First track weekend in ACR Sebring

[Snorman]

Over two weeks was able to get enough miles, two oil changes, alignment, extreme aero installed and clear bra to make the event at Sebring this weekend. It was great to be out in my own car rather than in a "race car" for the weekend.
Ran 7 sessions over the the two days plus about 15 minutes of "happy hour" on Saturday. Had only planned on a few laps of happy hour, but ran up on a ZR1 on slicks and decided to definitively solve the question of who was faster that day. So around 250 miles of hot on-track time. Saturday was four full sessions with the exception of the first, which had two black flags as a result of breaks, so probably 18-20 minutes hot track. Sunday was three sessions, two full and the third cut short at ~20 minutes after the low-brake pad warning light lit.
Notes:

• "Track" alignment, ~-2.5* camber, 6.0* caster, 0 toe; rear -1.6* camber
• Wing at position 1
• All fender and hood vents removed
• Did not pit out with less than 27 psi, and today, pitted in after 4-5 laps to bleed down from mid-upper 30's to 33 psi each session

I'm very happy with tire wear at this point and think I could get another day out of these, especially at a track like Daytona-Rolex, COTA or VIR. That being said, Saturday was "get-acquainted day", so might get a little more wear.
The goal of this weekend was to really get a grip on tire and other consumable wear. LF outer pad is shot and suspect that there is a bit of air in the RF caliper contributing to a bit of squirrel and two incidents of fade into T7...I opted for the run off during one. Next time out will be on fresh pads and SRF. But am skeptical of any more than two days on pads at Sebring.
Lap times were in the :19's today even in very light traffic. No video, as I was having too much fun to worry about putting a GoPro on the car. Hoping to get back out in December, but have an out-of-town friend in for the weekend, so likely will have to wait until January.
Car went on the trailer as it came off, just with a lot of tire snot and dirt so a good ending.
S.

[NT-ACR]

Interesting about the seemingly uneven pad wear.

[Snakebit10]

Nice read. Results of ACR vs ZR1 on slicks???

[Snorman]

Interesting about the seemingly uneven pad wear.

Agreed, pics below.
S.

[Snorman]

Nice read. Results of ACR vs ZR1 on slicks???

Car was fast on the straights and would slightly pull me but didn't stand a chance anywhere else. Followed him for half a lap with no point then went around and left him very convincingly.
The ACR is really a beast on-track and so much fun.
S.

[Snakebit10]

Nice. I figured it would have been close in the straights but no chance for the Z in the turns.

[DADS ACR]

Very nice driving and hope to follow you around Sebring soon.
Hope I can stay with the ZR1 on the straights?

[allans]

Snorman, Tires look very good but pad wear is scary. Are the pics the same front pad shot from top and bottom? Thanks, Allan

[Snorman]

No...it's LF and RF pads. LF pad appears to have worn much more aggressively than RF pad. And that's only a pic from the top of the caliper.
S.

[Werks]

Keep an eye on the pads try as you will note that it's not unusual to see quite a bit of pad taper so taking your LF pad in the picture it looks like you have about 4mm of pad left. Due to taper you may very well be on the backing plate on the other side so watch that. I generally make it a habit to pull my front pads after each track day and inspect them for wear, it only takes a few minutes to do so and with rotors costing what they do it's an added measure of safety. Also as far as pad wear and how far to run them down to you are going to want to replace your pads when the friction material remaining is roughly equal to the thickness of the backing plate that it is attached to (so about 6-7mm). Once they have worn to that point you will start to see golden colored streaks on your rotors. Those streaks come from brass pins which are attached to the back plate and go partially through the friction material. Those are there as a secondary bonding method to ensure that the friction material stays attached to the iron backing plate if the traditional adhesive bonding agents fail (due to the elevated temperatures that these CCM rotors see). One of the I guess you would call them drawbacks of CCM rotors is that they generate a tremendous amount of heat but they also dissipate heat much faster that traditional iron rotors. That is part of the reason that CCM pad volume is so large, the pads absorb and then dissipate tremendous amounts of heat and act like a heat sink pulling heat out of the rotor. As the pads wear and become thinner, their ability to dissipate heat decreases and hence operating temperature of the remaining friction material and rotor increases which in turn again increases pad wear and also rotor wear (oxidation) rates. So again I'd suggest that you try to make it a habit to replace pads when the remaining friction material thickness is roughly equal to the backing plate.

