Braking & total stopping distances.

[empip]

Cars.

MPH ÷ 20 x MPH = Braking distance in feet.
Same as MPH² ÷ 20

( ( MPH ÷ 20 ) +1 ) x MPH = Total stopping distance inc' reaction time.
Same as MPH² ÷ 20 + MPH

The figures produced reflect the Highway Code typical stopping distances.
eg.
70 mph ....... divide by 20 = 3.5. add 1 = 4.5. times 70 = 315 ft total.

Never be flummoxed on the figures again... Those of us that might be, that is...

 

[wms]

I don't usually have time to calculate how long it will take me to stop,when some muppet pulls out,I just stand on the breaks and pray

 

[toptec]

Aren't the Highway Code ones out of date now that most cars come with ABS?

 

[empip]

They are using about 0.68 g for their braking figures and 0.68 secs for the reaction time .... I think the g figure is near the bottom end of expected performance under good conditions ... Most cars will probably improve on the distances quoted.
--

 

[foxhole]

Of course the reation time in the US will be slower than in the UK

 

[tim west]

Not all cars have ABS so the highway code should err on the side of caution and quote the worst case figures. ie the ones set by a master police driver that no normal person has a hell in hopes chance of matching should be scrapped

 

[noseall]

i once read that abs actually prolonged the stopping time slightly and that it afforded the driver control of the steering, due to the fact that the wheels did not lock up.

 

[megawatt]

Stopping distances with ABS are less than without ABS.

 

[noseall]

in abnormal conditions, i.e. surface snow, stopping distances can be longer with abs.

 

[blondini]

ABS is principally designed to retain steering control under braking. It does not always improve braking distances and on some surfaces it will make them worse. A highly skilled driver without ABS should usually be able to improve on the braking distance versus ABS.

 

[megawatt]

ABS is principally designed to stop the wheels locking when braking

I agree that skidding loses control so ABS will help to retain directional control.

In my own experience I can stop quicker with ABS than without.

 

[tim west]

If you had a car with ABS on a conveyor that stop started 180 degrees out of phase with the pulsed braking of the ABS would the car stop, skid or just keep going?

 

[empip]

ABS is principally designed to retain steering control under braking. It does not always improve braking distances and on some surfaces it will make them worse. A highly skilled driver without ABS should usually be able to improve on the braking distance versus ABS.

Some say highly skilled drivers shouldn't find themselves in the position to need random emergency braking, enough times to become - an expert - one thing on a skid pan, another ball game on the public roads.
In fact I cannot, and I am sure many others will not recall our most recent Em stop.

I have, in my time driven on some pretty dangerous surfaces, no matter how skilled one is, if the surface condition changes suddenly - in the midst of an emergency in restricted road space - the best can get caught out when old Issac takes over...

Shut up Tin Vest !! Worse than my missus

 

[blondini]

I agree empip, but some say that all drivers should practice emergency stops so that they are aware of how their vehicle will perform, not wait until a random genuine emergency stop is needed. Apparently a lot of drivers are so startled by the pedal vibration when abs kicks in that they release pressure on the pedal

I have practised a little on deserted roads and in conditions of poor grip, controlled braking just below the threshold of the abs seems to give better braking performance. Whilst stamping hard on the pedal makes the abs kick in and it then feels like braking effort is much reduced. In a genuine emergency I expect it would be very hard not to just stamp on the pedal.

 

[megawatt]

In a genuine emergency I expect it would be very hard not to just stamp on the pedal.

Indeed, it takes much training and practice to be able to resist this urge and carry out the cadence braking technique advanced drivers are taught.

ABS is far safer and, like many technologies around in cars today, it cut its teeth in the aerospace industry ... In my time in the RAF ABS was known as a Maxaret (can't remember why though unless it was the name of the manufacturer of course).

MW