village idiot

I doubt rotor temp affects braking much. Pad temp does, but a good track pad shouldn't vary its friction coefficient much in operating range. Heck, my outside tires and rotors are always hotter than my inside.

Everything is dynamic on the track.

froggy47

My 2 cents, ice mode on my c5z many times, I as others would be happy to settle for zero abs with zero ice mode. Tadge won't say but I will the FEDS won't allow.

NSFW

I was assuming rotor and pad temps would be pretty similar during braking. Is that wrong? How much do they diverge?

village idiot

No idea, but I'm guessing it's different because rotors cool off a lot faster. if nothing else, you'd be starting off a lot cooler of a rotor.

tommyc6z06

regardless of extrapolating, the fact is that rear rotors are smaller, have smaller pads, less pistons (area), lower pressure, less cooling and the manufacturer calculated using the same lining material.
So...my issue was/is, why the heck was it recommended to me to use a different compound in the rear? Not just by one supplier, but several.

As far as I'm concerned now, this is misinformation and reduces overall braking effectiveness. I will be using the same lining material all round in the future.

village idiot

I asked this question a long time ago, got a good answer, but I can't remember it entirely. I *think* the reasoning was that at the track you're braking harder, so you have more weight distribution to the front than the street AND your fronts get hotter. You need to more aggressive front pad to compensate for that. In effect, the bias your car comes with is for the street, or at least, not for the track.

tommyc6z06

village idiot

It's 4 channel, but you don't want ABS on one corner and the other 3 tires still haven't hit threshold. Not to mention, most of the time you shouldn't be in ABS.

NSFW

I think this is one of those things where the only way to know is to test. For street use and stock brakes, the same compound on all pads probably makes sense. For track use, where braking is much more aggressive, and the weight shifts to the front wheels, the fronts probably heat up much faster than the rears. If you upgrade your brakes, but not your rears, maybe it balances out again and maybe it doesn't. If you upgrade both ends, maybe it balances out, maybe it doesn't. If you add a rear wing... If you add an air dam up front... If you change from a square tire setup to staggered, or vice versa... and so on.

Not sure how much ABS should be a factor. Wouldn't you want your car's brake bias set up so that all four lock up as close to simultaneously as possible? If one end locks up first, you're not getting as much braking power from the other end as you could be.

pkincy

Times do change and things get more complex. Re: different pads front and rear. At FBody 98 in Memphis I spoke with one of Tadge's colleague's/predecessors. At the time he was Chief Engineer for Camaro not Corvette. I had a new at that time stock 98 1LE and was experiencing horrible wheel hop under hard braking particularly with race tires. He acknowledged the problem and said that to tune the ABS system for the street they had put in too much rear brake bias. He recommended a proportioning valve to take brake pressure out of the rears. At the time I was competing nationally in a class where that was a no go. So he said, use your race pads up front and stock pads in the rear and actually chamfer the rear pad so only a quarter sized spot on the center of the rear pad contacts the rotor. I took out my handy grinder and did that and voila! No more wheel hop. So we definitely are using the car in ways that it is not designed for on a track or even an autox course.

And why not pulll the ABS fuse? After the 98 season I built a race car (CamaroMustangChallenge) that was a near stock car but one rule was no ABS which was to keep us even with the older cars in the class that had no ABS. It only took flatspotting a couple of expensive race tires before we would learn to threshold brake right at the traction circle liimit. So kinda a human ABS. And it is amazingly easy to do. So if so called "ice mode" is bothering you try it without ABS and learn to threshold brake. I don't think I would run without ABS on the street however.

Apparently there is really not an "ice mode" if I read his response correctlly. Just for some reason the system is not cycling fast enough to give full hydraulic pressure for the second application of the brakes. At least that is the only time I have ever experienced it. One hard brake application followed by another hard application with little time between applications. And that 2nd application gives no brakes (i think, due to no hydraulic pressure). I have never run into that on a road course although I have experienced it repeatedly on the smaller tighter autox courses.

