I have an automatic safe distance warning on the passenger seat of my car. i can detect when she grips the armrests and hisses.
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I have an automatic safe distance warning on the passenger seat of my car. i can detect when she grips the armrests and hisses.
LOL
I have heard it said in the past that the best aid to raod safety would be a large spike mounted in the centre of every steering wheel.
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It would be interesting to see some actual braking distances for modern cars, but the main thrust of the article is drivers reaction times.
Highway code assumes a reaction time of 0.7 seconds. How many people can actually achieve that. When I was at school doing a pre driving course we had our reaction times.measured. Most of us could manage 0.3 to 0.4 second. I don't think I could manage that now though.
An increase of 0.3 seconds in reaction time adds about 8 metres to the stopping distance at 60 mph.
There are a few 'reaction test' sites on-line, I have tried a few and my average is 0.28/0.34 seconds and I've been drawing State Pension for almost ten years.
Engineer Andy's post is absolutely spot on, road test results on modern cars show braking distances at most 2/3rd Highway Code distances, often much less.
The original 'thinking distances' assumed drivers were alert, sober, not drug users, not fiddling with mobile phones, not adjusting entertainment systems (radios were extra-cost options and needed a £1 radio licence!).
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Highway code assumes a reaction time of 0.7 seconds. How many people can actually achieve that. When I was at school doing a pre driving course we had our reaction times.measured. Most of us could manage 0.3 to 0.4 second. I don't think I could manage that now though.
Buried in my records is the printout of my BMW Fahrer-Training taken at a demo in Munich where we were watching tennis many years ago. At the age of 55 I managed 0.48secs and 62.3kg 'Bremskraft' before 'training', and 0.42secs and 93.3Kg after. So 0.7 probably about right for healthy OAPs.
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There are reaction times and reaction times though. You may note the car in front braking because its lights have gone on and lift off the accelerator but then a further time is needed for that "oh s***" conclusion to be drawn and the brake pedal pushed to the floor. Automated braking is a wonderful invention though.
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OK so the stopping distances have remained unchanged since the 1950's. The efficiency of brakes has improved tremendously since then. However the human body has not evolved and now deals with a greater range of distractions.
Also the braking figures in the Highway code work on brake efficiency of 50%. Modern cars achieve much higher figures. However the to get an MoT pass, guess what the minimum efficiency is, yep 50%.
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Automated braking is a wonderful invention though
It certainly is, but should have been fitted to cars years ago for those who are distracted by a phone call/text message or someone walking in front of them (often happens now)
but maybe too many rely on automated braking on modern cars
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Reaction time is not the only factor impacting braking distance:
- tyres - new, part worn, on the limt, tread pattern
- road condition - wet, dry, worn and glazed, newly surfaced
- traffic volume may anyway compromise ideal vehicle separation.
I'm not sure stopping distances are of any relevance - tthe average driver is incapable of estimating distance with accuracy.
Or you could adopt the Clarkson wisdom - speed does not cause. accidents, accidents are caused by not stopping in time.
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Reaction time is not the only factor impacting braking distance:
- tyres - new, part worn, on the limt, tread pattern
.
Never ceases to amaze me how many very new, expensive (and usually German) cars I see in the supermarket car park with bald tyres. I assume the ignorant owners just drive them until they fail the MoT? Not many spot checks carried out by plod these days afterall, (drove 400 miles to London and back yesterday and never saw one police car).
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If any safety device is fitted to a vehicle some drivers will rely on it, not only new drivers either.
What we have to watch out for now-a-days is people walking out into the road while using mobile phones. I had one person walking on the pavement with their back to me turn onto a zebra crossing without looking or giving any sign. That must have been a very important phone call.
Tue 25 Jul 2017 14:46
Braking distances - bolt
Automated braking is a wonderful invention though
It certainly is, but should have been fitted to cars years ago for those who are distracted by a phone call/text message or someone walking in front of them (often happens now)
but maybe too many rely on automated braking on modern cars
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The highway code states a typical braking distance from 60mph as 240 feet. After a quick search, I found an article by motor trend, which is a US website/magazine, from 2015. This compiled their top 20 shortest braking distances from their road tests. The shortest distance recorded was by a 2014 corvette stingray roadster at 90 feet!.
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The highway code states a typical braking distance from 60mph as 240 feet. After a quick search, I found an article by motor trend, which is a US website/magazine, from 2015. This compiled their top 20 shortest braking distances from their road tests. The shortest distance recorded was by a 2014 corvette stingray roadster at 90 feet!.
OK, so a corvette is a high performance sports car with enormous brakes and tyres. So here is a more conventional comparison with the highway code braking distance from the autocar (dated 17/5/17) road test of the new suzuki swift in top of the range SZ5 spec and riding on 185/55x16 tyres.
Braking distance from 70mph according to the highway code is 96m (315'), the suzuki did it in 48.1m (157'9.7")
From 50mph according to the highway code is 53m (175'), the suzuki did it in 24.7m (81')
That is essentially half the distance!. So yes, maybe the highway code should be updated to show longer 'thinking time', but if so, it should also be updated to show the vastly shorter braking distances.
