Discussion
A Tesla Model 3 drove past me recently, then slowed to a stop before flooring it - I guess somebody was showing off the acceleration.
Impressive to see but one thing that struck me was hearing the tyres scrabbling against the road and you could just sense the energy being put into the tarmac.
Now I've been looking into EVs recently and according to Parker's, I noticed the Peugeot e-208 EV is 500kg heavier than the petrol version and has a similar leap in torque. It seems obvious that as the transition to EVs continues, the average weight of our cars is going to go up significantly, as is the amount of energy they can put down.
How are our roads going to cope with this? Is our tarmac going to get more chewed up or do cars cause relatively little damage overall?
Impressive to see but one thing that struck me was hearing the tyres scrabbling against the road and you could just sense the energy being put into the tarmac.
Now I've been looking into EVs recently and according to Parker's, I noticed the Peugeot e-208 EV is 500kg heavier than the petrol version and has a similar leap in torque. It seems obvious that as the transition to EVs continues, the average weight of our cars is going to go up significantly, as is the amount of energy they can put down.
How are our roads going to cope with this? Is our tarmac going to get more chewed up or do cars cause relatively little damage overall?
durbster said:
A Tesla Model 3 drove past me recently, then slowed to a stop before flooring it - I guess somebody was showing off the acceleration.
Impressive to see but one thing that struck me was hearing the tyres scrabbling against the road and you could just sense the energy being put into the tarmac.
Now I've been looking into EVs recently and according to Parker's, I noticed the Peugeot e-208 EV is 500kg heavier than the petrol version and has a similar leap in torque. It seems obvious that as the transition to EVs continues, the average weight of our cars is going to go up significantly, as is the amount of energy they can put down.
How are our roads going to cope with this? Is our tarmac going to get more chewed up or do cars cause relatively little damage overall?
Roads are designed for 44 ton semi artics, so cars should not be a problem. I imagine a few block-paved driveways will sag though.Impressive to see but one thing that struck me was hearing the tyres scrabbling against the road and you could just sense the energy being put into the tarmac.
Now I've been looking into EVs recently and according to Parker's, I noticed the Peugeot e-208 EV is 500kg heavier than the petrol version and has a similar leap in torque. It seems obvious that as the transition to EVs continues, the average weight of our cars is going to go up significantly, as is the amount of energy they can put down.
How are our roads going to cope with this? Is our tarmac going to get more chewed up or do cars cause relatively little damage overall?
While the roads should be fine, as stated, heavier cars do raise some other questions.
A lot of multi-storeys were designed back in the days of the original Mini and the Mk1 Cortina. Average car weight was probably well under a ton. That average has probably doubled with the trend to bigger cars with much stronger structures, the rising popularity of SUVs and now the move to BEVs.
How much margin was allowed in those designs?
Another one is particulates: I've read that 50 - 60% are generated from road/tyre wear and friction braking and that heavier vehicles produce more, logically. That said, it is still much better than smokey old taxis!
A lot of multi-storeys were designed back in the days of the original Mini and the Mk1 Cortina. Average car weight was probably well under a ton. That average has probably doubled with the trend to bigger cars with much stronger structures, the rising popularity of SUVs and now the move to BEVs.
How much margin was allowed in those designs?
Another one is particulates: I've read that 50 - 60% are generated from road/tyre wear and friction braking and that heavier vehicles produce more, logically. That said, it is still much better than smokey old taxis!
Mikehig said:
Another one is particulates: I've read that 50 - 60% are generated from road/tyre wear and friction braking and that heavier vehicles produce more, logically. That said, it is still much better than smokey old taxis!
I would imagine that tyre technology will improve and most EV's use regenerative braking without using disks and pads don't they? I'd imagine with technology improvements in road surfaces too we would see a negligible difference in particulates but I'm no scientist!RazerSauber said:
I would imagine that tyre technology will improve and most EV's use regenerative braking without using disks and pads don't they? I'd imagine with technology improvements in road surfaces too we would see a negligible difference in particulates but I'm no scientist!
I would guess that 90% of our braking is done via regen in daily use so the dics/pads get very little wear at all. With regards to tyres I've found that the linear nature of the power delivery combined with very clever traction control results in very little tyre scrabble even with 500bhp/500lb-ft being put through them on a regular basis. After 8k miles our tyres are barely worn at all despite it being a relatively heavy car and driven 'enthusiastically' often. 
EVs do tend to be very light on tyres. Partly because their torque modulation is better than an ICE car and I believe partly because EVs don't generally need to play the tricks with suspension geometry that ICE cars to do tame torque steer which means they run closer to pure ackermann geometry more of the time, leading to less tyre scrub. Of course EVs tend to also run harder, more economy focused tyres.
