[flash]

it works fine on my car, but i did not do an unbalanced caliper size setup either

if you can't get it to work, my recommendation is to balance your rear caliper size to the front

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[mattipuh]

Shouldn't fronts get still more braking because front brakes are bigger? Proportional valve still limits braking to rear.
think I'll intall similar pads (Ds2500) to rear aswell + do bleeding once more time.
cannot think that 968 couldn't handle 5/33 valve if 951's do. and caliber area shouldn't be so different compared in 996 turbo's vs. to Big reds. . .

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[flash]

no - while the fronts will always work harder than the rears, due to weight transfer, that's not the way to set it up

big reds up front without also doing them in the back results in unbalanced braking and actually increases braking distance - it only "feels" like you're braking better because the nose dives more due to the higher clamping force of the larger brake - but nose dive is NOT a good thing - that transfers all of the load to the front of the car, and then the rear brakes aren't doing anything for stopping, and can actually lock up - you need to keep the weight on the rear - you do this by having the rear brakes grab as hard as the front and pull the whole car down more evenly

in a 50/50 car, braking should be more balanced - weight transfer will do the rest - i know it sounds odd, but it's right

you can see more about this on the stoptech site

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[mattipuh]

when the ABS is working, I have to disagree with you, really. car stops quite a much faster now than before. trust me. [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]
have to figure out the ABS unit functionality (most likely air in system). but seems not to be problem on normal street driving - just when tracking and using more brakes.

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[flash]

measure the comparative stopping distances - unless you have the ass end of the car starting from much lower than the front, or you have a lot of weight back there, i'm willing to bet that is not the case - i know it "feels" like you are, and the initial grab sure fakes you out that way, but the physics isn't there

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[mattipuh]

Challenge is taken!
I'll try to measure stopping distance from 60 to 0 mph some day. could be next summer also (because have to soon put winter tires).
It's not really scientific measruement because pads won't be OEM, but still I believe we should get some kind of direction wheter it's better or worse.

60-0 is maybe wrong scale for measurement, should be smth like 100 - 0, just to give brakes really some work.

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[flash]

no worries - it's a very odd thing to wrap one's head around, but after 30 years of setting up brakes, and unfortunately having to learn the hard way, i've learned a few things about weight transfer and how it dramatically affects braking - in a straight line, it's often hard to tell what's really going on, but do a lock up brake in a turn, and things start to quickly tell a story

this article is pretty good at explaining it:

http://www.stoptech.com/tech_info/wp_brake...rformance.shtml

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[mattipuh]

Tested brakes on asphalt few times, and abs hits normally for fronts first. cannot still understand what went wrong on the track when abs was lost for some brakings. ..
maybe there was some air in the abs unit, and now it's somewhere in the braking lines, and not bugging abs anymore. well, don't care really, as long as the abs works.

one quote came to my mind: "it's good to own a porsche with good brakes - you don't need to find gravel road to do abs test". ,)

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[flash]

since we have a 3 channel system abs system, with the rears sharing a channel, i tend to think the problem is weight transfer related

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[mattipuh]

how would the weight transfer be different on a track than on street?
and if rear(s) would start lock up, it shouldn't affect front. or is abs so slow in these cars, that it cannot catch everything, if there start smth happen in rear?

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[flash]

weight transfer is a function of speed as much as anything - on the street you don't incur the forces that you do on the track, especially related to braking - brakes will act totally differently on the track versus on the street

the abs system in these cars is very primitive - i would not be surprised if it could not keep up - most guys disconnect it on the track

if you insist on running the bigger rotors and calipers up front and not changing the rear, and ignoring the physics, then i would recommend at least changing to a 5/45 bias valve - the 5/33 is barely enough for balancing the stock setup, and is not enough to balance the larger calipers

pete at rs barn would be happy to relate his experiences and insights regarding exactly this issue

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