DaveHAT
15-11-2006, 11:16 AM
Something that has always perplexed me when observing the behaviour of others and myself when driving on the road and on race circuits is the perceived idea of "safe braking distances". This has led me to do a wee bit of research on the subject which I hope will be of some use to others.
Some years ago, I attended an advanced driving course with Ian Luff at Oran Park and at the commencement of the day they covered the physics of stopping a road car and why so many people get it wrong. The 1st part of this equation is:
Perception Times.:idea:
Simply put, this means how long it takes the soft tissue behind the wheel to process the "holy shit" element and realise that the conditions or situation immediately surrounding them has been altered (ie dog on road, rear end accident, competitor spinning off the circuit in front at a rate of knots). The numbers that were quoted by the instructors were something in the vicinity of 0.25 - 0.5 seconds.
Part II: Reaction times: :sleep:
Now we're talking about the soft tissue actually doing something about avoiding or correcting the situation, or moving their foot from the accelerator to the brake pedal, remembering..... we haven't even begun ot brake yet. Times quoted for average reaction times were 0.25 - 0.75 seconds.
The above 2 factors can obviously be effected by other things such as fatigue, alcohol, drugs and many others. So now we have a total of up to almost 1.5 seconds (given none of the mitigating factors) that has elapsed since "danger" was recognised and nothing other than mental activity has actually happened. Bare in mind that the car is still moving during this time. We probably should look at stopping the car some time soon hey? :werd:
Part III: Braking and stopping the car.:burnout:
As a starting point, it was pointed out to us that @ 60km/h a vehicle travlel approximately 20mtrs per second, now given that we have a up to 1.5 second time lapse occuring between recognising that a change has occurred and beginning to brake. A VEHICLE WILL HAVE TRAVELLED UP TO 30 MTRS WHEN TRAVELLLING AT 60 KM/H AND NOTHING HAS ACTUALLY HAPPENED YET ! To me that is a bloody scarey thought because how many cars do you see travelling with at least a 30mtr gap between them?
There are many other variable to be considered also. To name a few:
the type of braking system, (2 piston, 12 piston for Nick, ABS/Non ABS)
brake pad material,
tyre pressures,
tyre tread and grip,
vehicle weight,
suspension system,
slope of road,
surface smoothness (hot mix, concrete etc)
driver age & experience.
How many people have all of these in mind when they are driving their cars? More importantly how many people have done the simple thing of checking the tyre tread on their cars? My guess would be not a lot. Commodore rear camber wear is a classic example of this. Regardless, there are so many factors involved in braking that many people I feel take for granted.
Some interesting figures provided to us about the braking distances of certain cars and other figures are as follows: (source - Ian Luff Motivation)
Worth noting is that from 50 to 100 kph the braking distance of a car will increase from 10 metres to 40 metres. When you double the speed of a car braking distance quadruples.
This is based on the laws of physics. When a car is moving it has kinetic energy, ?mv2. When the velocity doubles the kinetic energy quadruples. The braking capability does not increase when driving faster, there are no reserves of friction. As such in any vehicle when your speed doubles braking distance is four times larger.
BRAKING DISTANCE (in Mtrs) FROM 90 km/hr and 120 km/hr
Honda Integra GS-R 42 74.4
Audi A4 43.5....80.7
BMW Z3 (2.8) 36.9.... 64.5
Ferrari 550 Maranello 33.6 ....59.7
Lexus ES300 42 ....73.8
Lexus LS400 45.3.... 78
Mazda MX-5 45.6 ....76.8
Mazda Protege 47.4 ....86.1
Mercedes C36 36 ....63
Mercedes SLK230 Kompressor 36.... 62.7
Nissan Maxima 42 ....72.9
Nissan 200SX 38.7 ....68.4
Saab 9000 Aero 36.6 ....66.3
Subaru Liberty RX 40.8 ....70.8
Toyota Camry V6 43.5 ....82.2
Toyota Corolla 55.8 ....95.7
Porsche 911 Carrera 4 37.8 ....66.9
Some people may find this information useful in day to day driving, some may find it useful on the track, some may think... BAH what a load of bollocks I'm a good driver and that doesn't mean squat, fair enough too I say, I'm no qualified driving instructor. This information is just what I was given by people who were and is in some part personal opinion but mostly factual. You may want to think about this simple thing next time your trucking along the M7 or Westgate freeway..........
At 60km/h the average car takes 40-ish metres to stop (insert image of olympic swimming pool here) given "ideal" driver and road conditions..... At double the speed or 120km/h my braking distance will have quadrupled (120mtrs) but my car doesn't stop any better than it did when doing 60km/h......................................How far ahead of or behind me are those other cars???? :driving: :up2sum:
Scarey to contemplate :shock:
Cheers.
