Braking distance concern by Consumer Reports

[mongo]

Think about what ABS does. It releases the brake long enough for the wheel/tire to reaccelerate to rolling at vehicle speed ( re-obtain static coefficient of friction). The forces reaccelerating the wheel are also frictional forces that are calculated using the downward force and some estimated coefficient of friction. If the front brakes stay off too long, ( maybe because they do not account for the extra normal force helping reaccelerate the tire), the car will take longer to stop.

It is fairly safe to say that the off time on the front brakes is too long, as "on" times being too long on any wheel would create commentary about skidding sounds and ABS not working, rather than unexplained long stopping distances.

ABS is multiple stage. The first step uses a valve to isolate the brake from the pedal, preventing more force. The second step uses a valve to divert brake pressure to an accumulator. The third step uses a pump to increase the pressure in the brake once it is rotating again.
f the ABS was preemptively reducing braking force in anticipation of skidding (learning the available friction) and leaned toward the not locking up side of things, it would increase the stopping distance.

 

[T34ME]

You nailed it! I'm 71, old-school, and was taught to keep my eyes on the road and keep one car's length of distance between me and the car in front of me per 10 mph of speed. I'll probably continue this strategy until I have full-blown Alzheimer's and need the car to autonomously delivery me to my head shrink!

Hey, amigo, you and I need to hang together. We can discuss the pros and cons of Depends, whether there is in fact "no pain" catheters, those little blue pills ain't worth sugar anymore, while we consume a Senior Moments Cocktail.......Vodka and Geritol. Real life begins at 70!

 

[shrspeedblade]

Don't know if this has been said or not and I didn't feel like plowing through all 6 pages to find out, but at 60mph you are traveling at 88 feet every second.

In layman's terms, that means a 75 Pinto with a highly attentive driver will out brake a moderately attentive driver in a modern Porsche. Modern media is about sensationalist headlines to get clicks. CR has always pontificated in such a way to make them a self-appointed authority to garner subscribers.

That having been said, I'm glad Tesla is looking into it as any responsible company would.

 

[electracity]

Will the dual motor model 3 have the same e brakes? I’m surprised he didn’t just outsource to brembo.

Also someone asked me to post a pic of my Model 3 with two thumbs down lol. I’m assuming this is to prove I have a model 3. Will do when I head to work this morning

The physical braking system is almost certainly adequate. The software is the problem. Ready-Fire-Aim. "We''l figure out blending regen with braking after delivery".

 

[mongo]

Don't know if this has been said or not and I didn't feel like plowing through all 6 pages to find out, but at 66mph you are traveling at 88 feet every second.

In layman's terms, that means a 75 Pinto with a highly attentive driver will out brake a moderately attentive driver in a modern Porsche. Modern media is about sensationalist headlines to get clicks. CR has always pontificated in such a way to make them a self-appointed authority to garner subscribers.

That having been said, I'm glad Tesla is looking into it as any responsible company would.

88 fps is 60 MPH (same as CR test)

 

[electracity]

the ABS was preemptively reducing braking force in anticipation of skidding (learning the available friction) and leaned toward the not locking up side of things, it would increase the stopping distance.

Regen with ABS is probably the complication. Without regen the braking vendor would have had this dialed in before production.

 

[shrspeedblade]

88 fps is 60 MPH (same as CR test)

I can do math, I just evidently can't type or proofread!
Thank you.

 

[ai4px]

What annoys me most about braking distance numbers is they leave out the decision and reaction time of the driver. Monash University in Australia have shown that a typical driver will need 1.5 seconds to make a decision and get their foot on the brake. 60 mph = 88 feet per second, thus it takes a driver 132 feet before they touch the brake. If the driver is alert and concentrating, this distance can be halved, If the driver is distracted then it can be doubled! When the biggest determinant of overall braking distance is down to the driver, hand-wringing over 20 or 30 feet seems trivial.

I took a ridiculous driver's ed course in the 1980's to keep from losing the last two points on my license. The class was a waste of time and the material was generic and inapplicable to even modern 1980's cars... but that 1.5 second stat was in there. I took thought it was a crazy huge number... until LED 3rd brake lights started appearing. Then it dawned on me that it takes the better part of one second just for incandescent brake lights to even come on! So if the lamp takes 3/4 of a second to come on, it would leave 3/4 of a second for reaction time... some of that is time used between your eyeballs and brain, the rest of the remaining time is for your foot to move to the brake.

