Review: Carbotech AX6 front brake pads

flatlander937

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'11 Mazda2 Sport
Well I've taken way longer than I originally planned before writing a review, but I've put about 5k miles on my Carbotech AX6 pads, with 44 auto-x runs(15 of which were from codrivers).

I'll add just to note that I also installed DDMWorks stainless braided brake lines at the same time as these. Also they went on with brand new Centric Premium rotors.

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So I installed them and my initial impression on the first couple stops leaving my street are "hmmm feel pretty good."

When I came toward the stop sign leaving the neighborhood, I gently tapped the brakes and WHOOOOAAAA!! The car just instantly stopped. It was pretty close to feeling like a light switch. So I adjusted my braking/driving habits accordingly. I've got to be honest that while they were acting like this, I was thinking to myself "man I hope these weren't a $160 mistake."

I was getting into the ABS just coming to stop lights. It took physical restraint to NOT bring the car to a complete stop early. Once they get a bit of heat in them they are the equivalent of throwing an anchor out the window... engaging ABS along the way. Not exactly good.

I drove the car for 4 more days, so about 400 miles were put on them, I got used to the pedal, but was still hard to modulate without looking like an idiot.

One day sitting in traffic looking at my car's reflection on the car behind me through the rearview mirror, I noticed that the brake lights were not coming on until about 1/2in of travel or so(I'd estimate the pads started to bite about 3/8in of travel or so), and I didn't want to start actually slowing down BEFORE the lights were coming on, so I decided to adjust the brake switch up one click. I did this by pressing the brake pedal down, and putting a -thin- screwdriver between the brake switch and the pedal, then let the pedal up and allowed it to "self adjust" while the screwdriver was taking up a bit more room.

I tested the lights out, they come on a bit sooner now... awesome.

Take it on a test drive. Woah! Brake pedal feels much more mellowed out. You can modulate it exceptionally easily now. Hard stopping is still just like before, stops you in a freaking hurry. If not now even better. It felt like the brake bias was shifted rearwards some under most conditions.

It felt like the stock brakes under about 70% pedal effort, but push harder and it's like the stock pads turned up to 12. It's exactly what I was looking for!



So why did this happen?

Electronic brake force distribution. We don't have a mechanical proportioning valve. EBD works by starting out with 100%(or very close to it) rear brake bias with the front pressure limited to some lesser percent.

As you start slowing down, the HCU(hydraulic control unit as Mazda calls it, or ABS module) monitors the wheel speed sensors, various other sensors(assuming the g sensors built into the SRS module) and detects the rate of deceleration. Once it gets to a certain threshold, the front brake force starts ramping up/getting added more and more bias the harder it slows down. There is also a point at which the rear brake force stops increasing and pressure is held constant.

This is what I learned based on reading a Ford Fiesta factory service manual. Mazda does not publish anything really useful, but this is a pretty basic concept among many manufacturers. It can also incorporate yaw rate and steering angle sensors, which is likely since we have DSC.


Now why would the brake light switch have that much effect on it?

Especially since it's nothing more than a simple on/off switch(not like a GM brake pedal pressure sensor where it's variable depending on pressure applied)?

To be honest, I can't tell you the exact reason, but doing an A-B-A test tonight, I confirmed that is what caused the change.

Since I pressed the brake switch self adjustment in one extra click to get the lights to engage sooner, I taped a penny to the pedal bracket where the brake switch touches to simulate about where it was previously adjusted(make brake lights come on a bit later). After this it went back to being super touchy sensitive on initial bite. Took the penny away, back to normal feeling brakes.





If I had to wager a guess... it's one of the following reasons:

-The EBD internal black magic doesn't start moving brake bias around until it sees that the brake pedal is pressed(via the brake switch)... so since my front pads are so aggressive so early on in pedal travel, the front was starting to bite before the HCU even knows the brakes are being pressed.

