Dual Masters w/ Stock Calipers - worthwhile?

john vanlandingham Wrote:
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> Dave Clark, for all his evident bitterness in his
> old age,

Bitterness huh? Not sure where you get that. Old age? OK, you got me there.

Doivi Clarkinen Wrote:
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> Cosworth Wrote:
> --------------------------------------------------
> -----
> >Blah blah blah... (just edited out for space)
>
>
> The above points are all very good.
>
> >As finally the cross over pipes are really
> not an
> > issue for leaks or crushes etc... For example
> the
> > Evo Gr N setup uses a rear 4 pot brembo
> (same
> > caliper used by Dallara in F3) with extranal
> cross
> > over, and working in the business I have yet
> to
> > hear of a DNF from caliper failure.
> >
>
> Apparently you don't rally on gravel? There are
> lots of stones flying around the wheels on gravel
> stage rallies. I've had plenty of
> crushed/bent/punctured/torn loose crossover pipes
> on Wilwoods, Brembos, and others, even with
> various methods of stone protection. Usually it's
> not too much of a problem on the fronts but the
> rears take a beating.
>

And apparently you dont know how to read or are just plain narrow minded to even comprehend what I wrote. Like I said, the Gr N Evo HOMOLOGATED rear caliper has external x-overs, and in working for the motorsports world and dealling directly with race teams that run that setup I have yet to hear of a DNF, is that not clear enough? And for example the AP Gr N rears, WITH internal X-overs, the gravel quickly grinds down the caliper body exposing the x-over rendering the caliper useless, meanwhile a x-over pipe being a wear item costs 20-30 bux.

Cosworth Wrote:
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> That comes out to be 82% front if you're using the
> same pad friction. That seems waaaay to much
> front.

It wouldn't surprise me in the slightest if that is true. I have the bias adjustment set so I get just a hint of rear bias under hard braking on tarmac, which works out pretty good on gravel, basically by making the pushrod pressure unequal on the two master cylinders.

So as not someone who understands the sizing of the MC relative to the calipers, would I need a larger or smaller front MC to get it closer? Any recommended reading anywhere as to the engineering here?

What if I just swap the two MC's? Maybe I got them in there backwards at some point?

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http://www.ckrally.com

cblakely Wrote:
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> What if I just swap the two MC's? Maybe I got them
> in there backwards at some point?

Switching them around would get you right about 60-40. That wouldnt be too good unless it was snow conditions, but then turning the balance bar all the way would get you about 70-30 more like it for gravel but with that much offset on the balance bar you would have bias migration as the bar would start pivoting on the front master.

The best solution would be to get another 5/8's for the rear and run some front bias on the bar or a 7/10's and turn some rear bias. Also make sure your front m/c rod is about 5mm longer than the rear.

so I found a form on tilton's website that you can fill out with your pertinent information, and I gave that a try. link: http://www.tiltonracing.com/content.php?page=faq&view=9

They came back with almost exactly what I have now

(here's the info I posted)

Make: Volkswagen
Model: GTI

Front Brake Information

Number of pistons within each front caliper: 1
Are pistons on one side or both sides of caliper: one

Diameter of pistons on one side of caliper (list all):

Piston 1: 2.125 in
Front rotor diameter: 11 in

Rear Brake Information

Number of pistons within each rear caliper: 1
Are pistons on one side or both sides of caliper: one

Diameter of pistons on one side of caliper (list all):

Piston 1: 1.5 in
Rear rotor diameter: 8.9 in

General Information

What is the motion ratio of your brake pedal (5.5:1, 6.2:1, etc)? 4.2:1
Vehicle weight (with driver and fuel): 2800 pounds
Vehicle Weight Distribution (with driver and fuel): 64 / 36
Vehicle wheelbase: 97.2 in.
Front tire diameter (outer): 62 cm
Rear tire diameter (outer): 62 cm
What is the vehicle being used for (street, road racing, circle track, drag,
etc)?: rally racing


The response:

My calcs predict 5/8" front a 3/4" rear. I used a tire coefficient of 1.1,
a CG height of 16" and a pedal effort of 100 pounds (at lockup) to achieve
these numbers.