Some years ago, I attended an advanced driving course with Ian Luff at Oran Park and at the commencement of the day they covered the physics of stopping a road car and why so many people get it wrong. The 1st part of this equation is:
Perception Times.:idea:
Simply put, this means how long it takes the soft tissue behind the wheel to process the "holy shit" element and realise that the conditions or situation immediately surrounding them has been altered (ie dog on road, rear end accident, competitor spinning off the circuit in front at a rate of knots). The numbers that were quoted by the instructors were something in the vicinity of 0.25 - 0.5 seconds.
Part II: Reaction times: :sleep:
Now we're talking about the soft tissue actually doing something about avoiding or correcting the situation, or moving their foot from the accelerator to the brake pedal, remembering..... we haven't even begun ot brake yet. Times quoted for average reaction times were 0.25 - 0.75 seconds.
The above 2 factors can obviously be effected by other things such as fatigue, alcohol, drugs and many others. So now we have a total of up to almost 1.5 seconds (given none of the mitigating factors) that has elapsed since "danger" was recognised and nothing other than mental activity has actually happened. Bare in mind that the car is still moving during this time. We probably should look at stopping the car some time soon hey? :werd:
Part III: Braking and stopping the car.:burnout:
As a starting point, it was pointed out to us that @ 60km/h a vehicle travlel approximately 20mtrs per second, now given that we have a up to 1.5 second time lapse occuring between recognising that a change has occurred and beginning to brake. A VEHICLE WILL HAVE TRAVELLED UP TO 30 MTRS WHEN TRAVELLLING AT 60 KM/H AND NOTHING HAS ACTUALLY HAPPENED YET ! To me that is a bloody scarey thought because how many cars do you see travelling with at least a 30mtr gap between them?
There are many other variable to be considered also. To name a few:
the type of braking system, (2 piston, 12 piston for Nick, ABS/Non ABS)
brake pad material,
tyre pressures,
tyre tread and grip,
vehicle weight,
suspension system,
slope of road,
surface smoothness (hot mix, concrete etc)
driver age & experience.
How many people have all of these in mind when they are driving their cars? More importantly how many people have done the simple thing of checking the tyre tread on their cars? My guess would be not a lot. Commodore rear camber wear is a classic example of this. Regardless, there are so many factors involved in braking that many people I feel take for granted.
Some interesting figures provided to us about the braking distances of certain cars and other figures are as follows: (source - Ian Luff Motivation)
Worth noting is that from 50 to 100 kph the braking distance of a car will increase from 10 metres to 40 metres. When you double the speed of a car braking distance quadruples.
This is based on the laws of physics. When a car is moving it has kinetic energy, ?mv2. When the velocity doubles the kinetic energy quadruples. The braking capability does not increase when driving faster, there are no reserves of friction. As such in any vehicle when your speed doubles braking distance is four times larger.
BRAKING DISTANCE (in Mtrs) FROM 90 km/hr and 120 km/hr
Honda Integra GS-R 42 74.4
Audi A4 43.5....80.7
BMW Z3 (2.8) 36.9.... 64.5
Ferrari 550 Maranello 33.6 ....59.7
Lexus ES300 42 ....73.8
Lexus LS400 45.3.... 78
Mazda MX-5 45.6 ....76.8
Mazda Protege 47.4 ....86.1
Mercedes C36 36 ....63
Mercedes SLK230 Kompressor 36.... 62.7
Nissan Maxima 42 ....72.9
Nissan 200SX 38.7 ....68.4
Saab 9000 Aero 36.6 ....66.3
Subaru Liberty RX 40.8 ....70.8
Toyota Camry V6 43.5 ....82.2
Toyota Corolla 55.8 ....95.7
Porsche 911 Carrera 4 37.8 ....66.9
Some people may find this information useful in day to day driving, some may find it useful on the track, some may think... BAH what a load of bollocks I'm a good driver and that doesn't mean squat, fair enough too I say, I'm no qualified driving instructor. This information is just what I was given by people who were and is in some part personal opinion but mostly factual. You may want to think about this simple thing next time your trucking along the M7 or Westgate freeway..........
At 60km/h the average car takes 40-ish metres to stop (insert image of olympic swimming pool here) given "ideal" driver and road conditions..... At double the speed or 120km/h my braking distance will have quadrupled (120mtrs) but my car doesn't stop any better than it did when doing 60km/h......................................How far ahead of or behind me are those other cars???? :driving: :up2sum:
Scarey to contemplate :shock:
Cheers.