Concerns over Model 3 Performance brakes efficiency. How good is it? After market brakes?

[gearchruncher]

You'll notice the brake pedal only recedes when the car is 'Holding' after coming to a complete stop.
This tells me that regen is capable of stopping the car to 0 mph

This appears to be quite the debate: One pedal mode uses the brakes?

Regen and Friction Brakes to Full Stop – TeslaTap

teslatap.com

The correct analysis would be to look at actual brake line pressure. The pedal is not the only way a Tesla can generate pressure- the ABS pump can as well.

I can tell you that "Regen" cannot stop the car. It takes work to stop a car. The back EMF in a motor is proportional to speed. This means at 0 MPH/RPM, it cannot do any work. Which means at 0.1 MPH, it basically can't do any work. Regen cannot stop a vehicle by itself, and this is even more true when you have non-superconducting systems that have voltage thresholds and power losses as you get near zero RPM. Hence the reason that pre-2019 Teslas can't do one pedal driving, and require you to press the brakes when you get down to about 5 MPH and they just go into coast mode.

So, it might be possible that Tesla is actively putting the motor into REVERSE and actually pumping power into the motor to bring it to a stop without using the brakes. This would waste more energy than pure friction brakes, as it would actively take power out of the battery as you stop, but it would prevent the use of the brakes. The real question is if they can do this, why they can't do it on a 2017 Model S/X.

 

[Knightshade]

. Hence the reason that pre-2019 Teslas can't do one pedal driving, and require you to press the brakes when you get down to about 5 MPH and they just go into coast mode.

Uh...what?

Mine is a 2018 and it one-pedal-drives just fine in HOLD mode. Never "requires" me to press the brake pedal other than to shift out of park.

So, it might be possible that Tesla is actively putting the motor into REVERSE and actually pumping power into the motor to bring it to a stop without using the brakes. This would waste more energy than pure friction brakes, as it would actively take power out of the battery as you stop, but it would prevent the use of the brakes. The real question is if they can do this, why they can't do it on a 2017 Model S/X.

One significant difference I can think of- older S/X use induction motors front and rear.

Newer ones, and all 3/Y going back to the 2017 launch of the 3, have at least 1 non-induction motor.

 

[gearchruncher]

Uh...what?

Mine is a 2018

Yes, this was imprecise. Not all pre-2019 Teslas can do this. Specifically the S/X started in 2019. Only the "Raven" and newer can, at which point all Teslas could, which is why I listed that.

One significant difference I can think of- older S/X use induction motors front and rear.

Yes, this does seem to be related. That doesn't mean that it's *regen* all the way down to zero though, since a IPMsynRM or PMSR motor can't produce regen torque at zero RPM any better than an induction motor.

 

[Dangerous Fish]

The Model 3 uses regen to 0mph. The most obvous proof of this is all of us with track pads not getting any brake squeal when we use regen to stop the car. There really is no debate to be had about this point.

 

[gearchruncher]

Anyone have a datalog of the car pulling a lot of current while going down a steep hill at low speed? This would be required for a motor to create useful torque at low RPM. Maybe I need to go try this in my driveway which is so steep the car won't ever stop on it with only regen and without applying friction brakes.

 

[Mash]

This appears to be quite the debate: One pedal mode uses the brakes?

Regen and Friction Brakes to Full Stop – TeslaTap

teslatap.com

The correct analysis would be to look at actual brake line pressure. The pedal is not the only way a Tesla can generate pressure- the ABS pump can as well.

I can tell you that "Regen" cannot stop the car. It takes work to stop a car. The back EMF in a motor is proportional to speed. This means at 0 MPH/RPM, it cannot do any work. Which means at 0.1 MPH, it basically can't do any work. Regen cannot stop a vehicle by itself, and this is even more true when you have non-superconducting systems that have voltage thresholds and power losses as you get near zero RPM. Hence the reason that pre-2019 Teslas can't do one pedal driving, and require you to press the brakes when you get down to about 5 MPH and they just go into coast mode.

So, it might be possible that Tesla is actively putting the motor into REVERSE and actually pumping power into the motor to bring it to a stop without using the brakes. This would waste more energy than pure friction brakes, as it would actively take power out of the battery as you stop, but it would prevent the use of the brakes. The real question is if they can do this, why they can't do it on a 2017 Model S/X.

It's worth making a log of single drive and stop at hold, but nothing prevents Tesla from actually applying braking torque by motors. All of them capable to have holding torque. They don't have very precise encoder to hold it like servo, but they for sure can hold enough to stop a car.

