naschmitz

Had an Ice Mode event in my C6 Base Coupe on Thursday at VIR on the North course heading into T14 (start of Roller Coaster). This was the first time it happened while I was running the Aim Solo DL which logs individual wheel RPMs and that tells the following story.

Front: Hoosier 295/30/18 37 psi 25.3” diameter
Rear: Hoosier 315/30/18 35 psi 25.6” diameter

Hoosier specs say rears are 1% larger circumference.

Now the Aim Solo DL Data:

• Under acceleration, rear tires turn 2.8% faster than fronts (1298 vs. 1262 rpm for example)
• Coasting during an upshift, rear tires turn 0.5% slower than fronts (1285 vs. 1291 rpm)
• Under heavy braking, rear tires turn 1.6% slower than fronts (1427 vs. 1451 rpm)

During the transition from 100% to 0% throttle, there is a 0.1s driveline lag until engine braking kicks in and RPMs go up after briefly descending and then begin to fall again (5569 to 5352 to 5492 rpms for example). During that time the rear tires go from turning faster than the fronts to slower than the fronts.

Ice Mode Initiation

• Steady state braking, rear wheels turning 2.0% slower than fronts (1246 vs. 1271 rpm)
• Both fronts and right rear wheels go into ABS simultaneously initiating Ice Mode
• Ice Mode shifts brake bias drastically rearward and changes ABS program, dragging rear wheels turning them 31% slower than the fronts (700 vs. 1023 rpm). With reduced braking due to the skid, the car is traveling faster than expected.
• Driver can't turn in at this speed and prepares for lawn mowing mode.
• Left front tire leaves the track and goes into ABS even with Ice Mode brake bias. This event ends Ice Mode. All four wheels experience ABS events because we are driving on grass.

Aim Data:

froggy47

Thanks for the post.

My experience with Ice Mode is on a 2004 C5z, no doubt GM has "improved" this function since then.

On 04 c5z once you encountered Ice Mode you stayed in it a long time (until you hit something or slowed down with almost no braking function) if you stayed on the brake.

The only way out was 100% release of brakes & then reapply. That would reengage normal abs function.

I assume there was no time or no attempt to do that.

I guess the system improvement is that it comes out of ice mode on it's own when enough parameters are satisified?

Is that the "recommended" technique by racers with c6 system? Stay on the brakes?

That would be good to know, what you recommend.

Solofast

As counterintutitive as it seems, the best thing to do is let off the brakes and then get back into them. Staying in the pedal limits the braking and you are heading for the weeds. Even though you think it's going to be worse, you'll slow down a lot faster in the normal mode.

naschmitz

I would agree with that on an autocross or track where there is extra pavement.

In this case, if you look at the Aim data there is less than 0.75 sec from onset of Ice Mode to Lawn Mowing. Initial braking force was normal for the first 0.25 sec, then rear wheel lockup in Ice Mode. I doubt I could recognize the problem and get all the way off the brakes and then back on and stop quicker before I run out of pavement.

froggy47

So we are all on the same page, runoff area allowing, it's still best (c5, c6 maybe c7) to quickly get off the brake & get back on (hitting the reset parameter).



I wonder how the German cars do it.

Solofast

My experience is limited to C4's and C5's. Even in the grass, getting out of the pedal will give you a lot more braking than what you get in ice mode. Just my experience, but ice mode sucks. I'm of the opinion that it is really dangerous, and it shouldn't be invoked unless it actually is below freezing, something the folks programming the car could easily have done. Just because you have a wheel stopping at a high rate, doesn't mean you are on ice, it just means you lost traction momentarily and the system should reset itself rather than stay locked in.

If someone was to get in a big time crash due to ice mode there would be big time legal problems. I'm sure the postmortem would be that the car was operating correctly, but now with recording systems, the car will tell what really happened. Up to now the lawyers wouldn't have a chance to prove it, but if it comes up in court there would be problems.

Since GM is actively promoting tracking the car if someone were to end up in a tire wall due to ice mode I would think GM might end up buying them new car.

