Braking news: Tesla preps firmware fling to 'fix' Model 3's inability to stop in time Tesla is to issue a firmware update before the weekend for its Model 3 to deal with a critical brake weakness that was highlighted by US website Consumer Reports. The publication found lots to like about the 'leccy saloon, particularly its record-setting range and insanely fast acceleration – but when it came to slowing down …
Only if people are twats and drive exactly on their minimal braking distance all the time.
Braking distance is more seriously affected by how much G you can subject the user to than anything else. You can make the car stop on a sixpence, it'll just break your neck and make you unconscious in your burning vehicle.
Braking distance is more seriously affected by how much G you can subject the user to than anything else. You can make the car stop on a sixpence, it'll just break your neck and make you unconscious in your burning vehicle.
Captain Pedant here. If you had said "stopping distance"*, that might have been mildly funny. Yes, the car will stop on a dime by crashing into a suitably substantial object, but that's not "braking", that's crashing. Braking distance remains limited by the traction of the tyres and the heat dissipation/sinking capability of the brakes.
*"breaking distance" might also have worked.
> traction of the tyres and the heat dissipation/sinking capability of the brakes.
If you were being Captain Pedant, then you should have at least made an effort to split out the "traction" element, for example:
- Tread depth (the legal limit is the legal limit, its. not an indicator that braking distance will be as good)
- Tyre makeup (there is a massive difference between cheap and expensive tyres)
- Coefficient of friction (and whether you are in a μ or split-μ situation)
- Tyre mismatch (hello tyre rotating wallies)
Whilst μ is an important factor, tyres and your attitude to changing them has the most substantial effect. Most people are unfortunately tightwads in that area.
Obviously you don't watch me driving.
It does help to be driving in a part of the country where others also most often leave sensible distances. Of course there are idiots, but far fewer than where I used to live.
Interestingly, both the distance that my car's adaptive cruise control uses and my own judgement are in quite close agreement.
> Interestingly, both the distance that my car's adaptive cruise control uses and my own judgement are in quite close agreement.
Mine is usually set at two seconds, save in wet conditions or bad visibility when I go full scale (four or five seconds, don't remember).
Braking distance is more seriously affected by how much G you can subject the user to than anything else. You can make the car stop on a sixpence, it'll just break your neck and make you unconscious in your burning vehicle.
The maximum deceleration to which you can safely subject a sitting human is around 9G - above that and internal organs start tearing off their mountings, which is a Bad Thing. For normal driving, you won't get tyres with a higher coefficient of friction than 1, so 1G is your maximum. Do what you like with brakes, ABS and regeneration - you're not going to hurt the driver.
F1 cars manage about 5.5 deceleration at high speeds, by the way, but that's because (1) their slicks have a friction coefficient of around 1.5 and (b) aerodynamic downforce means they have several times their weight to play with.
Well, that's some strange maths then.
"The stopping distance of 152 feet from 60mph was “far worse” than any of the 500 “contemporary” cars the publication has previously put through their paces."
152 feet = 46.3 m
60 mph = 96.6 km/h
https://www.johannes-strommer.com/diverses/pages-in-english/stopping-distance-acceleration-speed/
from 96.6 to 0 km/g in 46.3m = -18.494 ~= 2G.
And that's regarded as - I quote - FAR WORSE than any of the 500 contemporaries.
1G is by far nowhere near your maximum just under braking.
You can brake a pushbike and get 0.6-0.8 G under your own pedal power.
And even then.... even 1 G of acceleration is like entering freefall FORWARDS. Falling from, say, two feet onto glass head-first. It's someone picking you up by your ankles and holding you 2 feet above a windscreen and then letting go.
Even the Tesla does TWICE that and is being berated for poor braking.
Lee D - I'm not sure how you did your calculations, but you've made the classic mistake of believing the output of a calculator without filtering it through critical thought. Short of sticky tyres, fancier aerodynamics than a Tesla or running into something, the maximum achievable rate of change of velocity of a car is 1G.
Putting your numbers into the calculator you chose gives a deceleration of 7.8 m/s^2, which is far more reasonable.
I typed your numbers into the online calculator you cited, and it returned 0.8g deceleration. Since they're using the standard A=(V*V)/(2*D) equation, you might want to check your numbers. (Braking system strength tests intentionally do not test driver reaction time.)
Under 1g of deceleration, it's like coming down a 1:1 gradient on a planet 40% denser than earth. (SpaceX has no plans to test it on a planet like that, AFAIK.)
@Lee D - I am not entirely sure what exactly you input into the various fields of that online calculator.
