Ice mode solution?

Originally Posted by wstar

Hmm yeah the Corvette issue is obviously related. These posts in particular are interesting:

Corvette Forum - View Single Post - ICE MOde ! ... off track event is there a fix ?

Corvette Forum - View Single Post - ICE MOde ! ... off track event is there a fix ?

They seem to be focusing in the other direction (increase rear bite to lessen the problem), but that's probably just differences in the overall setup and use of the vette versus ours, and/or some minor revision to ice-mode programming in some shared ABS controller code.

I think the bottom line for both cars is roughly what that second link talks about though: if one or two wheels wheel decelerate/lock *much* faster than the others (and probably if all 4 decel/lock much faster than should be possible on a grippy surface), the car assumes it's on ice and limits overall braking force heavily. When you think about it, with all four wheels firmly planted to the pavement the wheels should be decelerating evenly. Their (the ABS programmers') logic almost makes sense, except they're not accounting for the possibility very uneven dynamic corner weight loading, and they're not accounting for the possibility of a bumpy but otherwise grippy surface (esp combined with harder suspension setup).

Stabbing exacerbates this, and it makes sense to me that higher rear bias (due to grabby rear pads, due to front fade, etc) would exacerbate it in many common scenarios, since the initial stab will unload weight from the rear wheels, allowing them to lock up quickly under reduced weight with a hard-biting pad. Having wheels unloaded due to bumpy pavement, suspension setup, and brake timing relative to all of that would exacerbate it as well.

And really, I'm not buying the idea that this is a good tradeoff on the street, either. It might be a good tradeoff for Nissan and Bosch's wallets from a lawyer perspective when running some statistics on which scenario results in more total lawsuit damages, but even a consumer street driver shouldn't have to take the tradeoff of "ABS might totally screw me if the pavement is too bumpy or I was cornering hard when I first hit the pedal" just to get it to work right in icy conditions.

I guess they figure in those scenarios anyone driving fast enough on bumps to feel them hard, or anyone braking while still under dynamic loading from a hard corner, could probably be written off as "it's your own fault you wrecked, you weren't driving safely on the street to begin with"? Their code works great for probably the two most common ABS lawsuit cases for them: straight line stabbing-the-brakes stop in commuter traffic way too late because the driver wasn't paying enough attention, either dry or in slippery conditions.

EDIT: I wonder if it would be possible for someone to dig up a Bosch (or other ABS mfg) engineer to discuss this on the side and confirm exactly what the behavior is and why?