Edited by kambites on Friday 30th October 13:05
Isn't the Tesla about the same weight as the equivalent BMW? It's a bit of a myth EVs will be heavier, just badly designed ones are heavier.
If they are made from the ground up as an EV they are not much different in weight it would appear, I think Tesla are trying to make their cars lighter than the equivalent ICE with their new 'battery is part of the frame' design they spoke about on battery day.
If they are made from the ground up as an EV they are not much different in weight it would appear, I think Tesla are trying to make their cars lighter than the equivalent ICE with their new 'battery is part of the frame' design they spoke about on battery day.
The weight difference with smaller cars is more pronounced. For example the Renault Zoe and Honda E are both about 1.5 tonnes. A typical petrol supermini is about 1.2.
Also the Model-3 is unusually light (the critics would say that's because it's so poorly built). The Polestar 2, for example, weighs well over two tonnes.
Also the Model-3 is unusually light (the critics would say that's because it's so poorly built). The Polestar 2, for example, weighs well over two tonnes.
EVs have significantly lower tyre wear under heavy acceleration than ICE's because they have much lower driveline torsional vibration and therefore have much lower "macro slip", which is also why they generally are capable of faster 0-60 times (because the tyre spends more time gripping and less time slipping, ie it can transfer a greater overall tractive effort to the road).
Macro slip occurs because your ICE is not actually a continuous process. Individual cylinders are filled with air and fuel, and ignited, and power is produced each time, not continuously but in sudden pulses. The more cylinders your engine has, the smoother the output is, but all ICEs actually have massive torsional vibrations that are transmitted though to the tyres, and on each firing event, the tyre slips a tiny bit under the load.
For a 4 cyl engine, every 180 deg of crank revolution there is one firing pulse. Yes ICE use tricks like dual mass flywheels to try to minimise the amount of TV that gets to the driveline, but it's a significant effect, especially on heavily boosted low cylinder count engines (ie modern ones!)
And EV has practically no torsional vibration because its electric motor is effectively continous, making broadly the same output at all point in its revolution, menaing tyre slip is significantly less, even if the average slip is comparable.
Finally, because the torque of an electric motor can both be modulated very quickly (approx 1,000 times a second or more) and very accurately (+- 1Nm at the drive wheel or better), and with full bi-directionality (ie it can both generate and absorb torque) the control system can manage overal slip extremely well.
Macro slip occurs because your ICE is not actually a continuous process. Individual cylinders are filled with air and fuel, and ignited, and power is produced each time, not continuously but in sudden pulses. The more cylinders your engine has, the smoother the output is, but all ICEs actually have massive torsional vibrations that are transmitted though to the tyres, and on each firing event, the tyre slips a tiny bit under the load.
For a 4 cyl engine, every 180 deg of crank revolution there is one firing pulse. Yes ICE use tricks like dual mass flywheels to try to minimise the amount of TV that gets to the driveline, but it's a significant effect, especially on heavily boosted low cylinder count engines (ie modern ones!)
And EV has practically no torsional vibration because its electric motor is effectively continous, making broadly the same output at all point in its revolution, menaing tyre slip is significantly less, even if the average slip is comparable.
Finally, because the torque of an electric motor can both be modulated very quickly (approx 1,000 times a second or more) and very accurately (+- 1Nm at the drive wheel or better), and with full bi-directionality (ie it can both generate and absorb torque) the control system can manage overal slip extremely well.
What would a torque graph of a typical modern four-pot petrol turbo look like, measured at the wheels? Just how big is the differential in torque between the peak of a combustion stroke and the trough midway between strokes once all the mush in the drivetrain has been overcome? Are we talking a 1% difference in torque? 5%? 50%?
kambites said:
What would a torque graph of a typical modern four-pot petrol turbo look like, measured at the wheels? Just how big is the differential in torque between the peak of a combustion stroke and the trough midway between strokes once all the mush in the drivetrain has been overcome? Are we talking a 1% difference in torque? 5%? 50%?
It really only becomes significant at higher loads where dynamic firing torques at the flywheel can approach 100% of the average torque for low cylinder count engines. ie an engine that makes 300Nm of peak static torque could have 300Nm of dynamic spike torque impossed on that mean. A DMF has something like 60 degree or more of "sprung free play" to try to decouple the drivetrain from the crank TV's, and the transmission itself has a finite stiffness and inertia. Typically the wheel and tyre inertia dominate the effect because they are relatively massive (heavy and large diameter)"race" engines,ie high output engines with minimised inertia,often coupled to high stiffness, low mass, drivetrains can suffer from terrible Torsional vibrations. It's been reported that motorcycle racing engine manfacturers have tried to optimise firing pulses to get the highest tyre traction, with deliberately un-even firing orders to try to avoid continous resonance in the tread/carcass.