JMHO

trackboss

Back when raced I ran cars with no abs. Ran as hard as anyone ever and not once did I ever have any serious incident. I even ran in the rain. Third time I ever took my c5 out to the track I encountered "ice mode" and damn near lost my whole car.
I don't care what anyone says. I can race better with properly setup brakes than with factory abs systems. I can understand ultra high dollar abs systems being a benefit, but otherwise anyone that thinks they need abs is really not an experienced racer.
Here's a rear view from a faster car back in, I think '03 or '04 at california speedway. Coming off the oval (5th gear full throttle) into a 90* left hand super short corner that immediately turns right(T3-T4). This is about as hard on the brakes as one can get. FF to about :36 seconds and you will see me (black car)dive inside and gain multiple positions without losing control any way. There is almost no room for error in that corner with other cars around.

froggy47

Nice pass(es).

BEZ06

The lawyers would probably say that the problem was owner/operator induced.

The OE tire size diameters are 25.7" front and 26.9" rear.

The C6 ABS is not very happy when the tire sizes aren't pretty close to the OE ratio. Many owners have larger than stock rear tires, and that just causes a "Drag Control Active" event when during deceleration when you lift off the throttle the large rear tires aren't rotating as fast as the ABS programming thinks they should, it interprets that as the rears slipping, and it tells the PCM to add a little power to stop the skid. That doesn't do anything much but not give you full engine braking.

Butt.....mess with the OE ratio by running a much smaller diameter in the rear and you run into the problem naschmitz experienced.

I suspect the lawyers would say that when you run odd size tires that confuse the ABS, you're on your own.

The easiest way to keep the problem from happening is to pull the ABS fuse, but as mentioned in another recent thread, many forum members feel the ABS is a very important system.

Bob

JerryTX

Great job capturing this, thank you! I had a GM engineer recently tell me it would be easy to reverse engineer the ebcm, especially when compared to reverse engineering the ECU. Imagine how many of us would be glad to pay for a box that

1. Defeated ice mode 100% of the time
2. Was configurable for tire stagger, and
3. Provided a dial with selectable brake bias so we could tweak it per track, and actually USE more rear brake!

fatbillybob

I would buy this. But I would settle for just learning to avoid ice mode. The op setup is quite normal tire size wise. In fact all use t1 racers run 315's square. We never get into ice mode except sometimes we do and don't know why. The op probably entered this event more than once. Why did ice mode come on now. What was the situation that caused it? Not tire sizes we race them for years like this and have miles of data showing it works. Why icemode and why now?

JerryTX

Classic perfect scenario: braking hard over a rise.

froggy47

Plus the blacker asphalt looks like much less grip than the track (like say hitting ice).

Probably worked 100% like GM designed it to work. Not that it's of any use on track.

naschmitz

I would agree with this because I've had that happen in the T1 braking zone where the track crests at the 4 brake marker. In this case, the data doesn't support it. The decimal numbers in the video inside the track map is the vertical slope. The car is still climbing when Ice Mode initiates.

It looks more like the pavement change causes it.

fatbillybob

So this is your first time on this course?

naschmitz

Second time on the North Course. Many times on the Full Course. This turn is where the North course rejoins the Full course.

trackboss

I'd buy that box too. So who's gonna make it?

JerryTX

Exactly. When you hit the rise, the tires went into ABS. I'll bet you'd even find the slope was falling slightly right to left hence why the right wheel maintained some extra wheel speed. Did you log Lat G? It would show how much the car was unloading at the time of the event.

You can see my event at around 55 sec into the vid posted in this thread:

http://forums.corvetteforum.com/1582200192-post107.html

I will say that I have not had a reoccurence of ice mode since finding a melted rear ABS sensor wire that was touching the exhaust dump. Did you have any DIC messages or the ABS light on after the event? Did you pull codes? It will be hard to find a reader that cost less than $300 that will read the GM Specific codes. I think I was finally able to use HP Tuners to see the RR ABS error and that got me what I needed. Bottom line a bad wire can cause you to lose ABS altogether but yours clearly worked as the pressure went up despite not releasing the pedal so I doubt you had the error light.

naschmitz

G-forces are logged and shown in the video. The car is not unloading because it is still climbing and has zero steering input. The G-force graph shows dead straight braking until Ice Mode noses the car left.

ABS light is not on -- Ice Mode is a design "feature" -- not a malfunction.

John B

Ice mode sucks for its intended purpose also. I can't believe there haven't been many law suits over it. Must be due to people not realizing what happened as they buzzed into oncoming traffic. Here in Northern Mn it will get you killed in snow/slush/ ice. In all the GM vehicles