[flash]

seven - if you think that's something, you should come hang out at one of our events - we often have some really good discussions

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[Willem968RS]

<!--fonto:Calibri--><!--/fonto-->Welcome to the forum Seven!<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->I myself am fairly new to this forum as well and also very enthusiastic. Learning every time I visit!<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->In the meantime I've been reading the tech papers of the stoptech.com site as recommended by Flash, which is a fantastic source of information on the subject of braking. The site makes It all to clear.. Everything has to come together when you change your brakes. It's not about just about putting on bigger brakes and expect them to work right away! As far as I can see now, I guess I've been looking to long at the setup of shocks, springs and caster, which are of course important too, but cannot be the cause of the enormous difference in braking with my old (944 S2) racecar and my current 968.. In the old car, I've been playing with different setups, springs, shocks, braces, tires, brake pads and sway bars. Often I experienced a difference in braking, but never was it as bad as it is in my 968! <!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->Now I'm waiting on a reply from Tiltonracing.com, the manufacturer of my paddlebox. I briefed them on various matters they needed to know to determine what size of master cylinder bores I need in the car, like;<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->1.<!--fontc-->
<!--/fontc--> <!--fonto:Calibri--><!--/fonto-->Number of pistons within each caliper (front & rear)<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->2.<!--fontc-->
<!--/fontc--> <!--fonto:Calibri--><!--/fonto-->Are the pistons on one side or both of caliper?<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->3.<!--fontc-->
<!--/fontc--> <!--fonto:Calibri--><!--/fonto-->Diameter of each piston<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->4.<!--fontc-->
<!--/fontc--> <!--fonto:Calibri--><!--/fonto-->Rotor diameter<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->5.<!--fontc-->
<!--/fontc--> <!--fonto:Calibri--><!--/fonto-->Motion ratio of the brake pedal<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->6.<!--fontc-->
<!--/fontc--> <!--fonto:Calibri--><!--/fonto-->Vehicle weight (with driver and fuel)<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->7.<!--fontc-->
<!--/fontc--> <!--fonto:Calibri--><!--/fonto-->Vehicle wheelbase<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->8.<!--fontc-->
<!--/fontc--> <!--fonto:Calibri--><!--/fonto-->Front & rear tire diameter (outer)<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->9.<!--fontc-->
<!--/fontc--> <!--fonto:Calibri--><!--/fonto-->Use of vehicle (street, road racing, circle track, drag, etc.)?<!--fontc-->
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<!--fonto:Calibri--><!--/fonto-->I don't know if all these parameters have been taken into account when the car was build, but by now I'm almost sure that they were not. So when the right master cylinders are in the car, I hope I will be able to brake with the car like it should with those big RS-brakes! The only other thing I expect have to do is upgrade the rear brakes as well, because they are the 944 type I brakes. Expecting to have the right cylinders installed next week and do a test at Zandvoort on the 27^th.. I'll be posting the results!<!--fontc-->
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[flash]

upgrading the rear brakes, specifically to the point of increasing braking surface, will go a long way toward the balance - while adjusting hydraulic pressure will facilitate the initial gab balance, how fast they heat up and how well they brake will be dependent on the surface area as well

you're on the right track

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[333pg333]

Very interesting thread. Looking forward to the results.

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[Seven30]

Flash - Please let me know if the following describes, in simplified terms, why you need softer springs in the rear to reduce nose dive during braking:

Try picking up a weight from the ground with a bungy cord versus picking up the same weight with a non-flexible wire: With the bungy cord, it takes longer before you pick up the weight from the ground. It is the same with the rear wheels during braking: a stiffer spring will pick up the rear wheels faster.

Just trying to learn [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]

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[flash]

well, the result is the same, though a bungy cord is an elastic, which has no compression resistance to speak of, and only reacts in one direction, whereas a spring acts in two directions

a spring has a resistance measured in pounds per inch of compression - it compresses a fixed amount in static load, constantly pushing upward with that fixed force - lower the amount of weight on it, and it will extend by the corresponding amount, based on the spring rate

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[Willem968RS]

Still no answer from Tilton, but an appointment next Wednesday with a veteran racer, who has a lot of experience with paddle boxes and knows how to calculate the right brake cylinders. If that’s not the solution we are installing a brake proportioning valve, which will provide the right pressure in different situations of hard or less hard braking.

