[Thejoyofdriving]

Originally Posted by Flycaster

MGizzle, could you please explain the need for a M/C brace? I hadn't heard this before, and I'm trying to wrap my head around the issue. Lines, pads, rotors, fluid, I'm good with all that, but the M/C brace just took me by ignorant surprise. Thanks.

Im not MGizzle, but ill give it a shot, basically, under extreme braking, the master cylinder moves, or more accurately, flex's in its brackets, which creates a inefficient transfer of energy, the M/C brace stiffens the M/C thus leading to a stiffer pedal feel and more efficient transfer of energy.

[Flycaster]

Interesting, makes sense, thanks.

[MGizzle]

As far as the MC brace, bottom line is I did it because I hate our STi pedal feel. I want a brick for a pedal and the brace made the biggest difference. The SS lines were hard to feel at all but should work better when tracking as compared to stock. More firm pedal to me means less time to achieve the force I want at the brakes instead of it going to waste to other things like flexing the fire wall, booster etc.

Alright, as far as the ABS unit having logic for tires that is a pretty broad statement. How can it know what you have on your car?? Impossible unless you tell it (calibrate it).

The ABS unit reads differences in the 4 tires. If it is set to let go when it reads a 15% speed difference how is it going to get the most out of a R compound that can read 30% difference or 10% difference?? It can't. It is going to let go of the brakes when it sees what it has been calibrated to. This is set by the calibration engineers driving the crap out of this car and is mostly looked at during wet or icy conditions so dry is not the main concern here (unless it is calibrated for a sports car, which ours is and BOSCH has the ESP SPORT ABS unit on our cars supposedly).

Again, the ABS unit is going to let go when it sees the difference it has been calibrated too. Yes, your tires can have the same difference as optimum but they could be way off as well. Again, look at tuner shoot outs vs. stock and look at the 60-0 or 100-0 numbers. R compunds might be better but you will laugh when you notice by how much the stock car looses. I have not see any comparison so far that has the stock car beat but supposedly there was with some WRX's in a tuner magazine where the R compounds have it beat. Also, you have to make sure that in that comparison they did use the ABS unit since to my knowledge a lot of guys runing serious R compound tires take the ABS fuze out since this way they can modulate the lock up of the tires and get better stopping (duuuhhh stickier tires).

Anyhow, let me know if I am not making sense again.

[Mykl]

Originally Posted by Flycaster

MGizzle, could you please explain the need for a M/C brace? I hadn't heard this before, and I'm trying to wrap my head around the issue. Lines, pads, rotors, fluid, I'm good with all that, but the M/C brace just took me by ignorant surprise. Thanks.

This is simple...

With the car at rest, have a buddy stomp on the brake pedal as hard as they can. Watch the master cylinder dance. This is translated through your pedal as slop.

With the brace equipped and the car at rest, do the same thing. Watch as the master cylinder brace doesn't move.

Basically, during threshold braking it makes the pedal feel more precise. The difference is really only felt when you're braking at 75% or greater. The difference is subtle, but but nice.

[CGMDan]

Originally Posted by FHItoSTI

If the rotors arent drilled or slotted they cant cool fast enough thus resulting in loss of braking power. Regardless of what other mods you have done to the brake system.

Nope. You might want to re-educate yourself on brakes then rejoin the discussion.

[CGMDan]

To throw something else out there, at what point does caliper flex start becoming an issue? I know when you start adding multiple pot calipers the open area on top will start flexing. Hense the reason for having 4 to 6 pads per rotor. It limits the open area and keeps the calipers more rigid.

[seattle944t]

Originally Posted by MGizzle

<snip>

Alright, as far as the ABS unit having logic for tires that is a pretty broad statement. How can it know what you have on your car?? Impossible unless you tell it (calibrate it).

