Stopping Distances
Discussion
rhinocar said:The Highway Code assumes 0.67 seconds thinking time and 0.67G deceleration (67% brake efficiency).
Has anyone got any recent data on real world stopping distances?
The figures on the back of the Highway Code seem to relate to supertankers!
I have figures for my Noble, but I am interested in mid-range family salons.
Thanks
I reckon an alert driver can be on the brake pedal within 0.5 seconds of the hazard presenting itself. A good modern car can easily reach 1G deceleration.
If you wish, I’ll crunch some numbers based on these estimates.
Everything you need here >> www.safespeed.org.uk/braking.html
includes a downloadable Excel sheet where you can play with the parameters.
Incidentally although 0.97g might be a real world figure for a full anchors out stop, obviously higher for supercars. Seem to recall that design parameters for road engineers suggest that not much over 0.4 to 0.5 should be considered.
includes a downloadable Excel sheet where you can play with the parameters.
Incidentally although 0.97g might be a real world figure for a full anchors out stop, obviously higher for supercars. Seem to recall that design parameters for road engineers suggest that not much over 0.4 to 0.5 should be considered.
Flat in Fifth said:
Seem to recall that design parameters for road engineers suggest that not much over 0.4 to 0.5 should be considered.
thats because the vast majority of people are scared to brake hard at high speed. you might hit the pedal fast but not hard. ie most people will brake a little then harder and harder until you put your foot through the bulkhead just before mating with the car infront..
that was the thinking behind mercedes brake assist (iirc the name correctly) it monitors how quickly you hit the pedal, decides if its an emergency then triggers full abs, supposedly a great system.
francisb said:
Seem to recall that design parameters for road engineers suggest that not much over 0.4 to 0.5 should be considered.
thats because the vast majority of people are scared to brake hard at high speed. you might hit the pedal fast but not hard. ie most people will brake a little then harder and harder until you put your foot through the bulkhead just before mating with the car infront..
that was the thinking behind mercedes brake assist (iirc the name correctly) it monitors how quickly you hit the pedal, decides if its an emergency then triggers full abs, supposedly a great system.
Merc's brake system is awesome. Tried it on a big merc during a test drive last week. Got a telling off from the passenger, but the car stopped VERY quickly and in a straight line
Brake assist is amazing, funny thing is you can set it off with little or no effort eg your fingers tapping the brake pedal in rapid manner can have you doing a stoppie in no time. try it some time on a private track.
IMHO the biggest safety system since ABS only numpties on motorways who don'y look ahead will be using every 30 seconds with the "lemming Bunching Effect"
try it some time on a private track. IMHO the biggest safety system since ABS only numpties on motorways who don'y look ahead will be using every 30 seconds with the "lemming Bunching Effect"
cptsideways said:
Brake assist is amazing, funny thing is you can set it off with little or no effort eg your fingers tapping the brake pedal in rapid manner can have you doing a stoppie in no time.
IMHO the biggest safety system since ABS only numpties on motorways who don'y look ahead will be using every 30 seconds with the "lemming Bunching Effect"
Brake Assist attempts to sense when full braking is required and applies full braking regardless of pedal pressure. Despite what many people say the stopping distance of most modern cars within a given category is about the same (in real terms). For example most "high performance" cars eg big engine mondeo, Vectra, Impreza, BMW, Mercs etc will stop from 60 in around 120 feet give or take a few feet.
The "difference" in braking is normally due to real high speed stopping eg 150mph to zero or repeatability eg fade.
The "feel" of the brakes creates a significant driving experience and as such is adjusted to give the right "impression" for that vechicle.
Similar tricks are played with on ABS and the point it will activate in terms of post or pre lock up
bluepolarbear said:
...
Despite what many people say the stopping distance of most modern cars within a given category is about the same (in real terms)...
is that true?
i assume by same category you mean roughly same weight else your comment is really that new cars weigh more. the limiting factor for 1 stop say 70-0 is tyre grip which is vastly better 30 years on as is body control, antidive etc... furthermore any idiot can hit the brakes and let 4 channel ABS do all the work for them, without ABS you need a modicum of talent to stop at the tyres limit
>> Edited by francisb on Monday 9th May 21:53
francisb said:
bluepolarbear said:
...
Despite what many people say the stopping distance of most modern cars within a given category is about the same (in real terms)...
is that true?
i assume by same category you mean roughly same weight else your comment is really that new cars weigh more. the limiting factor for 1 stop say 70-0 is tyre grip which is vastly better 30 years on as is body control, antidive etc... furthermore any idiot can hit the brakes and let 4 channel ABS do all the work for them, without ABS you need a modicum of talent to stop at the tyres limit
>> Edited by francisb on Monday 9th May 21:53
Yes you take for example a Porche boxter, BMW M3, Subaru Impreza WRX, Vectra 2.5, Modeo ST220, Merc 220, Audi A4 - they will all stop from 60 in around 120feet.
The use of the catagories was to prevent the pendantic bringing up Land Rovers. The vast majority of modern cars will stop from 60 in about 3 secs give or take a couple of 10ths - check yours out.
