21MPH difference disputed !
Discussion
That advert, and the Police line is troubling me. So I went and did some measured emergency stops last night.
2 stops at 30, within 10cm of eachother, average 5M, 69cm.
2 stops at 35, within 11cm of eachother, average 7M, 72cm.
I was very surprised at it taking two metres more, six foot approx, just for 5 mph.
But look at the distances. THIS WAS ON A WET ROAD.
I put it to you that at the 5M mark, it was only 10MPH different, and that on a DRY road it would be nearer 5MPH.
Defy the LIE, or tell me why my "ordinary" car is capable of stopping so quickly.
Statistics: 90% made up on the spot, unlike this posting.
rgds, and Merry Christmas. Carl
2 stops at 30, within 10cm of eachother, average 5M, 69cm.
2 stops at 35, within 11cm of eachother, average 7M, 72cm.
I was very surprised at it taking two metres more, six foot approx, just for 5 mph.
But look at the distances. THIS WAS ON A WET ROAD.
I put it to you that at the 5M mark, it was only 10MPH different, and that on a DRY road it would be nearer 5MPH.
Defy the LIE, or tell me why my "ordinary" car is capable of stopping so quickly.
Statistics: 90% made up on the spot, unlike this posting.
rgds, and Merry Christmas. Carl
Interesting experiment Carl.
To check if the advert was true, you'd have to also measure how long it takes to stop from 21mph.
If the advert is correct, the 21mph stopping distance should equal the difference in stopping distance between 30mph and 35mph in the same conditions.
Obviously if the stopping distance from 21 is greater than that difference, then the advert's 21 is too high.
I (and someone else who posted) think it'll be more like 18mph (energy to dissipate is proportional to speed squared. 35^2 - 30^2 = 18^2).
What's the highway code stopping distance from 30? I can't remember off hand but I'm sure it's a lot higher than 5.7m.
Edit: There's an old airstrip near me. I'm going to try and have a go as well before I go back to work next year () and see how the results compare.
>> Edited by JohnL on Tuesday 24th December 10:17
To check if the advert was true, you'd have to also measure how long it takes to stop from 21mph.
If the advert is correct, the 21mph stopping distance should equal the difference in stopping distance between 30mph and 35mph in the same conditions.
Obviously if the stopping distance from 21 is greater than that difference, then the advert's 21 is too high.
I (and someone else who posted) think it'll be more like 18mph (energy to dissipate is proportional to speed squared. 35^2 - 30^2 = 18^2).
What's the highway code stopping distance from 30? I can't remember off hand but I'm sure it's a lot higher than 5.7m.
Edit: There's an old airstrip near me. I'm going to try and have a go as well before I go back to work next year (
) and see how the results compare. >> Edited by JohnL on Tuesday 24th December 10:17
are you saying that it should take 2 metres to stop from 21mph, based on my previous figures?
Tell you what, it was frighteningly rapid decelleration. The EBD/ABS module worked overtime, and the disks & tyres steamed !
I'm sure the highway code meantions 30ft @ 30mph, which is nearer 10M ? moral of the story, don't tailgate a 307.
I don't fancy doing any more such tests as it can't do the car much good!
C
Tell you what, it was frighteningly rapid decelleration. The EBD/ABS module worked overtime, and the disks & tyres steamed !
I'm sure the highway code meantions 30ft @ 30mph, which is nearer 10M ? moral of the story, don't tailgate a 307.
I don't fancy doing any more such tests as it can't do the car much good!
C
I dont understand the point of these stupid ad campaigns.
Has anyone else here thought about these stats?
You did the tests Hertsbiker and came up with your own figures, good on ya.
Heres where i have a problem, but not with your measurements m8, the governments line.
You measured a difference of 2metres you said between 30 and 35mph right?
Well at a guess how fast would you have been going in those last 2metres before coming to a stop?
Hard to measure that i think, cos youd still be under deceleration.
Now, if the w*nkers in power say that youll still be doing, oh i dunno, say 18mph at that point, whats their problem with that?
At that impact point youll be doin well under the "most people will die speed".
See my point?
