BBK bias discussion

[IJ.]

Not being a prick or a smartarse here at all Eric but seriously what did you expect only upgrading half of the braking system?.... :nono:

As I previously mentioned a well set up Mk3 chassis can use a LOT of rear brake, I've had mine blue on a few occasions and can't think of another car I've owned that could do that matter how much bias I wound into the rears (you lock the rears long before the discs turn blue)

I put this down to the double a arm suspension at both ends of the car it's vastly superior to the bulk of designs used.

 

[adampecush]

Should be easy enough with a pair of 0>2000 psi gauges.

this is true....

Hmm...my parts car still has the prop valve, and i have access to more gauges than you can shake a stick at...

what is the thread size for flared brake fittings?

 

[supraguru05]

this is true....

Hmm...my parts car still has the prop valve, and i have access to more gauges than you can shake a stick at...

what is the thread size for flared brake fittings?

adam it would be awesome if you can do the test

here is what your going to see.

the front versus rear pressure will be equal up to a certain breakaway pressure. lets just say 400 psi. (not a accurate pressure). from that point on there will be some constant changing the rate that the rear pressure is increased relative to the front for instance 0.3

so for our example at 400 psi inlet the outlets would be 400psi to the front and 400 psi to the rear. at 600 psi inlet the front pressure would be 600 psi and the rear pressure would be 400 +0.3*600 .

this would be called a 400/0.3 proportioning valve. if you get these numbers i can do some serious braking performance calculations

 

[Doward]

Adam, I agree, that would be excellent information to have! I'm bouncing between a 12.6" and 12.9" rear rotor, so the actual prop valve information would be very handy to see which way I need to go

 

[Poodles]

Not to be a prick, but diving unloads the back tires and will cause them to lock up easier. Diving is based on suspension NOT brakes.

 

[crisp]

Not to be a prick, but diving unloads the back tires and will cause them to lock up easier. Diving is based on suspension NOT brakes.

...not to identify with the guy ^^^ that MIGHT be coming ACROSS as a dick (even though he wants to avoid it... as do I...:naughty but the SUSPENSION VARIABLE weighs heavily in my mind in this whole equation as well.:1zhelp:



I see proportional control of pressure as logical in the vacuum of pure mathematics of distribution of load vs applied force, but it seems some of these calculations would be DYNAMIC and dependent on "real-time" telemetry to fully manipulate.

...on the other hand, I don't think it "hurts", but could certainly help to control the setup to a TARGET WINDOW of behavior (or brake force baseline) that is warranted by what the science of static equation can indicate.

On the other hand, perhaps I don't understand the principles of proportioning well... me still learning.


...carry on...:biglaugh:



-crisp

 

[tacoma_kyle]

so for our example at 400 psi inlet the outlets would be 400psi to the front and 400 psi to the rear. at 600 psi inlet the front pressure would be 600 psi and the rear pressure would be 400 +0.3*600 .

You sure?

So lets give another example...just with 500 psi. 500psi goes to the front. THe rear gets 400+(.3•500) = 550psi

Does that make sense? By your statement, for pressures between 400 and about 571psi, the rear brakes will get MORE pressure than the MC is supplying. You sure about this? BEcause it doesnt make sense. I dont know how proportioning valves work, but maybe it is 400+.3•(P-400)=rear pressure. P=MC pressure.

Rember....IN THE GIVEN EXAMPLE....completely hypothetical numbers!

 

[Doward]

Crisp has it right - the calculations I'm doing are all rough estimates to get in a 'window' of values close enough.

 

[crisp]

Crisp has it right - the calculations I'm doing are all rough estimates to get in a 'window' of values close enough.

This is consistent with most dynamic system performance evaluations for DV (Design Validation) and PV (Product Validation) testing going into manufacture. Specifications for performance and relative Marketability Test Specifications are all directed toward a specific "design position" test parameter, which enables subjective evaluation. Often, such values have projected or actual correlation with performance behavior in "real-world" emulations, such as sled or crash testing.

NHTSA/FMVSS/DIN/IIHS and related governing bodies have various performance REQUIREMENTS that usually involve three categories:

- STRENGTH
- SAFETY
- REGULATORY

Each identify specific metrics that are often a "TARGET RANGE" to be achieved in a "fixed position" or "state" that is clearly prescribed. What happens in every OTHER state is generally either PROJECTED and considered accordingly or a COMPROMISE of what can and cannot be defined within repeatable terms.


/ramble.:icon_surp




-crisp

 

[IJ.]