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K, so a corvette is a high performance sports car with enormous brakes and tyres. So here is a more conventional comparison with the highway code braking distance from the autocar (dated 17/5/17) road test of the new suzuki swift in top of the range SZ5 spec and riding on 185/55x16 tyres.
Braking distance from 70mph according to the highway code is 96m (315'), the suzuki did it in 48.1m (157'9.7")
From 50mph according to the highway code is 53m (175'), the suzuki did it in 24.7m (81')
That is essentially half the distance!. So yes, maybe the highway code should be updated to show longer 'thinking time', but if so, it should also be updated to show the vastly shorter braking distances.
The Highway Code's implied approach does not represent the real world, not because the reaction times and stopping distances are all wrong but because people don't generally drive by observing only the back of the vehicle in front (when they do of course, typically in fog, it all goes horribly and predictably wrong).
Most people, most of the time, are seeing beyind the vehicle in front. Occasionally this leads to its own problems, as with my wife when she looked ahead, saw the roundabout was clear, and srove straight into the car she had looked through/over/around!
If you are driving properly, you are not driving on your reactions anyway. In the event that something totally unexpected happens, and when reactions matter, most people just crash. The trick is to drive well enough that the unexpected is a very rare event.
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<< Never ceases to amaze me how many very new, expensive (and usually German) cars I see in the supermarket car park with bald tyres. I assume the ignorant owners just drive them until they fail the MoT? >>
Perhaps the owners have been driving long enough to expect that they will get 40K miles or even more from tyres. When cars were lighter (< 1 ton) with smaller, narrower tyres, 50K was not unusual. I think 20-30K is more normal nowadays, probably (my guess) because softer rubber with better grip wears out faster?
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“Only a fool breaks the two second rule”....
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<< Never ceases to amaze me how many very new, expensive (and usually German) cars I see in the supermarket car park with bald tyres. I assume the ignorant owners just drive them until they fail the MoT? >>
Perhaps the owners have been driving long enough to expect that they will get 40K miles or even more from tyres. When cars were lighter (< 1 ton) with smaller, narrower tyres, 50K was not unusual. I think 20-30K is more normal nowadays, probably (my guess) because softer rubber with better grip wears out faster?
Quite possibly, though, like others' comments earlier about younger drivers driving within one car length of the one in front at high speed and thinking their car's new brakes (and ABS) will save them should they need to slam the anchors on, I see many people (especially younger drivers) drive their cars as if their life depended on it, or as if they are trying to achieve their car's 0-60mph time every time they accelerate away. I too also see many older higher performance cars (presumably owned by less well-off people hoping for some reflected status in their purchase) with tyres in poor condition.
I can still achieve decent mileages from a set of tyres - 50k or so from those (175/60 R13, slightly sporty) on my old mid 90s Micra, and 40k+ on my current Mazda3 (shod in 205/55 R16 tyres). As has been said, we just need to be reasonably (not Captain slow) light-footed, aware of other road users so we can reasonably anticipate future maneuvres, and calm so we don't give in to the red mist if and when we come across poor or reckless driving from others.
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Andy, your Micra reinforces my earlier point. Our now long-gone Pug 205 Dturbo managed about 50K on a set, but they had to be rotated periodically as the fronts wore about 3 times as fast as the rears because of the weight distribution and power steering.
Most modern cars have PAS and wide tyres, which must increase the wear rate of front tyres?
I don't think boy-racing is a particularly recent phenomenon though.
Edited by Andrew-T on 26/07/2017 at 10:56
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Most modern cars have PAS and wide tyres, which must increase the wear rate of front tyres?
Can I assume that the PAS comment on tyre wear is related to those people who dry steer? because I can't see any other reason why PAS would cause quicker tyre wear over non PAS steering.
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<< I can't see any other reason why PAS would cause quicker tyre wear over non PAS steering. >>
Surely because PAS can apply more force to turn the wheels than unassisted steering, where drivers have to take their corners more slowly (I'm talking mainly about slow manoeuvres such as parking, where PAS is most useful). Turning the wheels when stationary can strip tarmac, so tyre rubber won't be unaffected.
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re the 2 second rule mentioned above, this is a different but relevant issue. It takes into account that traffic is flowing and the car in front will not normally stop instantly. At 70 mph you cover a little over 200' in 2 seconds.
Reference has been made to the tests that show modern cars can stop in less than this distance. You might assume you could stop in the event of an immediate obstacle in your lane, such as debris, as long as you had 2 seconds clear view. I would suggest that in reality this is beyond many drivers in real life driving (as compared to being specifically prepared for a brake test). Braking in traffic from 70 mph in 200 feet to avoid hitting a pallet in the road is a real brown trouser moment.
Then when you consider that on a busy motorway the real gaps at 70 are likely to be a lot less than 200 feet and its easy to see why many accidents happen. Whatever the Highway Code might say and whatever a modern car can do in test conditions it pays to take a conservative view of the car and driver real life capabilities.
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