 

[lklundin]

Regen would help with brake fade by offloading some (albeit a small amount, 1/7 in your example) of the braking force.

Yes.

Let's assume an M3 has its regen set to active and that the battery can take some charge.

If the brake pedal is pressed, is the regen then also assisting in the braking?

Secondly, if driving downhill with little tire-to-road friction (e.g. a snowy road) with the same assumptions as above and a wheel starts to slip, will the ABS then also reduce the regen?

 

[mongo]

Yes.

Let's assume an M3 has its regen set to active and that the battery can take some charge.

If the brake pedal is pressed, is the regen then also assisting in the braking?

Secondly, if driving downhill with little tire-to-road friction (e.g. a snowy road) with the same assumptions as above and a wheel starts to slip, will the ABS then also reduce the regen?

My understanding:
Lift up on accelerator: regen kicks in. If DU sees wheel spin, it drops regen.
Press brake: ABS is active, if ABS see wheel slip it backs off braking force.

So each system can back off on its own independently, but for best operation need to coordinate. (you brake, no, you brake, ok, I'll brake, me too, too much!!!)

 

[vinnie97]

Acknowledged by Elon today, so now we can stop with the incendiary CR attacks (and goofy comparisons that result in nothing but strife-laden political debates).

 

[Sharkbait]

Elon admits the cars have a problem. So much for your earlier (lame) comments

CR got a bad copy? As I said before, the problem really isn't that some of the cars may not stop as fast as others but it can perhaps be fixed with a firmware push. The problem is with the sensationalism associated with the message. Much of the media is eager to get a bit of news like this, a blow it up and create a stir. Much of what necessitates bringing an ICE to the dealer for a fix, Tesla can do with an OTA update. The news and media never grab that and run. People that drive irresponsibly will ultimately crash their cars.

 

[Driver Dave]

View attachment 302930

Serious. You just can't compare tesla or really any electric cars to gas cars.

Gas cars just plain suck now that electric is an option..

 

[MarcoRP]

@Doug_G

 

[mongo]

Read what Elon actually said instead of just relying on the click bait title.

He didn't admit the cars have a problem at all. He just said it is strange and might be earlier model and regardless they are going to go beyond spec.

Amazing how people get misled from the actual facts of things by articles trying to get clicks.

There is an issue, and they are fixing it, (early model referred to suspension/ride and wind noise)
Tesla Says It Will Issue Fix for Model 3 Brakes

 

[Driver Dave]

There is an issue, and they are fixing it, (early model referred to suspension/ride and wind noise)
Tesla Says It Will Issue Fix for Model 3 Brakes
View attachment 302997

I wonder if CR will update their article to point out how the CEO responded and is addressing?

Nah, they like the click bait article the way it is.

 

[bro1999]

Regen with ABS is probably the complication. Without regen the braking vendor would have had this dialed in before production.

There is an issue, and they are fixing it, (early model referred to suspension/ride and wind noise)
Tesla Says It Will Issue Fix for Model 3 Brakes
View attachment 302997

Whelp, someone just got pwned. Lol

 

[bro1999]

I wonder if CR will update their article to point out how the CEO responded and is addressing?

Nah, they like the click bait article the way it is.

Tesla Says It Will Issue Fix for Model 3 Brakes

Seriously, put away the FUDster pitchfork take a deep breath or 2. Despite your beliefs, the whole world is not out to destroy Elon and Tesla.

Original article was also updated with info from the tweets.
Tesla Model 3 Falls Short of a CR Recommendation

 

[jtpassat]

how can telling the truth about the testing results click bait. the fact that Elon acknowledged there's a problem vindicates CR's report.

I wonder if CR will update their article to point out how the CEO responded and is addressing?

Nah, they like the click bait article the way it is.

 

[Driver Dave]

the whole world is not out to destroy Elon and Tesla.

Are you serious? Auto dealerships, Car companies, Oil companies, short selling wall street... you think that is nothing against Tesla?

Tesla is up against maybe not the whole world, but definitely some of most powerful forces that any start up had to go against.

Sure Tesla is definitely not perfect, but you delude yourself if you think there are not big players out there that are using small solvable problems to try to take down the bigger picture that is coming to destroy their industries.