So why are they being so dildo-ish about speeding?
And theyre advocating 20mph limits all over the shop!
Also that advert where the nissan sunny saloon car hits little jonny, cos hes in the road (accident cause), has anyone else noticed that the rear wheels never even locked up at all?
Thats not an unusual occurence under panic braking yet the fronts WERE well and truly locked up.
I also notice that his tyres were less than top of the line, all helps to lengthen the stopping distances.
I also wonder if the tyre pressures wernt a little on the high side too!
I smell a cheat. Yet more manipulation of facts by these turds.
Had a peice in the paper last night that says a 1mph drop in speeds equals a 5percent drop in accidents...
More government bullshit!
Has anyone else here thought about these stats?
You did the tests Hertsbiker and came up with your own figures, good on ya.
Heres where i have a problem, but not with your measurements m8, the governments line.
You measured a difference of 2metres you said between 30 and 35mph right?
Well at a guess how fast would you have been going in those last 2metres before coming to a stop?
Hard to measure that i think, cos youd still be under deceleration.
Now, if the w*nkers in power say that youll still be doing, oh i dunno, say 18mph at that point, whats their problem with that?
At that impact point youll be doin well under the "most people will die speed".
See my point?
So why are they being so dildo-ish about speeding?
And theyre advocating 20mph limits all over the shop!
Also that advert where the nissan sunny saloon car hits little jonny, cos hes in the road (accident cause), has anyone else noticed that the rear wheels never even locked up at all?
Thats not an unusual occurence under panic braking yet the fronts WERE well and truly locked up.
I also notice that his tyres were less than top of the line, all helps to lengthen the stopping distances.
I also wonder if the tyre pressures wernt a little on the high side too!
I smell a cheat. Yet more manipulation of facts by these turds.
Had a peice in the paper last night that says a 1mph drop in speeds equals a 5percent drop in accidents...
More government bullshit!
Don't know for sure - but I'd think, from your tests, it should take 2 odd metres for you to stop in the wet from 18mph.
If it takes 5.7m to stop from 30 that seems fairly credible.
All the distances would reduce in the dry, so you'd stop quicker from 35, 30, 21 and 18 - but the difference between the 35 and 30 distances in the dry should still be the same as the distance to stop from 21/18/whatever the right answer is.
I've got a car I'm in the process of trying to sell. I don't think half a dozen emergency stops will affect the value
(ABS to protect the tyres ), I'll try and have a go in the next couple of weeks, if my wife lets me out the house for an hour or two!
If it takes 5.7m to stop from 30 that seems fairly credible.
All the distances would reduce in the dry, so you'd stop quicker from 35, 30, 21 and 18 - but the difference between the 35 and 30 distances in the dry should still be the same as the distance to stop from 21/18/whatever the right answer is.
I've got a car I'm in the process of trying to sell. I don't think half a dozen emergency stops will affect the value
(ABS to protect the tyres ), I'll try and have a go in the next couple of weeks, if my wife lets me out the house for an hour or two! Deltaf (are you a Welshman called Derek by the way? Sorry, sorry ) I assume the point is to raise awareness of the potential consequences of inappropriate speed, and to make the point that a difference between travelling speeds of 5mph can be an impact speed of much more than 5mph.
How you determine what is inappropriate is of course much more in dispute. But used properly this kind of info should make it easier for you to determine what an "appropriate" speed is.
) I assume the point is to raise awareness of the potential consequences of inappropriate speed, and to make the point that a difference between travelling speeds of 5mph can be an impact speed of much more than 5mph. How you determine what is inappropriate is of course much more in dispute. But used properly this kind of info should make it easier for you to determine what an "appropriate" speed is.
Dont call me Welsh.........
My point here is that the government are saying silly things such as hitting someone at 40 and most people die.
If youve already decelerated to say 18mph, then i suggest that theyre not gonna die are they, its well under the 40 mph speed at which "most will die".
So theyre talking bollox (anglo saxon expression of disbelief).
Spin et spin et spin.......
My point here is that the government are saying silly things such as hitting someone at 40 and most people die.