The point of the orginal post was to say that when someone jumps into a (say) M3 and comes away saying "the brakes are awesome" it is a subjective comment and not objective. It will stop in about the same distance as their own (modern)car for the reasons you have given.
Agree with your post and previous that the biggest two factor in stopping distance is not the car, tyres, weight or even speed. It is reaction time (and in real world add in anticipation time) and whether you actually brake at full pressure - most drivers will not. I guess most Phers here have but the vast majority of people have not stood on brakes at 70 to see what happens.
At the risk of being sexist I suspect many women are not physically capable of stopping a car at max pressure. If you can't get the ABS to activate when stopping from 70 you either haven't got it or haven't pressed the pedal hard enough.
>> Edited by bluepolarbear on Monday 9th May 22:27
bluepolarbear said:
Yes you take for example a Porche boxter, BMW M3, Subaru Impreza WRX, Vectra 2.5, Modeo ST220, Merc 220, Audi A4 - they will all stop from 60 in around 120feet.
appologies i read your previous post wrong. thought you were comparing modern to old, my mistake.
yep i agree.
francis (dunces hat in the corner)
bluepolarbear said:
bluepolarbear said:
...
Despite what many people say the stopping distance of most modern cars within a given category is about the same (in real terms)...
is that true?
i assume by same category you mean roughly same weight else your comment is really that new cars weigh more. the limiting factor for 1 stop say 70-0 is tyre grip which is vastly better 30 years on as is body control, antidive etc... furthermore any idiot can hit the brakes and let 4 channel ABS do all the work for them, without ABS you need a modicum of talent to stop at the tyres limit
>> Edited by francisb on Monday 9th May 21:53
Yes you take for example a Porche boxter, BMW M3, Subaru Impreza WRX, Vectra 2.5, Modeo ST220, Merc 220, Audi A4 - they will all stop from 60 in around 120feet.
The use of the catagories was to prevent the pendantic bringing up Land Rovers. The vast majority of modern cars will stop from 60 in about 3 secs give or take a couple of 10ths - check yours out.
The point of the orginal post was to say that when someone jumps into a (say) M3 and comes away saying "the brakes are awesome" it is a subjective comment and not objective. It will stop in about the same distance as their own (modern)car for the reasons you have given.
Agree with your post and previous that the biggest two factor in stopping distance is not the car, tyres, weight or even speed. It is reaction time (and in real world add in anticipation time) and whether you actually brake at full pressure - most drivers will not. I guess most Phers here have but the vast majority of people have not stood on brakes at 70 to see what happens.
At the risk of being sexist I suspect many women are not physically capable of stopping a car at max pressure. If you can't get the ABS to activate when stopping from 70 you either haven't got it or haven't pressed the pedal hard enough.
>> Edited by bluepolarbear on Monday 9th May 22:27
Sorry,
this view is dangerously simplistic.
Stopping distances are VASTLY affected by a number of factors, and the different types of vehicles here have widely varying stopping distances in the real world.
In the real world Fast Sid's BMW has great brakes and he knows the car well and knows how much he can get away with.
However Mrs Sid goes to the song and dance men with a puncture, and in their usual inimitable style they tell her every tyre on the car is dangerous but it's not a problem coz they can do her a "deal".
Mrs. Sid then drives home on a set of the best that the Korean Crap Rubber Co. can manufacture and discovers, much to her cost, which is sometimes a life, that the stopping distance of the BMW has now been extended by about 30%, 'specially in the wet!!
Same car, same driver, new tyres, different stopping distance.
Suspension reaction and downforce also play a major part in reducing stopping distances. The better the suspension control on the vehicle, the shorter the stopping distance; this is hewn in stone and very easy to prove.
When I ran my performance shop I used to fit Koni kits to vehicles, and drivers would come back in asking if I had done anything to the brakes because their car was stopping very much quicker and in a controlled manner.
ABS is not always the quickest way to stop a vehicle in certain weather conditions, which is why Audi made it switchable on their early cars.
Remember my post about the dreadful Nissan kills child government ad; fix the back brakes and see what happens to your stopping distance; horrendous!
Reaction times also vary enormously with physical fitness; the fitter you are, the sharper and quicker your brain reacts.
What is printed on the back of the Highway Code is utter fantasy, and has not been relevant for years.
IOLAIRE said:
Sorry, this view is dangerously simplistic.
Stopping distances are VASTLY affected by a number of factors, and the different types of vehicles here have widely varying stopping distances in the real world. ....
This wasn't what the orginal post was about. It was an observation on a statement that a car had awesome brakes. Most "capable" modern cars will, stop once, from a given [legal] speed in about the same distance [capable meaning they have a reasonable brakes, tyres, weight etc]. People are perceiving the feel of the brakes and the handling of the car under braking and equating it to the effectiveness of the brakes and generally this is not the case. For example 2.5L Vectra man will get into, say an M3, slam the anchors on at 60 and wonder at the braking system when in fact his own car will stop in, as near as damn it, the same distance. However, he will not be able to do it a second time and the car will make it clear that it is not happy, whereas the M3 will do it all day long and not complain.
