what we set the bias valve to with his own experimentation. We set the bias at "3 turns" back where Hershal uses 3 1/4 turns.

The is a personal thing and will also vary from one car to another. By this I mean that one driver will prefer for the front brakes to grab first, another driver will prefer if the front and rear brakes grab together and other drivers will prefer if the rear brakes grab first. All these can be adjusted for with the Brake Bias Vavle as we use. The second part of this answer deals with the difference between the tolerances used in all the components used in our breaking syatem. As these tolerances vary from component to component and therefore from car to car again the Brake Bias Valve system can be used to even out the systems.

Good luck and I must reinforce the "grass" bit as a good skid pan.

Best wishes,

Robert

[ChrisL]

Thanks all for your replies. I thought about the "grass" solution and kinda rejected it on the basis that weight transfer would be very different. I think that you would effectively end up with a car that is rear biased. Having said that though, it probably would have been a good known starting point. I say "probably" because the track day has come and gone. Philip Island incidentally is one heck of a track to be playing with brake bias. Turn one is a high speed corner and approached at around 240kmh. With the car a little floaty at that speed (my fault but more on that later) applying the brake with rear bias into the corner (which is what I found I had at first) is not for the faint hearted, the car trying to spin with even a light brake. Conversely, approaching Honda corner, a slow speed +90 deg corner, the rear brake bias helped to set it up for the corner. Overall, I found a neutral balance was best for PI. Not enough laps left to then go for my best time though [img]/ubbthreads/images/graemlins/frown.gif[/img]

Just as a foot note to the aerodynamics at 240kmh. My front clip hinges are located higher than RF intended. The result was that whenever the front clip was raised, the nose of the clip would foul the short section of panel that lives between the lower edge of the nose and the leading lower edge of the space frame. The quick solution was to simply remove that panel until I could come up with a more permanent solution. Consequently some air is now being deflected off the radiator and under the car. I know that this has a noticeable effect at 240kmh because I lost my number plate (that was mounted just ahead of the radiator and also angled down) half way through the day and a significant improvement was noticed. Here is a pic of the car just before I lost the number plate.