-The pads were biting RIGHT before the brake switch was pressed, so when I started pressing the pedal it WAS doing it's rear-bias thing like it's supposed to, with just a bit of front bite, then right at the brake light switch point the bite of the front pads are slowing the car down just fast
enough that it allows more pressure at the front(so biased more forward), and due to the nature of the pads they bite harder, more bias, bite harder
yet, etc etc.



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I do NOT recommend doing this unless you have a spare brake light switch ready to go on, or are prepared to let the car sit for a few days if you mess up the switch. They are one time use, if you push it too far in with the pedal then it's technically ruined.

I think this may be something worth playing with, but am not sure if benefits are to be had with stock pads or not. I'm taming some relatively aggressive pads so this may well be unique to my situation. It's definitely worth experimenting with, but know that you should have a good switch ready to go.
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Now back to my impression of the pads:

I did the bedding in process, when they get hot they squeal. It's hard to describe, but it's not the same obnoxious shrill squeal when someone has the pad squeal indicator rubbing the rotor(or anything near as obnoxious as Hawk HP+ on a Camaro), but it will certainly let itself be known.

When you get them even hotter, they start changing in tone, sometimes it's a squeal similar to holding a cat by it's sides and rubbing it claws out against a chalkboard(mostly light braking), and sometimes it sounds like straight up metal on metal grinding(harder braking).90% of the time it's just a light almost whistle-like sound for just normal driving.

I have been doing 85 to 100 miles daily for a while now. I don't generally hear a peep from them when it's below about 60F, and they get louder from there. Mostly highway driving you won't hear a whole lot except when you slow down some under light pedal pressure.

I have had an occasion here and there where I'll get a "squeak squeak squeak" just driving down the road, not even touching the brakes. It'll change in tone with left and right turns or go away when you tap the brakes. I've heard others with this happen as well. It's always been at lower speeds like 25-35mph. It's done it like 3 times for less than 20 seconds each time over the course of nearly 5000 miles to get an idea of how rare this happens(in my experience). EDIT: After about 6500+ mi and multiple autocrosses, they now do this much more often, see my update post below.

Now for autocross... they are freaking AWESOME. They have about the same amount of initial bite as the stock pads(honestly could be a bit more, or a bit less, it's too hard to truly tell), are super easy to modulate, and when you really need to stop, you give it more pressure and it stops like
you're throwing an anchor out the window in a very controlled way.

Jeff(user jasyatz) codrive my car at an event recently and this was probably one of his favorite attributes of my car. Here's a quote from him:

jasyatz said:
And holy crap the brakes are fantastic! Like plant your face on the steering wheel awesome.



They're pretty much exactly what I was looking for(after doing the brake switch adjustment) performance and driveability wise.


The only downside... they dust like you wouldn't believe. The dust comes off incredibly easily *IF* you get it off before it rains.

After 2 days(200mi of all highway driving and very minimal city driving) my wheels are completely caked in dust. The awesome thing is if you take just a garden hose to the wheels, the dust literally about 95% of it just flows right off. The not so awesome thing is when it rains, it flows somewhat off the wheel, but dries back on in splotches and looks like complete crap.



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When it does this over the course of 2 or 3 weeks multiple times and you have been lazy about cleaning the car/wheels, it requires scrubbing and doesn't come off quite as easily. There are some tiny speckled spots in the crevices of the wheels where it's pretty hard to remove. Still not as awful as HP+ dust FROM WHAT I'VE HEARD. I know they have a reputation of being corrosive to the wheel and being impossible to remove. FWIW I suspect the little speckles of crap that require more time to remove may be bits of the rotor and not the pad, though they are not brown/rust colored so that may not be it. Just speculation.


So in a nutshell I'd give them the following ratings, 1 being poor or bad, 10 being great or desirable, etc.


Initial bite/feel: 10

Full pressure stopping power: 9

Ease of modulation: 9

Noise(normal conditions): 3

Dust(amount): 2

Dust(ease of cleaning): 9 if it has not been rained on and de-dried... 3 if it's been rained on a couple times. You will NOT get them clean easily if so.