If youve already decelerated to say 18mph, then i suggest that theyre not gonna die are they, its well under the 40 mph speed at which "most will die".
So theyre talking bollox (anglo saxon expression of disbelief).
Spin et spin et spin.......
I am under the immpression though, that any impact above 12mph with a solid object and you are like to break bones !!! My computer is thinking, so I've got a bit of time to get into this from an academic POV - although, I should know by not to avoid this type of thread.
hertsbiker, at 30mph, you achieved an average deceleration of 15.805ms^-2, at 35mph, the average was 15.856ms^-2. I think that these are reasonably consistant, so we can take an average deceleration of 15.831ms^-2.
From this average, the distance taken to stop at 30 would be 5681mm and at 35, 7732mm, which is pretty close to what you measured.
Now, decelerating at this rate from 35, over the 5681m distance would leave you travelling at 18.026 mph (which is damn close to what I got using a different method on another thread).
To complete the cycle, the stopping distance, using this deceleration from 18.026mph is 2051mm.
As mentioned above, for constant deceleration, it is the square of the velocity that comes down as a straight line.
Obviously, there are lots of other factors, but the basic principle remains the same - you are going a lot faster than you think you would be over a common disatnce, simply by travelling 5mph faster.
Before the blow torches come out - for the avoidance of all doubt, I do strongly support the 30mph built up speed limit, and often travel a good margin under it (wimp?), BUT I do not, should I repeat this, do not advocate achieving this by constantly looking at the spedo and ignoring the road. On this forum, everybody likes drving, there are a lot of race drivers, and many of those that aren't, such as myself, have done at least an IAM course, and get to the track when possible. With this level of experience, we should all know what 30mph feels like.
Yes Deltaf, roads are for cars, not pedestrians. And we would all like to control our kids (ourselves when drunk???) a little better. At the end of the day though, a Range Rover hitting you at 18mph isn't half going to hurt
. If the driver, who is doing nothing technically wrong, can reduce these risks in these built up areas, then IMHO, they should do.
Edit -> I'd dispute the 21 mph purely from these simple figures, and put it at 18mph. But there are a lot of other factors, and reaction times are not built into these calcs, which would increase the terminal speed.
:mustremembertoanswerquestion:
Back to work
>> Edited by daydreamer on Tuesday 24th December 11:38
hertsbiker, at 30mph, you achieved an average deceleration of 15.805ms^-2, at 35mph, the average was 15.856ms^-2. I think that these are reasonably consistant, so we can take an average deceleration of 15.831ms^-2.
From this average, the distance taken to stop at 30 would be 5681mm and at 35, 7732mm, which is pretty close to what you measured.
Now, decelerating at this rate from 35, over the 5681m distance would leave you travelling at 18.026 mph (which is damn close to what I got using a different method on another thread).
To complete the cycle, the stopping distance, using this deceleration from 18.026mph is 2051mm.
As mentioned above, for constant deceleration, it is the square of the velocity that comes down as a straight line.
Obviously, there are lots of other factors, but the basic principle remains the same - you are going a lot faster than you think you would be over a common disatnce, simply by travelling 5mph faster.
Before the blow torches come out - for the avoidance of all doubt, I do strongly support the 30mph built up speed limit, and often travel a good margin under it (wimp?), BUT I do not, should I repeat this, do not advocate achieving this by constantly looking at the spedo and ignoring the road. On this forum, everybody likes drving, there are a lot of race drivers, and many of those that aren't, such as myself, have done at least an IAM course, and get to the track when possible. With this level of experience, we should all know what 30mph feels like.
Yes Deltaf, roads are for cars, not pedestrians. And we would all like to control our kids (ourselves when drunk???) a little better. At the end of the day though, a Range Rover hitting you at 18mph isn't half going to hurt
. If the driver, who is doing nothing technically wrong, can reduce these risks in these built up areas, then IMHO, they should do. Edit -> I'd dispute the 21 mph purely from these simple figures, and put it at 18mph. But there are a lot of other factors, and reaction times are not built into these calcs, which would increase the terminal speed.
