Braking Under "Spirited" Driving

[Last ICE]

I know we've discussed the sometimes unpredictable nature of the regenerative braking in the past. I had been surprised by the response when taking an on ramp at speed expecting regen braking and there was none (no, I was not near full charge). Took that same on ramp last night and was prepared to use the brake pedal and when I did the response was not good and not what I expected. The pedal almost felt like the anti-lock was activating when it was not. The braking definitely didn't grab as I expected. I am spooked enough where I simply will not take my Lucid into aggressive braking/turning situations. Has anyone else experienced similar with braking under spirited driving? Is this normal?

I've read and watched enough on the Sapphire to know how good it's braking is on the track. I know my DE is no Sapphire, but I expect more responsive braking than what I've experienced. My last car was a Cadillac CT5-V Blackwing so maybe I have false expectations for the Lucid after driving that car, including tracking it at the Cadillac-sponsored driving school in Nevada.

 

[Steveinarizona]

Your brake pedal drives the friction brake, no regen. I would suggest trying to replicate on an empty stretch of highway using the brake pedal. If the friction brake is not grabbing, as it should, you need service and I would say right away. You have an incredible amount of HP and if the brake isn't working to spec, that is dangerous.

 

[segbrk]

Regen absolutely feels different at high speeds, it feels like it's doing almost nothing until you drop under 100 or so, then it starts to kick in. That's not actually how it works, but that's how it feels to me. I will say I have braked hard (with the friction brakes) from 145 and, while I didn't measure the stopping distance or anything, it did not disappoint. I do feel a gravelly ABS-like rumble in the pedal when I do that, but whatever the reason, it does its job and stops me. Either way, no harm in getting it checked out if it makes you uncomfortable.

... all of the above refers, of course, to driving on long day trips in Mexico.

 

[hydbob]

I know we've discussed the sometimes unpredictable nature of the regenerative braking in the past. I had been surprised by the response when taking an on ramp at speed expecting regen braking and there was none (no, I was not near full charge). Took that same on ramp last night and was prepared to use the brake pedal and when I did the response was not good and not what I expected. The pedal almost felt like the anti-lock was activating when it was not. The braking definitely didn't grab as I expected. I am spooked enough where I simply will not take my Lucid into aggressive braking/turning situations. Has anyone else experienced similar with braking under spirited driving? Is this normal?

I've read and watched enough on the Sapphire to know how good it's braking is on the track. I know my DE is no Sapphire, but I expect more responsive braking than what I've experienced. My last car was a Cadillac CT5-V Blackwing so maybe I have false expectations for the Lucid after driving that car, including tracking it at the Cadillac-sponsored driving school in Nevada.

A little more detail would be helpful. I've also stopped from high speed in Mexico like @segbrk and the brakes felt good and solid.

 

[Last ICE]

Yes, I do plan to test in an appropriately safe environment (i.e. Mexico) to try to determine if there's a legitimate issue or just normal behavior for this car. A straight line braking test using the brake pedal (with and without antilock engaging) will tell me more. Definitely got my heartrate up going into a turn where braking was needed and I did not get the expected response. I have a service appointment coming up in April for a software update (my VIN is locked for OTA updates currently) and my toggling on/off headlights. If I truly like there is abnormal braking I will plan to add that to the list.

 

[hmp10]

Regen absolutely feels different at high speeds, it feels like it's doing almost nothing until you drop under 100 or so, then it starts to kick in.

I think this is normal. Batteries are limited in how much power they can absorb how fast. Regenerative braking energy recovery is most efficient in low-speed driving when more of the regenerative energy can be taken up by the cells. You're converting a lot of energy very rapidly when slowing from speeds above 100mph, and the battery pack isn't going to be able to take much of it.

 

[xponents]

Yes, I do plan to test in an appropriately safe environment (i.e. Mexico) to try to determine if there's a legitimate issue or just normal behavior for this car. A straight line braking test using the brake pedal (with and without antilock engaging) will tell me more. Definitely got my heartrate up going into a turn where braking was needed and I did not get the expected response. I have a service appointment coming up in April for a software update (my VIN is locked for OTA updates currently) and my toggling on/off headlights. If I truly like there is abnormal braking I will plan to add that to the list.

“Mexico”

 

[segbrk]

I think this is normal. Batteries are limited in how much power they can absorb how fast. Regenerative braking energy recovery is most efficient in low-speed driving when more of the regenerative energy can be taken up by the cells. You're converting a lot of energy very rapidly when slowing from speeds above 100mph, and the battery pack isn't going to be able to take much of it.

Right, that makes perfect sense, the strange feeling is that it seems like almost nothing happens when I take my foot off the pedal at that speed. If I take my foot off the pedal at 70mph it feels like I've just stepped on the brake. I get that the battery can't take all that power over 100mph, but my expectation would be that regen applies roughly the same amount of deceleration force, taking the same amount of power to the battery, whether at 70 or 145. Just like putting the same pressure on the brake pedal should feel like roughly the same deceleration force regardless of your speed.