I just rely on my own understanding of kinematics for order of magnitude estimates. With constant deceleration the braking distance (i.e., without taking into account the driver's reaction time that can easily be 0.7s for an alert driver, adding ~18m at 96.6km/h to the stopping distance) is
x = vt - at^2/2
where v=96.6km/h is the initial velocity and a is the deceleration that we want to compute. The deceleration time is t=v/a, which yields
a = v^2/(2x) = (96600m/3600s)^2/(2*46.3m) = 7.3 m/s^2 ~ 0.75g
for the Tesla. It is not clear to me what exactly "far worse" means in the context, but presumably other cars get closer to 1g and the corresponding 35m (115ft) that other posters assert as the best in class.
from 96.6 to 0 km/g in 46.3m = -18.494 ~= 2G.
s(t) = s(0) + v0 * t + 0.5 * a * t^2 and v(t) = v0 + a * t. So with v0 = 26.8 m/s, v(t) = 0 and s(t) = 46.3m you get
a * t = -26.8 m/s , 46.3 m = (a * t) * t - 0.5 * (a * t) * t , 46.3 m = 0.5 * 28.6 m/s * t
t = 3.2 s, a = 26.8 / 3.2 = 8.2 m/s^2, slightly under 1G.
And your dropping your head on to a glass plate as a comparison is neither here nor there, because that is a (gravitational) acceleration suddenly changing to an abrupt stop over very little distance, so there's at least a third order component at play. It's not at all comparable to tootling along at some speed, then stomping on the brakes.
And in addition, attainable deceleration has nothing to do with initial speed nor with the motive power used for reaching that speed.
> The maximum deceleration to which you can safely subject a sitting human is around 9G
You forgot to your time units. 50G for a few microseconds is quite OK (I can attest). 5G for two hours you will probably not be so healthy afterwards (5G sustained for a few seconds is my personal record doing aerobatics).
If remember correctly an america miltary guy (probably air force) did a lot of deceleration research by strapping himself on to a rocket sled and stopping it quickly. I think he got upto 50G before getting detached retinas, longer then a few microseconds but less than a second.
I think you can sustain 9G for a few seconds in a Typhoon in a G suit which covers both you torso and legs with the proper training and practice.
"I think you can sustain 9G for a few seconds in a Typhoon in a G suit "
That would be "positive G" i.e. being pushed into your seat by a "pull up" maneouvre. The safe value for "Negative G" (pushing the nose of the aircraft down) is lower, and can't be mitigated by a G suit in the same way.
Either way, the "50 G" figure you're quoting will be from a sensor bolted to a sled, and although the seat attachment and straps holding the chap to the sled might seem stiff, they will have smoothed out the acceleration and he *won't* have experienced the full 50 G.
50G for 10 μs corresponds to a change in velocity of 0.018 km/h. Therefore, if he's resorting to a rocket sled, I would guess he's dealing with a time that is much longer than a few microseconds.
I doubt it makes sense to talk about applying an acceleration to the human body for a few microseconds. The speed of sound in water is about 1500 m/s, so it'll take at least about 0.1 ms for a mechanical force to be transmitted through the body. If you apply a force for a shorter time than that then I would guess that you're dealing with an acoustic shockwave, whose physiological effects probably need to be assessed in a different way, and you'd have to either immerse the victim in water or use some kind of gel to transmit the acoustic shockwave into the victim's body. Experimental subject, I mean.
Nissan GTR would like a word. Several in fact. It not only does more decelerating but also accelerating and cornering. "chief engineer Kazutoshi Mizuno’s team has recorded a maximum of 2.8 g in the corners and 1.9 g under full braking at the Nurburgring."
Yes, might be on the "ring" but doesn't stop me doing 70mph and jumping on the (w)anchors to see what is possible.
"Braking distance is more seriously affected by how much G you can subject the user to than anything else"
Just to show how fast you can stop (and accelerate a car) look at a proper sports car.
"braked to zero from 100mph in a mind blowing 3.6 seconds"
http://www.ultimasports.co.uk/Records/0-100-0
> are we going to have a whole set of freeway pileups when half the cars in a stream of traffic can stop in 1/4 the distance of the others ?
No, because the braking assistance system purposefully stops you literally a couple of inches from the car in front. This is to a) leave as much stopping room as possible to the car behind you and b) make it *very* uncomfortable for the driver not to intervene before the car does.
It is the human driver that is more the risk, as our tendency is to just slam hard on the brakes.
Believe it or not, there are dozen / hundreds of engineers involved in every aspect of vehicle design, and if you thought about it, so have they.