These predictions are not guaranteed since there are many variables for
which we have to take educated guesses at. Consider them to be a good
starting point. Once your car in on the track, I will be happy to help you
tune the system.


Regards,
Jason Wahl
Tilton Engineering


So that seems pretty different from the #'s you've tossed out here, I wonder why the difference in theory?

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http://www.ckrally.com

Probably had to do with pedal ratio? But that might not really change the ratio between masters, just size.

cblakely Wrote:
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> so I found a form on tilton's website that you can
> fill out with your pertinent information, and I
> gave that a try. link:
>
> They came back with almost exactly what I have
> now
>
> (here's the info I posted)
>
> Make: Volkswagen
> Model: GTI
>
> Front Brake Information
>
> Number of pistons within each front caliper: 1
> Are pistons on one side or both sides of caliper:
> one
>
> Diameter of pistons on one side of caliper (list
> all):
>
> Piston 1: 2.125 in
> Front rotor diameter: 11 in
>
> Rear Brake Information
>
> Number of pistons within each rear caliper: 1
> Are pistons on one side or both sides of caliper:
> one
>
> Diameter of pistons on one side of caliper (list
> all):
>
> Piston 1: 1.5 in
> Rear rotor diameter: 8.9 in
>
> General Information
>
> What is the motion ratio of your brake pedal
> (5.5:1, 6.2:1, etc)? 4.2:1
> Vehicle weight (with driver and fuel): 2800
> pounds
> Vehicle Weight Distribution (with driver and
> fuel): 64 / 36
> Vehicle wheelbase: 97.2 in.
> Front tire diameter (outer): 62 cm
> Rear tire diameter (outer): 62 cm
> What is the vehicle being used for (street, road
> racing, circle track, drag,
> etc)?: rally racing
>
>
> The response:
>
> My calcs predict 5/8" front a 3/4" rear. I used a
> tire coefficient of 1.1,
> a CG height of 16" and a pedal effort of 100
> pounds (at lockup) to achieve
> these numbers.
>
> These predictions are not guaranteed since there
> are many variables for
> which we have to take educated guesses at.
> Consider them to be a good
> starting point. Once your car in on the track, I
> will be happy to help you
> tune the system.
>
>
> Regards,
> Jason Wahl
> Tilton Engineering
>
>
> So that seems pretty different from the #'s you've
> tossed out here, I wonder why the difference in
> theory?
>
>
> ------------------------------------

Well Jason recommended a 3/4 rear, which is only 1 step higher (safer/less agressive) than what I recommended. As for the theory, there's no theory, just math. The pedal ratio has nothing to do with the bias, only for torque output. Both me and Jason work in the motorsport industry and deal with brakes everyday, the only difference is I rally myself and deal with rally teams on a daily basis (including VTcar) and know that he's calculating based on a lot of tire grip which will get you more weight transfer (on a gravel tire I would use no more than .7 mu for grip). Good for tarmac but for gravel or snow where you need much more rear, the car wont rotate and just tend to understeer.

I would recommend a 7/10 m/c given that normally people tend to run a less aggressive pad in the rear due to the lower temp range.

But even the pro's go out a test even after all the calcs have been made by the best in the business, so, go out there and tear some roads to find out.

Cosworth Wrote:
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>
> I would recommend a 7/10 m/c given that normally
> people tend to run a less aggressive pad in the
> rear due to the lower temp range.
>
> But even the pro's go out a test even after all
> the calcs have been made by the best in the
> business, so, go out there and tear some roads to
> find out.


Hey, this last bit Paulinho writes needs to be stressed.
Calculations are nice but in the end you have to try things out and YOUR foot on YOUR car is decisive.

