when to change track pads

[kojo911]

I'm using Pagids orange pads the fronts are more than halfway gone. I think they start out at 17mm, they're down to 7mm. They look pretty skinny. I probably have 8 or so DEs on them. When do you change these out?

TIA

[KTL]

Typical rule of thumb is to change the pads when the friction material thickness is the same as the backing plate. The issue with letting the pads get really thin is you lose the insulation benefit as they wear down. Thicker pads better insulate the caliper pistons from heat transfer.

Another rule of thumb i've seen is DE tech forms that indicate they want to see 50% pad thickness to ensure you've got enough to last you the day. However, how do they know what your max thickness is, to know what 50% is?

I think the way to gauge yourself is knowing how much pad wear you experience per day/event. What I mean is, if you have basically stock brakes and get fairly rapid pad wear? You need to be more wary of thin-ish pads. However if you've got good cooling and some brake improvements, you can get away with thin pads for a longer period of time.

Good example is a buddy's '87 911 i've helped him set up the brakes. On stock brakes he never had a problem with boiling brake fluid, despite him being fast and very hard on the brakes. Basically he's a fantastic user of the brakes. But still he'd go thru a set of track pads in about 5 or 6 DE days.

We got him some cooling ducts up front and some slightly larger diameter, thicker front rotors with small Brembo calipers from a 944 Turbo. The additional cooling and thermal mass of the rotors, plus better overall brake balance front-to-rear, made a huge difference. His pad life has more than doubled, almost tripled.

[kojo911]

Thanks Kevin. Car has big brakes but I suspect I could use more rearward brake bias. The pads on the rear are pretty fresh. Saw a post on this site, the guy made his own "SCR" style dual master cylinder pedal assembly. I was going to take a swing at it but haven't gotten around to it. Of course I had all winter to freshen up the car, just getting to it now because there is a track day coming up. Typical, need a deadline to get anything done.

[fredmeister]

Kevin nailed it.

The rule of thumb I hear around town is 2mm and they are junk. I monitor them after every run just to be sure. Make it part of your routine to check this and it becomes habit. Sometimes its hard to nail down a wear rate because of things on track or other variables and its very bad if you get down to the backing plates during a session.

Best thing you can do is add as much cooling ot the rotors as you can. This is key to avoiding fade, wear, and putting heat into the hubs and bearings as well.

[moneymanager]

All this is good advice but I'd say you're ready for new pads.

[Cajundaddy]

Agree that backing plate thickness is a good rule for trashing your pads. If you like Pagid and want more rear bias, try orange on the front and black on the rear. This effectively moves bias to the rear without fussing with hydraulics and the possibility of getting it really wrong. Too much rear bias is pretty scary.

I always save the best of the old pads and keep em in my spares box. If I get to the end of an event and my pads are at zero going into timed runs, I always have enough backup spares to finish the day. Since my switch from Pagid to Raybestos ST-43, I have been getting 20 track days on the fronts and 50 days on the rears. Nice!

[kojo911]

Cajun & Moneymanager, Thanks for the input. Got new orange pads on the way, will keep the old ones in my track box.

Cajun do you have first hand experience running the blacks out back? Sounds like a cost effective first swipe. Also, I'm running an un-boosted set how do the Raybestos stack up to the pagids in terms of bite modulation etc.

[Cajundaddy]

Originally Posted by kojo911

Cajun & Moneymanager, Thanks for the input. Got new orange pads on the way, will keep the old ones in my track box.

Cajun do you have first hand experience running the blacks out back? Sounds like a cost effective first swipe. Also, I'm running an un-boosted set how do the Raybestos stack up to the pagids in terms of bite modulation etc.

I ran orange/black and yellow/black effectively a few years ago while running 255 square and it really helped to move the bias aft. Running the same pad all around and 255s on the front really tended to put the car on it's nose under heavy braking. It worked best orange/black for me but it really depends on your setup and tire choices. Most of the Boxster Spec race cars in TX run 255 square with blacks on the rear.

I have gone back to a staggered tire setup so tire grip differences moved brake bias aft. I now run ST-43 all around with good balance. They will stand up to a ton of heat with good bite and modulation at temp. Good for 20 track days on the front.

[Jnduda]

For what it's worth, I run the Black pads all around and it's a great improvement over the Orange/Black set up from before. Be careful with modifying the brake bias, locking the back tires is for drifting.