 

[MasterC17]

The Model 3 uses regen to 0mph. The most obvous proof of this is all of us with track pads not getting any brake squeal when we use regen to stop the car. There really is no debate to be had about this point.

Completely agreed. I've had no brake squeal when using "Hold Mode" down to 0mph, whereas any minor application of the brake pedal with the Carbotech's would result in loud squealing noises.

 

[Dangerous Fish]

It's also possible to hold the car on a slight slope just using the motor, so it doesn't engage the brakes in hold mode. Just like holding a manual car using the clutch.
At no time (other than with autopilot engaged or if AEB operates) does the car apply the brakes until it's come to a complete stop at which point you hear the click and the (H) appears.
There are other ways to prove this but I really don't feel inclined to spend any time on it myself, as I know how these cars work in that respect.

 

[gearchruncher]

but nothing prevents Tesla from actually applying braking torque by motors. All of them capable to have holding torque. They don't have very precise encoder to hold it like servo, but they for sure can hold enough to stop a car.

Yet they won't do it on a 2012-2019 Model S....

 

[tm1v2]

Yet they won't do it on a 2012-2019 Model S....

Tesla only supports it on cars with a permanent magnet motor. Make of that what you will. I am guessing the ease and efficiency of bringing the car to a complete stop is very different than with an induction motor.

Other EV makers implement things like blended braking on the brake pedal, and even blended braking for one pedal driving to hide scenarios where the battery can't accept full regen. Tesla has a clear philosophy of the opposite - keep everything separate, let the driver understand and control what the systems are actually doing individually. (I happen to like Tesla's philosophy on this but I am biased having only owned Tesla EVs.)

 

[gearchruncher]

Tesla has a clear philosophy of the opposite - keep everything separate, let the driver understand and control what the systems are actually doing individually.

Just to point out, if it was actually that clear, none of this discussion would exist.
Tesla does blend the brakes in without driver intervention, the question just is when. Is it before 0 MPH, or only after?

 

[timcking]

And how do you know it's 85%? Maybe it's just lower tire friction than you expecting due to cold road and tires?

Mash, you're right. This could be what's happening. The ABS is really crude compared to what I'm used to.

 

[timcking]

Does this setup maintain the same brake ratio front and rear, and are the same pads front/rear? The basic question here is if this setup messed with the front/rear bias.
Also, did you make any changes at the same time? Tires, alignment, shocks, can all dramatically change braking capabilities.

Yes to both questions.

Perhpas...Which performance aftermarket pads are you running? They could be too aggressive for the type of driving you do.

They're street performance pads from RB Performance Brakes.

 

[gearchruncher]

Yes to both questions.

Well, then if you changed a bunch of other stuff at the same time, it's probably not the brakes.
I track the Model 3P quite a bit and I don't find the ABS crude at all, and it's pretty non-intrusive. I've had lots of very fast drivers actually remark at how effective the brakes are and how a lot of speed in these cars comes from confidence in the brakes.

You can always go pull a wheel sensor and go see what the car can do without ABS

 

[Motion122]

Yes to both questions.

They're street performance pads from RB Performance Brakes.

I doubt you are having wheel speed sensor issues. If the pads are properly bedded-in, how are your tires? Is the premature activation just in the front, rear or both axles? Perhaps a pad with a different torque curve can help.

 

[tm1v2]

@timcking I'll also chime that my October 2021 build M3P's ABS and EBD (brake force distribution) have felt pretty good to me in my limited experience with the car so far. "Really crude" doesn't match what I've felt at all, and I have owned cars with really bad/crude ABS, I'm very aware from experience how big a difference good vs bad ABS+EBD can make. So I'm also thinking something might be wrong with your car (and therefore fixable), or as @Motion122 is suggesting, maybe the systems (especially EBD) aren't adjusting well to those pads.

I haven't tracked my M3P or driven it on snow or ice yet, I really can't say if its ABS+EBD are truly great or not, but I can tell from panic stops alone that it's certainly not bad, and far from the worst out there!

 

[gearchruncher]

I switched from the stock pads to the RB XT910's, and have been AutoX'ing them for a while now. Found no difference in braking capability or ABS intervention. The XT910's seem to have a slightly lower Mu than the stock pads and need a bit more pedal pressure, but besides that no changes. The stock pads are really excellent unless you are running actual track days, or have to spend money for them because you wore them out.

If anyone's swapped away from their stock pads and wants to sell them, hit me up

 

[mattack4000]

Buy mine, I took them off the first month before my track day. I have all the shins and stuff, made by brembo

 

[_panda]

I only read the first 4 pages of this thread and what a read… fascinating back and forth