Brake Energy Recuperation aka Regenerative Braking Wears Out Brake Pads?

[ELECTROMAN]

Still experiencing my first week with my eGolf. I talked to the salesman that sold me the car, today. I told him how it took me a bit to figure out the different regen levels, and that I came to the conclusion to just keep it in B. He warned me that the brakes are always applied a little bit in that mode and it will wear out my brake pads quicker. He said his coworker wore out their pads in about one year. This can't possibly be true right? I'm thinking if anything his coworker kept the selector lever in D and that's why his brakes wore out so quickly. I would still think in D the pads would last longer than a year. Did I just enter the Twilight Zone?

 

[f1geek]

Another example of a VW salesman spouting pure and unadulterated BS. The e-Golf is designed to first use regen and only add friction brakes when the regen can’t slow you down fast enough (based on how hard you press the brake pedal) or for the last few mph when coming to a complete stop. If you drive in B when lifting off the accelerator pedal, regen slows the car. B mode, aka one pedal driving. Even in D if you brake normally, most slowing is by regen. The BS salesman’s coworker must have been either braking like a race car driver or this is just more BS. If you are gentle with how you slow the car, I bet the brake pads could last for 60,000 to 80,000 miles, if not more.

 

[P63]

Previous poster is correct.

FWIW, without regen braking, slowing a car will wear out tires, brakes, or both. Light application of the brakes while slowly decelerating is great for tire wear, but will eat through the brake pads quickly. Panicked, last-second hard braking wears out tires, but not so much brake pads (and is way more fun).

Regen braking allows long, slow deceleration without any wear to the pads.

Car salesmen generally don't know the answer to any technical questions. I had one salesperson who didn't know why alloy wheels are superior to steel wheels, another claim that a 240 hp OHV V8 was a 300 hp DOHC V8, and another salesman say that we could charge our hybrid's battery for free by clicking the regen paddles while on the freeway. <facepalm>

All that said, why would you want to drive around in B? There's a lot of economy to be had in coasting.

 

[ELECTROMAN]

All that said, why would you want to drive around in B? There's a lot of economy to be had in coasting.

It saves on brakes and increases your range. I live in a hilly area, so that might make a difference. My daughter drives a few miles down to her school and arrives with more range than she left with. I also find one pedal driving to be much more enjoyable.

I had the same experience with Tesla sales people not knowing what they were talking about. I would imagine that the misinformation is significantly worse at an ice car dealership.

 

[JoulesThief]

Light application of the brakes while slowly decelerating is great for tire wear, but will eat through the brake pads quickly.

Panicked, last-second hard braking wears out tires, but not so much brake pads (and is way more fun

Complete rubbish. All you have to do, on any german car, is look at how much brake dust is sitting on your rims between car washes, to know the statements above are patently false.

Brake gently, and your brake pads last much, much longer. Brake hard and your pad and rotor life will be much, much shorter.

Panicked Braking is way more fun? It is irrelevant in how long your brake pads last. Panicked braking is terror that you are going to hit something, due to being inattentive in your driving, how in the hell is that fun?


Poster above has lost all veracity.

 

[Sparklebeard]

All that said, why would you want to drive around in B? There's a lot of economy to be had in coasting.

It saves on brakes and increases your range. I live in a hilly area, so that might make a difference. My daughter drives a few miles down to her school and arrives with more range than she left with. I also find one pedal driving to be much more enjoyable.

I had the same experience with Tesla sales people not knowing what they were talking about. I would imagine that the misinformation is significantly worse at an ice car dealership.

The e-Golf will use the regex brake when you press the brake pedal in D mode, and will only engage the friction brakes once the braking force requested is stronger than the regen brake can offer (or if there's wheel slip)

B mode only has the effect of making the car apply regenerative braking when you lift your foot off the pedal (i.e. the regen brake is ON, unless you're pushing the 'gas' pedal). The brake pedal responds the same way in B and D mode. The only way to really wear down the brake pads on the e-Golf is lots and lots of hard stops. If your "charge" needle on the dash is lower than ~90%, its likely that you're only using regen, even in D mode!

Range increase is a complex topic here, for certain driving conditions B mode will increase range, for other conditions it will actually rob you of range. The reason is that regenerative braking isn't 100% efficient, so you will always regenerate less energy than you spent to accelerate. As such, the "perfect" efficiency would be to accelerate with precisely enough energy that you get up to a speed, take your foot off the pedals and just coast to a stop, exactly where you needed to stop, without ever touching the brake pedal so as not to lose any energy to friction or to heat through regeneration. This is, of course, completely unrealistic!

