Turbo brakes, axxis ultimates, mxv4+ vs. re92

[scottzg]

Start- L brakes with dot 4 fluid on wrx rims w/ re-92 and 17$ pads
For testing- Turbo brakes with dot 3 fluid and wagon proportioning valve w/ same wrx rims and axxis ultimates.
Now on car- Turbo brakes with dot 3 fluid and wagon proportioning valve w/ 94 turbo rims with michelin mxv4+ tires.


Pedal feel is the same between the turbo brakes and the L brakes, although the turbo brakes had dot 3 and the NA had dot 4. Dissappointing, especially considering that the L rotors were glazed as hell and the turbo rotors are not.

Stopping distance, surprisingly, was 3 feet longer with the turbo brakes. This was an average of 5 consecutive 60-0 stops with my buddy the G-tech. The longest distance was thrown out. Numbers were 122 and 125. I'll attribute this to the shifted forward brake bias. Evidently the sedan prop valve will not alter the split point (or doesn't alter it enough) before traction is lost.

Using the same test method, the michelin tires averaged a 124 foot stopping distance on the turbo brakes. The re's were s205/55r16, the michelins 195/60r15. The re's are a bit flatspotted and have been through too many heat cycles though. Still, The re's don't impress me terribly.

I would like to mention im very happy with these braking distances in general though; they're really excellent.

On road, the turbo brakes really excel. My normal hwy 9 run is 7 miles downhill, with 2 predictable stops because my brakes are overheated. This run did not seem to phase the turbo brake/ultimates though, which is the reason for the upgrade. I am completely satisfied. I can't tell that the bias is different on road.


I'm not a scientist or anything, and my testing is 'informal' to say the least.

[-K-]

re92's are pure crap. I can't believe they are even DOT approved.

[skid542]

Nice little review.

Did you put turbo brakes on all 4 corners or just the front? I know I'm kinda the exception with turbo rears and L fronts but I still smile and get all warm and fuzzy inside when I think about my new brakes. I can definately notice decreased brake fade and love my biasing...still waiting to get my new Axxis front pads though. What did you think of the wagon prop valve?

And yeah, good rubber makes a world of difference.

[scottzg]

re92's are pure crap. I can't believe they are even DOT approved.

I liked them

[scottzg]

Nice little review.

Did you put turbo brakes on all 4 corners or just the front? I know I'm kinda the exception with turbo rears and L fronts but I still smile and get all warm and fuzzy inside when I think about my new brakes. I can definately notice decreased brake fade and love my biasing...still waiting to get my new Axxis front pads though. What did you think of the wagon prop valve?

And yeah, good rubber makes a world of difference.

just turbo fronts, i don't need vented rears. I originally had intended to go with wagon rears, but i ended up with 1 wagon rear in the giant box of brake parts i bought. The wagon prop valve was kind of a 'fix.' I can't report on it individually because i put it on with the turbo brakes, i didnt want to bleed them 2x for comparison. When driving i can't really tell a difference in the biasing, i think the difference would only manifest itself in a panic stop. I'm not sure whether i will stick the wagon calipers on when i get them, I kinda doubt it.

I'm really happy that i dont have to have an 'oh shit' moment followed by some scenery gazing 2 or 3 times per outing, but i think if i were to do it again i'd just slap in some perf. pads and be done with it.

I kinda wanna sample your brakes for the novelty, skid.

[skid542]

Lol, love the picture.

Okay so it you did replace just the fronts. Those are on my list but will probably end up as next year's 'spring break present' to myself. I couldn't imagine putting just turbo fronts on mine though, it'd be too much forward bias for me I think. But then again I know I'm hard on my brakes and expect a lot out of them. If you aren't really pushing it I wouldn't think the vented rears would be worth it either but I bet you like it more with just some wagon calipers on it. As far as just slapping performance pads on instead ... the first time a deer hops out in front of you, you'll be happy with the upgrade .

I would like to try your brakes too, we essentially went in opposite directions. I'll try to get a video of me under hard braking.

[scottzg]

it'd be too much forward bias for me I think.

My understanding is it doesn't really matter what the bias is until one wheel locks up. My thinking with the bias valve was that although i'd have more front bias at low pedal pressure, id have relatively less front bias at higher pressure. I can't really tell a difference in my 1 spirited run i've made on them.

If you aren't really pushing it I wouldn't think the vented rears would be worth it either but I bet you like it more with just some wagon calipers on it.

Vented rotors certainly aren't worthwhile if you're just cruising around town. Since the front brakes do the vast majority of your braking, the rears don't heat up nearly as much. Thus big brake kits sell only front brakes. The wagon calipers would shift the bias back. Wagon calipers, sedan bias valve and turbo fronts would get me SS bias with less thermal capacity in the rear, which im not sure i need. I'd have to get a laser thermometer and do more research to know for certain though.

