Discussion
We can hear you, no need to shout.
EVs have regenerate braking and in practice use their mechanical brakes far less.
For 100 years, car makers have been fitting bigger brakes to their heavier cars.
Why would you think they will all of sudden stop doing this because the drivetrain is different?
The majority of the weight of an EV is low and concentrated at the centre of the car.
The actual weight increase % wise isn’t that great.
Weight transfer during braking is well controlled leading to better stability.
Speed limits in the UK are under significant downward pressure, predominantly due to local air pollution issues.
Fuel consumption increases exponentially with speed, and so does pollution.
Do your road safety concerns extend to those living near roads and the quality of the air they breathe?
EVs have regenerate braking and in practice use their mechanical brakes far less.
For 100 years, car makers have been fitting bigger brakes to their heavier cars.
Why would you think they will all of sudden stop doing this because the drivetrain is different?
The majority of the weight of an EV is low and concentrated at the centre of the car.
The actual weight increase % wise isn’t that great.
Weight transfer during braking is well controlled leading to better stability.
Speed limits in the UK are under significant downward pressure, predominantly due to local air pollution issues.
Fuel consumption increases exponentially with speed, and so does pollution.
Do your road safety concerns extend to those living near roads and the quality of the air they breathe?
GT911 said:
We can hear you, no need to shout.
EVs have regenerate braking and in practice use their mechanical brakes far less.
For 100 years, car makers have been fitting bigger brakes to their heavier cars.
Why would you think they will all of sudden stop doing this because the drivetrain is different?
The majority of the weight of an EV is low and concentrated at the centre of the car.
The actual weight increase % wise isn’t that great.
Weight transfer during braking is well controlled leading to better stability.
Speed limits in the UK are under significant downward pressure, predominantly due to local air pollution issues.
Fuel consumption increases exponentially with speed, and so does pollution.
Do your road safety concerns extend to those living near roads and the quality of the air they breathe?
Playing devils advocate, regen is low/absent at very high states if charge, cold batteries etc shifting the workload to friction brakes which alone are generally smaller than equivalent ICE.EVs have regenerate braking and in practice use their mechanical brakes far less.
For 100 years, car makers have been fitting bigger brakes to their heavier cars.
Why would you think they will all of sudden stop doing this because the drivetrain is different?
The majority of the weight of an EV is low and concentrated at the centre of the car.
The actual weight increase % wise isn’t that great.
Weight transfer during braking is well controlled leading to better stability.
Speed limits in the UK are under significant downward pressure, predominantly due to local air pollution issues.
Fuel consumption increases exponentially with speed, and so does pollution.
Do your road safety concerns extend to those living near roads and the quality of the air they breathe?
Weight is also generally up in EVs, but they also have a tendency to smaller tyres to reduce drag so the contact patch doing the work is reduced.
On a typical day with an 80% battery and a good road they’re fine, but I have to say none have been outstanding compared to other cars I’ve owned.
On a cold morning they’ve been very underwhelming,
…but then so were the ceramics on the Aston I had for a while until things warmed up.
Heres Johnny said:
Playing devils advocate, regen is low/absent at very high states if charge, cold batteries etc shifting the workload to friction brakes which alone are generally smaller than equivalent ICE.
There was a post a while back from someone who lives at the top of a long hill and had to rely on mechanical braking in their i3 (I think) each morning after a full charge. I think they were more concerned that they were losing the potential energy they had put into the car by driving up the hill the previous day, rather than braking distances.The only way to fix this would be to stop charging at 95% or whatever to leave enough capacity for the downhill run.
It should be quite easy for manufacturers to include a software option to allow users to choose their max. SOC to cater for this sort of thing. But yeah, I agree in certain circumstances, it requires a bit of extra thought and planning.
Given that most EV's have a regen system, I would argue that in most cases an EV is going to be able to react better than many normal cars. For the average driver, we are taught to use one foot for accelerator and brake - so something happens in front of you, you step off the accelerator (starts braking) and then step on the brake (brake harder). In that case, its going to be a little more predictable and reasonable.
And of course, no manufacturer is going to sell a car with an elongated distance to stop. They just ramp up the brake sizes to cope - and even when you factor in the weight, most EV's will be utilizing regen under heavy braking anyway, so it gives a much more predictable process anyway. Now, if the technology fails, that might be interesting. But also remember that your average EV is going to be using regen braking more often, brakes tend to last longer and less wear over an extended period of time - so its all good.
Now, handing a 1000 BHP car that weighs 2 tons to a novice driver - now thats something that needs consideration. No matter how big your brakes are, its going to struggle to haul a heavy car down from deeply illegal speeds - but thats true of anything at that point. 600+BHP SUV's fall into the same camp, and are in many cases, even heavier!!
And of course, no manufacturer is going to sell a car with an elongated distance to stop. They just ramp up the brake sizes to cope - and even when you factor in the weight, most EV's will be utilizing regen under heavy braking anyway, so it gives a much more predictable process anyway. Now, if the technology fails, that might be interesting. But also remember that your average EV is going to be using regen braking more often, brakes tend to last longer and less wear over an extended period of time - so its all good.
Now, handing a 1000 BHP car that weighs 2 tons to a novice driver - now thats something that needs consideration. No matter how big your brakes are, its going to struggle to haul a heavy car down from deeply illegal speeds - but thats true of anything at that point. 600+BHP SUV's fall into the same camp, and are in many cases, even heavier!!
off_again said:
Now, handing a 1000 BHP car that weighs 2 tons to a novice driver - now thats something that needs consideration.
