Well, that was Ludicrous!

[whitenemesis]

Sat at traffic lights, HGV on the inside line, me in the centre and a white Tesla in the outside. A long shallow left curve ahead, no traffic.
Lights change and ..... gone! The Tesla just, well, went. Just a dot in the distance. I was still breathing in, ready to move off!
My first experience in the real world of what must have been Ludicrous mode. First time I'd seen a Tesla driven anything other than steadily. He wasn't eking out the last mile from the battery that's for sure!
Impressive ...

 

[Bobby Dazzler]

Sat at traffic lights, HGV on the inside line, me in the centre and a white Tesla in the outside. A long shallow left curve ahead, no traffic.
Lights change and ..... gone! The Tesla just, well, went. Just a dot in the distance. I was still breathing in, ready to move off!
My first experience in the real world of what must have been Ludicrous mode. First time I'd seen a Tesla driven anything other than steadily. He wasn't eking out the last mile from the battery that's for sure!
Impressive ...

Sounds familiar.

EV Acceleration + Idiot - Experience = Dangerous? | Driving/Incidents/Roadrage

Please don’t confuse this with an anti-EV thread, because it’s not (and I’m not). Also apologies that this will be a long post, but I think the context is key. Today I was sat first in the queue at a set of traffic lights, in the left of two lanes. To the right of me - in the second of the two...

forums.mbclub.co.uk

 

[whitenemesis]

Sounds familiar.

EV Acceleration + Idiot - Experience = Dangerous? | Driving/Incidents/Roadrage

Please don’t confuse this with an anti-EV thread, because it’s not (and I’m not). Also apologies that this will be a long post, but I think the context is key. Today I was sat first in the queue at a set of traffic lights, in the left of two lanes. To the right of me - in the second of the two...

forums.mbclub.co.uk

Similar but in no way was this instance dangerous. Completely clear road, that's what made it all the more impressive, just a receding dot whilst I was still just thinking of moving off. No tyre squeal, no sound at all. There one second, gone the next

 

[Bobby Dazzler]

Similar but in no way was this instance dangerous. Completely clear road, that's what made it all the more impressive, just a receding dot whilst I was still just thinking of moving off. No tyre squeal, no sound at all. There one second, gone the next

It is a remarkable sight to see (but barely hear) one at full tilt.

 

[BigEyd]

They are horrible looking though so they actually done you a favour

 

[ChipChop]

The lack of recognisable car noises from EV's is not at all good for the cyclists they share the roads with.

 

[Bellow]

The lack of recognisable car noises from EV's is not at all good for the cyclists they share the roads with.

Ask them to remove their headphones - not that they'll hear you.

 

[Dryce]

Impressive ...

The problem is that you end up with a car suddenly turning up where it is not expected.

One of the things I learned with a motorcycle many moons ago was that I could end up in places where other drivers assumed would be no vehicle.

My concern with EVs doing this is that at least with a motorcycle you traditionally provide an audible warning of your presence when zipping about - whereas with a quick EV you turn up somewhere unexpected relatively quietly.

 

[Fastcar155]

Hi , do they stop as quickly as they accelerate ?

 

[fabes]

I saw one a few years ago just do 30 to '70 something' on a motorway when traffic opened up
It was like watching a 2T white block teleport from there to 'over there'
No travel or journey, it just arrived.
It was amazing.

What was also amazing but (I suppose) wrong is a YT short I fell across of a van unable to pass two adult cyclists who were riding side by side (possibly with earphones in so they didn't hear the van rather than being obnoxious) finally get past them and brake check them.
This didn't hit but both came off from swerving and stopping....

As I said, wrong, but you could see where he or she was coming from (it was a motor factor van and they are often piloted by ladies round my way)

An EV might have been able to pass them quick enough in traffic, so there's that positive to the EV trend.

 

[fabes]

Hi , do they stop as quickly as they accelerate ?

Watch some of the Carwow drag races with the brake test at the end.
No, no they don't!

 

[markjay]

Hi , do they stop as quickly as they accelerate ?

Interesting question.

Instinctively I would expect cars to brake quicker than they accelerate, but with a Tesla Model S Plaid doing 0-60 in 2.5 seconds, I can't see it stopping from 60mph in 2.5 seconds.

But the issue is that car tests seem to measure acceleration by time, but braking by distance. So it's not easy to compare. Not sure if this has ever been measured and compared? I'll have a Google and post any findings.

 

[Dryce]

Interesting question.

At these sorts of performance levels the issue is not just mechanical performance - but driver anticipation / reaction / thinking time - basically not getting yourself into trouble so quickly that you don't end up having a bad day.

 

[markjay]

Found this:

https://nacto.org/docs/usdg/vehicle_stopping_distance_and_time_upenn.pdf

"60 MPH = 88 fps. (fps=1.467 * MPH). If the vehicle deceleration rate is 20 fpsps (rather
than the previously calculated 15 fps), then stopping time = 88/20 = 4.4 seconds. Since
there is a 1 second delay (driver reaction time) in hitting your brakes (both recognition
and reaction time is often 2 seconds), the total time to stop is 5.4 seconds to 6.4 seconds"

That's for an average car ("automobile or light truck") in dry conditions (using typical tyres presumably).