Then we will change the Audi RS brakes for big reds to test if it helps to make the difference between the front and rear breaks smaller.

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[flash]

question: do you mean pedal box, when you say paddle box?

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[Willem968RS]

The Tilton site indicates it as a: "Tilton Floor-mount Pedal Assembly - Dual Pedal, Triple Cylinder" Flash.

I thought it was called a paddlebox, but probably not?!

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[flash]

no worries - i was just making sure i was thinking it was what i thought it was

i wonder how they are going to figure out what cylinder size, and if they are going to anticipate other changes?

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[Willem968RS]

<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->Did not do the test at Zandvoort because the car was not ready because of a wrong send cylinder..<!--fontc-->
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<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->A few days later I had my race, which was the first opportunity to try the new cylinder. It seemed that the front cylinder that I had in the car before was far too small, about 18mm and was changed for a 22mm (7/8 inch). The front 18mm cylinder was the right size for the rear, so it was swapped..<!--fontc-->
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<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->Free practice the track was a bit wet, so not ideal to test the brakes with slicks, but the brakes felt different/better. They had a better and consistent feel and no slack and spongy feeling anymore. In qualifying I was busy putting on a good time more than experiment with braking and did only 4 laps to save the tires.. During the race the plan was to brake a little harder before the different corners until lockups would appear, but unfortunately the car broke down in the third lap with a broken ball joint pin.<!--fontc-->
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<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->I shaved a second from my best time at Zandvoort, so guess the brakes were working better already, but did not have enough laps to really try them out.. <!--fontc-->
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<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->Anyway now we are collecting all the parts for reinstalling ABS, so with that in mind I can't wait for the next change to test the car at the 10^th of October at the Assen circuit! <!--fontc-->
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[Willem968RS]

Did a test last Thursday at Zandvoort. The first time to really try the new setup with the different brake-cylinders on a dry track and in relaxed conditions. Before the test I had read the "Porsche High-performance driving handbook" from Vic Elford, which is fun to read and has given me more understanding about several race related issues, especially about the technique of braking. I realized that after a long time braking with ABS and just slamming the brake-pedal before every corner, to do it right, there was a bit more to it than that. The book explains the importance of smooth braking and the technique to start braking with a little jab at about 4 on a scale of 10 (10 being the point just before lockup), causing a weight transfer toward the front wheels and then increasing the pressure to 10.

<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->I was not looking at the lap times, but just concentrating on braking and trying to brake a little harder each time until lockups would appear. At first had a lockup in the rear and I gave the brake balance one click to the front. Then I started braking harder every time and really started to enjoy those big RS brakes for the first time. After inspection of the brakes we found out that for the first time the brake pads got to the right temperature as well. I pushed the brakes harder every lap and really noticed my problems were solved! Sadly the datalogger did not work, so I was not able to see the g's I was pulling whilst breaking. Is there anybody who knows how much g's you should be able to pull with a 968 with a good setup, brakes and tires? Anyway it felt a whole lot better and the breaking points were a lot later every time.. I 'am even wondering if the ABS is going back on, but need some more time to get used to the new characteristic of the brakes, before I make that decision. Getting used to, and having confidence, will take some time after such a long time having unpredictable brakes and being scared to end up in the gravel. <!--fontc-->
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<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->Next Saturday is the last race of the season, and the opportunity to try braking under race-conditions.. <!--fontc-->
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[Willem968RS]

<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->Problem solved!! <!--fontc-->
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<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->Did not do very well at the race, but that was my own fault.. The brakes are finally working top! Shaved 1.45 second off my fastest lap time, and could brake later every lap without a single lockup.. So at the end it was all in two little cylinders.<!--fontc-->
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<!--sizeo:3--><!--/sizeo--><!--fonto:Calibri--><!--/fonto-->I will move on to a next question, because I want to make my car even faster.. Thanks everyone for all the help!<!--fontc-->
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[Fox944]

Nice car...and in for reading later

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