 

[hmp10]

. . . but my expectation would be that regen applies roughly the same amount of deceleration force, taking the same amount of power to the battery, whether at 70 or 145. Just like putting the same pressure on the brake pedal should feel like roughly the same deceleration force regardless of your speed.

The energy going into the batteries might remain the same, but the car has to convert of lot more energy to slow from 145mph than from 70mph, and that excess energy has to be converted into heat by the friction brakes, as the batteries can't take it.

 

[segbrk]

The energy going into the batteries might remain the same, but the car has to convert of lot more energy to slow from 145mph than from 70mph, and that excess energy has to be converted into heat by the friction brakes, as the batteries can't take it.

This still doesn't make sense to me. Yes motors will produce more power at 145mph than 70mph, but taking constant power from the motors should result in the same rate of deceleration - which is what you actually feel - regardless of speed, no? You won't get to 0 at the same speed, but I don't understand why going from 145 to 100 is much different from going from 70 to 25.

 

[Lucken]

Moral of the story- Don’t drive over 100 mph.

 

[borski]

For what it’s worth, I have slammed on the brakes many times at high speed and it has kept me stable every time, in my DE.

Regen is entirely a different thing. I find it changes slightly in feel based on speed or SOC.

 

[segbrk]

Moral of the story- Don’t drive over 100 mph.

I hear Mexico has a speed minimum. I'm sorry, but I just can't drive under 100 there.

 

[bdham]

Regen absolutely feels different at high speeds, it feels like it's doing almost nothing until you drop under 100 or so, then it starts to kick in. That's not actually how it works, but that's how it feels to me. I will say I have braked hard (with the friction brakes) from 145 and, while I didn't measure the stopping distance or anything, it did not disappoint. I do feel a gravelly ABS-like rumble in the pedal when I do that, but whatever the reason, it does its job and stops me. Either way, no harm in getting it checked out if it makes you uncomfortable.

... all of the above refers, of course, to driving on long day trips in Mexico.

I would agree that regen braking now feels much weaker when being used at highway speeds. I don't recall this being the case previously and therefore its probably related to one of the last few OTA updates. I'm hoping that this gets addressed by Lucid because the inconsistency in regen braking is not a good thing. When driving a low speeds, I know that regen will work as expected but on highway speeds, I have to prepare myself to use the friction brake.

 

[SaratogaLefty]

I have definitely also noticed much less regen when I let off the accelerator at higher speeds. I keep my regen on High but there is a very real change in decelerating at freeway speeds now.

 

[hmp10]

This still doesn't make sense to me. Yes motors will produce more power at 145mph than 70mph, but taking constant power from the motors should result in the same rate of deceleration - which is what you actually feel - regardless of speed, no? You won't get to 0 at the same speed, but I don't understand why going from 145 to 100 is much different from going from 70 to 25.

A motor in regen is acting as a generator. It gets its motive power from the car’s momentum. A faster car is driving the generator harder as the car begins to slow, as it has more momentum to convert.

 

[Lucken]

I can’t say I’ve noticed any difference in regen on the highway.

 

[becauseracecar]

Right, that makes perfect sense, the strange feeling is that it seems like almost nothing happens when I take my foot off the pedal at that speed. If I take my foot off the pedal at 70mph it feels like I've just stepped on the brake. I get that the battery can't take all that power over 100mph, but my expectation would be that regen applies roughly the same amount of deceleration force, taking the same amount of power to the battery, whether at 70 or 145. Just like putting the same pressure on the brake pedal should feel like roughly the same deceleration force regardless of your speed.

Regen absorbs a constant amount of energy per time (constant power), which results in a speed dependent amount of braking
To understand this think back to high school physics and recall that kinetic energy is 1/2*m*v^2

It's the v squared that gets you, if you compare (145^2 - 100^2) to (70^2 - 25^2) you find the first is 2.6 times bigger than the second, i.e. the batteries need to absorb 2.6 times more energy to slow you down from 145mph to 100mph than from 70 mph to 25mph. If regen is working as hard as it can to absorb energy at the same rate in both cases, it'll need 2.6 times longer for the 145mph case.

Another way to look at this is to recall Power = torque * angular velocity (at least instantaneously)
If regen can only absorb at a fixed max power, and angular velocity goes up, then the torque that will be applied to slow the wheels will have to go down to keep the power the same (since motor/battery can only generate/absorb a certain max power)

 

[hmp10]

What he said.

 

[kort6776]

from the videos that I've seen the brakes on the car are not really great. regen is for slowing down at lower speeds, I'm talking about hard braking from speed