I do remember an American show test driving an E30 M3 many, many moons ago and concluding that it was outright dangerous on the road because it could stop in under 130 feet from 60mph. Though this would be back in the days when your average North American car was a 2 ton barge, and it quite probably *was* dangerous to use that sort of braking power on a highway.
Though I still take issue with declaring it to be dangerous to have the *ability* to stop quickly when needed. The problem is drivers using that capability when they perhaps shouldn't. Motorcyclists die in hordes, but not usually via being rear-ended.
My car already has a radar for stopping but don't really want to test it so will have to take their word that it'll apply brakes (more than just me pressing the pedal) to avoid a crash.
I, of course, am not an Audi/BMW driver so leave plenty of stopping distance (3 seconds) between the car in front.
Sadly - Audi/BMW driver seems to always want to get in that gap ..
I really want a Tesla - I test drove a Model X and it was great but expensive. The Model 3 will be great if they can get the kinks out of it and mass produce it.
AFAIK, the 'stopping distances' chart in the UK 'Highway Code' hasn't changed since the first edition* - when a typical family saloon had drum brakes, operating on cross-ply tires a few inches wide.. There's no reason for the 'thinking distance' to change, but the braking distance really ought to be around half (or, more accurately, the assumed rate of deceleration should be doubled).
* It certainly hasn't changed since I took my test nearly 50 years ago.
I remember watching that consumer show on BBC where they where moaning about fake brake pads (i only fit oem on my car and performance after market on my bike, i got fed up with squealing brakes from cheap third parties). The brand new fake pads did take longer than the genuine ones already fitted to the car but the fake pads stopped well within the Highway Code limit and not actually that much longer than the bedded in genuine pads iirc ~10% but thefake pads where strait out of the packet and even new pads out of the packet take a little longer especially if paired with new disks. i think it was this show
https://www.bbc.co.uk/programmes/b06qz9y2
the Highway Code stopping distances need to be updated to reflect modern cars, brakes, tyres, road surfaces etc. I bet even most brake & tyre MOT failures would stop within the limit.
Clarkson and chums demonstrated the misinformation that is the Highway Code stopping distances when they put a range of cards through a braking test from sports to cheap shitbox. All pulled up well within the distance.
Problem as I see it is that common sense is in short supply on the roads. Many a time I've witnessed some tit in the outside lane racing the bollocks off of a Yaris and getting up the arse of something like an M3 or other car that would likely stop in half the distance it would.
> some tit in the outside lane racing the bollocks off of a Yaris and getting up the arse of something like an M3 or other car that would likely stop in half the distance it would.
Or, more importantly, a heavy vehicle or a bus. Except when fully laden (and even) stopping distance is far shorter than most cars. This is something that people who like to sneak behind fire engines¹ (in countries where people do that) would do well to keep in mind.
¹ Not to mention battle tanks. You definitely do not want to be too close behind one of those.
"Many a time I've witnessed some tit in the outside lane racing the bollocks off of a Yaris and getting up the arse of something like an M3 or other car that would likely stop in half the distance it would."
I was watching Car S.O.S the other week and Tim Shaw was trying to blag (like he usually does) performance brake pads for a car they were working on. The guy showed him several types of pads, and he gave them the highest performing pad that was road legal. Shaw asked why they couldn't have the higher performing pads and why they weren't legal. The guy said the higher performing pads are illegal because the car would stop too quick.
In your scenario, the Yaris could have far better tyres and pads than the M3. More often than not (in Birmingham at least), the rude bois who drive the M3's throw on the cheapest tyres they can find and the cheapest parts they can afford, while spunking the rest of the money on removing the DPF and getting more power from the car.
Before the advent of all the brake pad compounds now available the split was fast road/rally and competition.
Competition pads may fail an MOT because at the speed the test rollers run they don`t get warm enough to exert their full friction characteristics. There is min spec when cold for road legal.
There was a classic mintex formulation (177?) and a non asbestos later version too that passed the MOT limits cold and were road legal.
I found a motorsport garage through a mate from work cos i got fed up with being told that the pads needed changing soon. In the days before ABS with over servo`ed brakes they were a boon, If you found yourself in emergency stop you could stomp with at least half a second in hand to then cadence and lock and unlock as needed and they didn`t fade with disks glowing red down a 1 in 4 for a mile in first gear ( they exist) in Yorkshire.
The biggest problem (IMHO) is driver awareness and reaction time. You need to put the fools on a simulator and see how many times they crash and maybe it will sink in. Maybe.
My driving instructor was an ex RCT HGV instructor.
It is very reducible:
What can you see?
Can you guarantee to stop in what you can see?
If not F------well slow down.
