the k11 abs sensors consist of a hall sensor in the hub upright and the rotating abs ring on the outer CV joint.
has nothing to do with the calipers or disc.
imo ABS isn't mainly to reduce stopping distances but rather instead it tries to provide some steering control whilst threshold braking so the driver can steer away from the obstical (provided they haven't soiled emselves yet).
it works by crudely modulating/pulsing the brakes fully on/off to balance between maximum braking force when on and lateral steering grip when off and letting the tyres rotate n grip the tarmac. the moment it has to release the brakes to allow the tyre to spin back up n regain lateral grip, you've potentially lost a moment of braking hence longer braking distance & time.
on the other hand it's common sense that if a driver just simply stamps hard on the brake and locks the wheels, you won't have as much potential braking force and no steering control
the best braking force you can acheive for a particular "tyre" is the point just before the wheel locks ie. Threshold Braking, as used in motor racing
http://en.wikipedia.org/wiki/Threshold_braking
on a side note: during trackdays with upgraded pulsar front brakes upto temperature and ABS on, the ABS tends to activate prematurely and really unsettles the balance of the car so i was abit cautious. when I turned ABS off it was dramatically much more stable under threshold braking and i could fully utilise the power of the GTIR brakes.
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ok lets work back systematically through the braking system:
Tyres - k you upgraded to grippier tyre compound which can withstand a higher braking force before breaking traction. So the braking power required to get the optimum braking force out of them is set higher, as proven by ur lack of tyre screech cos there's more grip than what the brakes can throw at it.
Discs - are they smooth and uncontaminated with no grease/oil
Pads (important) - different pads display various behaviour/character as to how much "coefficient of friction/braking" they can provide at certain temperatures.
some provide their most optimum braking during high/med/low operating temps. some have a wide optimum operating temperature range and some don't.
so its very important to choose the type of pad material with the optimum operating heat range thats suitable for ur application (ie low heat street use).
if using say high heat trackday pads under low heat street roads, they may not (or take awhile to) get upto working temperature so you may have minimal or no braking force when you need it.
if using a low heat street pad under high heat loads (trackdays or steep downhill braking with a heavy load), the pads could be pushed beyond their maximum operating temp and begin to fade
has the new pads been bedding-In? to get the most out of the pads & discs you have to go through a bedding procedure which cleans the disc from the previous pad material, cures the pad binding material and ensures the pad & disc surfaces match and fully contact each other.
make sure the pads slide along the pad carrier freely
Calipers - does the piston & guide pins slide in n out freely without any binding/seizing at all? no air in the fluid.
Brake pedal - is the pedal operating range correct? so the master cylinder piston is fully extended when the pedal is resting fully up and the piston travels all the way in just before the pedal reaches the floor/bulkhead (can be tested when say ur bleeding the brakes)
Driver Psychology - i personally find that braking under stressful demands or startle is different to when braking intentially in a controlled condition.
when I'm like testing/bedding my brakes on a quiet road or braking for a corner during trackdays I can brake as hard as i can till my face tears off
but when I have to brake unexpectedly (someone suddenly pulls out or motorway congestion suddenly halts) i sometimes feel as though I'm not pushing the brake as hard as i know i can. it's like my startled brain didn't wanna push too hard to lock the brakes and make the person behind rear end me hence kinda hold back abit. or maybe twas cos the brake pads were still stone cold and takes afew millisec to get upto temp before beginning to provide good braking
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