Flaperon
Full Member

I’ve gone right off the Tesla. The adaptive cruise control is so bad now that it’s unusable. When you’re driving on the motorway you get random emergency braking if the car nearby drifts in their lane, so you have to turn all the collision mitigation stuff off before you leave.

To be honest, the behaviour of Musk was putting me off having another but this seals it. Worst thing is that it used to be fine on the motorway and now it’s awful. Everyone is assuming that Tesla drivers are brake-testing them and it’s just the car itself.

My friend has this problem on his one, and it was something to do with the camera alignment being wrong. Tesla diagnosed it remotely somehow when he complained about it.

Just been to Mercedes dealer again for some cheap part, walking past all their lovely new cars. They had an AMG EQE-63.. Oof.

Interesting Flaperon – which model is that? recent software update

A 2021 Model 3, on 2023.38.6. I’ve had a bloody good whinge to Tesla about it and their service response was along the lines of “we know, everyone is complaining about it but we [Tesla UK] can’t fix it”. Because you need to dive into the settings and inhibit the emergency braking system on every journey, it’s easy to forget if you’ve jumped out to open a gate or something.

It stamped on the anchors in front of a police car the other day, who judging by the siren and blue lights wasn’t particularly impressed. Although maybe he just learned a valuable lesson about keeping his distance from Muskmobiles. Anyway, I’m worried sick now.

Is that a fleet car? Can you return it if not fit for purpose? Sounds a real PITA. It seems all modern cars are going this way, not just EVs.

There is nothing intrinsically electric about that fault, for sure.

Sounds like something the DVSA should be aware of. My Leaf had a very rare fault where it would accelerate when cruise control was disengaged in very rare cases, and Nissan had to recall them all. This sounds way worse.

DVSA: “…if the emergency brakes are applied by the Front Assist system, the driver will be alerted by the infotainment system and the brake lights will function to warn other road users. To conclude, whilst I acknowledge a performance concern may exist, DVSA are currently unable to conclude that this concern meets the definition of a safety defect.”

Doesn’t seem to mention anything about the driver of the car behind sitting up to their neck in their own excrement.

I guess they are expecting other drivers to be prepared for the driver in front to brake at any time….

It stamped on the anchors in front of a police car the other day, who judging by the siren and blue lights wasn’t particularly impressed.

What did they say?, shirley it’s their responsibility to leave the appropriate braking distance for just this reason ie emergency braking.

Must admit i generally didn’t have a problem and what odd daft stuff autopilot did was fairly consistent so I knew when to be ready to act. Slamming the brakes on the motorway does sound decidedly unhealthy and I’d be pretty cheesed off about that as it’s the main place you want to use it to make the journey a slightly more relaxing experience.

interestingly on the consumption, I had a very slow rush hour drive from west of Glasgow to Leith this morning, in air temps of about 1.5 degrees.  Average speed was 25.2mph, and car did 3.7mi/kWh, taking 2hrs and 6 minutes to cover the 51 miles.  The exact return journey at lunchtime, took 1hr 16 mins, at an average of 39.7mph (and sitting at 70 ish when I could on the M8) and consumption was 3.2mi/kWh, air temp about 3.5 degrees.
so slower is better !  total consumption for the day, 29.1 kWh, at a grand cost of £2.18 :)

BMW i4, air on at 20 degrees throughout, heated seat and wheel for first 10 mins of each trip.

slower is better

Yes, very much so. The most efficient speed for an EV is around 20MPH ish from memory – although that probably changes with temperature as the parasitic losses due to heating change. There are some graphs published for Teslas if you google it – the absolute efficiency values might change but the shape of the curves should be pretty much the same

It did seem a bit of a backward step for Tesla to move from camera + Lidar to camera-only, even the former isn’t 100% accurate when it comes to object detection etc. but it’s a lot better than camera alone. Similar madness to remove the parking sensors and rely on cameras only to.

The most efficient speed for an EV is around 20MPH ish from memory

I don’t think you can give a number. It’ll depend on the car and all sorts of other things. The motor has an efficiency curve but the actual speed that corresponds to depends on the final drive ratio and the wheel size. And the efficiency of the car’s other electrical systems, aerodynamics and the driver’s preferences all play a part. The more you use for cabin heating, the faster you have to go to offset that against miles driven.

It may vary a bit with the factors you mention but all the analysis I’ve seen suggests that EVs are very much more efficient at lower speeds and tail off quite poorly when going fast whereas ICE have a bit of a sweet spot more like 50mph.

Incidentally I looked a bit more carefully at my heating cost and it’s more like 7% of the range when I turn it on and off, a bit lower than the 10% I mentioned before. I’m pretty sure it’s a heat pump but could be wrong.

all the analysis I’ve seen suggests that EVs are very much more efficient at lower speeds

This is true yes, but whilst the optimum speed is low it varies a lot by car. And in ICEs it varies a lot more and on more factors. I pretty much always set the cruise control to 70mph in any car, but certain journeys give better results in some cars but not others. It’s a pretty complicated calculation in an ICE I think.