If you're able to coast in B mode without inadvertently speeding up and then slowing back down from minor foot pedal motions, you'll find that you can achieve excellent efficiency. I also find that in stop start traffic, coasting slowly while traffic is creeping tends to save me energy vs the more 'stop start' style that the one-pedal driving lends itself to in that situation.

With all that said, one pedal driving is very enjoyable, and your own personal driving style may be completely different to mine. There's no wrong way to drive the car! I often use one-pedal driving because for 95% of my driving I could be getting utterly terrible range and still never run into issues.

Regarding your daughter arriving at school with more range than she left with, unless the trip is significantly downhill the whole way its more likely that the guess-o-meter is recalculating range from driving efficiently. compared with actually ending up with more energy in the battery than it started with.

sorry for the wall of text! Hopefully this helps with some info, though. The dealerships are worse than clueless.

 

[P63]

Complete rubbish. All you have to do, on any german car, is look at how much brake dust is sitting on your rims between car washes, to know the statements above are patently false.

Brake gently, and your brake pads last much, much longer. Brake hard and your pad and rotor life will be much, much shorter.

Panicked Braking is way more fun? It is irrelevant in how long your brake pads last. Panicked braking is terror that you are going to hit something, due to being inattentive in your driving, how in the hell is that fun?


Poster above has lost all veracity.

It appears that you have no automotive knowledge at all.
Firstly, instead of science or engineering you cited anecdotal evidence: German cars have brake dust on the wheels.... that doesn't even qualify as anecdotal evidence, it's just a statement... and without any supporting facts.
No offense, I'm just pointing out that you don't know anything technical. It's important that technically ignorant people not post on technical boards. My goodness I saw a fellow on Youtube showing a very unsafe way to remove tension from a Honda serpentine belt, so I called him out too.


The science of braking is that any car at speed has a given amount of kinetic energy. In order to stop this kinetic energy is converted into heat (neglecting regen for now).
Dragging the brakes for a longer distance for a calmer stop creates heat in the brakes during the entire stop, but not much in the tires. Thus the tread lasts longer. But wait! We all know that racerboy who jams the brakes at the last moment has hot brakes; what gives? The answer is that he generated heat for a shorter amount of time while the calm stopper's brakes have been cooling as quickly as the heat is generated.
The total amount of heat generated by the brakes during a harder stop is less than the heat generated by a long stop, but the tires had to generate more force and they got hotter and more tread was lost.
It's really basic stuff that braking is a tradeoff between whether you want to spend tread or brake pads. But I'm not surprised you didn't know this.

The anecdote you presented was basically that of a race driver getting his rotors red hot versus a wimpy little economy car in economy mode. In that comparison only are you correct: the race driver is burning pad AND tread faster than the economy car commuting to work. <shakehead>


And yes, spirited driving is more fun than hypermiling. "Panic braking" clearly scares you, so I suggest that you stick to driving slowly.

 

[P63]

All that said, why would you want to drive around in B? There's a lot of economy to be had in coasting.

It saves on brakes and increases your range.

I agree that B is appropriate when a downslope is taking us above the speed limit or when we want to gradually slow to a stop. I use it all the time and love it.

I'm just pointing out that certain hills lend themselves well to coasting, and that on these hills superior economy is achieved by coasting than by driving with B on....
We're probably saying the same thing, because when you're on that same hill in B, you're not adding current to the engine nor is the computer engaging regen.

Regards,

 

[JoulesThief]

Please show other industry sources supporting your statement that braking gently wears the brake pads out more quickly than braking aggressively, Victor Marshall.

Every VW dealership that measures my brake pad thickness while rotating my tires asks me how recently I did a brake job. I get both great tire life and great brake pad and rotor life on my VW's with the way I drive.

Ask any married man that complains about a wife that drives poorly hard and fast on the throttle and brakes, how much he spends doing brakes and tires on the wife's car, "because she drives with a lead foot."

Compare that to the results of "the smooth driver" that does drive fast, but doesn't tear up their equipment, or warp their brake rotors or glaze them.