[juanbenae]

Originally Posted by fredmeister

Kevin nailed it.

that's what he does! have you not been following along, fred? at all?

[juanbenae]

save the current used mostly set in the spares box. you can use them if you are to busy to post next time, or give them to another driver that's less prepared than you & in need trackside... great to give old spares to a fellow driver to keep them lapping mid weekend... kevin does that kinda stuff all the time...

[Walt Fricke]

Every so often I have to thin out my boxes full of used pads. You can only give so many away, and the lure of new full pads is pretty strong. Most of mine measured out at half original thickness, and there is still a lot of life left in a good track or racing pad there. They look a lot thinner on the car than when you actually measure.

Wilwood had (or at least had) some interesting information on pad wear/thickness in a FAQ on its website. They said that, as long as you can keep the fluid from boiling (and, one supposes, the pad within its operating temperature range) with adequate brake cooling, the pads will be good down to the very last millimeter. Which isn't to say that is a positive (other than perhaps to the bank balance over time), but it won't affect braking performance.

One thing to consider, though, is that as the pad thins the piston extends farther out, which can affect wear some and expose areas otherwise shielded to the environment. If rotors are also thin, perhaps you could even push the piston out to where the seal wouldn't work. You can compensate for this, if using very thin pads, by using an old backing plate (with the pad knocked off) as a spacer. That will also help with heat transfer to the caliper (though I'm pretty sure steel transfers heat faster than does pad material). I made up a set of these, but have yet to run my current pads down far enough that I could get such a thick spacer in.

It is also comforting to know that you can stop better than you would think with steel backing plate on steel rotor! Doesn't help rotor longevity, and tends to be noisy (which can be the first clue, although usually this happens on only one pad first and the car pulls away from that side). Try that too long, though, and you may end up with the piston punching through the backing plate.

[VaSteve]

Originally Posted by Walt Fricke

It is also comforting to know that you can stop better than you would think with steel backing plate on steel rotor! Doesn't help rotor longevity, and tends to be noisy (which can be the first clue, although usually this happens on only one pad first and the car pulls away from that side). Try that too long, though, and you may end up with the piston punching through the backing plate.

I've seen that happen, and it was pretty cool. Except that it wrecked the seals on the piston. Driver had to go get another caliper to make it home.

[Matt Romanowski]

Originally Posted by Walt Fricke

Wilwood had (or at least had) some interesting information on pad wear/thickness in a FAQ on its website. They said that, as long as you can keep the fluid from boiling (and, one supposes, the pad within its operating temperature range) with adequate brake cooling, the pads will be good down to the very last millimeter. Which isn't to say that is a positive (other than perhaps to the bank balance over time), but it won't affect braking performance.

This isn't totally true. Pad materials oxidize and that changes their friction characteristics. Some compounds are more susceptible to this than others, but they all do it. One popular brand of pad is especially susceptible to this.

Also, the insulation affects of new to old pads are overstated, IMHO. I have data on brake fluid temps in the caliper from my car that show the fluid temp is only mildly affected by the thickness of the pads.

[Dave at Pelican Parts]

Interesting what the data can teach us! Have you tried any of the other gizmos that are supposed to insulate the caliper from the pad? (E.g., the titanium shields that were supposed to go between the pad and caliper?)

--DD

[Matt Romanowski]

Originally Posted by Dave at Pelican Parts

Interesting what the data can teach us! Have you tried any of the other gizmos that are supposed to insulate the caliper from the pad? (E.g., the titanium shields that were supposed to go between the pad and caliper?)

--DD

I haven't yet. I had planned on it, but it didn't work out to get it done this year and winter is upon us. Hopefully in 2016 I'm going to do some comparisons on things like the heat sheilds, different brake ducts, and more.

[OffCamber00]

Originally Posted by Dave at Pelican Parts

Interesting what the data can teach us! Have you tried any of the other gizmos that are supposed to insulate the caliper from the pad? (E.g., the titanium shields that were supposed to go between the pad and caliper?)

--DD

I tried these when i was running the stock calipers on my '88. I didn't seem to notice any improvement.

[Dave at Pelican Parts]

Did you log temps?

--DD

[OffCamber00]

Originally Posted by Dave at Pelican Parts

Did you log temps?

--DD

Honestly, no. My barometer for success was whether i still had fade at CMP which is notoriously hard on brakes. Probably unfair to ask the Ti Shields to fix that.

At any rate, problem is solved now.