The impression I get is that EVs are a lot more susceptible to headwinds because 100% of the energy generated goes to propulsion, whereas for an ICE vehicle it’s only about 10%. So going slightly faster has a much greater effect, and a 20mph headwind is like bumping your speed from 70mph to 90mph (worse, actually, because you don’t actually get to your destination any faster).

In 40mph sections of roadworks I see my predicted range well in excess of 450 miles.

The impression I get is that EVs are a lot more susceptible to headwinds because 100% of the energy generated goes to propulsion, whereas for an ICE vehicle it’s only about 10%.

Hmm no, don’t think so – most of the energy in any car goes against air resistance. In a headwind, both kinds of car will do the same amount of extra work, but in the ICE two thirds of the fuel will still be wasted either way (diesel engines about 35% efficient ish).

‘Making progress’ driving, temp set at 21 degrees,  outside 5 degrees, 2020 tesla without a heat pump. Cabin heating is an astonishing amount of the total.

Note re the most efficient speed – Molgrips is correct, you can’t it changes between cars and conditions – hence why I said “20MPH ISH”

Drive ratios etc don’t matter for EV efficiency by the way unless they’re way out of wack- that just changes where the motor is operating in its speed range and the efficiency curve is fairly flat compared to the large change in power consumption with speed.

What determines the most efficient speed is a pretty basic balance between speed independent  “per time” energy usage rate – e.g. power for the lights, heating etc etc and the “per distance travelled” energy usage rate. Given that the “per distance travelled” rate increases with higher speed (rolling resistance a bit, but aerodynamic drag increases with the square of speed).

If the fixed energy rate loss was not there then the most efficient speed would be almost zero, to minimise drag. But of course fixed losses are real, so whilst driving at 1MPH might be efficient from a drag point of view you’d drain your battery before getting very far.    What makes an ICE cars most efficient speed so much higher are the increased fixed losses – even at low speed and engine power you’re losing quite a lot to waste heat. They’re typically more like 40-50 MPH ish.  ICEs are also more variable in terms of where this most efficient speed is for various reasons, a key one is that an ICE engine has a much less flat efficiency curve than an electric motor both in terms of speed and load, and each engine and car setup is different. It’s also rare to drive an ICE at its most efficient point in its operating map which is typically around 2-2.5K RPM and 3/4 of full throttle ish. (getting closer to doing so is one of the points of a hybrid system).

One outcome of all this is that the most efficient speed for an EV will likely actually be slightly higher in winter than summer as the fixed losses (heating) are greater.   Either way the EV max efficiency speed is typically so low that for real world driving “slower is more efficient” is generally true.

Re headwinds – the same lack of fixed losses mean that the increased power that has to expended to drive into a headwind is more noticeable, it’s not “diluted” by the higher fixed losses of an ICE.

Hmm no, don’t think so – most of the energy in any car goes against air resistance.

Propulsion is equal to air resistance plus tyre drag…

In that screenshot posted by Picton road it says that the brake pedal cost 0.6% and that you should use regeneration where possible instead of braking, which implies that a tesla doesn’t automatically use regeneration when you press the brake pedal.

Is that right that tesla don’t regenerate automatically when you press the brake pedal? Seems a bit backward if that’s the case, but tesla are usually pretty sharp so what’s going on with this.

I haven’t been in many evs but I think they all automatically regenerated when you pressed the brake pedal, up to a point where the retardation requested could not be achieved by regen alone and then they engaged the friction brakes as well as regen.

Is that right that tesla don’t regenerate automatically when you press the brake pedal?

On mine you get full regen by lifting off the accelerator. Brake pedal is just normal brakes but rarely touched.

On mine you get full regen by lifting off the accelerator. Brake pedal is just normal brakes but rarely touched.

Does that mean the brake lights come on when you lift off part/most of the way or is it just like engine braking on an ICE?

Sorry maybe a numpty question but I followed a model 3 the other day and the brake lights were on and off like they were being operated by a sugar loaded toddler who’d just discovered the light switch.  Just wondering if they were utterly incompetent or this was some EV trait.

Their driving style was very much “surge, slow, repeat”.

On mine you get full regen by lifting off the accelerator. Brake pedal is just normal brakes but rarely touched

So it doesn’t coast when you lift off the accelerator? Again i thought that was supposed to be pretty inefficient…

Edit: ignore have read that tesla do coast it just doesn’t need lift of the accelerator to do it

@flaperon kind of

The impression I get is that EVs are a lot more susceptible to headwinds because 100% of the energy generated goes to propulsion, whereas for an ICE vehicle it’s only about 10%.