I'd also lean toward 0.7 but hey swapping just 1 master out and trying is no big deal, so have both, try them, see which you like best.

Learning to use brakes--and making sure they worked and using them right EVERYTIME was the difference between me being just some local Northern California "Ex-spurt" and being able to race International level moto-cross full time..

Gassing it takes no brains, and you could put a cinderblock on the gas, and that would work fine.
THE critical thing in racing, especially on loose surface, is maybe the hardest thing to do but the rewards are huge in both time and control.

And again I stress what we're aiming to do is not just say "I can lock my brakes---so why do i need bigger" but "I can modulate just short of lock up consistently no problem" it's CONTROL.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Don't know how many watched Warwick's excellent behind the scenes with SRTUSA video, but they show a part with Travis riding along with Mirra and that's the one thing he really points out as where Mirra is losing time. In braking. Confidence and experience in braking is consistently listed as the most important thing in rallying.
What was that one quote of Derek Bottles' I liked. Something along the line of, I wait until I feel like it's time to brake, then I wait a little longer...

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Grant Hughes

I will definately be testing ... If it came across as that I just wanted to figure out the maths and theorys and all that and IF THAT ISNT RIGHT BYGOD I WONT BE RACING IT! ROAR - that was not the intent I always set the bias on tarmac before (i didn't really live all that close to any rally-like gravel roads) with just a hint of rear lockup before fronts, and that translated into a pretty predictable braking setup on gravel stages.

honestly I loved the way they worked as they are on now. It was a night and day difference when I swapped to the dual masters and ditched the boosters. I remember at the end of a pretty fast stage on the shelton roads my co-driver commented on the change in braking (before it was never an issue, after the change he noticed that we were going much later while approaching the corners).


My concern (and hence the multi-part thread jack) is when I moved it over to the new shell I was noticing exactly what you were saying paul, which is that the balancer adjuster seems to pivot on the front pushrod for a small amount of time before it actually engages the front brakes.

So ... maybe I order up a slightly smaller rear MC than my 13/16ths and reset the bias and give that a shot.

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http://www.ckrally.com

>NoCoast Wrote:
>-------------------------------------------------------
> What was that one quote of Derek Bottles' I liked.
> Something along the line of, I wait until I feel
> like it's time to brake, then I wait a little
> longer...
>
> Grant Hughes
> www.nocoastmotorsports.net
> Denver, CO


I've got a road racing buddy who swears by:

Wait till you see god, count to 3 and THEN brake!


Dave

I'm pretty sure that Cody is running bone stock.

On gravel with the Hondas there isn't a lot that has to be done. Are you having problems with pad fade?

Use good pads with decent cold performance--like a Hawk HP+. I prefer discs in the back, easier to service but adds a few pounds. Bleed the brakes often.

For me its all about good fluid, good pads and stainless brake lines.

BillyElliot Wrote:
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> Well he's still going to have some sort of
> limiting/proportion valve that's in the car if he
> swaps to disc on top of the mis-matches brake
> master. ABS equipped Hondas still have that whole
> rat's nest limiter/prop meet up but they don't
> limit since all the proportioning is done in the
> ABS module. Don't remember any EF (pre 1992)
> hatch models that had ABS so a direct drop in
> probably doesn't exist.

Actually all you need is a prop valve from a non-abs version of the car--it is how we eliminated ABS on the Integra. Civics and Integras were available with or without ABS.

My vote:

Choice 2.

Stock ends, add a proportioning valve to adjust the rear.

That's what I did, it cost about $100, and did everything I needed it to. Also, for $100, an amazing ability to change the behavior of the car dynamically. I use the 7 position lever (not the dial).
2 for the street.
4-5 for rally.
7 for rallycross.

I'm sure pedal boxes with balance bars are even more delicately adjustable... but it's gravel.

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Grassroots rally. It's what I think about.