brake bias adjuster vs. Brake Proportioning Valve

[scott.k]

Hello,
I am trying to figure out the difference between the two and trying to figure out which you would want on a race car (or both). I am looking at tiltons products (they make both). The bias adjuster adjusts brake force from front to rear. The Proportioning adjusted allows more brake force to a particular wheel or wheels. Does the proportioning adjuster do side to side force adjustments?
Thanks
Scott

[Won]

StopTech : Balanced Brake Upgrades

Bias adjust changes the slope of the line on front vs. rear pressure plot:



Proportioning valve introduces the "knee" in the line:

[petevb]

Originally Posted by scott.k

Hello,
I am trying to figure out the difference between the two and trying to figure out which you would want on a race car (or both). I am looking at tiltons products (they make both). The bias adjuster adjusts brake force from front to rear. The Proportioning adjusted allows more brake force to a particular wheel or wheels. Does the proportioning adjuster do side to side force adjustments?
Thanks
Scott

You probably want a cockpit adjustable dual master cylinder setup, not a proportioning valve or both.

The downside of a dual master setup is that it requires much more adjustment to work properly. The correct setting in slippery conditions (rain) is very different from dry, sticky tires are different again, etc, so you're constantly adjusting the setup to maximize brake force. A prop valve, on the other hand, is pretty close over most of the range when well adjusted, making it more suitable for a street car.

However the big advantage of a dual master setup, especially in a 911, is increased braking stability while cornering. The engine breaking adds to the force of the rear brakes, and the combination plus the heavy rear engine overwhelms the rear tires leading to over-steer. Hence the mantra of the early 911: "brake in a straight line". The bias valve has less rear brake at less than threshold braking, meaning you can do more trail-braking and the car has greater stability on corner entry.

The other advantages of the dual master are IMHO probably minor, things like brake feel, consistency, etc.

I ran and advocated both a dual master as well as a prop valve for a while, but I pulled the prop valve out. Better (for a race 911 IMHO).

[Bill Verburg]

Originally Posted by scott.k

Hello,
I am trying to figure out the difference between the two and trying to figure out which you would want on a race car (or both). I am looking at tiltons products (they make both). The bias adjuster adjusts brake force from front to rear. The Proportioning adjusted allows more brake force to a particular wheel or wheels. Does the proportioning adjuster do side to side force adjustments?
Thanks
Scott

You misunderstand

a bias adjuster and a proportioning valve are one and the same product. What ever you wish to call it, it is a device(x2 for 4 channel setups) that goes on the rear circuit of some cars which will reduce line pressure above a pressure called the 'knee', as illustrated in the last diagram above in post#2. It can be used in conjunction w/ dual master setups though it rarely is

w/o a p/v you brake system has a native bias determined by the ratio f/r of slave piston sizes and rotors and brake pad coefficients, this native bias will graph as a straight line, the more front bias the steeper the slope, as in pic 1, the less native bias the lower the slope as in pic 2

your '80 SC has a hyd bias(just considering the slave pistons) of 1.596 and brake toque(considering all the variables) bias of 1.491. This is right where you want to be.

Now those that change the brakes setups from stock will sometimes need to adjust the bias, this can be done in 2 ways
1) bias or proportioning valve can move bias to the front by reducing rear line pressure above the knee. It does not work the other way
2) dual master setup that allows a total change of the slope, it can move bias forward as well as backward and has no knee

It's best to have good native bias, a p/v on the rear is a good trim solution because it only works to relieve rear line pressure in very high load conditions where rear axle loads have been reduced by forward weight transfer. The p/v is a nice complement to and correction for axle load variations

many race cars have a dual master setup, this allows a lot of variation and can compensate for changing fuel loads and track conditions

Both dual master and p/v can be cockpit adjustable, it just has to be setup that way.

