Another Ice Mode Thread - LotusTalk - The Lotus Cars Community
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post #1 of 70 (permalink) Old 08-10-2014, 01:19 PM Thread Starter
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Another Ice Mode Thread

I went out for my first Elise track day in my new-to-me Elise yesterday (I've done probably ~80 track days in various other cars), and immediately got to re-live my old hell -- Ice Mode. From reading a bunch of threads, it seems like no one has really nailed this one down fully.

I ran an Elise in 08-09 in SS for autocross and regularly ran into the ice mode problem when I least wanted it, and could never find a really repeatable cause for it. The best I could figure out was that it seemed to be when you caused any ABS event while the car was even slightly turned, but sometimes that worked and sometimes it didn't for me.

Fast forward to my track day yesterday, and I had 2 really close calls due to ice mode, which is making me really want to track this down, if possible. Our local track has a high speed sweeper into a pretty big braking zone for a lower speed corner, so you're going from ~98mph down to ~50mph, usually starting to roll into your braking while still turned from the previous corner a bit. After one event where I came around there and ice moded straight off the track (fortunately this corner has quite a bit of runoff), I started playing around with it a bit more. It was actually fairly repeatable -- if the wheel was turned at all when you got into the brakes hard, ice mode kicked in and the brakes do nothing. I spent the rest of the day making sure I was only braking in incredibly straight lines, and only had the problem once more when I tried a slightly different line through a corner and ended up braking in a slight corner, which, of course, kicked it right in again.

I'm on stock calipers/discs/lines, upgraded fluid, and carbotech AX6 pads (hybrid autocross pad with decent but not really high temp sensitivity). My autocross car had the same exact setup. I've never tried another setup, so there may be something sensitive about these pads that cause the ABS system to hate it more than other setups.

The car is lowered, on penske doubles, and BWR FSB, with other misc mods, so it really shouldn't be picking up a wheel in a lightly-turned braking event, so it seems likely to be some other sort of thing that the ABS hates.

Any thoughts about how to improve the situation? Different caliper balance, adjustable brake bias to move more to rears help? Just different pad altogether?

David de Regt - Bellevue, WA
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post #2 of 70 (permalink) Old 08-10-2014, 01:41 PM
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I can repeat ice mode at will on local tracks, and it really does come down to the unloaded front wheel decelerating too fast, it doesn't have to be up in the air, all it takes is less traction. I've not found a way around it other than braking in a straighter line in the places where it kicks in, but that does mean compromising some corners.
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post #3 of 70 (permalink) Old 08-10-2014, 02:03 PM
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For track use, I hear people pulling the ABS fuse.
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post #4 of 70 (permalink) Old 08-10-2014, 05:42 PM
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For track use, I hear people pulling the ABS fuse.
Not the fuse, disconnect the right front wheel sensor. Easy, and it disables only the ABS. This is what I have been doing with decent results. However, yesterday I had the opportunity to ride with a VERY good Exige driver and he was amazing on the brakes using the ABS....so I will be addressing this another way.

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post #5 of 70 (permalink) Old 08-10-2014, 06:32 PM
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what marcinr said. I experience this if I come into a braking zone with some load on one side or the other, resolved by braking in a straighter line.

Its the abs thinking that if you apply more brake to the rear the back end will come out. To prevent that from happening it locks you out of applying more brake to the rear wheels. The only way "around it" is to disable abs.

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post #6 of 70 (permalink) Old 08-10-2014, 07:38 PM
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this happens to me from time to time on the road and it's the most annoying thing ever! (and I am NOT speeding when it happens)
sometimes it's absolutely uncalled for and I could swear that something is wrong with the abs sensors or the way that Lotus set up the system.
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post #7 of 70 (permalink) Old 08-10-2014, 07:56 PM Thread Starter
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Is there any chance that moving some of the bias rearward will help this? So that at least before you get to the threshold for ABS to kick in, you're getting more braking out of the rears?

