sothpaw2

Hi,

Prepping here for the next event & wondering about min. thickness for pads. At PCA event I was just at, for day 2, they threw out 4mm as the min they would accept (although obviously they couldn't see).

Now wear out is different for different pads--obviously you need enough to get you through without going backer-to-metal rotor. But in terms of heat and fluid punishment, what is too thin? I'm sure there is a practical rule of thumb, I just don't know what that rule is.

Thanks

davidfarmer

pads are good until you get to the metal, unless you have a compound know to chunk as the get low. However, you often get excess heat into the caliper as you get below about 1/3 of the pad.

I generally run the pad down to around 20-25% of it's initial thickness, although changing pads is so easy I've run them to the backing plates at events before.

John Shiels

You really don't want to hit metal it may be the wrong time it happens. I have had it happen few times. I have run down to 1/8" at the lowest point on the pad and it is still Ok except as Dave said heat transfer becomes a problem or even chunking of the pads. 20% is a good limit as Dave said.

Zenak

1.) How many laps you think you want to get out of the pad?
rotor on metal = no stop = death. If its a one day event track without much braking then you might get away with an 3/16" for the day. Remember rears dont abuse like fronts. You need way more in front than rear.

2.) Do you want to / can you swap your own pads at the track yourself?
I will often hit the track with a "easy days worth" of pad. At lunch or day end will do a fast swap so i can get the last little bit of $$ outa a pad.

3.) why does PCA do this?
Because HPDE attracts newbies that dont know SH-T about their car, let alone own tools. This is their way of avoiding a disaster and being liable for the injury or crash.

4.) what to do with low pads that you dont trust on a road course?
Simple Auto Cross. I save my old pads with an 1/8" or less for autocross. Sell them cheap to your autocross buddies! A great race pad can cost $400+ for four corners. And its hard to heat cycle a pad for autocross. Sell your used pads already heat cycled to the Cone bashers for like $50 - $75 for the 4 corners. You get some $$ towards new pads, they get killer pads to shave tenths that are way fine for their needs and will never risk their life and limb. A whole day at autocross will never take out a 1/8" pad. How many runs you get 4 - 6 on average for a total driving time of like 5 to 10 minutes? And autoX never has enough heat or speed to kill the pads the way RR does.

drivinhard

get all the good out of 'em. run 'em flat, then flip 'em over

sothpaw2

This is 25% of the thickness of the pad material, not counting the backing plate I assume. Sounds good. Thanks

I agree especially w/the fronts, pads are so easy to change--it doesn't make sense to throw them away long before they are done. I find the Wil H pad does not wear too fast.

ryan0

OEM... run em till the backing plate..

After market, it depends on how deep the piston sits in the bore of the caliper. I'm finding that with the SL6 narrow, you cant go much less than 1/2 pad or else the pistons start to move around and score up the bores.

plus... new pads always feel SO much better.

mousecatcher

I make sure I start a day with at least 50% of pad.

95jersey

I try to run them until they are within a couple mm of the backing plate and always carry spare pads in the truck for both front and back. That way no mater how far they wear, I don't have to worry about hanging up up early for a 2 day (or 1 day) event.

Worst case you could always use your street pads as long as you adjust your driving to compensate on the track.

0Louis @ LG Motorsports

There is a thermal isolator the last 1.5mm of any race worthy pad. Its not a pad compound, so it lacks the performance of the regular compound that you just got done using.

People often bring up heat as an issue as the pad wears- Yes, that is an issue, however, not for most on here. The issue is that the thermal barrier will not stop the car like the compound that was glued to it.

Throw them in the garbage with .125 left.

John Shiels

bearnest

Hey Sothpaw, did you ever find out if my c6 pads will fit your car??? I had the white 911
next to you at summit point.

Dan Wendling

ryan0 .. I might take your 50% pads if you are just going to throw them out, save the landfill !!

What pad type do you run?

ryan0

right now... wilwood H

Zenak

Me Me Me! I'll take 50% pads too!
i can swap out sets in no time! Hell to save money I will swap them between session to afford more seat time!

sothpaw2

Hi there! Yeah the base C6 and C6Z51 caliper is the same size as the C5 and the pads are the same. The different pad is the C6Z06 or C6 ZR1. So I suspect the pads you have will fit nearly all Corvettes from 1997-2009 (before we started having Grandsports etc) making it probably the most common pad size out there for a Corvette.

Let me know what you have in front pads--how much min. thickness & type. I think I'd try XP10 but maybe try XP12 --I know the XP12 wears very fast though. And my Wilwoods are at over 50% so I still don't have to have 'em yet--had a bad alignment (contributed to the push) so have to get that fixed & front tires (alignment nuked them).

A-Z

The Carbotech package insert for AX and XP Series compounds states: "If the pads are wearing evenly, they can be used until worn within 5/32" (3.9mm) of the backing plate."

The rule of thumb used by my race shop: use until friction material is down to the thickness of the backing plate. This seems to be consistent with most of the recommendations.

Andy

kentz06

Another issue that happened to me for the second time yesterday is that the seals/dust shields on the pistons can get knocked out as the pistons have to reach out furthur as the pad thickness declines. I swap in race pads for track days and had installed a set with approximately .2" remaining since it was going to be a cold, short day with 3 students.

I am using Stoptech ST-60/ST-40 calipers and Hawk DTC-70 pads.

Front: HB122U.710 new pad thickness = .710"
Rear: HB141U.650 new pad thickness = .650"

I've been having great results with this combination of calipers/pads with fantastic stopping/modulation and respectable pad/rotor life. Front ducting with backing plate probably helps by keeping temps down. Seals/dust shields are the only issue.

If the new pad starts at .710" and you run it down to .16" that means the pistons end up being extended an extra .55" at the end of the pad life. That is a big percentage of the piston diameter and length. Even if you only use 50% of the pad the pistons are still extending out .355".

I have decided to try an experiment to mitigate some of this problem. I am going to build some shims to install behind the pads. If the shims were approximately .25" thick you could use half the available pad thickness then install the shim behind the pad and use the second half of the pad thickness. This would protect the caliper by keeping the pistons more engaged in their bore and would also reduce heat transfer.

I just happen to have some leftover 6Al-4V Titanium from a completed F-22 Raptor project that is just about the correct size.

Thermal conductivity of metals (BTU/(hr-ft-deg f):

Aluminum ~ 136
Mild steel ~ 31
Titanium ~ 13

If I'm going to build one set, guess I should build a few...

Does anyone know of a good source for the Stoptech caliper rebuild kit and some instructions???

Dean

Dirty Howie

John Shiels

Shims and spacers I have used for years to keep the pistons in the bores and they are cheap and work great as the pad wears and or to insulate.