Overzealous ABS While Cornering

[Reid_S]

Hey folks,

I'm experiencing some odd behavior with my Model 3 Performance's brakes. Yesterday while exiting the highway on a clover-leaf offramp, I lightly hit the brakes and the ABS intervened to the extent that the brakes barely engaged. I came in pretty hot, but nothing out of the ordinary.

Immediately afterward, I pulled into an office park to do some testing. I did a straight-line, simulated panic brake from 30 mph and the ABS engaged normally. Then I simulated a low speed corner and took it fast--but again, nothing crazy--and gently pressed the brakes. Once again, the ABS engaged immediately.

I am aware there is some cornering ABS built-in to keep drivers from stabbing the brakes mid-corner and flying off the road, but this seemed excessive and not at all what I'm used to (I've had the car for two years).

There are two things I think could be contributing factors and I would love to hear some opinions:
1. I just had my local shop (not a TSC) flush my brake fluid last week. This isn't the kind of symptom I usually think of with air trapped in the ABS module, but I suppose it's possible.
2. I installed the UP adjustable AutoX shocks and the MPP FLCA bushings two weeks ago. No idea how that would impact the ABS while cornering, but it's the only other thing that changed.

Thanks in advance.
--Reid

 

[MODEL+]

I believe your issue is braking WHILE cornering...
Your mechanical grip is only limited to only what your tires are able to handle and ABS will react accordingly.

Danny

 

[MountainPass]

Hey folks,

I'm experiencing some odd behavior with my Model 3 Performance's brakes. Yesterday while exiting the highway on a clover-leaf offramp, I lightly hit the brakes and the ABS intervened to the extent that the brakes barely engaged. I came in pretty hot, but nothing out of the ordinary.

Immediately afterward, I pulled into an office park to do some testing. I did a straight-line, simulated panic brake from 30 mph and the ABS engaged normally. Then I simulated a low speed corner and took it fast--but again, nothing crazy--and gently pressed the brakes. Once again, the ABS engaged immediately.

I am aware there is some cornering ABS built-in to keep drivers from stabbing the brakes mid-corner and flying off the road, but this seemed excessive and not at all what I'm used to (I've had the car for two years).

There are two things I think could be contributing factors and I would love to hear some opinions:
1. I just had my local shop (not a TSC) flush my brake fluid last week. This isn't the kind of symptom I usually think of with air trapped in the ABS module, but I suppose it's possible.
2. I installed the UP adjustable AutoX shocks and the MPP FLCA bushings two weeks ago. No idea how that would impact the ABS while cornering, but it's the only other thing that changed.

Thanks in advance.
--Reid

What is your alignment and wheel/tire setup?

 

[Reid_S]

What is your alignment and wheel/tire setup?

Thanks for your response! I had it aligned to factory specs after installing the shocks and bushings. I'm running 19" x 9" Titan 7 wheels with 245/40ZR19 Michelin Pilot Sport 4S tires. The normal 4S--not the acoustic ones or the runflats.

 

[MountainPass]

Thanks for your response! I had it aligned to factory specs after installing the shocks and bushings. I'm running 19" x 9" Titan 7 wheels with 245/40ZR19 Michelin Pilot Sport 4S tires. The normal 4S--not the acoustic ones or the runflats.

No problem! None of those things are red flags to me. What happens if you put the car in Track Mode with more lenient nannies?

 

[Reid_S]

I believe your issue is braking WHILE cornering...
Your mechanical grip is only limited to only what your tires are able to handle and ABS will react accordingly.

Danny

This is a fair point, but I take that exit at about the same speed several times a week and have never had the ABS step in on me before.

 

[Reid_S]

No problem! None of those things are red flags to me. What happens if you put the car in Track Mode with more lenient nannies?

I didn't try it in Track Mode. I'll check this evening and update the thread. I'm also taking it back to the shop tomorrow to have them make sure they purged all the air out when they flushed the brake system.

 

[Mash]

It's possible that you had air trapped, since your local shop can't really engage flush sequence at all. So what happened possibly - ABS saw inconsistent response to brake application and started pumping brakes to compress air. Its a standard Tesla function. But you have to hold a pedal.

Anyway, read that page about brakes in manual and flush your brakes. That might help.

 

[Reid_S]

Well, I have an answer. Sort of.

It turns out the shop noticed the rear tires had 1/16" less tread than the front tires and rotated them while they were servicing the brakes. This seems to have messed with the wheel speed sensors and caused the car to think the front tires were slipping while braking.

Just out of curiosity, I went out to a curvy road and did some fast corners. The traction control system was pulling power well before I was at the limit.

So, I rotated the tires back to the way they were and sure enough, the ABS stopped being overly aggressive. I went to the same curvy section of road and no traction control issues.

It's surprising to me that 1/16" would cause the front tires to rotate fast enough, relative to the rear tires, to throw off the ABS and traction control, but I guess it's not crazy.

Anyways, moral of the story, use caution when rotating your tires.

 

[MP3Mike]

So, I rotated the tires back to the way they were and sure enough, the ABS stopped being overly aggressive. I went to the same curvy section of road and no traction control issues.

Any chance they didn't have the tires mounted perfectly centered/flat? (I assume you would have noticed other vibrations/issues, so that probably isn't it.)

But after some amount of time the traction control/ABS system should learn the new tires and go back to normal. (It is like when switching to/from winter tires ABS/regen/etc act a little funky while it learns.)

 

[dsgerbc]

Well, I have an answer. Sort of.

It turns out the shop noticed the rear tires had 1/16" less tread than the front tires and rotated them while they were servicing the brakes. This seems to have messed with the wheel speed sensors and caused the car to think the front tires were slipping while braking.

Just out of curiosity, I went out to a curvy road and did some fast corners. The traction control system was pulling power well before I was at the limit.

So, I rotated the tires back to the way they were and sure enough, the ABS stopped being overly aggressive. I went to the same curvy section of road and no traction control issues.

It's surprising to me that 1/16" would cause the front tires to rotate fast enough, relative to the rear tires, to throw off the ABS and traction control, but I guess it's not crazy.

Anyways, moral of the story, use caution when rotating your tires.

TBH, that doesn't sound like 1/16" difference is the issue, but the rotation w/o a sensor reset. The car was possibly sensing the front tire slip as if they were the rear ones (or the opposite) and reacting.

 

[Reid_S]

Any chance they didn't have the tires mounted perfectly centered/flat? (I assume you would have noticed other vibrations/issues, so that probably isn't it.)

But after some amount of time the traction control/ABS system should learn the new tires and go back to normal. (It is like when switching to/from winter tires ABS/regen/etc act a little funky while it learns.)

Yeah, wheels were definitely centered on the hub.

I would have also expected the system to learn the new setup, but I probably put ~200 mi on the car with the tires swapped and it never figured it out.

 

[AlanSubie4Life]

Yeah, wheels were definitely centered on the hub.

I would have also expected the system to learn the new setup, but I probably put ~200 mi on the car with the tires swapped and it never figured it out.

I guess it is too late now since you've rotated them back, but did you try resetting the TPMS when the wheels were rotated? I wonder whether as part of that reset (which you might do if changing wheels or whatever), maybe it resets any learned values for tire diameters. No idea what it keeps track of...or whether it can be relearned.

Still, seems weird. I've transferred front and back before and pretty sure I had a couple 1/32" difference between front and rears. Never had any such problem, though perhaps I'm just not driving aggressively enough on the street to notice.

Glad you figured it out, anyway. Definitely I've heard of cars having traction control problems due to small differences in front and rear tire diameters before. But it certainly seems like something the car should be able to learn and figure out.