Brake wear rate distribution (or why do I even have rear brakes)

I have been monitoring brake pad wear on my 2006 Miata and they currently have approximately 230 track miles at Gingerman Raceway and 1650 street miles which also included (3) autox events.

Brake pads all the way around are PowerStop Track Day Spec pads with new Centric basic rotors. They are not intended to be daily driven yet they do not squeal on the street for me but of course they dust pretty heavily. They grip well enough at street temperatures and have handled the higher heats that caused my prior Hawk HPS+ to fade significantly so overall I am happy with them for a budget pad.

One thing I did not expect to see is such a huge wear differential between the front and rear pads.

I measure and then convert to "percent of life remaining" based on original friction material thickness and remaining friction material thickness with the thought being that I would not head to a track day with less then 30%-40% of the pad remaining.

Currently the fronts have 58%-59% material remaining and the rears 93%-94% remaining with even wear on the  inside/outside pads and across the face of the pads.

At this rate I might go through 5-6 sets of front pads for a single set of rear pads. 

Is this common/uncommon for pads used on the track? I have had cars that wear at maybe a 2:1 or 3:1 front to rear pads but this is a new level of difference for me.

Track day use means heavier braking, which means more weight transfer, which means the front brakes are doing proportionally more work than they do on the street. If you're running stickier tires, even more so. 12% of your mileage on the track (well done!) is a pretty significant percentage.

It's also possible you're getting the pads hot enough to cause accelerated wear even if they're still stopping. I don't know the pad well enough to say. Note that the rate of wear will increase as the pad wears down and loses heat capacity, so 50% material thickness is not 50% life remaining. It's a good idea to monitor it.

Even with the active handling leaning on the rear brakes to direct traffic, my Volvo's rear pads still have plenty of life left, and I have not touched them in 104k miles of ownership.

Have replaced the front pads twice, which is a record for me.  Most of my cars have had manual transmissions, so I never had to change pads.  (Had appx. 240k or so on the RX-7's front pads until I changed them because the backing plates were worn...)

Most of the weight is up front to begin with, and then heavy braking transfers even more of it forward. And like keith said, the more overall braking you're doing, the more work the fronts are doing proportionally. Also most/all stock braking systems are designed with a touch of extra front bias for safety.

My cayman still wears the fronts more, but with the 10% rear weight shift versus a front engine car, it's a lot closer to even and does put noticeable wear on the rear brakes. 911s tend to have nearly the same size brakes front to rear because of the even more rear biased initial weight distribution. On the other hand, it's not unusual to see stock rear drum brakes work just fine on older fwd track cars. The rear brakes just aren't doing anything but keeping the rear in line.

In reply to dps214 :

FYI, the Miata is pretty darn close to 50:50 static weight distribution out of the box. 

File under "why I think rear disk brakes are BS"

They don't get used enough to burn off overnight rust.  Then the rotors look like this very soon, and you are replacing rotors and pads.

Pete. (l33t FS) said:

File under "why I think rear disk brakes are BS"

They don't get used enough to burn off overnight rust.  Then the rotors look like this very soon, and you are replacing rotors and pads.

That's a car specific problem.  Plenty of cars with rear discs don't have that problem.  Personally, I think drums are awful enough to work on that I absolutely refuse to own a car with them unless there's an easy disc conversion option.  

I typically run a lot of rear brake bias relative to other drivers and I still burn through the fronts faster..........even on my disc/drum Datsun.

All of our Korean cars use the rear discs quite well. Wife's car ran out of pads front and rear about the same time (around 95k miles). After a full season of use on the Porterfield R4S on the Rio the fronts and rears were worn about equally. The R4 I'm currently using are the same. Rears get hot enough to turn the rotors the same color as the fronts, but then again for a FWD crap box I am carrying more of my weight over the rears than some of my competitors. The ABS is really good on that car so YMMV, IANAL, BBQ, BLT, YOLO

Pete. (l33t FS) said:

File under "why I think rear disk brakes are BS"

They don't get used enough to burn off overnight rust.  Then the rotors look like this very soon, and you are replacing rotors and pads.

That looks more like a caliper froze because the e-brake was never used to me.

In reply to bobzilla :

It is a Forte, drum handbrake.  Pistons and slide pins move freely...

Pete. (l33t FS) said:

In reply to bobzilla :

It is a Forte, drum handbrake.  Pistons and slide pins move freely...

Interesting.  From the look of the rotors, the rear brakes are not applying very well.  Pete, are you sure that the rear calipers are even working?  Is brake line pressure getting to the rear of the car?

And the thread theft is done!

The front pads on the Lemons Civic lasted 2 events. The rear pads lasted 12 years.

Fronts were Porterfield R4E endurance pads. 

The rears were Autozone off the shelf.

Noddaz said:

Pete. (l33t FS) said:

In reply to bobzilla :

It is a Forte, drum handbrake.  Pistons and slide pins move freely...

Interesting.  From the look of the rotors, the rear brakes are not applying very well.  Pete, are you sure that the rear calipers are even working?  Is brake line pressure getting to the rear of the car?

 

And the thread theft is done!

 

You don't live in the rust belt, do you?

I'm not as familiar with the NCs, but on my 07 Rx-8, I had three front pad replacements vs. one rear @ 90k, and they weren't even completely gone.  That car saw a decent bit of autocross in its early days and a few track days, but 90% was straight up street miles.

On my 94 Miata, I'm probably at a 2:1 ratio on brake pads, but I have a bias adjustment so I use the rears a lot more, and that car is about 60% track miles (it's a dedicated track car that I drive to events in).   I get about a 40 hours (one season) out of the fronts, and two seasons out of the rear.

Noddaz said:

Pete. (l33t FS) said:

In reply to bobzilla :

It is a Forte, drum handbrake.  Pistons and slide pins move freely...

Interesting.  From the look of the rotors, the rear brakes are not applying very well.  Pete, are you sure that the rear calipers are even working?  Is brake line pressure getting to the rear of the car?

 

And the thread theft is done!

 

I still think this is a caliper issue and not a bias issue. I wore pads evenly on my SX. 

In reply to Streetwiseguy :

I'm in the rust belt and haven't ever had rear discs crap up like that.  The ones on the Jeep do enough work to stay as clean as the fronts.  The BMW ones get a little crappy when they corrode after rain, etc. but they do clean up (just not as fast or nicely as the fronts).  I will note that running more rotor-aggressive pads seems to help keep brakes happy in the winter in the rust belt, as they do a better job of scrubbing the junk off the rotor surfaces. 

The worst brake rust I've seen was on SWMBO's Prius where the brakes don't do a lot of work.  The OE front pads made it about 150k, at which point they got so rusty that the friction material started chunking off the backing plates. 

On my track cars, I've typically worn out three sets of fronts for every set of rears. On my C5 Z06, looks like the pads will last longer than the rotors (surface cracking of rotors), and yes, I drive it with the nannies turned off!

I appreciate all of the feedback and data points from various applications. 

I will chalk this up to acceptable for the application and just keep monitoring the fronts for replacement to avoid any issues while on track.

Thanks!

The OPs front to rear wear ratio seems unusually high.  I'm wondering if it's not due to using a track pad on the street.  I see closer to 1.5 to 1 front to rear wear ratio with Hawk Blues on Spec Miatas.

In reply to glyn ellis :

I used to run PFC97s and they were like that. I was replacing rotors twice as often as pads due to sheer erosion. The pads would always stop the car under all conditions, from a hurricane to a V8 Miata on track. But they would ask for rotors as sacrifice.

I used to get about a season of racing out of front pads and maybe a decade on the rears.

I once had an Aeroquip hose pinhole on the rear (still not sure how it did that) so I pulled the  line stuck a bleed nipple in the union to seal it off and ran a race with no rear brakes (I needed the race credit for season standings). I think I was less than a second a lap off my usual times, and I did note a sort of uneasiness about the car under hard braking and had to concentrate to keep it going in straight.

I also run high performance pads on the front of my street sports cars and stock or lower spec on the rear.

In reply to APEowner :

I have heard/read about excessive wear using track pads on the street, often associated with excessive rotor wear as the transfer layer isn't maintained at lower energy input. 

I measured my rotors and new nominal is .866" with mine currently at .861". Discard thickness is .787".

In this case with this car and these pads it appears that the set-up is rotor friendly but pad hostile which is a bit of a bummer as new rotors are 50% of the new pad cost. 

I will be tempted to try another pad when I replace these and see if I can get more life by paying more

Hey GRM!  Just for giggles maybe you could do a story on brake bias on popular stock vehicles and what to do to improve it if necessary!

Just a thought...

APEowner said:

The OPs front to rear wear ratio seems unusually high.  I'm wondering if it's not due to using a track pad on the street.  I see closer to 1.5 to 1 front to rear wear ratio with Hawk Blues on Spec Miatas.

 

I think the blues are just kind soft.. I liked the feel, but hated the dust and fast wear.  Blacks were better, but I'm on g-loc r8s and much happier with net stopping ability and life.. oh and dusting!