badhabit_wb

Thanks. I've run stock, st-43's, and Dsuno's on the track. I'm running the 2500's on the street. I hope you get it figured out. I'm surprised with the Dsuno's and st-43's I didn't have an issue but they both bite so hard I was probably easing into it more than I would have with different pads.

lobsterroboto

I did almost exactly that last October for the NASA TX event at NOLA and once again that same weekend going straight off T1.

dar02081961

I thought about this and a few other ways a brake system can fail or become less efficient that might explain this.
A booster failure gets us to the hard pedal and possibly not enough pedal force to activate ABS.

But we always end up with 2 things that can't coexist with reduced brake efficiency or a brake failure as suggested.

These 2 things being.
1. The car starts a significant deceleration almost immediately (within tenths of a second after the driver releases the throttle).
2. The car reaches a deceleration in excess of 1.25g within 1 second of indicated brake application after the driver releases the throttle.

So even If we accept the pedal is like a brick (for whatever reason), we are still left with a car that is stopping at greater than 1.25g's shortly after indicated brake application by the driver.

This is where it gets frustrating. I am not one to tell a driver what they did or didn’t experience, but at the same time it's hard to claim a car decelerating at greater than 1.25g's is having brake failure.

fleming23

Dude....did you even read my comment or watch my video?

I'll break it down for you..

Both cars were doing 120+ after apex, both cars were doing 116-117 when brake pedal was applied. You can see both by the G-meter and the indicated speed that ICE mode was happening as initial brake application was of the same intensity and location on track for both laps.

ICE MODE (possibly more pedal travel indicated as I stand on the brake as hard as possible immediately after hard pedal is recognized.)

.

NO ICE MODE (I'm actually beginning to ease off the brake here after initial application)

grandsport2017

You've probably already seen this, but the existence of the problem is not in question and has been acknowledged by the engineers. See this post from the Ask Tadge forum:
https://www.corvetteforum.com/forums...post1597614359

badhabit_wb

After reading this I'm wondering what tires were on the cars that see ice mode as well. I've been running cup 2's except when it's raining and I run mpss's.

fleming23

Mine has been almost 100% on 18" BFG Rival S tires in 315/335 sizes. The Rival is on par with all but a sticker set of Cup2s in my opinion.

badhabit_wb

I wonder if there's enough difference in diameter, unsprung weight, traction, etc to be the cause, or at least a contributing factor, in the ice mode. I wonder if it would do the same thing with factory wheels and cup 2's.

fleming23

All certainly a possibility, all unknown. The diameter difference is pretty minimal, just a couple percent (2-3, or less IIRC) but haven't done the math recently.

Edit found my spreadsheet. The front tire is .3" shorter, the rear is .7" shorter. The stagger on the OEM is 3.01% and my tires are 1.54% (closer to being the same front & rear but still staggered), or 1.46% different.

badhabit_wb

It would be nice to find some commonality between the cars, or drivers, that experience it. I'd hate to have it happen on the front straight at VIR going into turn one when I hit the brakes at 150!

fleming23

Same at Road Atlanta 10a. What I think is somewhat comforting for these corners we mentioned is that this issue only seems to rear it's head after/during abrupt steering/braking/throttle transitions. This is why it is so much more common during autocross than road course, and in my experience why it only happens after a fast transition, regardless of speed.

badhabit_wb

Makes sense. Probably why I haven't seen it. I've been using pads with a high initial bite so I have to be careful not to hit them too hard. When I switch to my street pads it's almost like I have to push the pedal twice as hard to get anything to happen.

Mikec7z

If you go back through the whole thread, you will see this was already covered, and it happens on all the tires. It happens on tires that lock up easily... which can be cup tires when they are cold. Or it can be super sports at any temp. Stronger brake pads with great initial bite, escalate the likelihood it happens. The tires locking up is the key.

Elk

These were great meetups. I was at all of them, instructing and helping run the road course event. Great to see another alum.

Shaving the rear brake pads and chamfering the edges helped a great deal.

dar02081961

Here what the data shows.

In shot 1 you are at 121mph accelerating at WOT towards a turn that is less than 450 feet away.
Note the lap time is 123.10.
120 mph is 176 feet per second. You are less than 4 seconds from the turn in a WOT acceleration.




In shot 2 you are at 122mph,have released the throttle, and the car has traveled 50 feet or so since shot 1.
Note 1/10th of a second has passed the time now is 123.20



In shot 3 you at 112 mph, on the brakes at about 55% pedal, decelerating at about .6g, just shy of the 300 foot marker.
Note the clock at 123.80. In 6/10ths of a second since shot 2 you have scrubbed off 10 mph and traveled 100 feet.
So in 6/10ths of second and 100 feet the car has achieved a .6g deceleration with 55% pedal.




In shot 4 is where trouble begins. You are at 109 mph, AND you have less than 200 feet left to get down to maximum turn speed. But for whatever reason the brake pedal is now at 40%, and the car is only decelerating at about .4g's,You have already started your turn in towards the apex, with 30 degrees of steering angle cranked in.
Note the clock at 124.40.
So in 6/10ths of a second since shot 3 you only slowed 3 additional mph in the last 100 feet.




