Electric car thread

[spacesailor]

Problem is , the car has overruled any other escape , from disaster. 

Turn your car even slightly , with that breaking & you loose control,  all the motoring organisations tell you,

BREAK IN A STRAIGHT LINE .

What next " automatic locking steering " .

Just to keep you aimed  at the ' suicidal nutter ' .

spacesailor

[nomadpete]

According to Qld Transport Dept:

 

https://www.qld.gov.au/transport/safety/road-safety/driving-safely/stopping-distances

 

Average stopping distance from 100kph (about 60mph) in a straight line on dry bitumen is 56 metres (plus another 42mtrs reaction time).

 

We are talking about braking distance, aren't we? Not breaking distance.

 

However, Consumer Reports in US say:

 

"The Tesla’s stopping distance of 152 feet from 60 mph was far worse than any contemporary car we’ve tested and about 7 feet longer than the stopping distance of a Ford F-150 full-sized pickup."

 

And they didn’t  like it at all.

 

Maybe they have different rubber compounds over there?

Edited March 21 by nomadpete

[old man emu]

OK, here goes. Trust me, I studied the Physics involved in traffic accident reconstruction at The Traffic Institute, Northwestern University, Evanston Illinois and wa certified by the Illinois Law Enforcement Officers Training Board. I think that proves my credentials to comment on the improbability of the claim in the ad.

 

So, we have a normal passenger vehicle that is said to stop from 100 kph in 2.4 seconds.

 

To calculate the rate of deceleration that would be required to achieve that we use the formula t = (Final velocity - Initial velocity)/ rate of acceleration

 

This can be written in shorthand as t = (Vf - Vi)/ a

 

Since the units of "a" are metres/second/second we have to convert 100 kph to metres per second, and that is 27.7 m/s

 

Plugging in the numbers we get: 

2.4 = (0 - 27.7)/a

2.4 = -27.7/a

rearranging for "a"

2.4 x a = - 27.7

a = -27.7/2.4

a = - 11.54 m/s/s

 

On a typical sealed road surface, multitudes of tests have indicated that the rate of deceleration that a standard passenger vehicle can achieve with full wheel lock up is 0.7 x 9.81 m/s/s = 6.8 m/s/s

 

That 9.81 m/s/s/ is the acceleration due to gravity. If you say that 9.81 is 100%, then the ad is claiming a deceleration of 117% of the acceleration due to gravity. The only way to get a deceleration greater than 9.81 m/s/s is to hit a brick wall.

 

And before you bring up ABS improving stopping distance, due to the fact that ABS prevents wheel lock up, the actual rate of deceleration is a tad less than for a non-ABS stop. However, for the sake of this argument, I am happy to accept that the ABS and non-ABS stopping performance are the same.

 

[Marty_d]

10 minutes ago, old man emu said:

OK, here goes. Trust me, I studied the Physics involved in traffic accident reconstruction at The Traffic Institute, Northwestern University, Evanston Illinois and wa certified by the Illinois Law Enforcement Officers Training Board. I think that proves my credentials to comment on the improbability of the claim in the ad.

 

So, we have a normal passenger vehicle that is said to stop from 100 kph in 2.4 seconds.

 

To calculate the rate of deceleration that would be required to achieve that we use the formula t = (Final velocity - Initial velocity)/ rate of acceleration

 

This can be written in shorthand as t = (Vf - Vi)/ a

 

Since the units of "a" are metres/second/second we have to convert 100 kph to metres per second, and that is 27.7 m/s

 

Plugging in the numbers we get: 

2.4 = (0 - 27.7)/a

2.4 = -27.7/a

rearranging for "a"

2.4 x a = - 27.7

a = -27.7/2.4

a = - 11.54 m/s/s

 

On a typical sealed road surface, multitudes of tests have indicated that the rate of deceleration that a standard passenger vehicle can achieve with full wheel lock up is 0.7 x 9.81 m/s/s = 6.8 m/s/s

 

That 9.81 m/s/s/ is the acceleration due to gravity. If you say that 9.81 is 100%, then the ad is claiming a deceleration of 117% of the acceleration due to gravity. The only way to get a deceleration greater than 9.81 m/s/s is to hit a brick wall.