[petevb]

Originally Posted by Bill Verburg

You misunderstand

a bias adjuster and a proportioning valve are one and the same product. What ever you wish to call it, it is a device(x2 for 4 channel setups) that goes on the rear circuit of some cars which will reduce line pressure above a pressure called the 'knee', as illustrated in the last diagram above in post#2. It can be used in conjunction w/ dual master setups though it rarely is

w/o a p/v you brake system has a native bias determined by the ratio f/r of slave piston sizes and rotors and brake pad coefficients, this native bias will graph as a straight line, the more front bias the steeper the slope, as in pic 1, the less native bias the lower the slope as in pic 2

your '80 SC has a hyd bias(just considering the slave pistons) of 1.596 and brake toque(considering all the variables) bias of 1.491. This is right where you want to be.

Now those that change the brakes setups from stock will sometimes need to adjust the bias, this can be done in 2 ways
1) bias or proportioning valve can move bias to the front by reducing rear line pressure above the knee. It does not work the other way
2) dual master setup that allows a total change of the slope, it can move bias forward as well as backward and has no knee

It's best to have good native bias, a p/v on the rear is a good trim solution because it only works to relieve rear line pressure in very high load conditions where rear axle loads have been reduced by forward weight transfer. The p/v is a nice complement to and correction for axle load variations

many race cars have a dual master setup, this allows a lot of variation and can compensate for changing fuel loads and track conditions

Both dual master and p/v can be cockpit adjustable, it just has to be setup that way.

Bill, the Tilton site offers "Remote Brake Bias Adjusters" designed to hook to dual master cylinders, and "Brake Proportioning Valves".
Tilton Engineering
So in Tilton speak these are not the same product, and I answered the question based on that assumption. I think you did help clarify the issue otherwise...

[Bill Verburg]

Originally Posted by petevb

Bill, the Tilton site offers "Remote Brake Bias Adjusters" designed to hook to dual master cylinders, and "Brake Proportioning Valves".
Tilton Engineering
So in Tilton speak these are not the same product, and I answered the question based on that assumption. I think you did help clarify the issue otherwise...

and that's significant, in what way??

a remote bias adjuster just means that you can adjust bias from a knob on the dash board(or wherever you choose to put it)

perhaps the OP is confused by an adjustable bias bar(remote or otherwise) that is used in association w/ every dual master set up I have ever seen.
on most dual master setups bias is initially set by choosing m/c , you can use different sizes f/r to do this or you can use the same size f/r

on late GT3RSR a dual master is used w/ 18.8mm m/c f & r, no bias there

In addition to the hydraulic bias most twin master also have an adjustable fulcrum or bar/fulcrum which changes the mechanical forces seen by the 2 m/c, the cockpit adjuster changes the mechanical leverage each m/c exerts on it's assigned circuit

here's a GT3RSR setup




and the way bias is changed by moving the fulcrum in part#17

[Bill Verburg]

I forgot to add that even w/ a dual master setup w/ balance bar you still want to have the basic or native bias set at least in the ball park

on the RSR's mentioned above the basic hyd bias is 1.504, the differential rotor sizes move basic bias a bit to the front and the basic line pressures at 0 on the cockpit adjuster are 50bar front 49bar rear

[ErVikingo]

On a basic race car bias is OK if you want to get better control of your braking (especially upon releasing) get dual masters.

[petevb]

Originally Posted by Bill Verburg

and that's significant, in what way??

Simply that he asked "What's the difference between the Tilton Remote Bias Adjuster and the Tilton Brake Proportioning Valve" and you responded "a bias adjuster and a proportioning valve are one and the same product". Which I felt was confusing/ incorrect based on the Tilton web page and terminology he's looking at. Just trying to clarify- for the Tilton stuff he is looking at these are two different things, working as you describe.

[Bill Verburg]

Originally Posted by petevb

Simply that he asked "What's the difference between the Tilton Remote Bias Adjuster and the Tilton Brake Proportioning Valve" and you responded "a bias adjuster and a proportioning valve are one and the same product". Which I felt was confusing/ incorrect based on the Tilton web page and terminology he's looking at. Just trying to clarify- for the Tilton stuff he is looking at these are two different things, working as you describe.

I see,

I thought he was using a commonly used alternate name for a proportioning valve, not the bias bar adjustment