It's pretty interesting the amount of heat that these CCM rotors generate, some of you may be more familiar with traditional iron rotor braking systems and pads. Taking Hawk DTC-70 pads which according to their factory specs have an operating temperature range of 400-1600F (and most would consider a pretty serious track pad) I can tell you that within one lap on them with CCM rotors I was able to generate so much heat that I exceeded the operating range of the DTC-70 pads. When applying brakes so much heat was generated that the bonding agent used to hold the friction material mixture together failed literally turning the friction material into a cloud of dust.

[Snakebit10]

Hope I can stay with the ZR1 on the straights?

Ok Ill bite. No way you will keep up unless you have H/C mods and full bolt-ons.

[Snorman]

Keep an eye on the pads try as you will note that it's not unusual to see quite a bit of pad taper so taking your LF pad in the picture it looks like you have about 4mm of pad left. Due to taper you may very well be on the backing plate on the other side so watch that. I generally make it a habit to pull my front pads after each track day and inspect them for wear, it only takes a few minutes to do so and with rotors costing what they do it's an added measure of safety. Also as far as pad wear and how far to run them down to you are going to want to replace your pads when the friction material remaining is roughly equal to the thickness of the backing plate that it is attached to (so about 6-7mm). Once they have worn to that point you will start to see golden colored streaks on your rotors. Those streaks come from brass pins which are attached to the back plate and go partially through the friction material. Those are there as a secondary bonding method to ensure that the friction material stays attached to the iron backing plate if the traditional adhesive bonding agents fail (due to the elevated temperatures that these CCM rotors see). One of the I guess you would call them drawbacks of CCM rotors is that they generate a tremendous amount of heat but they also dissipate heat much faster that traditional iron rotors. That is part of the reason that CCM pad volume is so large, the pads absorb and then dissipate tremendous amounts of heat and act like a heat sink pulling heat out of the rotor. As the pads wear and become thinner, their ability to dissipate heat decreases and hence operating temperature of the remaining friction material and rotor increases which in turn again increases pad wear and also rotor wear (oxidation) rates. So again I'd suggest that you try to make it a habit to replace pads when the remaining friction material thickness is roughly equal to the backing plate.

It's pretty interesting the amount of heat that these CCM rotors generate, some of you may be more familiar with traditional iron rotor braking systems and pads. Taking Hawk DTC-70 pads which according to their factory specs have an operating temperature range of 400-1600F (and most would consider a pretty serious track pad) I can tell you that within one lap on them with CCM rotors I was able to generate so much heat that I exceeded the operating range of the DTC-70 pads. When applying brakes so much heat was generated that the bonding agent used to hold the friction material mixture together failed literally turning the friction material into a cloud of dust.

Thanks for the info and absolutely agree. I'm sure there is a bit of taper from the bottom so really won't be doing anything with the car until fresh front pads are on it.

Would you venture a guess as to why the LF pad wore so much more aggressively than the RF? I'm not a huge trail-braker, so don't think that would be a cause.
S.

