Ice mode solution?

wstar

Well, yesterday I finally had a hard ice mode condition on the track. It was a pretty scary experience. Now that I know for sure that this was ice mode and exactly what ice mode feels like, I know I've hit it before a little, too, just not as critically.

Luckily, this track I'm running at always has easy run-off on the braking zones (extra pavement, or at least grass). The setup was a long straight with a straight brake zone to scrub a little speed (~115 -> ~80), then maintenance throttle for a gradual sweeper to the left, then straighten up and a hard, short straight braking zone down to ~35-40-ish for a hard right. It was in that second braking zone that I hit it. I had been gradually raising my speed coming into there on each lap, and backing up my braking start. Then I nailed everything really great one lap going into there a bit faster than before, and the brakes just iced up. Hard firm pedal, ABS pulsing like crazy, and little to no braking force.

I wasn't really ready or expecting it, so I didn't even try to re-apply or modulate. I blew past my intended turn-in spot still going too fast for the turn, so I just held straight past it and then turned right a little for a bit of an angled slide, and eventually the brakes semi-fixed themselves and killed my speed just in time to bring the car to a stop at the brink of the pavement (and then I rolled it off the edge of the track to get out of the way and find a good time to re-enter).

It was the 3rd of 4 sessions, and I was able to avoid it on the 4th run by taking that spot a little "easier" and less aggressively. Going back out today on the same equipment, same track, so I came here to read back through all of this. Having done so, I think the trigger was that my initial pedal stab was a lot sharper than I normally do. Usually I'm pretty good about rolling into either pedal instead of stabbing them, but in this particular case I knew I was set up straight and perfect and had a lot of speed to scrub in a short distance, so I stabbed pretty hard.

I'm on half-decent street tires (Conti DW) and XP8 all around, stock calipers, RBF600 fluid, braided lines, and RA's 2-pc slotted rotors (which seem like they have a better-than-stock cooling vane setup), but no ducting for the fronts.

So for my sessions today, I think my focus for preventing a repeat will be (1) Don't initially stab too hard, and (2) if I feel it happening, try to re-apply / modulate repeatedly to kill it, and (3) Try to engine brake a little later (I normally downshift pretty much at the moment I'm getting on the brakes, when applicable).

In the longer term, I'm going to need to fix this up a little better though. I'm figuring bias is one of the key issues, but I don't think on these street tires it would be wise to go XP10 front, right? So that probably leaves me with downgrading the rear pads from XP8 to... I don't know. Something that can take the heat, but doesn't lock up as easy as XP8 rears do. Or do you think XP10+XP8 might fix it and not be too grabby for the tires?

That or try disabling ABS. I'm willing to learn to live without it, I hate it when it does engage. The simplistic "pull the ABS fuse in the center console" thing also kills your brake lights though, right? Is there a better way to disable it that I could put a dash switch on?

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travisjb

Glad you experienced it safely... today would be a good opp'n to make it happen intentionally in a safe spot and then try to recover... might want to tell the session organizer you are doing this as a heads up

If any of the wheel speed sensors stop working, ABS is disabled... one could wire a switch to any of those sensors... I don't recall if that dash light comes on, however... also, the car requires a restart to get ABS going again - likely will not be able to toggle it back on as a hot switch

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2009 370Z #104
*For Sale*

ChrisSlicks

Aggressive engine braking was one of the triggers for me, as even with the throttle blip it can cause the rear wheels to lock up when trying to brake with maximum potential (as the ABS tries to maximize rear braking potential). I downshift a lot later now so as to not send the RPM's too high.

Brake balance is critical. I can get the ice-mode a little when cold if I'm running different pad compounds front and rear that come up to temperature at different rates and have different sweet spots for their torque curve. When hot it is usually later in the session when the front pads get overheated and the ABS system has too much rear bias dialed in causing the rear to lock up especially if you stab the brake.

With the right pad setup and more calculated application of the brake pedal I can avoid it 99% of the time. Some brake ducting would help a lot as well I think.

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cossie1600

I have donr the xp10 and stock pads setup, you will dtill get ice mode

clintfocus

so the trick is to not have the rear bias get to high?

ChrisSlicks

Aggressive bit pads with street tires is a tough combination as well. It is very easy to over apply the brakes too quickly before the weight has transferred forwards, especially in the wet.


It is not a solution but it does help.

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Hotchkis ARB | Stillen CAI | Art Pipes | Berk CBE | Stillen AP Racing Brakes | AE Performance Oil Cooler | BC Racing ER Coilovers | Doran Control Arms

travisjb

very true! particularly with stiff springs up front and aggressive front pads - this car has forward weight bias and will bite hard... I found that by playing with tire pressures and dialing in the front dampers I was able to deal with it somewhat

tempting to run very soft brake compounds front and rear to see if the car behaves better... how much ice mode have we seen on completely stock brakes? there was that media incident... others?

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2009 370Z #104
*For Sale*

SPOHN

Could you please explain this more? It's obvious to me our cars have forward weight bias. So how does having stiffer springs up front effect weight transfer towards the front? Never really thought about this before so I don't really know. Seems it would be the opposite. But I also know how that goes.

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ChrisSlicks

In my experience it is worse with softer springs as there is more compression and a longer time period during which the weight transfer is occurring. I can reproduce this somewhat if I run the dampers near full soft as I do sometimes in the wet. With the stiffer setup there is less dynamic weight transfer and the time period during which the transfer occurs is shorter which means you can get on the brakes harder and sooner.

This is one of the reasons I like the lower torque compounds, however it can be tough finding a low torque compound that can handle the heat. Last year I ran an endurance racing compound, the (CL Brakes) RC6E which is only 0.5 on the friction scale but can take a ton of heat and is very consistent. It's probably a little harder on the rotors, but for me after a season they are done anyway from heat fatigue. I think the RC6 compound is very similar but more rotor friendly (and wears twice as fast). Next season I will compare them with the slightly more aggressive RC8 compound (about 0.62) and see if I have more difficultly staying out of ice mode. The comparable information I got about Carbotech is XP8 = 0.55, XP10 = 0.60, XP12 = 0.65.

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Hotchkis ARB | Stillen CAI | Art Pipes | Berk CBE | Stillen AP Racing Brakes | AE Performance Oil Cooler | BC Racing ER Coilovers | Doran Control Arms

SPOHN

This is how I would think of it also.

Stiffer springs up front along with stiffer damping would only allow slower resistance of weight transfer.

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travisjb

I'm running 18K springs up front and so load transition to front tires happens fast... would agree that soft springs also present a problem, as they can result in nose dive, which can shift the cg forward. My current thinking is that 16K/10K is just about right for this car.

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2009 370Z #104
*For Sale*

SPOHN

Good lord. I'm running 13K up front and I thought I was doing something. I know a lot of people love how planted my car is compaired to the rest.

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travisjb

18K is a little too twitchy!

16K is about right I think

I found 12K soft for track use, but it may be fine if you have high quality dampers and are running on tracks that favor a more compliant setup

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2009 370Z #104
*For Sale*

SPOHN

I have Stance true type coilovers. I know I like them. But I know they could be better. In the begining I didn't know the route I was heading and just settled. Only because I've ridden in a 370 with JRZ's. Mostly will be running at Road Atlanta.

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SPOHN

I have Stance true type coilovers. I know I like them. Only because I've ridden in a 370 with JRZ's. But I know they could be better. In the begining I didn't know the route I was heading and just settled. Mostly will be running at Road Atlanta.

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