 

And before you bring up ABS improving stopping distance, due to the fact that ABS prevents wheel lock up, the actual rate of deceleration is a tad less than for a non-ABS stop. However, for the sake of this argument, I am happy to accept that the ABS and non-ABS stopping performance are the same.

 

OME, I'm not doubting your qualifications.  You did say 2.8 seconds in a previous post then 2.4 above.

However either your maths are incorrect,  or the conclusions,  because another site lists 10 cars which all stop from 100 kmh in under 2.8 seconds.

https://thebrakereport.com/car-lists-10-fastest-cars-stopping-from-100-km-h/

[Jerry_Atrick]

Yeah.. but were there people in them, or crash test dummies?

[old man emu]

Sorry about the 2.4 -v- 2.8. I was relying on my memory of the ad, which I believe quotes 2.4. You can check if you happen to see the ad, but I can't remember what car it was, apart from being a normal passenger car.

 

The rate of deceleration (or acceleration) that a vehicle can achieve is dependent on the Coefficient of Friction (CoF) between the tyres and the road surface. The CoF (u) is the ratio of the vertical force the vehicle exerts on the surface ( Fn), which we call "weight" and is the product of mass x force of gravity, and the force required to move the vehicle horizontally on the surface (Ff). 

The Static CoF is just as we start trying to move an object, but as we get it going, and then it becomes easier to move and we measure Kinetic CoF. 

 

 

The CoF is applied to the value of acceleration (9.81 m/s/s). Since the CoF is a ratio, its maximum value can only ever be one (1). That's why I find those published figures unusual. You also have to remember that the tests, if done using a driver, would have had a very experienced test driver who knew exactly when an where to begin braking, and they don't indicate the road surface. 

[facthunter]

Some tyre compounds will give you a coeff. greater than one. Nev

[facthunter]

Don't take MY word for it . Look it up.   Nev

[old man emu]

2 hours ago, facthunter said:

Some tyre compounds will give you a coeff. greater than one. Nev

Quite correct! Drag slicks and F1 tyres stick like sh!t to a blanket, BUT don't last for the kilometres that the average consumer needs to make tyres economical. With that in mind, perhaps the tyre compounds used in the high performance cars listed above is not the same as that in the tyres of your average family vehicle. If you can afford to buy an expensive high performance car, you aren't likely to be worried about the cost of tyres. 

 

I have to draw your attention to the figures here  

 

I can't confirm where the tests that produced the figures were conducted, but if they are from Europe or the USA, we have to be careful because in those places they put down much more bitumen in their road surfaces which we can't do here because of our higher average air temperatures and levels of solar radiation. In my field test while investigating collisions, I found that an average CoF figure for road surfaces containing bitumen was around 0.7 to 0.75, giving a value of ug of 6.8 to 7.3 m/s/s.

 

Other factors are the type of surface seal - asphaltic concrete (hotmix) or coated gravel glued down with sprayed bitumen. Also, as the surface ages, both types get smoother and the CoF reduces from its newly laid value. Have you ever noticed the really rough-textured, pale road surface on the approach side to a set of traffic lights if the approach is downslope? That pale surface is there to increase the CoF to help yellow light runners stop before the light goes red.

[facthunter]

Antiskid operating will improve stopping distance,  except on gravel. Diesel spill will cut the coefficient to almost nothing on tar, Black ice and frost on wooden bridges and aquaplaning and leaf mould on  damp roads etc. These are the practical things an observant Motorcycle rider or Car driver will be wary of IF they drive to the conditions  .Nev

[old man emu]

2 hours ago, facthunter said:

Antiskid operating will improve stopping distance,  except on gravel.

Nothing stops well on a gravel road compared to a sealed road. 

 

Antiskid systems work by enabling the brakes to reach that point just before the wheels lock, which is the point at which the brakes reach their maximum ability TO STOP THE WHEEL'S ROTATION. When that point i reached, the system eases off the brakes momentarily, then has another go. The driver who is stamping on the brake pedal without letting off, feels that on/off application as shudder. Since the average driver never experiences this while learning to drive, when it does happen in a real world situation it becomes another source of scare in an already scary situation.