Crisp: From the non prick wannabe but you DID notice I addressed the suspension variable below? (bold type)

Adam: I believe m10x1.0 but I'll check when I go out to the shed later.

Not being a prick or a smartarse here at all Eric but seriously what did you expect only upgrading half of the braking system?.... :nono:

As I previously mentioned a well set up Mk3 chassis can use a LOT of rear brake, I've had mine blue on a few occasions and can't think of another car I've owned that could do that matter how much bias I wound into the rears (you lock the rears long before the discs turn blue)

I put this down to the double a arm suspension at both ends of the car it's vastly superior to the bulk of designs used.

 

[supradjza80]

Truthfully, the amount of dive doesn't matter either. What does matter for the brake proportioning front and rear is the CG location (longitudinal and height) and the acceleration of the vehicle. Then proportioning should be set up by determining the weight transfer on a max deceleration event. No matter how much the car dives, the weight transfer is determined by the deceleration rate. It is just helpful to control dive to limit unnecessary chassis movement and change the rate that the weight transfers but it does not change the amount of total weight transfer.

But as IJ said the supra is balanced much better than most cars ~ 53/47 F/R weight distribution and has a lower center of gravity so it will use more rear brake than a poorly balanced car with a higher CG.

Here is a good link for anyone interested in brake information.

http://www.stoptech.com/tech_info/The%20Physics of Braking Systems.pdf
http://www.stoptech.com/tech_info/tech_white_papers.shtml

 

[IJ.]

this is true....

Hmm...my parts car still has the prop valve, and i have access to more gauges than you can shake a stick at...

what is the thread size for flared brake fittings?

Confirmed m10x 1.0 Adam.

 

[tacoma_kyle]

Wow, good lniks from stoptech. THanks a lot.

 

[Zazzn]

Not to be a prick, but diving unloads the back tires and will cause them to lock up easier. Diving is based on suspension NOT brakes.

Agreed, but the amount of dive relative to the amount of stopping power is not equal to what it was with stock setup.

Not being a prick or a smartarse here at all Eric but seriously what did you expect only upgrading half of the braking system?.... :nono

Well I've never upgraded the breaks before, but I was hoping that it would simplely give me less fade by having a bigger heat sink. I didn't expect how touchy they would be to lock up. After all I could lock the up the fronts and backs if I needed on the stock system, it's just they fade like a SOB after a few hot stops.

 

[Doward]

The amount of dive should be greater - you're bringing a lot of weight down from speed in a much greater fashion!

 

[supraguru05]

You sure?

So lets give another example...just with 500 psi. 500psi goes to the front. THe rear gets 400+(.3•500) = 550psi

Does that make sense? By your statement, for pressures between 400 and about 571psi, the rear brakes will get MORE pressure than the MC is supplying. You sure about this? BEcause it doesnt make sense. I dont know how proportioning valves work, but maybe it is 400+.3•(P-400)=rear pressure. P=MC pressure.

Rember....IN THE GIVEN EXAMPLE....completely hypothetical numbers!

sorry your right i wasnt paying attention i meant the rear would get 400+(0.3*(500-400))

ie from the break away presssure on the front gets a full 100% of the mc pressure and the rears only get an additional 30% ie a ratio of 100:30

good catch


also along the diveing comments. since our car does not have anti dive or anti squat, the amount of weight transfer due to braking IS factored into tractive force calculations and is based SOLELY on braking force and the location of the CG and wheel base.
Here is a question you all can think about. if its wet outside would you want more front brake or more rear brake? and dont go google it sit and think.

 

[Poodles]

More front brake as I've experienced a rear lock up in the wet and never want to again...

Also Zazzn, humor me for a bit and loosen your brake master from the booster and see if it's leaking. Dying master causes all sorts of issues and you still need to fix the ABS system...

 

[supraguru05]

More front brake as I've experienced a rear lock up in the wet and never want to again...

Also Zazzn, humor me for a bit and loosen your brake master from the booster and see if it's leaking. Dying master causes all sorts of issues and you still need to fix the ABS system...

think a little more :naughty:

 

[Poodles]

Don't have to, rear lockup = sideways slide down a major road

Been there, done that.

 

[supraguru05]

however when it is wet out you have less grip therefore you cant decelerate at the same rate. since you have less deceleration you have less front grip relative to the rear so you actually want to increase the bias towards the rear. if you leave the bias alone you will lock up the front even sooner in the rain than the rears. effectively what i am saying is a decrease in road friction will increase the brake bias to the front so you have to counter act with bias to the rear.

not recommending this for a street car just saying from a tractive force perspective