In shot 4.5 you are at 101 mph, 50% brake pedal, both decelerating and turning in excess of 1.25g's at the 100 foot marker.
Note the clock at 124.90.
So in 5/10ths of a second since shot 4 you have slowed an additional 8 mph and have gone from a .4g deceleration to more than a 1.25g deceleration.




In shot 5 you are at 85 mph 60% brake pedal, still both decelerating AND turning in excess of 1.25g's near the apex of the curve.
Note the clock at 125.80.
So it took 9/10ths of a second to cover the last 100 feet. In that 100 feet the car slowed from 101 mph to 85 mph.




So looking at this we can see the braking forces (decel g's) correspond to the percentage of pedal travel.
This is important because a braking problem will always show a disparity between the two.
In every instance above more pedal resulted in more braking force and the opposite is demonstrated as well.

Shot 4 is the only shot during this entire sequence where we have a chance to question the brake systems effectiveness.
Reason being this is the only time during the sequence where the car reduces its deceleration rate.
In other words the brakes are not being applied as hard in a situation where the driver should be standing on the brakes.

Here in shot 4 is our only chance to claim "Ice Mode".
Except there are few problems for us in this video.

We can't say the brake pedal "bricked" at 40% because we just had it at 55% and will have it a 55% again shortly.
We can't say the pedal went soft because the pedal isn’t traveling further, its actually traveling less and now it's at only 40% for whatever reason.

We could say the brakes became ineffective at this point resulting in less deceleration.
But the problem here is how do we explain the pedal moving from 55% back to 40% in what is supposed to be a maximum braking effort by the driver?
There is no mechanism or force that can move the brake pedal back 15% while the driver is depressing the brake. By design the hydraulic forces exerted by the drivers leg and master cylinder are to great.
And here again understanding brake systems are hydraulic systems, we know when they become less effective the pedal always travels further, not less.
But even if this did somehow happen, 5/10s of second from now we are decelerating in excess of 1.25g's, so brake fluid can't be boiling, pads can't be overheated, or anything along those lines of thought.

So this leaves us one last option. That is to say during certain situations like this the ABS does weird things and releases brake pressure for a second.
Problem here is, once again, pedal travel. If the ABS intervened and created "Ice Mode" pedal travel would still increase at least a little, albiet with some pedal pulsation.
Both would be noticed in the PDR indication.

And we would see the ABS light activate as well. In this video there is no indication of ABS intervention (no sound, data, flashing light, pulsing peddle or increased pedal travel).

dar02081961

Ok thank you.
I hadnt seen this.

Whats described here is ABS intervention...... "It seems like it activates when a wheel is suddenly or quickly locked, like it would on ice or other low friction surface. Unfortunately, a wheel locking quickly happens a lot on the track because, generally, one or more tires are unloaded at any given time, plus things like bumps and curbing unload them."

If that is what others have been trying to convey then I will stand down,..... as I have felt this many times.
However none of the videos in this thread showed an ABS intervention.

fleming23

lots of information here, more than I have the time, or patience, to digest at the moment. You clearly don’t want to believe and I’m not going to engage in beating a dead horse over it.

Regarding the change from 55-40%, or whatever statistics you used, that is the driver recognizing ice mode, knowing instinctively that I need to let off to get it to go away, but not enough time to allow full release. That is all I have time to respond to regarding your lengthy post.

Good luck with your attempt to disprove what so many have experienced first hand.

EDIT - ****, I hate when someone quotes a long *** post. Sorry.

Mad Dog 24

This is some scary **** and hope it NEVER happens to me. This may help you guys figure out the possible cause or what combo or year \ model may not have the issue. My 2015 Z07 has stock ccb's and always stock GM pads also stock size speed line rims with only Cup2's and no electronic mods has never had the problem. I'm a very late rt foot heavy braker but progressive and not a stabber, many times have felt the abs kick in. I read a lot here about the rear tires locking up before the fronts could be the culprit. Not sure if I agree. I run just under 3.0 degrees of rear camber at a very high speed 11 turn track WGI, low 2's. You would think that the limited tire patch at braking would run a higher chance of the rears locking up before the fronts. I feel my rears doing exactly that especially into turn one at 140 to 50. Hope this helps.

I must say I hope all track folks read this thread and remember it. The comments and videos here from those that had it happened and the possible save can be priceless!

badhabit_wb

I have noticed that every time I hit the brakes at the end of the front street at VIR. When I first step on the brakes the rear end always feels loose there. It doesn't happen anywhere else on that track so I'm not sure what causes it. If I remember correctly Bill Dearborn ran into ice mode in the same place. Not sure why I don't feel that happening anywhere else.

Mikec7z

im not sure the rear getting loose is ice mode. Ice mode would not give you any braking at all hardly, so no reason for the rear to get loose