 

The reason for the installation of an ABS system is not primarily to shorten distance to stop, but to allow the driver some small amount of tyre/surface friction to make turning the steering wheel cause a change in direction, and possibly steer away from an impact.

 

Do you want me to go into how tyre/surface friction is used to move a vehicle and have it change direction at the same time (cornering)?

[facthunter]

My antiskid experience is primarily with aircraft where it provides max retardation without blowing tyres and most people  who can drive or ride know that you can't corner on the LIMIT and slow or accelerate MUCH at the same time.    Nev

[old man emu]

1 hour ago, facthunter said:

My antiskid experience is primarily with aircraft where it provides max retardation without blowing tyres

Yep. If you do full brake lock-up stops you put flat spots on the tyres. I used to stick on a set of worn tyres when I was doing those tests. 

[facthunter]

The F-27  had AIR brakes with MAX Arrets. Air brakes can you believe? .   Nev

[pmccarthy]

And pneumatic gear extension.

[spacesailor]

When you drop a car from a vertical hight , ( to gain the mps required ) , nose first onto a solid floor , that deceleration is Deadly. 

from ' Mithbusters ' . ( one dead Dummy ) .

ABS is shocking driving on sand , pushes you side to side , & if you go to fast , sends you into a " ground-loop''

My Pajero has it & I have to remove a fuse , while sand driving . ( another 4X4 driver showed me how ) .

spacesailor

 

 

Edited March 22 by spacesailor
It changed my spelling

[pmccarthy]

ABS = brake dancing

[onetrack]

Here's a little downside from the brave new world of EV's and their information-gathering (from the NY Times).

The Chevrolet Bolt is the latest EV product from GM.

 

"Automakers Are Sharing Consumers’ Driving Behaviour With Insurance Companies:
­

Kenn Dahl, a meticulous driver from Seattle, was puzzled by a 21% hike in his car insurance for his leased Chevrolet Bolt in 2022. Investigating further, he discovered that his driving data had been extensively tracked and shared with insurers by LexisNexis, a global data broker.

The data included detailed logs of every trip, revealing aspects like speed, hard braking, and rapid accelerations, but not the locations.

This information was sourced from General Motors, the Bolt's manufacturer, and used to create a risk score for insurance purposes.

Dahl felt betrayed, highlighting a broader issue where car companies and data brokers, under the guise of usage-based insurance and with often obscure consent from drivers, monitor and share detailed driving behaviours.

This practice raises significant privacy concerns and questions about transparency and the real intent behind data collection, leading to increased scrutiny from consumers and policymakers alike."

 

Edited March 22 by onetrack

[facthunter]

It's intermittent (Cycling)   brake releasing in it's crudest form. Till it was fitted to any plane with a bit of weight, blowing tyres was a common happening with associated deviations from the runway occurring..   Nev

[Jerry_Atrick]

It's not limited to EVs.. Here is the article; they are reporting with the example of a driver who happens to drive an EV: https://www.nytimes.com/2024/03/11/technology/carmakers-driver-tracking-insurance.html

 

Regardless of the car you buy, check whether it has Internet connectivity

[willedoo]

17 hours ago, spacesailor said:

When you drop a car from a vertical hight , ( to gain the mps required ) , nose first onto a solid floor , that deceleration is Deadly. 

from ' Mithbusters ' . ( one dead Dummy ) .

Almost as bad as driving a Phantom into a concrete wall.

 

 

[Marty_d]

In all of that, they never showed an "after" shot of the concrete wall.  Was there a crater?  Was it demolished?  Was there just a big black spot?

[facthunter]

The Law of conservation  of linear momentum should cause the cement block to move . Nev

[red750]

In the second section (left side of aircraft, you can see that the aircraft is demolished to the trailing edge of the wing before something breaks through the back of the concrete block.

[old man emu]

1 hour ago, facthunter said:

The Law of conservation  of linear momentum should cause the cement block to move . Nev

Theoretically, YES, but it also depends on the relative masses. That block would have a mass very many times that of the aircraft, despite the momentum the aircraft had due to its velocity.