The ABS unit reads differences in the 4 tires. If it is set to let go when it reads a 15% speed difference how is it going to get the most out of a R compound that can read 30% difference or 10% difference?? It can't. It is going to let go of the brakes when it sees what it has been calibrated to.<snip>

OK- What I am still missing is why are you saying the ABS is going to detect a difference when the tires have not exceeded their traction limit? What is preventing R compounds from reaching the traction limit on an ABS system? Because if the system it working off of wheel speed differences, there won't be wheel speed differences until a tire or tires have exceeded their traction limit - what ever that is, either higher, lower, or the same as stock. What am I missing?
Is there some hidden logic that there is a maximum deceleration rate? I know for a fact this logic doesn't exist on the 05 STi ABS system, as I have had the unfortunate experiences of driving on snow and ice on the RE070's. All four wheels can be locked at speeds over 30MPH in less than one second - of course w/o slowing the car down at all.

Originally Posted by MGizzle

Again, the ABS unit is going to let go when it sees the difference it has been calibrated too. Yes, your tires can have the same difference as optimum but they could be way off as well.

And I still don't see why this is such a detriment - 4 R compounds are going to have the same traction curve and rate of deceleration relative to each other, as 4 stock tires traction curves are relative to each other. The R-compounds just have a higher threshold that they reach before ever triggering the ABS. So while the ABS kicks in as the stock tires lose traction, the same car with R compounds will get into the ABS later, at a higher traction level because of the tires. Since the only input in most cases is wheel speeds the system is self calibrating for traction level. It has to be - other wise they would only work for a set traction level that was programmed in, which would defeat the whole purpose of the system in the first place.

Originally Posted by MGizzle

Again, look at tuner shoot outs vs. stock and look at the 60-0 or 100-0 numbers. R compunds might be better but you will laugh when you notice by how much the stock car looses. I have not see any comparison so far that has the stock car beat but supposedly there was with some WRX's in a tuner magazine where the R compounds have it beat. Also, you have to make sure that in that comparison they did use the ABS unit since to my knowledge a lot of guys runing serious R compound tires take the ABS fuze out since this way they can modulate the lock up of the tires and get better stopping (duuuhhh stickier tires).

Anyhow, let me know if I am not making sense again.

Found the article online:
Tuned Subaru WRX Cars vs. WRX STi Turning and Stopping - Road Test Comparison - Sport Compact Car Magazine

The vishnu WRX with R-compounds (Toyo's not Kuhmos) stops just as fast as the stock STI, 12 feet shorter than stock WRX (greater than 10% improvement) and 8 feet shorter (7% better) than the other WRXs using the same stoptech brake kit.
This is with all cars still using ABS, and in this case the lousy WRX system at that. So I still can't see how the ABS system is unable to account for increased traction levels of better tires - it has to be able to do this, traction is what its monitoring in the first place.

[Flycaster]

Originally Posted by Mykl

With the car at rest, have a buddy stomp on the brake pedal as hard as they can. Watch the master cylinder dance...

I'll do that, thanks. That's much easier to grasp than a technologoical explanation, at least for me.

[MGizzle]

seattle944t, that is actually the article I was thinking of too. 12ft better is not bad but I don't think it is all coming from R compounds. The vishnu car didn't only have R compunds, it had brake upgrades that in my opinion are necessary prior to going to R compunds (pads and rotors).

Anyhow, I know where you are coming from and as in my previous statement it depends on how the ABS unit is calibrated. Some guys don't use tire variables in calibrating the ABS (of course difference in size and weight will effect this hence why throwing 20'' rims will hurt you and I am not talking about this) but if somebody is using tire data and in some cases the vehicle reference speed vs. the wheel reference speed than you are sort of screwed, no? You will deccel faster with the r compounds but it will let go at the deccel that was used during calibration. Again, it depends and you have to be careful.

I am not sure how the BOSCH STi unit was calibrated and you could be right in that it does use the R compund max traction but my arguement is that we don't know this and in most cars this is something consumers don't know, hence you could hurt yourself depending on how it is done and what tire choice you make.

