Losing all regen braking during a bumpy stop

[knightmb]

I can confirm for my 2020 Leaf anyway (my 2013 was probably the same way), turning off the traction control reduces how sensitive ABS is, but does not disable it.

So, as part of my experiment (it was rainy again today, perfect for slipping around on), using the same section of road and a badly placed manhole cover right in the travel lane that causes the right wheel to skid across it and trigger ABS coming to a stop every time consistently. I did a half-dozen runs with traction on and off just to make sure it wasn't a fluke.
With transaction control on, as soon as the wheel hits the manhole cover, the ABS kicks in. With transaction control off, I can literally hear the wheel sliding across the manhole cover at low speed stops.

I don't know by how much it reduces this sensitivity since my evidence is anecdotal and not that scientific in precise terms since braking hard enough will get ABS to come on even with Traction Control turned off. But I can at least confirm is does have a tangible difference in ABS performance.

 

[alozzy]

To be clear, I'm not advocating that people should disable traction control. I mentioned it because I likewise found it all but eliminates the disheartening feeling of brake loss. I just found it interesting that doing that helps, as it suggests a more complex root cause.

 

[LeftieBiker]

The best solution would be a button (again) that disables it for just a minute or so.

 

[goldbrick]

I'm impressed on what y'all do 'for science'. Thanks!!

 

[knightmb]

The best solution would be a button (again) that disables it for just a minute or so.

Gen 1 had it right, button down by the left, instantly turn it on and off as one wished. Was disappointed when I saw they removed in the Gen 2 and stuck it in the Dash menu instead.

 

[knightmb]

I'm impressed on what y'all do 'for science'. Thanks!!

I tortured my Leaf with half a dozen gear oil changes last year and drilling a hole in a oil plug to stick a temperature sensor directly into the gear oil to get real-time temperature readings also. I'm still working on my cold torture design to freeze the battery and figure out how a "software" mode keeps the battery warm. :lol:

 

[LeftieBiker]

I'm, er, going to install footwell lights. Pretty ones!

 

[GerryAZ]

Knightmb gave a good description of ABS and traction control along with some great test results. I have driven LEAFs long enough that the loss of braking sensation when ABS causes loss of regeneration does not bother me. Although it feels like losing brakes momentarily, there is no impact to stopping distance if you step on the brakes hard. It is only noticeable when ABS senses wheel slip under gentle braking (using mostly regeneration).

ABS, traction control, and/or stability control can cause issues for drivers under certain conditions with any vehicle. Some examples;

Every vehicle that has stability control which I have driven on snow and ice caused severe loss of braking when right and left wheels had significantly different traction (one side breaking through to pavement while other side on snow/ice). I have learned to turn off stability control in those conditions. The systems in those vehicles work fine when all four wheels have similar traction. Most of the vehicles allow ABS to remain active when stability control is disabled and ABS by itself seems to be OK. I was also disappointed when I discovered the only way to disable traction control or stability control was through the menus for Gen 2 LEAFs.

I have one motorcycle with power-assisted ABS brakes that work great on wet or dry pavement even with bumps, but gravel roads cause complete loss of braking so I must ride very slowly through construction zones and plan to coast when stopping because the system cannot be disabled. I have another motorcycle which has ABS and traction control for normal riding. One or both of those systems can be switched off for riding on rough, low traction surfaces. I have learned that it is necessary to turn those systems off when riding on gravel roads or other rough surfaces.

 

[frontrangeleaf]

Hmmm. Interesting discussion. I haven't noticed these effects, I'll have to pay closer attention.

We've had extremely cold temps in Denver recently, with icy streets to go along with it. I do run severe winter rated snow tires, so I have a bit more traction to work with than one gets with all-seasons. I don't get ABS hardly ever with my driving style and these tires.

I have been to winter driving school, multiple times (it's fun). There we learned that ABS is really all about retaining your ability to steer, not about the shortest stopping distance. The shortest stopping distance is achieved with "threshold braking" - stomp, trigger ABS, then back off just enough for the ABS to stop firing. Your wheels are still rolling, and you can still steer, but you are braking continuously instead of many times a second. The difference under really slick conditions (we train on a frozen lake in the mountains west of Denver) can make a difference. The training is run by professional drivers associated with the Audi club here.

THIS TAKES PRACTICE. Don't try this in an emergency unless you know your car, your tires, and have practiced the technique under real world conditions. Stomp, Stay, Steer is the rule for everyone who hasn't learned threshold braking, which is also different for every vehicle/tire combo.

The number one takeaway from training has to do with the time it takes for your steering inputs to have effect, and how much input is effective (it's not much before the front tires begin sliding sideways and lose their steering effort). That also takes practice! Driving around on an icy lake is pretty much worst case scenario - you can hardly stand up (it's an uneven surface), we wear cleats on our shoes to help with traction when outside of the cars.

 

[LeftieBiker]

There we learned that ABS is really all about retaining your ability to steer, not about the shortest stopping distance.

Thank you! I keep meaning to post that, but haven't remembered while I'm here. ABS lets you steer around something in front of you, while you are instinctively standing on the brake pedal.

 

[GerryAZ]

Unfortunately, stability control gets in the way of threshold braking if there is a significant difference in traction between the left and right tires. That is why I have learned to turn it off on any vehicle under those conditions. And you are absolutely correct--threshold braking results in shorter stopping distance than just stomping on the pedal and allowing ABS to activate.