85nova

It probably goes without saying that Dave McLellan alludes to “ice mode” in his book Corvette from the Inside when he talks about Bosch’s anti-lock brake settings for the C4, which debuted ABS for GM.

Apparently, a GM development engineer experienced “ice mode” in a C4 at the Proving Ground precipitating Bosch’s reduction in the computer’s duration of delicate application from one to a half second. That had been in the development of the 1986 Vette [first generation mass production ABS] so I see NSFW’s rationalization for a privateer push to advance track ABS systems.

With autonomous vehicles on the horizon, it seems like processors would make it possible to have Corvettes fully pre-dialed for turnpike and track out of the box. However Chevrolet R&D likely has so many near-term demands, it may be hard to prioritize this effort based on customer impact per development dollar. Especially with all the tuners willing to take a crack at it.

I really appreciate Mr. Juechter’s response. I am also curious what Gary Pratt or Doug Fehan would say and what sort of “software, sensors, and actuators” help – or could help – the C7R with track braking.

LagunaSecaZ06

I have 2016 Z06-Z07-MPSC2 and the car worked flawlessly at Laguna Seca, Thunderhill and on the street. I converted to Girodiscs/ST43 and Michelin Pilot SS because I wore out front ceramic rotors after 8 track days(I was going through a set of Ceramic pads every track day). I was also going through MPSC2 every two track days, so I switched to MPSS(non-runflat) to reduce the tire expense. The Girodisc and Raybestos ST43 were having ice mode issues at Laguna Seca with MPSS. It was very problematic not having confidence slowing for turns or if I was going to make a corner. After talking to to Girodisc, I installed Raybestos ST31 front and back and no issues at Laguna Seca. I do ABS threshold braking(thats what I call it) I brake hard enough to engage the ABS and then back off so the ABS is not pulsing. With the ST43 I was only getting about 50% braking power (at Laguna Seca) and I could not engage the ABS pulsing. With the ST31, it works just as good as the stock carbon ceramic setup.

I used both the ST43 and ST31 on the street. The ST43 was much too noisy in slow driving(although quiet when not coming to a complete stop and quiet at the track). The ST31 is now noiseless after the track day on the street. The dust is pretty bad, so I have give the rims a good washing once week and the dust accumulates on the driveway after cleaning. So then I have to sweep and rinse off the driveway.

Overall, the situation is fixed.

Here is a gratuitous video my buddy put together of me(Silver Z06 #567) passing him. He was driving a 2009 Corvette Z51, 6speed and he runs Raybestos ST43 with Firehawk street tires with no issues. His rotor temperature is 700*+ in the pits after his session. My ST43 were under 400*(due to ice mode) and ST31 were about 500*+ in the pits.

fleming23

On the road course it is "fixed" but as soon as you do something like autocross you very likely will experience the conditions again, There are some race series where we have multiple segments we run with Road Course being only one of them and the resulting ICE mode is the most frustrating thing I've experienced.

pkincy

What is the time delay between brake applications to experience "ICE mode?" Does it happen if there are several 10s of seconds between hard brake applications, or only if there are seconds between hard brake applications or only if there are less than a second or 3 between hard applications?

village idiot

I think the real solution is to get pads that don't have a harsh initial bite.

LagunaSecaZ06

Agreed, the ST31 don't have the harsh initial bite of the ST43. I would bet that the stock pads would work ok on the track and just wear out fast. I tracked my 2013 ZL1 with the stock brembo pads and it braked fine. The pads wore out every two to three track days, but they were street pads. The ZL1 calipers did turn from black to bronze color due to heat and I never had a fade problem.

NSFW

I just watched a video with some Wilwood guys where they talk about using pad selection to adjust brake bias like it's a perfectly reasonable thing to do when the rules don't allow for tuning the bias with hydraulics. They do advise keeping the brakes at a consistent temperature range when doing so though, because the friction-vs-temperature curves can differ. Can't argue with the Pagid guy's preference for using hydraulics, but it's not the only tool in the box. The part about mixing pads is near the end, at about 9:20:

IAIA