Basic chemistry has elements in solid, liquid or gas phase. The higher the temperature, the more active the molecules are and in the case of brake rotors, the closer the state of the surface of the rotor gets from a solid to a liquid, the softer the surface of the rotor material gets, hence when it gets hot, it gets easier to strip off and remove both brake pads and rotor material, from friction. Dispensing the heat and keep both rotors and pads cooler while braking, extends the life of both of the brake mating materials.

It's why full metal pads in racing conditions, need to heat up some to become effective, to become "grabby" , shed material, and brake well, as well as the rotors getting hot. It's also why they don't recommend metallic pads for street day to day driving.

The other thing driving and braking aggressively with VW cars in day to day driving will do, with continued hard braking, now that VW sources cheap rotors from China, is warp your brake rotors and give you brakes that surge at the brake pedal. Really don't care if you believe me or not, it's not yet a factor on e-Golfs, but it sure affects a lot of their other models.

 

[msvphoto]

As they say in racing, "smooth is fast."

I can not imagine how using regen to assist with the energy required to slow the car result in increased wear in the devices (brakes) used also to slow the car. I have hear of rear rotors rusting due to lack of use on eGolfs, but that is an opposite scenario.

 

[P63]

Please show other industry sources supporting your statement that braking gently wears the brake pads out more quickly than braking aggressively, Victor Marshall.

Every VW dealership that measures my brake pad thickness while rotating my tires asks me how recently I did a brake job. I get both great tire life and great brake pad and rotor life on my VW's with the way I drive.

Ask any married man that complains about a wife that drives poorly hard and fast on the throttle and brakes, how much he spends doing brakes and tires on the wife's car, "because she drives with a lead foot."

Compare that to the results of "the smooth driver" that does drive fast, but doesn't tear up their equipment, or warp their brake rotors or glaze them.

Basic chemistry has elements in solid, liquid or gas phase. The higher the temperature, the more active the molecules are and in the case of brake rotors, the closer the state of the surface of the rotor gets from a solid to a liquid, the softer the surface of the rotor material gets, hence when it gets hot, it gets easier to strip off and remove both brake pads and rotor material, from friction. Dispensing the heat and keep both rotors and pads cooler while braking, extends the life of both of the brake mating materials.

It's why full metal pads in racing conditions, need to heat up some to become effective, to become "grabby" , shed material, and brake well, as well as the rotors getting hot. It's also why they don't recommend metallic pads for street day to day driving.

The other thing driving and braking aggressively with VW cars in day to day driving will do, with continued hard braking, now that VW sources cheap rotors from China, is warp your brake rotors and give you brakes that surge at the brake pedal. Really don't care if you believe me or not, it's not yet a factor on e-Golfs, but it sure affects a lot of their other models.

Yes, your tires and brakes last a long time because you drive for economy.
Brake rotors do not get anywhere near the temperature of fusion. They can glow read hot on race cars, which use high temp pads that murder the rotors because their priority is winning the race, not brake component life. It sounds like you might be aware that race pads have longer stopping distances if they're not heated up, I'll give you that one.

LOL, you explaining warped rotors to ME. BTW, have you ever done a brake job yourself?
Anyone who thinks an occasional hard stop from freeway speeds will warp rotors is uneducated. Rotors get warped:
1. when drivers who know what they are doing go onto a private raceway and tear the hell out of their car roadracing, getting their rotors red hot.
2. having some loser mechanic seriously overtorque the wheels
3. buying cheap rotors to start with
Honorable mention: Keeping your pads in hard contact with the rotors after hard stops, say at a red light, can eventually cause a buildup of material from the pads onto the rotors. Over time this can give noticeable pulsating during braking, and is mistaken for warped rotors.

I actually can not find links talking about the tradeoff between spending tread or pad on stopping the car. Back in the 80s, when I had my Scirocco and my buddies had their Porsches, and this one Lockheed engineer was a semi-pro racer, we all had a conversation and agreed to the obvious fact that a long drag versus shorter hard braking will spend the pads and tires respectively. Consumer Reports even talked about this IIRC.

 

[spinner85j]

My understanding is that when you use regen with adaptive cruise control off, the braking is almost entirely from engine braking.
But when you use ACC to automatically modulate speed to maintain distance interval, the software "blends" regen and disk braking to achieve the result.

 

[GadgetGav]

To answer the OP, I bet the salesperson is confusing the fact that the brake *lights* come on when using B and you lift off the accelerator. In a modern EV, that doesn't mean the friction brakes have been applied, just that the regen is enough that it will appear to the car behind that the brakes have been applied, hence it's good practice to put the brake lights on too.