One of the obvious differences between an EV and an ICE is the lack of gearbox.The gearbox is an interesting animal when you look at it objectively.
Basically it allows you to access the peak power of an engine at low road speeds.
Now we all know this is done to improve acceleration and also improve fuel consumption.
What we don't really think about is that the gearbox also costs quite a bit in terms of energy lost to heat and rotational inertia changes. It also creates power spikes that can break traction and unsettle the car when the next gear arrives.
When you remove it, you remove all of those downsides (dynamically speaking), and assuming you have enough torque, acceleration is relentless and often faster than a car with the same power to weight ratio. EVs are the perfect example.
When I say downsides, I'm not referring to the sensory aspects of using a gearbox, just the dynamics at play.
A really good example of this is in the drag races between the Koenigsegg Regera vs the One:1.
The Regera doesn't have a gearbox, but it does have relatively constant electric torque fill to bolster the engine. It is an almost unique concept for an ICE car, but look at the results.
Despite the lower power to weight, and the fact that there is no access to peak power at low road speeds, the Regera pulls away from the One:1 in a drag race and set a world record for 0-400-0 kph.
Without a gearbox remember, just a big fat wodge of relentless torque and a final drive in the diff.
The only time you can access the full power is when the road speed and drag is very high, so you end up with a much better match of the powerplant to the task at hand. Just like a boat or train.
I've been trying to describe this (with limited success I'd add) on the 1000 hp Chevy 10.3 litre crate engine thread. Basically, I've shown graphically how you can build an Ultima that should match the Regera on acceleration from standstill to 300 kph with just the Chevy engine, a torque converter and a diff. Assuming the sans-gearbox engine fits of course...
What I'm getting at is that the 1000 hp EV you are talking about won't have that power available for it to be misused at lower speeds, which can often be the cause of coming unstuck.
Some EVs have two-speed gearboxes, and the electrical drivetrain most likely also has a constant power section in the upper half of its speed range, so the rule above is not hard and fast, but its very different to deploying full power in the lower gears.
Edited by GT911 on Thursday 21st October 21:36
GT911 said:
What I'm getting at is that the 1000 hp EV you are talking about won't have that power available for it to be misused at lower speeds, which can often be the cause of coming unstuck.
No, you're going to have to run that one by me again. You have seen the Model S Plaid accelerate from 0-60 yes? SWoll said:
No, you're going to have to run that one by me again. You have seen the Model S Plaid accelerate from 0-60 yes?
The Model S has a single speed 'gearbox'. The speed ratio between the wheels and the motors is fixed by whatever final drive ratio they are using.The motor speed is therefore directly proportional to the road speed. So 100% motor speed = 100% road speed.
The motors produces a constant torque from standstill and then this tails off at higher motor speeds.
For the sake of simplicity, call it constant torque to 50% motor speed, and then constant power above that.
The only time an electric motor (or an engine for that matter) can produce its rated power is when speed multiplied by torque is at its highest.
Power = torque x speed
If speed is zero, power is zero.
The Tesla motors will therefore never be producing their maximum power until around 50% of their speed.
If you only have one ratio in the gearbox, therefore 50% motor speed can only ever be at 50% road speed, unless of course the tyres are spinning.
Therefore 100% power can only ever be accessed at 50% road speed.
It's an odd concept I get it, but because we've grown up with gearboxes, we take it for granted that we can access full power in most gear at lots of different road speeds.
Remove the gearbox, and without a clutch or torque converter to slip, you take away this access.
The way EVs accelerate is to throw a wall of continuous torque at the wheels, at all road speeds, usually without any gearchanges. There are some exceptions, the E-tron GT and Taycan have a 2-speed gearbox, so applying the same logic above, you can only access full power in those cars at 25% road speed.
It's an entirely different approach to trying to regularly but intermittently access full power through each gear. Which is ultimately just a half-hearted attempt at mimicking a high torque electric motor.
You have to do this an an ICE, because generally, they don't have wall of torque to throw at the wheels, so you need to multiply the torque of the engine at low road speeds to get the car to accelerate fast enough, and of course to avoid stalling the engine. But then you run out of revs and need to select another gear. This approach is much less efficient in transferring energy at the engine to energy at the wheels.
The gearless ' torque wall' approach is obviously very effective.
This is because you avoid the intermittent power spikes, that can also break traction, and the loss of useful energy and drive to the wheels every time you change gear.
The EV puts more energy into the wheels for more of the time, so it accelerates faster.
Actual power curve vs speed for Plaid, they have pulled the point at which it reached full power further down the full speed range, probably by playing a few tricks between the 3 motors:
Edited by GT911 on Friday 22 October 13:44
GT6k said:
OP where's your data? My BMW I3 weighs only 100kg more than my Cerbera did. And my Kia Sedona weighs the same as a Tesla Model X.
A little more. My Cerbera was 1170kg in 2007 with 3/4 tank of fuel, the i3 is a much smaller car and weighs 1370kg.If we're playing top trumps the Cerbera has 0-60 in 4 secs, the i3 almost twice that at 7.3. Range, 260+ miles on a tank full for the Cerbera, 130 for the i3? The i3 wins on cost per mile
But totally different cars for different jobs.The Sedona is a heavy beast though - almost 3 tonne, the Model x is around 2500kg and is probably better all around?
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