isleblue65

I have the 4-pad S4 calipers and S4 wheels on my 2000 2.7t and the brakes work fine. I have at my disposal a set of newer 2-pad S4 calipers that I believe are bolt-on. Are there any advantages or disadvantages of swapping out the 4 pad with the 2 pad S4 calipers?

Are the 2 pad calipers better, lighter or cost less to do brake jobs?

Thanks

Just Me

I think the 4/8 pad HP2 system is superior. I also believe the rotor changes when you change from the Lucas HP2 to the ATE caliper.

It was primarily a cost reduction. as was the switch from all aluminum to aluminum & steel

Or that's my opinion. Overall if they work smoothly the main differences will be pad material. So why bother?

G

isleblue65

Thanks for your reply and insight. This is helpful. The pad material on the 4 pad vs 2 pad calipers are different?

I have available the ATE calipers, rotors and pads, so it would be a cost-free and relatively easy exercise while flushing my brake fluid some Saturday. I agree, not worth it if there's no benefit.

Anyone else have a differing opinion?

SloopJohnB@mac.com

It appears the two pad calipers are smaller and lighter...at least shorter, subtending a shorter arc on the circumference of the rotor.

As for pad costs...probably less expensive for two pads than four...you can do your own research on pad costs.
Compare Hawk HPS for the four pad vs Hawk HPS for the two pad caliper.

Stock textar pads are hard to beat for the street....I use Jurid (textar) pads on my E46M3 convertible and am quite satisfied with feel...hard and immediate brake feel, just like stock.

AUJ

Clamping force at the wheel is simply a question of mechanical efficiency. There are many constants. Line pressure and rotor diameter are given at non-changing variables. Two variables when comparing the caliper systems related caliper clamping force or quite simple. The co-efficient of friction of the pads and the area of the caliper rotor. If you get the same pads, then the question of design comes down to piston surface area. Measure that on both caliper and you have your answer. Slider design is just doubled in mono-piston designed calipers for equation purposes. One potential advantage of a caliper using one backing plate for the pads is that clamping force application may be more uniformly applied. One potential advantage of the larger mass old calipers is that they may act as a better heat-sink judging purely on increased mass and not material used in design. Thermal storage capabilities and dissipation of such would have to be measured under strict controls to make a definitive judgment. The design downside of a large floating caliber body system is reduction of brake torque delivery to the rotor surface area secondary to increased caliper flex, hence less efficiency.

Audi engineers did update the design. Personally, I would love to see the evidence showing that it was purely a cost design intervention as suggested by "those in the know". LOL.

Bottom line is that design engineering approved the change, so the move was considered negligible, or at least acceptable; if not preferable to those who make informed decisions at THE SOURCE. Do the math on caliper clamping force focusing on the caliper pistons to get the best answer. As a recap, measure the piston surface area of half the caliper. The piston with the higher surface area wins; at least on white paper, with all other variables being constant. Also, if you unilaterally increase the co-efficient of friction of the brake pads at all four wheels, then you preserve the design balance as engineered for the vehicle.

Just Me

There is no relationship between surface area and total friction, except when you figure shear. Friction = Cf * applied force.

Larger mass means more unsprung mass. rarely a good thing.

Cost reduction is the name of the game. If you can do it with minimal negative impact, all the better.

Thinking otherwise is pretty optimistic.

End of day, likely little practical difference.

G

Just Me

Pad material and changing pads -------

I have no idea if they changed pad material, but i doubt it would change much. Mot companies work with standard supplies with off the shelf compounds. Its easier for you to simply change to a different pad - although i suspect most people do an inferior job of selection compared to the engineers who designed it.

That said your priorities may be very different. If you track a car, you NEED much higher temperature handling, and will trade off noise, dust etc to get it. Joe public won't, and need not.

One more thing int he HP2s favor - they make it easy to swap pads. Just pup the spring clip; tap out the pads, and swap away. Not quite as easy as Brembos, but a step above run of the mill.

Having struggled with some oddball brake issues with my car, which has HP2s, i was re-acquainted with how easy it is to get pads out, how nicely the work, and how difficult it is to get the calipers off! (unless you have a lift and can swing a big breaker bar completely under the car)

Bottom line, all this stuff aside, i see no glaring reason to change, and in fact see a few advantages to what you have. So "don't fix what ain't broken"

G

AUJ

Piston surface area is the sole determinate in which caliper will produce more clamping force, hence more brake torque at wheel. Line pressure is the same, rotor diameter is the same, and co-efficient of friction will be the same if the same pads are used for each caliper. HP-2s are huge and more likely to flex because of liberal use of aluminum. HP-2s were replaced by Audi engineering. The brake pad service area does not affect the co-efficient of friction. Nobody said different. Claims that the updated more recent calipers were a cost decision STILL remain to be proven; the usual.

With equal pads, add up the piston surface area of the two pistons of the HP-2s. If that is greater than the piston surface area of the updated calipers, then it produces more clamping force than the updated calipers on white paper, since they are both sliders. How much brake torque gets to the wheel depends on caliper flex. How short your reproducing consecutive stopping distances stay is a function of caliper heat dissipation abilities, performance of the fluid, and your tire condition and choice.

mithrilG60

Only on the 2.7T. On the 4.2L the HP2 calipers were retained for the entire model run. Could be cost, could be that they just decided any additional stopping power provided by the HP2's was overkill for the 2.7T. Could be that when they moved from the B5 S4 to the B6 gen and moved off the HP2's there as well that they didn't want to keep the tooling for the separate offsets (ie. 4.2L/S6 and 2.7T) within the same model line.

Just Me

But is clamping pressure really the issue? No All cars are limited:

1. shrt term by tire traction
2. long term by heat dissipation and maximum pad operating temp

So i see this largely a "which is lighter"; "which is designed to float more evenly"; and "which is easier to service"

I really dont know if one is significantly better than the other. The point is that its unlikely than the ATEs are significantly better ( i think they are probably worse) and the real issue is pads and condition.

So both of us are in effect recommending the same thing, i believe. Let's focus on the important - its work for little or no benefit.

G