IOLAIRE said:
ABS is not always the quickest way to stop a vehicle in certain weather conditions, which is why Audi made it switchable on their early cars....
Cadence braking will only outperform a modern ABS system in deep snow (not the slush you get 1 day a year in the UK)
IOLAIRE said:
Reaction times also vary enormously with physical fitness; the fitter you are, the sharper and quicker your brain reacts...
That was the point I was making. A 1 sec delay in reaction at 60mph increases braking distance by 75%. 1.3 Secs would mean doubling your stopping distance. While lots of things make a difference reaction time makes the biggest (along with weather).
IOLAIRE said:
What is printed on the back of the Highway Code is utter fantasy, and has not been relevant for years.
Agreed
>> Edited by bluepolarbear on Wednesday 11th May 22:52
Just out of interest, and related to another current thread about red light cameras, has anyone ever sat down and worked out the distance you need to be from a light when it turns amber to be able to stop prior to the red light.
I only ask because it used to be a 4 second phase between them, and I presume that was set for a reason(stopping distance seems reasonable), and now its only 3 seconds, I wondered if there might be cause for complaint?
I only ask because it used to be a 4 second phase between them, and I presume that was set for a reason(stopping distance seems reasonable), and now its only 3 seconds, I wondered if there might be cause for complaint?
I did some testing last year with my data logger, I used wifeys Rover 200td non ABS from 60mph to 0
The actual stopping distance I achieved was withing 10% of the higway codes (8.1 seconds on whole graph actual stoopy time 6.1 secs) I was amazed to say the least. This graph show the lock up & release/cadence that I achieved.
For those who are thinking about this, if you were to cadence as per me once a wheel locks you need to add the reaction time about 0.4 secs, plus the time to reach peak traction again 1.0 secs.
In reality it would have been quicker to use an ABS equipped car & stamp on the anchors, even better lets try a brake assist equipped car.
Couple of points
1) Dry new surface road
2) P6000 equipped car
3) Peak g is lock up point
4) Peak to next lower point is locked up whilst I react
5) Reapplication sees a slower pedal application using modulation to maintain peak g's
6) Driver is rather used to driving cars at or near extreme slip angles & using brake lock ups to assist with car control
Modern ABS cars sense peak G & will maintain peak pressure & modulate at or near that point to achieve peak stoppage.
Most modern cars you can pull very efficient braking using hand pressure only, very little effort is actually required. If you dont believe me try it with your left foot when no-one is behind
>> Edited by cptsideways on Thursday 12th May 09:46
The actual stopping distance I achieved was withing 10% of the higway codes (8.1 seconds on whole graph actual stoopy time 6.1 secs) I was amazed to say the least. This graph show the lock up & release/cadence that I achieved.
For those who are thinking about this, if you were to cadence as per me once a wheel locks you need to add the reaction time about 0.4 secs, plus the time to reach peak traction again 1.0 secs.
In reality it would have been quicker to use an ABS equipped car & stamp on the anchors, even better lets try a brake assist equipped car.
Couple of points
1) Dry new surface road
2) P6000 equipped car
3) Peak g is lock up point
4) Peak to next lower point is locked up whilst I react
5) Reapplication sees a slower pedal application using modulation to maintain peak g's
6) Driver is rather used to driving cars at or near extreme slip angles & using brake lock ups to assist with car control
Modern ABS cars sense peak G & will maintain peak pressure & modulate at or near that point to achieve peak stoppage.
Most modern cars you can pull very efficient braking using hand pressure only, very little effort is actually required. If you dont believe me try it with your left foot when no-one is behind
>> Edited by cptsideways on Thursday 12th May 09:46
randlemarcus said:There is an NSL DC near me (A2030) which is controlled by lights. I’m not sure if it’s 60 or 70 because there are streetlamps present (but there is a permanent construction between the carriageways at the section in question, what a confusing rule).
Just out of interest, and related to another current thread about red light cameras, has anyone ever sat down and worked out the distance you need to be from a light when it turns amber to be able to stop prior to the red light.
I only ask because it used to be a 4 second phase between them, and I presume that was set for a reason(stopping distance seems reasonable), and now its only 3 seconds, I wondered if there might be cause for complaint?
According to the Highway Code (including thinking time), stopping from:
60 requires 4.75 seconds (76 metres)
70 requires 5.43 seconds (95 metres)
I should time the amber phase to see if Portsmouth City Council also believes the stopping distances stated in the HC are out of date. We should all go out at the weekend and do a real world test.
Somewher empty obviously.
When data is collated we will be further educated in road safety and we can laugh at who has the worst distances (or avoid being near them!)
Cos lets face it it is getting harder to enjoy decent speeds on the road.
Somewher empty obviously.
When data is collated we will be further educated in road safety and we can laugh at who has the worst distances (or avoid being near them!)
Cos lets face it it is getting harder to enjoy decent speeds on the road.
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