[Werks]

In regards to the difference in pad wear I've noticed on my car that I track (C6Z) that I tend to see more wear on the front passenger side outer pad than on the the drivers side pads. Looking at the track that I run on I also noticed that it has more left turns than rights especially most high speed turns are left making the passenger side the outer side when cornering. So I think that it has something to do with either the g force when cornering pushing the rotor over against the outer pad on that side then rubbing on it or that when trail braking into corners the outer tires cover more distance hence wear the pads down more. I run with all nannies off on my car so I know it not traction control or anything like that kicking in but honestly it's pure speculation on my part as to why. As I mentioned though I inspect my pads after everyt track day and when doing so I grab some calipers, measure them and then rotate pads from side to side and then put the thickest one on the outer side of the caliper. That tends to even out pad wear so you do not end up with 3x good pads and 1x that it shot. For the rest you are going to find that brake pads are going to be one of your single highest consumable costs when tracking one of these cars with CCM (possibly rivaling tire costs). So save your used pads that have when you change them and just stack them up somewhere in the garage. As an example I have a stack of about 20 sets and periodically I go through it and match up sets with enough pad material on them for a track day or two which I then toss into my pit box and take with me as back up's. If you have a day where you are at the track and wear out your pads you can install these to make it through the day instead of having to install new ones and then try to find a place to do the burnishing process to outgass the new pads before you head out on track.

[Snorman]

I've tracked many times at Sebring, and have noticed negligible difference between LF and RF pad wear, so this is somewhat surprising but definitely something I'll watch when I'm back there in Dec or Jan. The big braking zones at Sebring are right handers as well, but I don't think a small amount of trail braking would cause such a disparity in pad wear. I do like the idea of rotating pads side to side if this will be regular with this car at this track.
S.

[Boba Fett]

You and I have def bumped heads over on CF, but I'll be big and say its all in the past. Congrats on the new car. Wish you the best of luck with it sincerely.

[Snorman]

You and I have def bumped heads over on CF, but I'll be big and say its all in the past. Congrats on the new car. Wish you the best of luck with it sincerely.

I appreciate that and likewise. Thanks for the welcome.
S.

[Gary Javo]

Great info. Are you running nannys full off?

[Snorman]

Great info. Are you running nannys full off?

Gary,
No...I ran it in Sport mode. Honestly, I slid the car around a good bit and didn't really notice much, if any, intervention. I had the car crossed up coming out of T7 a few times and it didn't feel like it laid down or pulled power at all. I was sliding around in T12 and T14 as well. In the C7 Z06, it would have definitely been pulling power and I couldn't drive that car (the way I drive) on track in anything less than one of the PTM modes. I like a little movement out of the rear and GM just kills the party once that starts unless you're in one of the Track PTM settings. But the Viper seemed very unintrusive.
S.

[VENOM V]

Glad you had a successful maiden voyage Sean! I have tapered pad wear as well, as I did on my GTS before.

Werks, good idea to rotate pads. I may try that.

[Boba Fett]

Lots of good info in here. Not surprised.

[Snorman]

Glad you had a successful maiden voyage Sean! I have tapered pad wear as well, as I did on my GTS before.

Werks, good idea to rotate pads. I may try that.

I looked more closely at the LF outer pad today. It's actually tapered from top to bottom, which is the opposite of what I'd expect. I figured it would taper from the leading edge (bottom of caliper). Strange indeed.
S.

[Racingbrake]

Rotating the brake pads (IB/OB, L/R) can only alleviate the uneven wear on "Leading' and "Trailing" due to unbalanced piston size/hydro pressure.

Top to bottom tapering is attributed to the flex of caliper (~75%) and upright (~25%) and how the pistons are positioned to the caliper body - As an example (G3-G5) if you replace stock pad (D968) with TA pad (D1001), you will see more wear on the top than bottom. Because D1001 is a taller pad @60mm (than D968 @51mm) while the caliper is designed for stock pad so the pistons will strike above the center of brake pads.

Here is a good thread in GTR forum detailing the loss of efficiency due to this kind of retrofit installation - Same as for GTR caliper (being stock pad is 65mm) installing a ZR1 pad @85mm)
http://www.gtrheritage.com/topic/429...ew/#entry68600

[Gary Javo]

That's what I've experienced as well. I don't see that there is anything to gain by "manning up" and turning everything off if it isn't stepping in when I leave it on. I've tried sport and track modes and haven't had it dampen the mood in either.