scutarius

Glad to finally hear someone else talk about it happening to a Lotud. Would you email me so we can talk more about it?

Nugget

I was out at Grandsport Speedway last Saturday and experienced this behavior in my '07 RS on several occasions, always when braking hard in a straight line with my tires way too hot.

I was running my street tires, not my Hoosiers (Bridgestone RE11s in the exact same size as the OEM/factory tires, so there was no weirdness with offsets or circumference differences). The RE11s heat up really fast and don't shed heat very well, and Grandsport Speedway is a tight track with little time for adequate cooling. You spend a lot of time slipping for rotation and hardly any time off the brakes, so everything gets hot quick and stays hot unless you back way off to let things cool down.

The biggest change to my car since the last time I was out was that I added camber plates so I could get to -2.7 degrees of camber up front. This was my first time out on track in street tires since I made the camber changes.

The street tires, especially once they got greasy, didn't have much grip, and with the camber up front I was only riding on the edges when braking in a straight line. I think the "ice mode" was kicking in because of the abject lack of grip.

Other times where I'm consistently able to induce ice mode is in periods of low grip due to elevation. Coming fast into turn 3 at TWS (clockwise) I've hit ice mode if brake at the crest of the hill at the intersection. Also if I brake too early coming down the hill after T4 at Harris Hill Road. Both times when the front suspension is unloaded and there's little grip up front.

I think the ice mode is a bad reaction by the ABS to unexpectedly poor grip in the front tires. It's certainly unnerving when it happens, and it's easy to envision an unavoidable problem if you hit it at the wrong moment.

I didn't take any heat measurements on my tires and I was on new pads/rotors up front. For now I'm just going to consider aggressive camber and street tires to be a poor combination.

cfjan

Is there a way to disable ABS all together when on track? (pull the fuse, etc.)

Terry L

I replaced the check valve on the Lotus and thought I had the problem licked. But I was wrong.I later talked to some engineers who told me that the brake booster should have retained plenty of vacuum for several hard brakes, even after a long run at WOT. So I never got to the bottom of it and sold the car for my GT3. Just so we're all on the same page, we are defining ice mode as a sudden high pedal, hard as a brick, and little or at least substantially reduced brake force - right? Pulsing or a soft pedal is something else.

Nugget

Yeah, Terry, that describes it well. Nothing at all like normal ABS pedal chatter or brake fade.

LehmanZ06

I would have Ice mode in my Z06 when I slammed the brake pedal.

When you suddenly go from zero to 100% braking hard.....well the system locks those wheels real fast, and figures you are on a slick surface and .....presto ICE MODE.

My advice squeeze the brakes instead of slamming them.

Try it.

TRAKCAR

I can't get on teamspeed; Will not load the last 4 days.
Has someone asked OP about:

Tires sizes, pads and rotors used?
Given the 12 hours of Sebring was just there and the ambient F I think the track could have been grippier then ever, maybe even slicks grippy on a Hoosier.
I've seen ABS failure (4 wheels locked up into the wall) and I've heard about ABS ICE mode on Slicks.
Never had it before, maybe we are running Toyo RA1, I guess similar grip to a MPSC.

Rob posted a few posts back that his problem went away when clearing the holes in the rotor. I've never understood why Porsche does not put slotted rotors on the CUP cars and GT3's. Maybe this has something to do with it?

Maybe the higher tems, slotted rotors and superstucky track/tires was a combo that made it happen.
Let's find out more details from OP on Teamspeed; I know if I go for brakes and get 25% into T17, I'm not coming out either...

equiraptor

Some of what Mach01 (the person who described the incident) said:
Green Pagid pads, PCCB rotors. He said the track was grippy. While Mach01 hasn't specifically stated he was using Hoosiers, others said the car was on Hoosiers and he did not correct them (he did correct people who said he was on 18" wheels - he was using 19").

In response to a comment about the Pagid Greens taking time to warm up, he said:Those aren't the complete comments from Mach01 or the thread, but it's a summary of critical bits of information. Mach01 did say the pads had enough material to "finish the day without being too low" (which isn't exactly a precise measure), but that part may already have been quoted.