ICE is at most 30-40% efficient. Most of the energy from fuel is turned into heat. The AAA had a nice headline ages ago along the lines of ‘2/3 of your fuel is wasted’.

EVs are about 90% efficient at turning stored energy into movement.

Both are affected by headwinds in the same way of course for a given drag factor. But I suppose you’ll notice the difference in consumption in the EV first as it will be proportionately bigger.

Edit – just saw @whatgoesup gave a comprehensive answer.

Sorry maybe a numpty question but I followed a model 3 the other day and the brake lights were on and off like they were being operated by a sugar loaded toddler who’d just discovered the light switch. Just wondering if they were utterly incompetent or this was some EV trait.

Their driving style was very much “surge, slow, repeat”.

In the Teslas if regen engages above some, fairly low, level the brake lights come on because the car is decelerating. It can look like folks are tap dancing on the brake pedal in slow moving traffic. Because of the deceleration, the brake lights are a reasonable warning measure.

The relatively quick acceleration and aggressive regen may take some getting used to for folks used to, for example, a sluggish diesel ICE I suppose.

Also the brake lights come on whenever the car stops. This seems common in most modern cars though.

@julians

In some ways it’s an atypical journey as it was almost all empty b roads so the brake pedal was deployed in a wanton manner.

I’d say you could drive almost every journey in a tesla without touching the brake pedal with just a hint of anticipation.

It does however illustrate that even when you’re acting the tit, regeneration takes care of most of your deceleration requirements.

On mine you get full regen by lifting off the accelerator. Brake pedal is just normal brakes but rarely touched.

Are you sure? Brake pedal should also activate regen unless the deceleration you’ve requested is greater than what can be obtained using regen. I’m pretty sure all EVs and hybrids blend regen and friction brakes regardless of what pedal you press except the BMW i3, which is one reason I didn’t get one.

Re brake lights, there is a rule that specifies they must come on when the deceleration is more than 0.7g I think again regardless of how that’s obtained. Although, 0.7g is quite a lot…

have read that tesla do coast

Of course, otherwise the wouldn’t be able to do consistent speeds. In an ICE, the accelerator and brake pedals operate mechanical systems, and you have to operate them to get the car to do what you want. An EV can do things differently, so now the pedals just indicate how fast you want to be going (or not) and the car takes care of the rest.

Are you sure? Brake pedal should also activate regen unless the deceleration you’ve requested is greater than what can be obtained using regen

not with teslas- apparently – brake pedal on tesla is purely friction brakes.

Interesting ish article here on the different strategies employed by various car manufacturers – TLDR : there are lots of different way of achieving the same end result.

https://www.roadandtrack.com/car-culture/a42268449/one-pedal-driving-isnt-necessarily-the-most-efficient-way-of-driving-an-ev/

I have my car set to coast when I lift off and only regen when I press the brake pedal – I tried the various other modes including one pedal mode and didnt like it much, but I guess I’d get used to it over time. Good to have the choice though.

Are you sure? Brake pedal should also activate regen unless the deceleration you’ve requested is greater than what can be obtained using regen. I’m pretty sure all EVs and hybrids blend regen and friction brakes regardless of what pedal you press except the BMW i3, which is one reason I didn’t get one.

Brake blending was developed for the XC40/PS2 launch, a couple of other manufacturers who use the same core brake module launched at almost the same time. Treats the motors and brakes as two braking systems and divides brake torque between the systems based on capacity. Does this continually, monitoring capacity of each system plus requested torque. So even if you do a full on stop, you’ll still be using as much regen as the car is capable of producing plus the friction brakes. (ignore ABS in this case!)

Prior to that you had systems that would only regen on accelerator lift off and use brakes if you pressed the brake pedal.

Other systems would also allow regen on brake pedal, but only in perfect conditions with no disturbances (or they would use, or suddenly switch, 100% to friction brakes, and then stay with friction brakes until stop). This wasn’t very good.

Brake lights usually come on at about 0,6 to 0,8 m/s2 with regen from lift off of the accelerator pedal, and immediately when you press the brake pedal.

I was convinced that the two braking systems were blended on my Prius. When the car had been sat for a few days you could hear the friction brakes working (or not) due to the rust on the discs, and it seemed to work as I described.

On the Leaf, there’s a regen meter and you get the same number of blue bars if you brake at roughly the same speed using the pedal, or using the one-pedal feature or B mode. Of course it’s not a scientific test. Certainly if you lift off you get some blue bars, then if you touch the brake pedal you get more blue bars.

Brake lights usually come on at about 0,6 to 0,8 m/s2

Ah yes, 0.7m/s2 makes way more sense than 0.7g!

What tyres for EVs ?  

Some random observations and anecdotes which may or may not be valid … EV are relatively heavy and hence wear out tyres more quickly than lighter cars. EVs are supplied with low resistance = low grip tyres in order to pump up the apparent range numbers. People are having to get new tyres as soon as 10k miles. Winter is coming.