They cost right about $160 from www.soloperformance.com

The biggest question is would I buy them again?

Absolutely. They fit my needs, the dust doesn't bother me too much, nor does the noise. I may try their less aggressive 1521 "bobcat" compound the next time around though.

Oh yeah. One last cool thing about them is they throw sparks at night time

under HARD braking :)

 
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sparks from hard breaking is a nice touch lol

When I go out riding with my friends on our motorcycles we sometime also emit sparks from the pads from braking hard.

Everybody hates dust and noise, from the picture, if that is at 200 miles it looks about the same, maybe even better than the HP+. I know on my rx7, if I clean my wheels, drive to work and back home, the dust is just a little worst than that picture. Its gotten to a point where I dont even care and just leave it there on the rims.
 
Yeah, but FWIW that's all highway miles.


Anyways small update:

After last weekend's test and tune on Saturday(45 runs on the car) and then event on Sunday(another 8 between me and my co-driver)... the brakes squeal like a train once they get a bit warm. It's also been 85 deg out which I think is the bigger factor for noise while braking.

However the annoying thing is that they now squeak-squeak just while moving, not touching the brakes... a LOT more often now. I'm pretty tolerant of a lot of things, but the chirping while moving between 20 and 45mph is getting pretty old pretty fast.

I'm going to try and pull the pads off and lube them up some time this weekend. I don't care about the squealing while braking(though it does sound like a small train), but the chirping while just moving is pretty irritating.

On a side note it's pretty funny getting odd faces from people while coming up to a stop. (boom05)
 
Here's a video to gauge the amount of noise/tone you can expect from them daily driving. My daily drive is 95% highway. When I get stuck in a traffic jam(which is really often) you get some... interesting looks... from people. The last two short clips in this video are about what you hear when in bumper to bumper traffic on a warm-hot day.

 
Just change pads. Carbotech makes good pads for performance, but just like any other performance pad unless you get enough heat into them they will dust and make noise. It takes no time to swap pads since it is only one bolt per pad, and in the end it will probably be cheaper since you won't be eating through them just driving on them. On my civic I had AX6's, but I went through them in 4 months as a DD pad.

I run hawk performance ceramics on the street and it would be more than enough for an autocross pad on the 2.
 
Just change pads. Carbotech makes good pads for performance, but just like any other performance pad unless you get enough heat into them they will dust and make noise. It takes no time to swap pads since it is only one bolt per pad, and in the end it will probably be cheaper since you won't be eating through them just driving on them. On my civic I had AX6's, but I went through them in 4 months as a DD pad.

I run hawk performance ceramics on the street and it would be more than enough for an autocross pad on the 2.

I regreased them Sunday and they're pretty quiet again.

I don't have issues with them performance wise, they feel pretty awesome. The dust does suck though.

I'll probably stick with them a while and try the HPS 5.0 next... A lot of people have been impressed with them... Maybe I'll cease my irrational Hawk hatred if I like them :p

Fwiw they haven't worn much in the 6000-7000ish miles I've put on them so far. And 90+ auto-x runs. I didn't think to measure them when I regreased them, but still close to new. I'd estimate 1-2/32 of wear. They are THICK as hell brand new. As in compress pistons all the way, and barely slip the caliper over them. No room to add shims if you wanted to.
 
Have you had any issues with the rotors at all? Shortly after I put my centric premium rotors and stoptech pads on, I have what feels like pad deposits on the rotor, only they don't go away (though they do temporarily get slightly better) after a bed-in session. I wonder if they could actually be warped...I've never come across this before. And usually I get the basic centrics or autozone rotors.
 
Have you had any issues with the rotors at all? Shortly after I put my centric premium rotors and stoptech pads on, I have what feels like pad deposits on the rotor, only they don't go away (though they do temporarily get slightly better) after a bed-in session. I wonder if they could actually be warped...I've never come across this before. And usually I get the basic centrics or autozone rotors.

