Speed limiters, driver monitors to become mandatory in EU
- Thread starter Shuggie
- Start date
S-Man
StrivingON
Have you been to Italy?
On the speedo topic. I set cruise at 72 on the motorway. That's 69.5MPH in reality.
Marchbanks
Hat and Beard member
With reductions to 110 and 90 respectively in times of high air pollution, as I saw for the first time in France last week.
Not driven in Italy but in France they seem to leave more space and use indicators when changing lane.
In Ecuador they're all totally mad; one local told me it was because most drivers hadn't been in cars as children.
I usually set cruise to 85, seems a sweet spot for our cars giving decent fuel economy and comfort; probably a good 75 in reality allowing for a bit of wheel slip.
When I was little used to cruise at 100 in my old Escort; gained about ten mpg by dropping that to 75. IIRC wind resistance is proportional to square of velocity.
On motorways it's much of a muchness; in cities they are uniformly mad. Either all the scooter riders in Napoli are more skilful than Valentino Rossi and can thread through traffic at 40mph, or the accident statistics are horrifying.
Wheels don't slip at a constant speed, but speedos generally read high. C&U allows them to be up to 10% optiistic and 0% pessimistic. Bear in mind that as the tyres wear you will get 1% or so difference in recorded speed because the circumference is getting smaller, and you can see why most manufacturers settle around 5% optimistic.
Not sure about this. Kinetic energy is proportional to the square, for sure. Half mv squared and all that. "Wind resistance" is complex, ISTR something about a square of one thing and a cube of something else, important factors being speed, frontal area and aero drag. I'll see if I can look it up.
Edit - checked the physics. Energy reqd to push a car through air is 1/2 x air density x coeff of drag x distance x speed x speed. So 2 x speed quadruples the energy used. Rolling resistance is fairly constant with speed and fairly insignificant at high speeds so for practical purposes it can be neglected. Bear in mind that you can move a car by yourself at very low speed, but most people can't keep even a bicycle going at 20-25 mph absolutely flat out. That's all air resistance because a bicycle will roll for ever at low speed on a tiny slope.
a.palfreyman
pfm Member
Presumably the X in 'V10 TXT' stands for 'wa' i.e. V10 TwaTDon't know if any of you guys saw this in the papers and on the news this week.
Super car driver leaving a car meeting in London last Sunday morning, I reckon he'd switched off all driver aids then ran out of talentOur local meets despise this type of behaviour.
An EU limiter may have saved him a few bob but he'd have turned that off as well probably. On a serious note anyone know if he's been charged for this? I'm guessing the way he took off he'd hit 80mph in that distance, amazed nobody was flattened there. Loads of other footage of his antics too on the web.
AP
a.palfreyman
pfm Member
Cocks who still use mobile phones whilst driving, despite this being legislated for some time ago. Very much a selfish 'no-one to stop me' attitude which seems to prevail amongst a growing number on the roads nowadays.No offence taken at all - the topic gets under my skin too.
I've spent a fair bit of time over the years competing in both bikes and cars, and used to be an active member on one of the IAM car-groups. I do take a fair bit of pride in my riding and driving, but do like everybody, probably fall into the trap of thinking I'm a better driver than I am. I do always try to keep a open mind and recognise when I'm taking more risk than I should.
What bugs the life out of me is the view from on-high that blanket / ever-tightening speed limits and enforcement are the panacea to road safety. It's driver attitudes and capabilities that are the big issues - and those are not (imho) going to be dealt with by the 'speed compliance' approach. Rant over
AP
The only time there's zero slip is when no power is being transmitted so the graph of power vs wheel slip has a peak somewhere and zero at each end.
In level one engineering only one person in the lecture got it right.
Be interesting to see what the exact relationship is between power and speed, wind resistance feels pretty solid at 150 on a track.
Interesting, thanks. I can see why engineers don't necessarily know this, it's not intuitive. As per my edit above, work done per unit distance (neglecting rolling resistance) is proportional to speed squared, so power being work done per unit time we can estimate:
Work reqd to overcome air resistance = [set of factors] x distance x velocity^2.
Distance covered is velocity x time.
Therefore Work done = [set of factors] x vt x v^2 = [set of factors] x t x v^3
Power is work done per unit time therefore:
Power = [set of factors] x v^3.
So if I remember my rudimentary physics correctly power is proportional to the cube of speed. That's where I got the cube bit from my distant memory.
Christ, I wish I could remember what happened yesterday as easily as I remember physics lessons from 35 years ago. Bloody head injuries. Nurse! Why isn't Terry Wogan doing the Radio 2 morning show this week?
Work reqd to overcome air resistance = [set of factors] x distance x velocity^2.
Distance covered is velocity x time.
Therefore Work done = [set of factors] x vt x v^2 = [set of factors] x t x v^3
Power is work done per unit time therefore:
Power = [set of factors] x v^3.
So if I remember my rudimentary physics correctly power is proportional to the cube of speed. That's where I got the cube bit from my distant memory.
Christ, I wish I could remember what happened yesterday as easily as I remember physics lessons from 35 years ago. Bloody head injuries. Nurse! Why isn't Terry Wogan doing the Radio 2 morning show this week?
S-Man
StrivingON
foxwelljsly
Me too, I ate one sour too.
As someone who conscientiously observes all limits below the national maximum, I have no problem with this and would actually welcome it. As someone that cruises on the motorway at 90+, it'll be a bit annoying. As someone of 46 who won't buy a car costing more than £2k as a matter of principal, it may transpire to be largely academic.
My token rant: Please can points be issued for failure to use indicators correctly?
My token rant: Please can points be issued for failure to use indicators correctly?
-alan-
pfm Member
Same. Nothing to do with head injuries man - that's age
Btw..
[Set of factors] x V^2 = Total Drag in this case I reckon
i.e. 1/2 Cd.ro.V^2 S - where Cd is the drag coefficient, ro the local air density, and S the frontal area
As power reqd = Total Drag x Velocity
Power = f(V^2) x V
thus..
Drag force is proportional to the square of the velocity
Power reqd for a given speed is proportional to the cube of the velocity
We're all as bad.
QED
darrenyeats
pfm Member
Power is cubed but energy used for a given distance is just squared. Remember the faster you go, the less time you spend moving for a given distance.
Tony Lockhart
Avoiding Stress, at Every Opportunity
“Just” squared
Tony Lockhart
Avoiding Stress, at Every Opportunity
Suffolk Tony
Aim low, achieve your goals, avoid disappointment.
It is if you're a resident of rural Suffolk.
Tony Lockhart
Avoiding Stress, at Every Opportunity
It really is getting bad, isn’t it, Tony. I just wish I could afford an old armoured personnel carrier. I’d drive flat out, hugging the centre line.