So should we be thinking of replacing our OEM tyres with 4-season, and if we do, what effect on the range can we expect?

I’m running CrossClimate 2 on my Model 3.

30,000 miles now of mostly motorway driving and still 5mm of tread all round. I think there’s a small hit in efficiency and noise levels but the trade off is worth it for me. I drive like James May which obviously helps.

On mine, the brake light comes on if you hard lift off the accelerator in ‘iPedal’ (one pedal) mode, but also the highest regen settings. Lifting off lightly has no effect on brake light, even thou there is a regen:/braking effect.  At the lower regen settings lifting off slows the car (mildly, as you would expect) but with no brake light activated. I assume this all correlates to the 0.7m/s^2 threshold. Though touching the brake pedal puts the brake light on irrespective of how lightly the braking force.

EDIT: just read Mert’s post above which corresponds exactly!

re tyres i got michelin primacy 4 for my ioniq last time – big improvement on the OEM michelins previously fitted. I was wavering about getting cross climates as had them on my previous corolla hybrid and they were excellent with no impact on efficiency, but i was swayed by A rating tyre efficiency and keeping range.  I think that when i next replace the tyres i will go with cross climates as have had a few moments recently to make me want the better mechanical grip year round over a few miles extra range (and there are more quick chargers on the few regular long journeys i do).

Re: blended braking – my corolla hybrid had this and it worked really well – initially was regen then on harder braking the ‘normal’ brakes would come in.  My ioniq does the same thing – as mentioned above can hear sometimes when the discs bite and scrape off the overnight rust – often not for quite a while into a journey if been braking gently.

Re tyres, is there really much real world range difference between say an A rated efficiency tyre and a C rated efficiency tyre?

Tried to find some objective independent testing for the above, but failed miserably, so can only conclude that the efficiency rating makes negligible difference to real world range.

I did find some results that said that some high efficiency tyres were notably worse for grip in certain circumstances though, think it might have been wet braking.

probably not much difference.  the primacy tyres i have are supposedly better in wet braking than a cross climate (according to labels) but reading up that is in the summer. living in a rural area with narrow roads, i will often have to dip the wheels onto the verge – with the current soft ground and the fact that regen means the car brakes as soon as i lift off this has led to a few no grip moments and i think that in future i would rather have the extra mud traction than save a few miles range! 

all the analysis I’ve seen suggests that EVs are very much more efficient at lower speeds

Ideal.

low resistance = low grip

Hold on a minute. Low rolling resistance does not always have to mean low grip. Yes, the ones that come on your car are shite, even those that bear the same name as aftermarket tyres, but if you buy quality you can get both low RR and good grip because rubber engineering and compounds and whatnot. Yes, the higher RR ones are a bit better, but only a bit.

Re tyres, is there really much real world range difference between say an A rated efficiency tyre and a C rated efficiency tyre?

People on the Leaf Facebook page are amazed that we still get over 4 m/kWh at 70mph in our Leaf even in winter, but we don’t do anything other than set the cruise control. The only difference is that we have Conti Eco Contact 6 tyres on.

On my Passat I went from 55mpg on a regular motorway run to 60mpg when moving from Dunlop Sport to Nokian H. Seems like 5-7% improvement is normal going from average to the best A rated tyres. I gained more on the Merc but that was an extreme case: I went from wide super low profile sporty tyres to still quite wide still quite low profile premium touring tyres and gained about 12% on a regular trip.

Tried to find some objective independent testing for the above, but failed miserably

The ratings are now A-E and each rating is a 0.1l/100km jump, presumably on some typical test setup. The more efficient your car to begin with, the more is saved in terms of litres.

For reviews, this guy does loads but he always seems to be at a Goodyear testing facility so, who knows. But he does compare a load of tyres most of which aren’t Goodyear. He does regular videos too when new things come out.

And there’s website version of the same content – mercifully!

https://www.tyrereviews.com/Article/2023-Tyre-Reviews-Summer-Tyre-Test.htm

I was convinced that the two braking systems were blended on my Prius.

There’s been a few attempts, mostly using some version of the “regen/friction until the car gets a wobble on, then use only friction until we either stop, or have xx seconds of no braking at all.”

“Proper” blending is continuous and can switch back and forth, except when ABS or TC is activated, which adds all sorts of extra, difficult to deal with, effects. And everyone deals with them differently.

I really like the regen on my kia. It’s not proper one-pedal driving but quite close to it, I hardly touch the brakes in normal driving around on local roads and it slows down nicely for corners etc.

I can tell from the sound when the proper brakes come on, at least early in a trip.

and edit, I do also use the paddles mentioned in that linked article, at least when I remember to. I have it set on the 2nd level, but may switch to the highest 3rd level for steep descents.