:mustremembertoanswerquestion:
Back to work
>> Edited by daydreamer on Tuesday 24th December 11:38
I have to agree with all of you guys. These government stats are b**lsh*t.
I'm annoyed the government persists on telling people these lies and I'm even more annoyed that I don't have a local airfield where I can do these tests myself! They sound fun... There won't even be any empty carparks today.
I'm annoyed the government persists on telling people these lies and I'm even more annoyed that I don't have a local airfield where I can do these tests myself! They sound fun... There won't even be any empty carparks today.
Daydreamer, are they right then? ooops. That is worrying. Wonder if many cars can stop faster? it was a "no skill" foot to the floor job, as I thought the computer would be more consistant than me.
Hard to imagine that in that last 2 metres I go from 18 to 0. I'll be upset if "their" figures are correct!
Hard to imagine that in that last 2 metres I go from 18 to 0. I'll be upset if "their" figures are correct!
That advert, and the Police line is troubling me. So I went and did some measured emergency stops last night.
2 stops at 30, within 10cm of eachother, average 5M, 69cm.
2 stops at 35, within 11cm of eachother, average 7M, 72cm.
I was very surprised at it taking two metres more, six foot approx, just for 5 mph.
But look at the distances. THIS WAS ON A WET ROAD.
I put it to you that at the 5M mark, it was only 10MPH different, and that on a DRY road it would be nearer 5MPH.
Defy the LIE, or tell me why my "ordinary" car is capable of stopping so quickly.
Statistics: 90% made up on the spot, unlike this posting.
rgds, and Merry Christmas. Carl
Those figures seem a bit hard to believe. They suggest you were averaging 15 ms-2 on a wet road. That's about 1.5 G. In perfect conditions in the dry on hot tyres you might just touch 1.1G, but cold tyres on a wet road? Half that if you're lucky, and generally down to about 0.6G. It would only take a small error in the speedo reading, or anticipating the braking point slightly, to throw the numbers right out.
Personally, I do think that modern cars can stop much quicker than people realize and the official 'stopping distances' are extremely pessimistic. But I don't think cars are *this* good yet!
By the way have you ever calculated your theoretical stopping distance on the motorway?
GreenV8S said:
By the way have you ever calculated your theoretical stopping distance on the motorway?At 40 ms-1, call it 90 mph, it'll take around 4 seconds of braking to stop. In that time you'll cover about 80 meters. It takes you about two seconds to drive 80 meters at 90 mph. So, ignoring reaction times, if you leave a two second gap you can actually stop before you reach the car in front, even if they were to stop instantly. (That's ignoring reaction times, and assuming prefect conditions.)
Surely, if it takes you 4s to stop, and you are 2s behind a car that stops instantly, you will hit it after 2s?? Or am I missing something? - I have been sulking at my desk all day so not the sharpest at the moment
I was the same as you hertsbiker - I first saw the stat on 5th gear last week and didn't believe it, so got the old pencil and paper out to prove it (I must admit though, much prefer your hands on method). It was a bit of a
moment when I realised that they were right.
Still, live and learn. It has actually made me think, which must be a good thing. I'm not completely on message yet though - still time myself across Snake Pass once or twice a week, even in my shopping car!
Edit-> 1.5G does sound quite good, but can't most cars approach 1G on cornering now. It isn't that hard to believe that they would be 50% better in a straight line, maximum contact patch etc under braking. Time for some more real world testing - cool
>> Edited by daydreamer on Tuesday 24th December 12:18
You are all forgetting one VERY important point REACTION TIME. I don't dispute the evidence that
1. Modern cars stop faster than the highway code suggests.
2. Just measuring breaking distance from the point of applying the breaks from 35 leaves you still doing 18mph when you would have stopped doing 30.
But when you add reaction time to this I bet the Governments figure is pretty spot on. NONE of you have mentioned this VERY crucial part of the equation. Especially at this speed where it probably takes as long to react than to stop.
If 2m distance is 18mph then add another 1/2 meter for reaction time difference - what does that do to your speed?