TRAKCAR

Equiraptor; Thank you.
Hopefully I will be able to get on Teamspeed again one of these days to follow that thread.

turbo911cm

I will reiterate what cfjan said:
Can we pull the fuse on the ABS system when we are at the track? I know it is not an ideal fix, but a flat spot on a tire is a cheaper fix then a trip to the body shop.

Spiffyjiff

i "only" have an S model but since this is not posted in that forum...

i have experienced this phenomenon also, but to date only after long straights (at summit point), braking from 140+. it sounds like this problem is bigger than just cleaning the ABS sensor but every little bit helps right? so can someone please tell me where the sensor at the wheel is/how to get to it? i will add this to my pre-track prep list.

thanks.

85Gold

Watched a 05 997S with the ABS disabled, no other changes, go off @ Homestead turn 2 and all I saw was a cloud of dust and him turning onto Nascar 2. Good thing it wasn't a turn like 17 @ Sebring where there is a wall to hit.

He disabled his ABS to try and eliminate Ice Mode caused by running same size tires all four corners instead of a taller rear as needed on the 997's. This is a NASA TT car and he has elected to run the tires he is on to remain in TTA instead of running bigger taller rear tires.

Peter

Fritz Flynn

Peter,
Are you saying after disabling the ABS he still had the hard/ICE pedal problem with no brakes or he simply had another issue related to not having the ABS in place?

997gt3north

As Terry has stated, it is best to in my opinion, to very narrowly define "Ice Mode" in this matter so that all other ABS intervention that the car does experience is not part of this discussion.

After much research after my incident, I came to the following conclusion. The OE Porsche Street ABS module's computer program is flawed from a logic perspective. Somewhere, deep in the logic (the final "IF" statement) after all limits have been triggered (yaw, friction level, speed of pedal application, force of pedal application, wheel sensor speeds, etc. etc.) the final solution the car's ABS unit spits out is, "Don't lock up the wheels and give approx 20% braking pressure to the front wheels" - thats it, thats what it does - those are the facts.

In everyday driving, and up to about 98.7% of DE driving there is an extremely low chance of ever triggering this very specific computer outcome - the outcomes that can and do get triggered are various different ABS interventions that Terry referred to and that we all know of having driven any modern car with ABS.

For the most part, in fact maybe all part, it is pretty well known how to avoid this situation:

1) keep proper diameter tires on front and rear
2) squeeze the brake pedal - no initial even remotely hard stab please
3) be very careful about initial brake application if the rears are about to even slightly unload (this is extremely key especially when combined with #2)
4) as you begin to see Red Mist, understand that as you look for that last 0.5second, you may not be as aware about #2 and also your braking markers (especially if using A6, R6, slicks) will when chasing that last 1/10th in each corner likely change enough that you may not be 100% aware of the exact track conditions where the brakes are now engaging.

The 'Failed Logic' from my perspective is this, I would rather the ABS unit not: "Don't lock up the wheels and give approx 20% braking pressure to the front wheels" but "lock up the wheels and flat spot the tires". To me, my version makes more sense as if I'm hitting the brakes, I am clearly placing a very high emphasis on wanting to slow down. I find it incredible that somehow buried deep in the code is an outcome that chooses to place such high importance on the ability to steer that it is willing to release so much brake pressure that speed retardation is made a very secondary outcome when in fact we all know that speed doesn't kill but very rapid deceleration does (i.e. hitting a wall that I am now able to comfortably steer into because my brakes were effectively turned off.

This is why, in my opinion, transforming any modern Porsche street car into a race car is potentially very dangerous. That said, humans are very smart and we all can learn to drive around known issues.

I never knew this issue could arise at Mosport #3 - but it can. I would now never, ever take this specific corner how you are suppose to but would enter mid track to buy yourself time to recover if this mode is triggered.

TRAKCAR

Does ICE mode happen on both steel brakes and PCCB?
I myself have only seen it on PCCB, but that might mean nothing..

I think ICE mode deserves a similar thread like the coolant hose amd RMS registry thread.
Maybe it should note:
Who's had it? How often?
Steel VS PCCB
Track experience? (Ithink it is mostly with faster drivers at the limit)
What tires, exact dimensions and condition?
What pads and exact material thickness left?
What rotors and condition?