The main problem is often the harmonic spurs rather than the base frequency of the TV. A 4 stroke 4 cyl engine at 3000 rpm has a fundamental firing frequency of 100Hz, so harmonics exist at 50, 25, 12.5, 6.25 Hz etc
It's extremely hard to measure in reality. To measure what the tyre sees's you need all the correct inertia's and stiffnesses. One way is to use a hub dyno where the inertia of the dyno elements is used to offset the inertia of the wheel/tyre (not fitted) , but this quickly gets complex and expensive.
One option that has been tried was to use highly sensitive accelerometers glued to the wheel to try to directly measure wheel dynamic accelerations in real time in real driving environments. I've also heard of tyre manufacturers using camera's below transparent sheets in the road to try to view the tyre/road interaction
Nothing intelligent to add to this, but thank you to all the posters so far this has been quite a fascinating thread.
I've had an EV now for 6 months and still occasionally exclaim out loud my surprise at how well my Model S puts down the power, especially at the moment with colder and wetter surfaces, it's appears to defy physics, or certainly everything I thought I knew about the limitations of a car over the last 26 years of driving!
I've had an EV now for 6 months and still occasionally exclaim out loud my surprise at how well my Model S puts down the power, especially at the moment with colder and wetter surfaces, it's appears to defy physics, or certainly everything I thought I knew about the limitations of a car over the last 26 years of driving!
Electronicpants said:
Nothing intelligent to add to this, but thank you to all the posters so far this has been quite a fascinating thread.
I've had an EV now for 6 months and still occasionally exclaim out loud my surprise at how well my Model S puts down the power, especially at the moment with colder and wetter surfaces, it's appears to defy physics, or certainly everything I thought I knew about the limitations of a car over the last 26 years of driving!
One issue with traditional cars is that the maximum tractive effort can only be obtained when the tyres normal (vertical) load is also the highest. This introduces a problem for fwd and 4wd cars, in that for maximum static traction the driving torque needs to be applied in direct refererence to the vehicles mass distribution, but then modifed to account for the longitudinal weight transfer generated as a result of that acceleration!I've had an EV now for 6 months and still occasionally exclaim out loud my surprise at how well my Model S puts down the power, especially at the moment with colder and wetter surfaces, it's appears to defy physics, or certainly everything I thought I knew about the limitations of a car over the last 26 years of driving!
This means that for a typical car, with the engine at the front, you want more torque on the front axle initally (at launch / tip in) but as the car starts to accelerate, and weight transfers backwards, you want to move that torque backwards. Of course, complex mechanical transmission systems, usually based on clutch pack controlled epicyclic geartrains, have been used on ICE cars to achieve this, with good results, but few of those systems get anywhere near the speed and capability of a pure 4wd EV, able to modulate torque at each axle over 1,000 times a second. So your Tesla, which knows it's static mass distribution, and knows how hard it is cornering or accelerating at any given moment, can simply and precisely apply exactly the maximum each tyre can cope with, and no more.
Because tyres actually grip more like velcro than using basic friction, the characteristic curve for grip vs slip is a complex shape, and it's far better to remain just under peak mu than to exceed it. Once a tyre is spinning it's harder to regain grip.
Mileage will vary on tires, but there a lot of horror stories of Tesla's eating through tires in a very short period of time!
Some owners are reporting going through a set of rears in 5000 miles or less, though what we dont necessarily know is if this is due to bad alignment, poor build or just a douchy owner, so you will have to take a lot of this with a pinch of salt. That said, there is enough evidence to suggest that some spirited driving will see you plough through them pretty quickly if you arent careful.
And while there maybe some technical reasons to suggest that they might last longer than in a IC car, a lot of people do drive them aggressively and this will absolutely eat the tires quickly. For example, rolling accelerations in a modern turbo car can be very impressive, but you arent deploying full torque in an instant. Even changing down a number of gears in a modern gearbox takes some time, restricting the power delivery. A higher performance EV does this much faster and aggressively, which absolutely will put the tires under increased pressure and wear, no matter which way you look at it.
Is this offset by the more relaxed driving to extend the range? Who knows, but to suggest that the tires on an EV will last longer isnt quite right. Its so much more dependent on weight, style of driving, type of tire etc.
Some owners are reporting going through a set of rears in 5000 miles or less, though what we dont necessarily know is if this is due to bad alignment, poor build or just a douchy owner, so you will have to take a lot of this with a pinch of salt. That said, there is enough evidence to suggest that some spirited driving will see you plough through them pretty quickly if you arent careful.