Add to all this that
A. Most cars on the road are older than you think and don't have ABS.
B. Most drivers don't check tyres and pressures anywhere near often enough. Giving poor braking performance.
C. Most drivers either break to hard or not hard enough. So don't get optimum breaking effect.
On the last point wasn't it Mercedes that worked out that most drivers with ABS don't break hard enough so fitted a system to sense emergency breaking and actually break harder than the driver was doing?
1. Modern cars stop faster than the highway code suggests.
2. Just measuring breaking distance from the point of applying the breaks from 35 leaves you still doing 18mph when you would have stopped doing 30.
But when you add reaction time to this I bet the Governments figure is pretty spot on. NONE of you have mentioned this VERY crucial part of the equation. Especially at this speed where it probably takes as long to react than to stop.
If 2m distance is 18mph then add another 1/2 meter for reaction time difference - what does that do to your speed?
Add to all this that
A. Most cars on the road are older than you think and don't have ABS.
B. Most drivers don't check tyres and pressures anywhere near often enough. Giving poor braking performance.
C. Most drivers either break to hard or not hard enough. So don't get optimum breaking effect.
On the last point wasn't it Mercedes that worked out that most drivers with ABS don't break hard enough so fitted a system to sense emergency breaking and actually break harder than the driver was doing?
I agree with GreenV8S point that 1.5G is way too high for normal road tyres and I would say that is "too high under any conditions"
1G and you would be doing well.
I've done the math and I think the figures are correct as on 5 Gear and on the ads. Well maintained cars do stop faster under normal conditions, but seriously different in some conditions, wet, greasy poorly maintained rough surfaces etc. Shocks play a significant part as well.
Phil
1G and you would be doing well.
I've done the math and I think the figures are correct as on 5 Gear and on the ads. Well maintained cars do stop faster under normal conditions, but seriously different in some conditions, wet, greasy poorly maintained rough surfaces etc. Shocks play a significant part as well.
Phil
(Makes sense to me!)
daydreamer said:
GreenV8S said:
By the way have you ever calculated your theoretical stopping distance on the motorway?At 40 ms-1, call it 90 mph, it'll take around 4 seconds of braking to stop. In that time you'll cover about 80 meters. It takes you about two seconds to drive 80 meters at 90 mph. So, ignoring reaction times, if you leave a two second gap you can actually stop before you reach the car in front, even if they were to stop instantly. (That's ignoring reaction times, and assuming prefect conditions.)
Surely, if it takes you 4s to stop, and you are 2s behind a car that stops instantly, you will hit it after 2s?? Or am I missing something? - I have been sulking at my desk all day so not the sharpest at the moment
I was the same as you hertsbiker - I first saw the stat on 5th gear last week and didn't believe it, so got the old pencil and paper out to prove it (I must admit though, much prefer your hands on method
Still, live and learn. It has actually made me think, which must be a good thing. I'm not completely on message yet though - still time myself across Snake Pass once or twice a week even in my shopping car!
Edit-> 1.5G does sound quite good, but can't most cars approach 1G on cornering now. It isn't that hard to believe that they would be 50% better in a straight line, maximum contact patch etc under braking. Time for some more real world testing - cool
>> Edited by daydreamer on Tuesday 24th December 12:18
In a word, no.
You travel the 80m at a constant speed in 2 secs
You travel the 80m at a constantly decreasing speed in 4secs
This could be shown on a graph quite easily, but I'm bored so I won't (why am I still at work. Grrr.).
However, this does only apply to braking distance minus reaction time and so assumes you brake instantly but it illustrates an interesting point.
Also, the only road cars that can approach 1.5G under braking are Radicals / Ferrari Enzo's etc. Even then we're talking nice warm sticky tyres on a nice smooth grippy circuit. In the real world nothing can get seriously over 1G deceleration.
icamm said: .
On the last point wasn't it Mercedes that worked out that most drivers with ABS don't break hard enough so fitted a system to sense emergency breaking and actually break harder than the driver was doing?
You'd be surprised the amount of people that will back off their braking when they feel the ABS cut in and out. That along with all the strange noises associated with it working, scared the sh*te out of me the first time I used ABS. Never had cause to use it in anger though, except when on ice and I wish it wasn't there as the car never stops
. Harry
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