And to stirr it up even more, we are talking "traction" differences in tires and not width, size, weight, inertia etc. Saying that "tires" will decrease your braking distance the most is a very very broad statement that can be as wrong as much as true depending on your choices.

Anyhow, I shot an email to one of the ABS calibration guys who has been doing it for dozen of years and I am trying to find out the actual calculations used and what his opinions are on swaping tires (street to R compound) and its effects on a OEM ABS unit. I'll hit this thread up when I hear back from him. I wish I had a simulation software with ABS in it.

[stretch]

Very interesting thread, but like seattle944t said, R-compounds are so much stickier than street rubber that they'd stop the car shorter even without ABS engaging. R-compounds at 9/10ths are still at least as sticky as good street tires, although I guess I shouldn't make that claim without data backing it up.

However:

Originally Posted by seattle944t

Found the article online:
Tuned Subaru WRX Cars vs. WRX STi Turning and Stopping - Road Test Comparison - Sport Compact Car Magazine

The vishnu WRX with R-compounds (Toyo's not Kuhmos) stops just as fast as the stock STI, 12 feet shorter than stock WRX (greater than 10% improvement) and 8 feet shorter (7% better) than the other WRXs using the same stoptech brake kit.
This is with all cars still using ABS, and in this case the lousy WRX system at that. So I still can't see how the ABS system is unable to account for increased traction levels of better tires - it has to be able to do this, traction is what its monitoring in the first place.

The Vishnu car was running RA-1's, specifically. For it to ONLY stop as fast as a stock STI is actually evidence demonstrating MGizzle's point. RA-1's are significantly stickier than any street tire (although still a far cry from Hoosiers), and to only *match* an STI's braking distance shows that something is awry. The WRX should've been lighter and lower, too, both of which make for easier loads on the tires. My guess is that it was running lots of negative camber, hurting its braking, but who knows.

Originally Posted by MGizzle

Vehicle Mass/Sprung: This will effect your dynamics a bit and going lighter might not improve it. Your car will lift, changing your suspension geometry and your weight distribution on all four corners (statically too). Hence, you need to drop some significant money and time to get this right. Without Coilovers or ballast I don't know how you can do it. You are putting less weight on the tires so you might effect the transient time to reach peak grip, hence lock up. With handling it is different.

I don't understand this. Ignoring front-to-rear brake bias, since that would clearly change, how would the transient time to load the tires change drastically, and why would the ABS system care? ABS could see certain tires as having more traction than others, but that's exactly what it's designed for.

Vehicle Mass/Unsprung: heavier tires, rotors, wheels etc. will kill your inertia and this will effect your brake output alone killing your distance. However, the ABS unit will hurt too because it is trying to release the tire at a time where the system still has enough inertia to roll the tire forward after it is released. I am telling you, we had issues with this when calibrating some heavier cars and you have to make sure you release with enough inertia left to spin the tire forward after you release.

I've seen this happen (the tires locking up, then spinning, over and over) before and always wondered why the heck the ABS was doing that. The guy was running very light wheels on an E36 M3. It makes sense now, thanks! Very interesting to know.

MGizzle- you mentioned Euro vehicles not need calibration because the tires are all so similarly good, but a lot of the same tires are sold here. This seems very contradictory to the rest fo your statements, since Europeans do run a wide variety of tires (winter to summer) just as Americans do. Could the various max-performance summer tires sold in America really vary that much?

Dennis Grant has mentioned being able to brake better himself than ABS (on a car with R-compounds) in the dry, but not in the wet, which he suggests is due to the ABS having lost its calibration. But he also mentions Chrysler's data of ABS not braking at peak grip (for ANY car), perhaps because they calibrate for a less-than-perfect surface:
DGs Autocross Secrets aka Autocross to Win

Lastly, just subjectively, I hate ABS. This is my first car with it, and I always feel it engages too early. It probably isn't, but I'd love to, someday, actually measure for myself how much improvement it makes. I felt my Mazda6, even on its not-aggressive stock pads and no ABS, stopped quicker on good tires (but again, I have no data).