And while there maybe some technical reasons to suggest that they might last longer than in a IC car, a lot of people do drive them aggressively and this will absolutely eat the tires quickly. For example, rolling accelerations in a modern turbo car can be very impressive, but you arent deploying full torque in an instant. Even changing down a number of gears in a modern gearbox takes some time, restricting the power delivery. A higher performance EV does this much faster and aggressively, which absolutely will put the tires under increased pressure and wear, no matter which way you look at it.
Is this offset by the more relaxed driving to extend the range? Who knows, but to suggest that the tires on an EV will last longer isnt quite right. Its so much more dependent on weight, style of driving, type of tire etc.
off_again said:
Mileage will vary on tires, but there a lot of horror stories of Tesla's eating through tires in a very short period of time!
Some owners are reporting going through a set of rears in 5000 miles or less, though what we dont necessarily know is if this is due to bad alignment, poor build or just a douchy owner, so you will have to take a lot of this with a pinch of salt. That said, there is enough evidence to suggest that some spirited driving will see you plough through them pretty quickly if you arent careful.
And while there maybe some technical reasons to suggest that they might last longer than in a IC car, a lot of people do drive them aggressively and this will absolutely eat the tires quickly. For example, rolling accelerations in a modern turbo car can be very impressive, but you arent deploying full torque in an instant. Even changing down a number of gears in a modern gearbox takes some time, restricting the power delivery. A higher performance EV does this much faster and aggressively, which absolutely will put the tires under increased pressure and wear, no matter which way you look at it.
Is this offset by the more relaxed driving to extend the range? Who knows, but to suggest that the tires on an EV will last longer isnt quite right. Its so much more dependent on weight, style of driving, type of tire etc.
er, i think you are wrong, sorrySome owners are reporting going through a set of rears in 5000 miles or less, though what we dont necessarily know is if this is due to bad alignment, poor build or just a douchy owner, so you will have to take a lot of this with a pinch of salt. That said, there is enough evidence to suggest that some spirited driving will see you plough through them pretty quickly if you arent careful.
And while there maybe some technical reasons to suggest that they might last longer than in a IC car, a lot of people do drive them aggressively and this will absolutely eat the tires quickly. For example, rolling accelerations in a modern turbo car can be very impressive, but you arent deploying full torque in an instant. Even changing down a number of gears in a modern gearbox takes some time, restricting the power delivery. A higher performance EV does this much faster and aggressively, which absolutely will put the tires under increased pressure and wear, no matter which way you look at it.
Is this offset by the more relaxed driving to extend the range? Who knows, but to suggest that the tires on an EV will last longer isnt quite right. Its so much more dependent on weight, style of driving, type of tire etc.
The "rate of application of acceleration" is pretty much irrelevant. A tyre wears every time it rolls over the road, because it must slip to generate grip. However, gross wear, the sort of wear that reduces a tyres life to just afew thousand miles only comes from gross slip, and EVs control slip far better than ICE's. In fact, they control slip better at all loads. For example, a Tesla Model S is faster to accelerate than a Lamborgini Invent-a-Door, and how many miles do you expect to get from a set of tyres on one of those?
And another significant factor is that EVs don't need to change gears. The tyre loads during a gear shift shift direction, resulting in tread shuffle and more slip, and EV loads the tyre once, when you tip in, and leaves it loaded until you lift off.
durbster said:
An Tesla Model 3 adorable novelty popemobile pastiche drove past me recently, then slowed to a stop before flooring it - I guess somebody was showing off the acceleration.
Impressive to see but one thing that struck me was hearing the tyres scrabbling against the road and you could just sense the energy being put into the tarmac.
Now I've been looking into EVs recently and according to Parker's, I noticed the Peugeot e-208 EV is 500kg heavier than the petrol version and has a similar leap in torque. It seems obvious that as the transition to EVs continues, the average weight of our cars is going to go up significantly, as is the amount of energy they can put down.
How are our roads going to cope with this? Is our tarmac going to get more chewed up or do cars cause relatively little damage overall?
ftfyImpressive to see but one thing that struck me was hearing the tyres scrabbling against the road and you could just sense the energy being put into the tarmac.
Now I've been looking into EVs recently and according to Parker's, I noticed the Peugeot e-208 EV is 500kg heavier than the petrol version and has a similar leap in torque. It seems obvious that as the transition to EVs continues, the average weight of our cars is going to go up significantly, as is the amount of energy they can put down.
How are our roads going to cope with this? Is our tarmac going to get more chewed up or do cars cause relatively little damage overall?
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