David de Regt - Bellevue, WA
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post #8 of 70 (permalink) Old 08-11-2014, 05:37 AM
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Oh that reminds me of something I've heard, but not yet tried. I've heard of people running LESS grippy pads in the rear to reduce rear wheel 'slippage' and alleviate this problem some. When I bought pads (XP10 front/XP8 rear) I went with the wisdom of others.

I do have a a set of XP10 rears I've been meaning to try and see if this phenomenon is better or worse.

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post #9 of 70 (permalink) Old 08-11-2014, 05:44 AM
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I've fixed it. It's all about bias. Find the right pads/tire combo and enjoy life.

The less initial bite your front pad has, the better. I think that's why the stock Lotus pads are so linear and lacking bite.
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post #10 of 70 (permalink) Old 08-11-2014, 05:45 AM
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Quote:
Originally Posted by marcinr View Post
I can repeat ice mode at will on local tracks, and it really does come down to the unloaded front wheel decelerating too fast, it doesn't have to be up in the air, all it takes is less traction. I've not found a way around it other than braking in a straighter line in the places where it kicks in, but that does mean compromising some corners.
^^^ Marc nailed it.

Also, the Lotus ABS doesn't like spins resulting in the car traveling backwards .... be prepared to use the parking brake (assuming you still have one) if you want to stop sooner than later.

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post #11 of 70 (permalink) Old 08-11-2014, 05:48 AM
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There have been long discussions on this subject. What it comes down to is poor brake balance on our cars. There is not enough rear bias to keep the fronts from beginning to lock and causing the ABS to intervene. If the brake balance was "perfect", the ABS would only come in to play in extraordinary conditions. Search front calipers to the rear for another discussion.

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post #12 of 70 (permalink) Old 08-11-2014, 06:00 AM
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^^^ Marc nailed it.

Also, the Lotus ABS doesn't like spins resulting in the car traveling backwards .... be prepared to use the parking brake (assuming you still have one) if you want to stop sooner than later.
True. I don't know the exact cause of this but I think it's again representative of weight distribution and brake bias. There's no reason the brakes would work any different if you are rolling backwards (assuming engine vacuum is maintained) than if you were rolling forward.
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post #13 of 70 (permalink) Old 08-11-2014, 06:33 AM
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Would buying a "big brake kit" with new/different calipers prevent ice mode, or are the new calipers going to be compromised by the same ABS system ?
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post #14 of 70 (permalink) Old 08-11-2014, 06:41 AM
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Would buying a "big brake kit" with new/different calipers prevent ice mode, or are the new calipers going to be compromised by the same ABS system ?
It totally depends on the bias of the kit when installed. It could help or hurt depending on the sum of the parts.
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post #15 of 70 (permalink) Old 08-11-2014, 06:42 AM
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Originally Posted by Mr Coughy View Post
Would buying a "big brake kit" with new/different calipers prevent ice mode, or are the new calipers going to be compromised by the same ABS system ?

As the guys above said, less bite will make it happen less easily. BBK = more bite due to better leverage if you run a pad with the same bite. Now, BBK in the rear only may help shift the brake bias rearward and that might help, but more braking on the front is not going to help prevent ice node


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post #16 of 70 (permalink) Old 08-11-2014, 11:49 AM
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Originally Posted by jds62f View Post
Oh that reminds me of something I've heard, but not yet tried. I've heard of people running LESS grippy pads in the rear to reduce rear wheel 'slippage' and alleviate this problem some. When I bought pads (XP10 front/XP8 rear) I went with the wisdom of others.

I do have a a set of XP10 rears I've been meaning to try and see if this phenomenon is better or worse.
I do this, it helps.

Ice mode happens less using XP12F/XP10R than it does using XP12 all around.
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post #17 of 70 (permalink) Old 08-11-2014, 12:01 PM
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Larger front brakes or "less grippy" rear pads will compound the problem. The base issue is that there is not enough rear brake. The evidence is overwhelming...if the car is going in to an ABS event because a front is starting to lock; there is far too much front brake bias. "Ice mode" is simply the ABS intervening as it would on any other vehicle equipped with ABS. It is far more annoying with the Elise as a result of a light front end with heavily front biased brakes.