What happens if the vehicle in front has a seized engine or a transmission failure, suddenly, do you have an escape route round the carnage? Can you rely on your reactions to save you? Back off give yourself thinking and reacting time. Space=time= safety margin.
I have a suspicion from the carnage word this was from being in convoys under fire and seeing the one in front go boom, but it is undeniably sensible
I get seriously baseball bat wielding inclined with the self relievers who slot into my reacton space which would be fine at 30, not at 70ish, so I pull back to make time. Time after time after.........
The most interesting thing was that some people teaching HGV now use the mantra gears for going, brakes for slowing, but in the days of only unassisted drum brakes you used what little airpump braking you get from the diseasel engine because a 5 mile descent isn`t a wise place to assume even disc brakes will stop all those tonnes or not fade like hell and have nothing at the bottom.
The old wisdom is you select the lowest gear that will not over-rev the engine because pumping loss and therefore engine retardation in diesels is most at high revs
I think the late Ian Dury summed up the " german car so rules don`t apply to me" syndrome with
"premature ejaculation drivers" on new boots and.....
"The biggest problem (IMHO) is driver awareness and reaction time. "
I didn't really think of it like that until the day before yesterday. Driving home I turned right at a big round about that a 50mph dual carriageway goes through, with an exit to a smaller country lane. Turning right, one car stopped as one idiot in a Ford Fiesta ST sped past. No bother, it didn't affect me. His friend though, following/racing him in a Corsa didn't stop, nearly smashed in to me.
I slammed the anchors on, he tried to. If I had relied on him to stop he'd have gone straight in to the side of the car. Thankfully, I know the roundabout and I anticipate dickheads like him speeding over. Throwing the car into 2nd gear while braking helps so much in reducing stopping distances.
The wife was next to me, and she panicked (as she'd have took the full force of the impact if it happened - also I was driving my small Peugeot 107 so not a massive car). I joked with her saying it was a good job I changed the brake pads last week with Mintex pads, along with the brake fluid.
Yesterday on the way home the wife said she had spoken to her friends about our near crash yesterday, and she believes if she was driving the car at the time she'd have smashed in to the prick and would've been badly hurt because of the speed he was going and the direction of our car. She wouldn't have used the engine to brake as she'd be worried she'd stall it. And she'd be right to think that, as it'd be easy done. But, like you say, it's the reactions. I didn't stall the car when I did an emergency stop, as I new I had high revs and could tell when the car was slowed down enough for me to engage the clutch.
I've done nothing though to convince her she should drive me home after work during the week now though.
While out riding my motorbike a few years ago, a tractor towing a large trailer pulled out in front of me blocking the road 100%. When I later calculated my stopping distance, I had approximately quartered the number given in the highway code. I was quite a bit above the limit initially - and hit the thing at ~10mph... Result was tractor 1, bike nil... I had a slightly broken leg.
So you don’t want algo between you and the breaks, so you drive a car pre ABS then? If not it’s already there.
On any electric car there isn’t a servo, it’s all drive by wire. So the breaking response can be changed. Difference is only Tesla can do that on the fly. Everybody else requires a trip to a dealer, if you have received the notification.
> So you don’t want algo between you and the breaks, so you drive a car pre ABS then?
A Tesla-esque braking algo is *NOTHING* to do with ABS.
Chalk cheese. Apples Oranges.
ABS is a specific and simple concept based around tire slip.
Tesla algo braking is some sort of blackbox "magic", that seemingly does not work that well.
You can still threshold brake in an ABS equipped car, you probably can't in a "brake-by-wire" Tesla.
I assume the poor braking performance of the Tesla is related to energy recovery. In order to maximize the range, they're trying to recover as much energy as possible under braking by using the electric motors to charge the batteries, rather than apply the regular brakes and just burn off the energy as waste heat.
But it would seem a bit clueless if they haven't programmed the braking system to be a little cleverer from the start - gentle braking using the recovery system (like F1 cars do when the driver lifts and coasts into a corner) but regular brakes with ABS and recovery if the pedal is hit hard. It shouldn't affect the range figures, as those I assume would generally be done while driving carefully, braking and accelerating gently, etc. rather than ragging it like you just stole it.
Looks like this can be fixed with a firmware update
As all car companies can tell Elon, that won't wash in a US class action suit. Whether it's this or something else, it's just a matter of time until the software industry finds the legal limits of providing software updates instead of product recalls and massive compensation and legal fees.
I admire Musk but the financing of Tesla means he has absolutely no wriggle room for legal issues. But I suspect he'll still be able to sell the company at a profit to GM, Ford or Geely.
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