Blackout with braking due to TC

[wiztecy]

I've been encountering this issue fairly often where I push my Roadster hard through turns where I believe the ABS kicks in and blacking out my brakes where I have ZERO braking and just rolling uncontrollably through in a turn. My momentum starts picking up even more then at the last moment braking recovers back in. It can be either in patches, usually bumps cause that and I understand that case, or long durations (in a not all that bumpy environment) where it recovers, or when I come in hard of a sharp fishhook at 20-35MPH and begin my turn then breaking around 33% into the turn.

Just today, the oddest one, I was in a long sweeping turn (65/75MPH) and braked smoothly and added more braking as was in and pulling harder in the turn. Again, no brakes. It wasn't a bumpy section at all, HWY 17 turns which is paved pretty well now.

Anyone else feeling this oddness? Really would love to fix it so I have brakes when I really need them. Never had an ABS system cutout 100% for a long time like that.

 

[Doug_G]

I believe this is an example of a well-known issue with the Roadster. This has to do with TC, not ABS.

The regenerative brakes provide a surprisingly large fraction of the braking force even when you are on the friction brakes. If you hit a hard bump while braking the traction control engages and the regen braking completely goes away. The loss of braking force is quite dramatic and can result in you overshooting your stopping point by six feet if you're not ready for it.

For this reason I usually disable TC on dry pavement, especially if I'm on a route where I can expect hard bumps. Please note that I do NOT recommend doing this in wet weather!!!

I've never had this happen in the Model S so they must have made some refinements...

 

[djp]

I've noticed the ABS pulses much more slowly than other ABS systems, which is a different effect than regen cutting out during TC. It feels like the brakes fade during a hard stop, then kick in again. I'm hoping it behaves better with Carbotech pads.

 

[7racer]

I have and like Doug, think it's from the TC.

If you look quick enough you can see the TC come on during these episodes.

 

[wiztecy]

I was thinking it was TC but it seriously feels as if I don't have any brakes at all, pedal feels firm but car's still rolling. Possibly its the overshooting feeling that Doug's talking about, I have the Carbotech AX6's and can make them squeal when I'm really hard on them and heating them up. I can feel them bite when I hammer down on the brakes big time in controlled turns and on a straight. I'll have to do some experiments and keep an eye on the TC light. I'm thinking I need to have an audible alarm connected to the TC light. Overshooting is not good, its the difference of overshooting a turn crashing or pulling it off and sailing away. I'm not looking at my instrument cluster for dimly lit lights during the day when I'm cornering. Would be nice to know when you're in this scenario but then again once your there you're committed and the alarm won't do you any good.

ABS should be decoupled from TC right?

 

[Doug_G]

Absolutely yes. ABS still engages with TC disabled.

And yes, when the TC triggers during braking, it's such a dramatic drop in braking power that you could swear the car was actually accelerating.

I'm also running AX6. That didn't change the behavior at all compared with the (inadequate) stock Lotus pads. The thing is, you instinctively modulate the braking power for the deceleration curve you want. When the hardware behavior changes under your feet you will always overshoot, even if the car was capable of stopping faster. Your reaction time simply isn't fast enough to compensate 100%.

 

[wiztecy]

Thanks Doug, appreciate your insight and feedback.

So the Moral of the story is don't get overly confident of the Roadster's handling on the street for that TC will bite you in an unforgiving way.

I'll do some warming up in turns with TC off and learn the feel / behavior. Possibly that's what I'll need to do to get more consistent braking behavior on dry twisty roads.

 

[Doug_G]

Glad to help.

FYI, I updated the thread title so it more accurately reflects the thread content.

 

[Pantera Dude]

Recently I approached a tight, corner on a winding road going downhill. TC was off but I got that "accelerating" feeling. I went back to try to figure out what caused the problem. Turns out there was a smooth six foot long manhole cover that was difficult to see while going downhill. Let's just say it was an invigorating feeling trying to avoid "tradin paint" with the guardrail. :biggrin: