Braking Distances - Which car determined the 'standard'?
Discussion
It's commonly said that todays cars easily out-perform the highway code stopping distances. So I was just wondering if anybody here knows how the braking distances in the Highway Code were established - which car(s)? I'm assuming they were 60s / 70s without power assistance and before ABS..
It would be useless knowing the car unless you knew a host of other conditions, so it's to a simple formula.
Reaction time 0.67 secs
Braking effort 0.67g
The reaction time is mostly optimistic, the braking mostly pessimistic for a good condition modern car on a dry road (but not so for a wet road).
Reaction time 0.67 secs
Braking effort 0.67g
The reaction time is mostly optimistic, the braking mostly pessimistic for a good condition modern car on a dry road (but not so for a wet road).
Engineer1 said:
Isn't it proven in most accidents people didn't brake as hard as the vehicle's maximum would allow.
That's why Merc came up with Emergency Brake Assist (or Distribution?). People brake faster and harder than they normally do. But they normally tickle the brake. So there is still plenty of brake capacity left. Then when it's clearly too late they push hard enough to kick the ABS in. EBA just notices stage one of that and throws everything it has at stopping the car before the "it's too late" stage comes about.Munter said:
Engineer1 said:
Isn't it proven in most accidents people didn't brake as hard as the vehicle's maximum would allow.
That's why Merc came up with Emergency Brake Assist (or Distribution?). People brake faster and harder than they normally do. But they normally tickle the brake. So there is still plenty of brake capacity left. Then when it's clearly too late they push hard enough to kick the ABS in. EBA just notices stage one of that and throws everything it has at stopping the car before the "it's too late" stage comes about.HustleRussell said:
I've heard the stopping distances were based on a Ford Anglia, but almost certainly wrong!
That was alluded to in this old Top Gear video - http://www.youtube.com/watch?v=KGkKDaYd3MoEngineer1 said:
It's not who can't press a pedal more people panic find their seat position is such that they can't push it to the floor or just fear the feeling of lack of control when the total available braking force is applied.
I guessed that's what you meant, but that's why they brought ABS in so that people didn't lock up. Still, if it helps some...A very long time ago I went around an open day at the Met police forensic labs, in the traffic section was a display on how they calibrated the skid mark length to speed calculations. This involved renting/borrowing a variety of cars from a Ferrari to an Escort and then doing emergency stops from various speeds. Strangely there seemed to be many more photos and measurements on the Ferrari than the Escort.
Engineer1 said:
It's not who can't press a pedal more people panic find their seat position is such that they can't push it to the floor or just fear the feeling of lack of control when the total available braking force is applied.
Daily driving is normally an exercise in avoiding heavy braking, so when the time comes to actually stand on the brakes as hard as possible, very few people are geared up to do so.
Having spent a couple of days on one of Rob Gravett's driving courses, I think everyone there without exception put their hands up to braking far harder by the end of it than at the beginning, despite their best intentions to brake as hard as possible from the outset. That was only achieved through many repeated hard stops. Definitely something of an eye opener.
The HWC says that to stop from 30 mph you require 6 car lengths, 75 feet, or 23 metres
when i cover emergency stops in my Corsa I explain that the distances printed are not what they will do when we do a stop from 30 mph, but, and a BIG BUT....there are cars out on the roads that still require those distances to stop owing to the age of the car and the type of brakes that they have along with the type of tyre on the wheels. I think that an old 100 year old steam car, or VW beetle camper van/car may well take a country mile to slow (especially if the driver is drunk/on drugs!
On a good surfaced road, with decent tyres on, in the dry, with a 17 year old kid at the wheel......expecting to to have to do an emergency stop they can stop my car from 30 mph in about 1 and a half to 2 car lengths.....proving that the printed word is not always right.
But, on a cold wet night, in rain, with tyres less than 3mm, that are under infalted/over inflated, on a poor surface with a little standing water, being distracted by a girlfriend touching him up, with a couple of pints in him, and 0n a "promise" at her house....I guess the drunk lad standing in the road, just around the bend in dark clothing has had it
For many people when i ask them if they think ABS will stop them quicker than a car with out ABS, many feel it will, but they could be very wrong as in some cases ABS will make the car stop over a longer distance. ALL ABS does is provide more steering control whilst the car is skidding in the majority of cases.... I have had a couple of cases where taking out "older" drivers who are "pre ABS" trained when they have braked hard enough for the ABS to kick in they have done the last thing they should and released the brake pedal as they believed that the brakes had "broken or something" owing to the grinding/noise/vibration through the wheel/pedals/and seat.......Most people have never done a decent brake test on their car to see how it reacts under heavy stressful braking to see how it pulls to one side or the other. ( Please if you are going to do this, make sure the road is very clear behind you, and you do it from low speeds upto a speed you can still keep control of your vehicle.....the driving test is set at a speed of upto 30 mph for safety reasons......I do not condone/suggest this is for everyone to do, if you do you do so at your own risk!)
RTFM...read the flipping manual......for your car, and only drive at a speed you can safely stop in the distance you can see to be clear in front of you......and you should never have to do an emergency stop.....simples !
when i cover emergency stops in my Corsa I explain that the distances printed are not what they will do when we do a stop from 30 mph, but, and a BIG BUT....there are cars out on the roads that still require those distances to stop owing to the age of the car and the type of brakes that they have along with the type of tyre on the wheels. I think that an old 100 year old steam car, or VW beetle camper van/car may well take a country mile to slow (especially if the driver is drunk/on drugs!
On a good surfaced road, with decent tyres on, in the dry, with a 17 year old kid at the wheel......expecting to to have to do an emergency stop they can stop my car from 30 mph in about 1 and a half to 2 car lengths.....proving that the printed word is not always right.
But, on a cold wet night, in rain, with tyres less than 3mm, that are under infalted/over inflated, on a poor surface with a little standing water, being distracted by a girlfriend touching him up, with a couple of pints in him, and 0n a "promise" at her house....I guess the drunk lad standing in the road, just around the bend in dark clothing has had it
For many people when i ask them if they think ABS will stop them quicker than a car with out ABS, many feel it will, but they could be very wrong as in some cases ABS will make the car stop over a longer distance. ALL ABS does is provide more steering control whilst the car is skidding in the majority of cases.... I have had a couple of cases where taking out "older" drivers who are "pre ABS" trained when they have braked hard enough for the ABS to kick in they have done the last thing they should and released the brake pedal as they believed that the brakes had "broken or something" owing to the grinding/noise/vibration through the wheel/pedals/and seat.......Most people have never done a decent brake test on their car to see how it reacts under heavy stressful braking to see how it pulls to one side or the other. ( Please if you are going to do this, make sure the road is very clear behind you, and you do it from low speeds upto a speed you can still keep control of your vehicle.....the driving test is set at a speed of upto 30 mph for safety reasons......I do not condone/suggest this is for everyone to do, if you do you do so at your own risk!)
RTFM...read the flipping manual......for your car, and only drive at a speed you can safely stop in the distance you can see to be clear in front of you......and you should never have to do an emergency stop.....simples !
Edited by watchnut on Tuesday 1st October 20:56
jagnet said:
Having spent a couple of days on one of Rob Gravett's driving courses, I think everyone there without exception put their hands up to braking far harder by the end of it than at the beginning, despite their best intentions to brake as hard as possible from the outset. That was only achieved through many repeated hard stops. Definitely something of an eye opener.
I did one of Rob's courses, and thoroughly concur with your points. I recall the instructor demanding the ABS kicking in every single time, it really took some re-calibration of expectations to achieve it. The brakes were smoking when I climbed out! I use the brakes very lightly and very little generally, so on a recent track day experience it took a while to again build up the confidence to really lean on the brakes. I thought I was braking sharply, but later I realised I was nowhere near full stopping power. Even with little wiggles on the way into one corner.I think the brake assist is a good idea, but I do wish manufacturers wouldn't over-servo the brakes so they ramp up so sharply, so early in the pedal. It makes being progressive and modulating the brakes smoothly much more challenging. The reverse means getting into an older car gives the impression of poor brakes, but actually you just need to lean on the pedal a bit harder, it will stop just as well.
I can't remember who told me (ADUK member I think), but they did suggest practicing an emergency stop every now and again (when it's safe to do so!) - wise words IMO.
John145 said:
andy_s said:
That's reassuring. Who can't press a brake pedal?
In my experience, about 80% of people I train will not brake hard enough to trigger the ABS in dry conditions without practicing.I understand to a point, I have this irrational idea that if I gave everything I have to pushing the pedal it would break or something, even though I know this isn't the case.
chris182 said:
I remember reading a figure somewhere that the force on the brake pedal required to give maximum braking/activate ABS was about 35kg. If this is true then that is a lot of force, enough for a smaller person to start pushing themselves up out of the seat.
I understand to a point, I have this irrational idea that if I gave everything I have to pushing the pedal it would break or something, even though I know this isn't the case.
Consider that an F1 driver can push 120kg+ when they hit the brakes - but that's easier when you have 4-5G on your body weight, you're an athlete and you're properly strapped in.I understand to a point, I have this irrational idea that if I gave everything I have to pushing the pedal it would break or something, even though I know this isn't the case.
Having designed brake pedals (for a Formula Student car) in the past, it is quite surprising how little steel you need to make something that can resist more than 100kg of load (I can't remember the loading I used, but it was something like the full weight of the heaviest person we could get in the car, then a safety factor on top). Add the necessary fatigue life for the millions of duty cycles, and in my mind you end up not far from what you get in a road car. In some cases, I'd prefer a bit more stiffness to the pedal box to improve the feel.
John145 said:
andy_s said:
That's reassuring. Who can't press a brake pedal?
In my experience, about 80% of people I train will not brake hard enough to trigger the ABS in dry conditions without practicing.I'm possibly not a typical driver, but even when I was learning to drive, I remember initially locking-up the wheels (no ABS on 1.0 Polos 20 years ago) when practising an emergency stop.
My mother (possibly more typical of a UK driver) possibly wouldn't though.
As somebody referred to above, I do often do an ABS-inducing brake test in cars I drive. It can also help to firm up the pedal (as can pressing the pedal right down when static).
Edited by MC Bodge on Thursday 3rd October 22:48
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