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post #18 of 70 (permalink) Old 08-11-2014, 12:26 PM
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Originally Posted by marcinr View Post
I do this, it helps.

Ice mode happens less using XP12F/XP10R than it does using XP12 all around.
Jeff, going from XP10/8 to 12/10 resolved ice mode in 3d at BFR and as I think about it I don't think I've experienced it since making the pad compound change.

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post #19 of 70 (permalink) Old 08-11-2014, 01:07 PM
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Larger front brakes or "less grippy" rear pads will compound the problem. The base issue is that there is not enough rear brake. The evidence is overwhelming...if the car is going in to an ABS event because a front is starting to lock; there is far too much front brake bias. "Ice mode" is simply the ABS intervening as it would on any other vehicle equipped with ABS. It is far more annoying with the Elise as a result of a light front end with heavily front biased brakes.
This makes sense to me...but, I am a bit slow. Why are there so many people that run a more aggressive pad on the front? For example, the Sector111 "hot set up" is Carbotech XP12 (front) and XP10 (rear). If you have ice mode issues, this would make it worse, right?.... and the opposite set up might help?

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post #20 of 70 (permalink) Old 08-11-2014, 01:19 PM
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Originally Posted by codingparadox View Post

The car is lowered, on penske doubles, and BWR FSB, with other misc mods, so it really shouldn't be picking up a wheel in a lightly-turned braking event, so it seems likely to be some other sort of thing that the ABS hates.
How are your Penske's adjusted? How much rebound damping? Too much rebound damping can cause the tire to not follow the surface of the road, and can cause a tire to lock up early under braking. The ABS doesn't like this and could lock out the rear brake circuit.

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The symptoms being described are a result of the Electronic Brake Distribution (EBD) system operating. This system is also referred to as Dynamic Rear Proportioning (DRP) and is, as the name implies an electronic system which, through the ABS control valve block restricts the line pressure to the rear brakes automatically to a pre-programmed algorithm. You can consider it as an electronically controlled proportioning valve which measures parameters like the rate of deceleration and rate of pedal application and uses this data to anticipate a rear wheel lock-up and then reduces the braking effort at the rear wheels as necessary. If the ABS system is left to do this, it can only react to a wheel as it starts to lock and therefore the car can already start to spin before the ABS can start to work. In extreme circumstances, if the driver brakes very suddenly the EBD system can lock off the pressure to the rear wheels completely; what pressure was at the rear brakes as the EBD system engaged remains there and the rear brakes are still working as a result, but further increases in pedal effort will not increase the braking at the rear of the car because the pressure to the rear brakes cannot increase. When this happens the brake pedal goes hard, as it is now pushing against the front callipers and a closed valve only, instead of against the front and rear callipers. The rear callipers are single piston and therefore quite flexible, so they are a major factor in making the brake pedal feel 'soft'. When the valve closes, the brake pedal pressure no longer flexes the rear callipers, hence the increase in pedal hardness. The front brakes are still working just as well as before the valve closed and will give more braking if the pedal effort is increased, while with the rear brakes working as hard as they can the braking is NOT affected. The problem is the driver feels like braking is reduced (even though it is not) because of the change in pedal feel. If the driver continues to push hard on the pedal, the car will continue to slow as fast as it possibly can in the circumstances. If he increases the pedal effort the front braking effort will increase and the rear effort will remain where it was. If he was to back off the pedal for a fraction of a second, the valve will reopen and the rear brakes will operate as normal again, with the pedal feel going back to normal.

In the case of releasing and re-engaging the pedal the car should not be able to slow any faster than it was with the system engaged unless either 1: the driver triggered the system in the first place by stamping on the pedal too fast or 2: the system triggered because a rear wheel was unloaded when the brakes were applied and would have locked up but is now fully loaded once again and able to sustain a greater braking torque. If the rate of deceleration does improve when the pedal is reapplied then it is telling the driver that he is over braking either in terms of the ultimate ability of the brakes (cause 1 above) or the track condition (cause 2 above) and needs to adjust his driving style to suit. If the system were not fitted or disabled and he continued to drive that way he would be in danger of spinning when applying the brakes.

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