As far as just slapping performance pads on instead ... the first time a deer hops out in front of you, you'll be happy with the upgrade .

As my numbers show, having 17$ pads and L brakes did not effect my braking distance in 1 panic stop. They did better due to better bias. Suspension is the big braking distance booster.

I would like to try your brakes too, we essentially went in opposite directions. I'll try to get a video of me under hard braking.

That'd be interesting, i wonder if you can actually see a difference.

[skid542]

Brake bias effects your braking under all braking conditions, it is just more noticable under hard braking. Most braking systems are front biased because it allows a larger margin of saftey when panic stopping and esspecially braking in corners. The more centered your baising is the more evenly your brakes are working. A bias too far foward will actually have a longer stopping distance than one that is shifted back since the rears aren't being used to their full potential before the fronts lock.

My bias is actually too far back, my rear wheels lock before my fronts. And let me tell you, it can be a real double edge sword. My entry speeds have increased slightly because there is less weight shift front to back during braking but you have to be real careful about when and how hard you apply brakes in curves. Yes I know ideally you don't brake in turns but when you're going downhill sometimes it's a neccesity. My back end will and has kicked out with light brake pressure when I'm at my tires limits. There has been a lot of getting re-adjusted to my brakes. I'm starting to get enough of a feel to do 'e-brake' slides in the rain and mud when making sharp turns (go FWD ).

I think though that if you got wagon calipers your stopping distance will impove more because your back brakes will be working harder. Right now I think your distance improved not because of better bias but just because the fronts can disipate more energy than before. I should pull up Josh's brake spreadsheet and have a closer look at our biasing.
As far as the prop valve, it is my understanding that it is a just a percentage split so that the ratio pressure to the front to the pressure going to the back is constant. The wagon prop valve just shifts the ratio a little further towards the rear, it sends more pressure to the rear. But yeah, the vented don't matter much for around town. I push mine hard enough that even after several miles of driving around easily in town after a 'run' and parking, the rotors will easily burn your fingers. I don't know if I've had them glowing like Phil has but I'm sure I've gotten them pretty toasty.

Yeah I want to see what my braking looks from the outside too. From what I can tell from the inside, my nose dive is essentially non-existent.

[scottzg]

I think though that if you got wagon calipers your stopping distance will impove more because your back brakes will be working harder.

it will be exactly the same as the stock na brakes, the larger pistons will offset eachother. That assumes no wagon bias valve, which according to g-tech, is less of an alteration than turbo front brakes in a panic stop.

Right now I think your distance improved not because of better bias but just because the fronts can disipate more energy than before.

My stopping distances suffered marginally because the brakes are more front biased now.

How much energy they can dissipate doesn't really effect how well they stop in 1 60-0 stop.

As far as the prop valve, it is my understanding that it is a just a percentage split so that the ratio pressure to the front to the pressure going to the back is constant.

The bias valve holds the pressure at 50% front 50% rear until a given pressure in the pedal line is reached (like in a panic stop), at which point is shifts the bias toward the front. The wagon valve has a higher threshold before this happens. thats what stoptech says anyway.

[skid542]

it will be exactly the same as the stock na brakes, the larger pistons will offset eachother. That assumes no wagon bias valve, which according to g-tech, is less of an alteration than turbo front brakes in a panic stop.

The larger pistons will apply greater force to your rotors and therefor have more braking torque being applied to the wheels. This will move the bias rearward regardless of the prop valve. I'm not following you on what you mean by they will offset each
other? Are you comparing "just putting on rear wagon calipers" vs. "just upgrading the front to turbo"?

How much energy they can dissipate doesn't really effect how well they stop in 1 60-0 stop.

Energy dissipation is everything in any stop. You are converting the kinetic energy of the forward moving car to thermal energy and sometimes a little sound energy, though the sound is really really minimal. The kinetic energy is dissipated by the heating of the
rotors and tires from friction which in turn dissipate their thermal energy to the air. Brake fade is a result of retaining too much heat in the system so that you can't effectively dissipate the kinetic energy of the car. A larger rotor gives more thermal capacity to the rotor system and also increases the braking torque that the tires experience which consequently causes the tires to produce greater friction and more heat, aka more energy dissipation. I will definately agree though that in a single 60-0 stop there will be little, difference between a vented and solid rotor so in those regards you are still right in that you don't really need the vented rears.

You are however right about the decrease in distance being due to the forward shift in bias. I'd forgotten/skipped over that line of your original post, sorry.

The bias valve holds the pressure at 50% front 50% rear until a given pressure in the pedal line is reached (like in a panic stop), at which point is shifts the bias toward the front. The wagon valve has a higher threshold before this happens. thats what stoptech says anyway.