I've experienced nothing like that. The rotors don't seem to be worn much at all. The edge where the pad doesn't touch isn't a big enough difference to catch a fingernail on yet.


After talking with others the horrid dust is most likely resins from the pad burning off then when wet, bonding to the wheels.


If you have access to a dial indicator you can check for rotor warpage. Generally more than 0.002in or so is where you'll start to notice it audibly and start to feel it.

Use a brake micrometer to check thickness at various spots, Mazda standard IIRC is 0.006in max, but in my experience you'll feel it more around 0.003-0.004 or so.
 
Don't have a dial indicator or micrometer, only a cheap digital caliper. I'll just swap in new rotors if it gets any worse, cheaper ones.

Back on topic though, that is probably the most thorough brake pad review I've ever seen. I've always heard good things about carbotech, though I didn't much like the bobcats on my wrx years ago. I'll be trying the xp8 compound on my miata soon.
 
Well, after 12k I decided to take them off... one of the rotors are now below minimum specification at 0.817, the other at 0.857. Minimum safe is 0.830... they start out around 0.914" thickness for reference.

The driver side was worn more, primarily the outside pad. I found that my slide pins seized in place... the lower ones with the rubber piece on them, requiring pliers for extra leverage to remove the pins, the uppers were a bit stuck in place, but not badly.

I temporarily replaced them with some extra solid pins I had laying around from a previous side job... The temporary ones I installed are a bit shorter than stock... I have some new correct slide pins on the way.



FWIW I used the Permatex Ceramic brake grease. Supposedly good to 3000F... doesn't seem to be the case.



The lowest worn pad was basically 1.5mm until hitting the rivets:



All others right at or around 4.5-4.6mm:



You can see the lip on the rotor from wearing down:





So if you're going to try these pads... MAKE DAMN SURE you keep the pins lubed. The passenger side rotors still had a good 0.027in left to min specification, and pads had 4.5mm left. I'm kicking myself for not measuring them before for reference, but that's still a good amount of pad left(between 5 and 6/32). I suspect if I hadn't been negligent of lubing the slide pins they'd still be useful. I'll also be going nuts buying a bunch of different lubes to try and find something that doesn't burn up so quickly.


So what did I replace them with? Hawk HPS 5.0 and new rotors from Carquest(the Centric Premiums are on a 3 week backorder, and I needed brakes this coming weekend). Bonus is I can get the 5.0 pads for $50 through work. Can't beat that right?

I hate these pads so much. They don't have near the initial bite of the Carbotechs, they don't have anywhere near the stopping power from higher speeds, and somehow Hawk managed to make a pad that sucks AND engages ABS easily... they have terrible modulation... these are just my initial impressions from two days of driving on them. I have broken them in, and they are feeling a bit better than the first few times I drove on them, so I'm hoping they get better once they wear in a bit more. They are just OK in my opinion, probably an improvement over stock, but not by much. Once I have a few thousand miles on them I'll post another more in-depth review on these pads. Then I'll probably take them off and happily spend 3x as much for Carbotechs(well, now G-LOCs since Carbotech's engineers left to start their own company)... because they are amazing brake pads and ruined my idea of what is acceptable.

Edit: I'll add I no longer feel this way about the Hawk pads, they're a really good DD/auto-x pad, and I even used them for a track day at NCCAR. They are WAAAY different feeling than the Carbotechs and I think I just had to adapt to that, and also probably let them bed in fully before passing judgement. I will type up an in depth review on them whenever I get a chance.
 
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much. Once I have a few thousand miles on them I'll post another more in-depth review on these pads. Then I'll probably take them off and happily spend 3x as much for Carbotechs(well, now G-LOCs since Carbotech's engineers left to start their own company)... because they are amazing brake pads and ruined my idea of what is acceptable.
Funny how a little quality product can completely re-define your standards, huh?
 
You should try the stoptechs. They're not expensive, feel great, and modulate well. They worked perfect during my 20 minute track sessions last week with non-sticky neogens. I think they'd work well for autocross.
 
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