Ice mode solution?

laze1

In a 350Z, even with VGC in the off position, EBD is still working, so if you are in a drifting condition...it will apply one or more brakes in an attempt to straighten out the car...however not sure about the 370Z.

Both my 350Zs had this issue (2004 & 2006), and was completely resolved by removing the Yaw sensor that drives all the VDC related computing.

Note: I have not tracked my 370Z, so I can't verify that condition exists in that model. We need some 370Z TT or W2W racers to speak up here.

cossie1600

you need to layoff the fast and furious bible or do some racing 101 classes. braking in the middle of a turn is like eating beans before an anal scene

laze1

?????

Note sure this is going anywhere, dropping out of this thread

Philipp

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ChrisSlicks

I read Mike's blog post and wanted to comment a little bit on the ice-mode as I had it on track for the first time this weekend (normally I just get it at auto-x). I was out in an open track session after the time trials, was running on the RE-11 street tires and had been out for 10 laps or so, the brakes were good and hot but not overheating. The suspension was dialed in fairly soft as the time trial ran under damp conditions and I had forgot to change the shock settings before going out.

Heading into the braking zone to turn 11 at NHMS is a gentle left with light to moderate acceleration followed by a pretty much straight braking zone but can be a little bit bumpy. As soon as I jumped on the brakes the pedal went hard and I only had about 50% braking force. I just rode it out as there was plenty of extra track and run off and I did manage to slow down enough in a straight line to eventually turn into the corner.

As it only happened the one time it is hard to say definitively what the issue is, but based on that experience and that of Travis's I'm thinking it is related to having a low traction situation in the rear and the ABS system's poor modulation. As the weight was transferring forward under braking the rear went light and the ABS system was unable to release enough pressure to the rear to unlock the wheel so instead it appears to release pressure to the entire braking system. It is also possible that I momentarily locked a front wheel by jumping onto the brakes too suddenly before the weight had transferred.

At this point the only factor I think heat plays in this is that the brake pads are performing better under the moderate heat and have a higher coefficient of friction. Similarly an aggressive bite pad can trigger the same condition with a much lower heat especially on a less grippy tire.

The other heat condition that seems to trigger an ice-mode like feeling is pad fade. If you get the pads outside of there operating range then their friction falls away, sometimes dramatically (especially the stock pads) and the rear brake is forced to do more of the braking causing rear lock up and poor braking performance. But with the proper track pads this shouldn't be an issue.

I was using the AP Racing rotor paint and caliper temperature stickers, the paint all turned white indicating rotor temperatures in excess of 1130F and the calipers peaked at just a hair under 500 degrees. There was some significant pedal fade on the slow in lap but not under racing conditions. Was running AP Racing 600 fluid. Rear brakes rotors reached 1050F and calipers were only 360F.

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Brazilbro

I think Laze1 was implying that the car would brake its self without applying the brakes to try and pull the car out of a drift. I don't know but I can drift my Z from side to side and the computer doesnt try and stop me

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cossie1600

See #83.

No the car would only brake itself if you leave the VDC on or you light up the inner rear. (it would apply brakes to control that at least)

cossie1600

I didn't think as much into it as you did, but I did a track day and autox in the same week. At Lime Rock, I didn't get into ice mode as the XP8s have much less bite. On top of the better pad, I ran mostly in the rain and the pavement at the track is only two years old. Three days later I did an autox in a lot that is over 40 years ago, I was hitting ice mode on and off at the start and end of the run (70 second) with the same XP8. As soon as I switched to the stock pads, problem went away. While there might be other factors contributing to ice mode, I personally believe rough pavement is a big one for me.

ChrisSlicks

It's not the pavement itself but rather the friction co-efficient, obviously (or not) older pavement has a much smaller contact patch with the tire due to more of the binding media getting eaten away, therefor less friction. Basically once the pad to rotor friction far exceeds the tire to pavement friction then there is problems.

For what it is worth I had ice-mode with the stock brakes and stock pads and RE-11 tires during auto-x, but only once the brakes got hot and on longer 90 second courses after about the 4th consecutive run. I'm guess that the bite of the pad just kept increasing due to the increasing heat.

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cossie1600

Yes it certainly can be the decrease of friction level on the old pavement, but the uneven surface on some of the older lots or corners (turn 1 at VIR) can have a field day with the ice mode

ChrisSlicks

Yes, bumps and pavement transitions certainly seem to be an issue as well.

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fritz

Question:

On an empty road turn off the engine, pump the brakes gently several times until there's no servo and the pedal gets rock hard. (Yup, if you can't think how to do this professionally, without killing some-one, you'd better not try!)

Do you now have "ice-mode" and have to push madly for any effect?

If so then ABS action is probably "beating" the vac servo (which on a 370 is a bit different anyhow).

Cure? Maybe a big vac tank or a diesel vac pump (diesels have no manifold vac)

Just a thought, Fritz

Guard Dad

A very interesting thought too! A temporary vacuum tank setup could be installed to test your very interesting theory. Let's hope some of the racers on the forum give it a try and post the results.

The more I think about it you could really be onto something. It's worth doing just to make sure that it ISN'T a lack of vacuum assist.

ChrisSlicks

I don't believe the ABS system is active with the car turned off (I could be mistaken) so I'm not sure what this would prove.

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Guard Dad

He's only trying to simulate ice mode in a non-track environment.

The essence of the matter is his speculation that ice mode is not a software problem but a power brake assist problem. What he's saying is that heavy braking on rough surfaces requires such aggressive ABS action that the vacuum assist for the power brakes becomes depleted with a resultant loss of braking power. This would explain the reduced braking power and rock hard brake pedal because these are the same symptoms that occur when the vacuum assist is depleted or fails.

If he's right the fix could be as simple as adding a supplemental vacuum canister to increase the volume of the available vacuum assist to meet these high demand situations. His theory is very insightful and virtually DEMANDS investigation to see if it has merit. All I know is that if my track days were being compromised by Ice Mode I'd install a vacuum gauge to monitor the available vacuum in my power brakes and I'd be looking into adding a remote vacuum canister/tank.