You're right, I searched the legacy forum and found several confirming posts. I'm still not sure about the 50/50 but according to Josh's brake spreadsheet though the wagon prop valve still applies greater force to the rears at the split point than the sedan. Granted if the split point is just merely higher then I suppose it could still be 50/50, I'm not expert on these prop valves.


I might not have been clear earlier when I was saying that you will see an improvement with the wagon caliper, I meant if you put it on in addition to your upgraded front. This should move the bias back a little and reduce your stopping distance, no?

[evolutionmovement]

Interesting about the split point ... do any others out there drive a WRX front braked wagon? With mine the brakes are phenomenal only once the weight has shifted. Just stomping the brakes results in too much forward bias and subsequent lock up while the stock system felt more balanced under all conditions. However, under high speed stops, if the brakes are given a short time of lesser braking, the brakes can then be laid into and the car hauls down from speed with much greater authority than the optimized stock system and they don't fade. I was thinking this was down to weight shift (and it still is likely a factor), but maybe it is also down to the split point in front/rear bias.

This is all unmeasured seat-of the pants stuff (or seat belt in the chest), but feels correspondingly close by my estimate to these numbers in terms of increased distance overall with the WRX brakes over stock, but better fade resistance and increased brake torque over stock after initial weight transfer. I feel the WRX system would be better on track or a mountain road, but the stock system better in a panic stop from speed.

I also have no ABS, so this experience would likely vary.

Steve

[skid542]

That's interesting Steve. It makes perfect sense that you have to wait just a tad before really laying into the brakes. Do you know your 60-0 stopping distance? I'd also like to see a video if you have one. I'm going to try a video this weekend hopefully or the start of the next week. I also don't have ABS but have a 60-0 including reaction time. Anybody else want to throw in their feelings?

[evolutionmovement]

Sorry, no video equipment and the old brakes are long gone so I wouldn't be able to compare anyway. By my estimate, though, I always thought the stock brakes were good for a little over 120 feet from 60 and the new ones slightly more due to the requirement to ease into hard braking and, of course, the alternative of locking the front brakes wouldn't beat the older system at all. Left foot braking in turns seems unchanged over stock in terms of balance change and is better if anything (although I'll give that advantage to the tires).

I feel it's a worthwhile upgrade only for those who drive fast and wouldn't recommend it to normal people as the stock setup in good repair with decent tires is excellent for everyday conditions with occasional hard use.

I'd like to see what I could do when I pick out the next set of pads.

I wish I could have gotten some hard numbers to contribute.

Steve

[scottzg]

So i just tried the threshold braking thing on a street near me that has been laid backwards, with the gravel on top of the tar... average braking distance... 98 feet!

All it goes to show is that you can't really compare stopping distances that were taken with different conditions on different roads.

All my numbers in the original review were taken on the same road under the same conditions, i even warmed up the tires first.

The last thing is that because ive been doing all these tests, ive gotten much better at threshold braking. I can nail the same distances within 2-3 feet just about every time now, where when i started it would be maybe 10 feet of slop. If ya'll can't tell, im having fun with the g-tech, and encourage everyone to go get one.

[BAC5.2]

I am going to borrow my friends g-tech and measure my stopping distance on my new setup with 225/45/17 RE070's

I'd eventually like to drop into the 100 to 110 foot range.

[skid542]

That's a nice distance Scott.

How do these things measure stopping distance anyhow. Do they measure deceleration times or what?

[vrg3]

They measure acceleration with an accelerometer and integrate twice.

[scottzg]

That's a nice distance Scott.

How do these things measure stopping distance anyhow. Do they measure deceleration times or what?

Yeah, it's nice, but it illustrates that comparing one set of numbers to another is pretty worthless.

The device measures how long at what rate you were decellerating. It also tells me that i generate well over 1g under braking. Neato.

[scottzg]

A little update.

I found the limit on this brake set up too, after 30 minutes of normal twisties and then about 8 70-30mph slows down a fairly steep (5%?) grade hill. The pads don't cook all at once, it took about 3 corners to be certain that they were overheated. This is something that makes me very happy; the old organics would give up the ghost all at once- kinda scary.

They were smoking when i pulled over to let them cool, which was a new thing, and they remained squishy for the rest of my drive home. They seem to have recovered though.

[scottzg]

One more update.

I haven't cooked my stuff since for some reason, but the bias shift has become noticable on tight turns that i can trail brake. With medium pedal pressure and turning, the front starts to let go before it should, and it just doesn't slow in a turn like it used to. It can be corrected by loosening my line a bit, but it's kind of annoying. I'm looking for some wagon rear calipers.

I doubt that 95% of people would notice this, but since i've been unemployed and out of school, i've been going driving every day and have gotten pretty comfortable with pushing the brakes.

[skid542]

I told you you'd end up looking for some wagon calipers .