So it does seem that performance cars - with 0-60 figures below 5-6 seconds - do stop slower than they accelerate.

I am guessing that the reason that no one seem to have asked this question before is that acceleration depends very much on the specific car model, but braking does not - once the brakes are applied, braking performance is probably determined to a large degree by the tyres and the road surface, to a lesser degree by car's kinetic energy at the time, but not really in the car's tech.

And so comparing stopping performance by braking in a straight line from 60mph between different cars is pointless. That's my guess, anything. But nevertheless it's a very interesting question - I hadn't thought about it before.

 

[markjay]

Thinking of this further, the other issue is that the only relevant parameter for braking performance is the car's speed, not the car's acceleration.

So if a 1975 Ford Granada with a 0-60 figure of 13.6 seconds starts accelerating in a straight line, and 10 seconds later a Models S with 3.6 seconds starts accelerating, then both cars will reach 60mph at the same time, and both will face (almost) the exact same difficulties in stopping.

In short, as far as stopping is concerned, it doesn't matter how long it took the car to get to 60mph, because braking performance is unaffected by the car's acceleration ability.

 

[BTB 500]

the only relevant parameter for braking performance is the car's speed, not the car's acceleration.

Obviously the issue is that a quick EV may be going a lot faster when it has to brake.

But in general terms the amount of grip from the tyres is surely the key factor. All cars are capable of applying braking force to the point where the wheels lock up, so the amount of friction available will be limited by the tyres (and will depend on the tread pattern and compound). Weight transfer from rear to front under braking (affected by the height of the vehicle) might come into it - I'm not sure whether the increased load on the front tyres would completely offset the reduced load on the rears. Vans used to have a load compensator valve that varied the amount of rear braking depending on the weight in the back (operated by the rear suspension compressing) - I assume ABS has made this redundant nowadays. Anyway I once hired one that turned out to have a stuck compensator valve - when it was empty even quite gentle braking at low speeds could result in the rears locking up with a deafening screech from the tyres. I had to drive it all the way round the North Circular on a Saturday morning, and was definitely the centre of attention

I'm sure modern tyres perform much better than ones from 40+ years ago, which is probably the reason for generally reduced stopping distances nowadays. I would expect an EV and an ICE one fitted with the exact same tyres to stop in pretty much the same distance (from the same speed on the same road surface).

 

[markjay]

Obviously the issue is that a quick EV may be going a lot faster when it has to brake.

But in general terms the amount of grip from the tyres is surely the key factor. All cars are capable of applying braking force to the point where the wheels lock up, so the amount of friction available will be limited by the tyres (and will depend on the tread pattern and compound). Weight transfer from rear to front under braking (affected by the height of the vehicle) might come into it - I'm not sure whether the increased load on the front tyres would completely offset the reduced load on the rears. Vans used to have a load compensator valve that varied the amount of rear braking depending on the weight in the back (operated by the rear suspension compressing) - I assume ABS has made this redundant nowadays. Anyway I once hired one that turned out to have a stuck compensator valve - when it was empty even quite gentle braking at low speeds could result in the rears locking up with a deafening screech from the tyres. I had to drive it all the way round the North Circular on a Saturday morning, and was definitely the centre of attention

I'm sure modern tyres perform much better than ones from 40+ years ago, which is probably the reason for generally reduced stopping distances nowadays. I would expect an EV and an ICE one fitted with the exact same tyres to stop in pretty much the same distance (from the same speed on the same road surface).

Agreed. It's worth adding that the concern with performance cars isn't stopping as such, but brake fade. The assumption is that a car capable of fast acceleration will be driven in a sporty manner that requires frequent use of the brakes, hence the performance brakes fitted to sport cars. But, as said, it will have no effect on straight-line emergency braking. Probably the key differenciating factor (for the same road surface and environmental conditions) would be the tyres (make and model, condition, air pressures) and to a much lesser extent the car's weigh distribution (given that it's probably managed by the ABS anyway).

 

[BTB 500]

I assume a 'performance EV' would make significant use of regenerative braking, which should make them less prone to brake fade?

 

[markjay]

I assume a 'performance EV' would make significant use of regenerative braking, which should make them less prone to brake fade?

Yes, though it's worth noting that for emergency braking both the regenerative braking and the discs are used, i.e. the regenerative braking isn't as efficient as the discs when it comes to 'panic stop', and also it produces very little energy anyway (because there's little movement of the wheels).

 

[Bellow]

If it has traction to accelerate to 60 mph in 3-4s, it will have grip enough for braking. Most cars can brake at around 1g. Unless it is accelerating harder than 1g then theoretically at least, braking capability exceeds accelerative capability.