braking distances

[vjck_uk]

A geezer was just on the radio and he had a 1939 highway code.
The braking distances were the same as the new books,(after conversion to yards).
Surely these should be revised as the modern vehicles with better tyres and brakes are vastly superior.
I once drove an Austin Seven with cable brakes and they were good to start with for normal steady braking,but once you tried to stop quick,any increased pressure just stretched the cables and made no difference at all.
Plus the tyres were almost the width of bicycle tyres.
I would hazard a guess that thinking distances were also quicker as people nowadays are more used to a hectic life and quick decisions.
Vaughan

[Ross9]

It's a long debated topic this one.

Car's these days will stop much quicker. I watched a program once where Jeremy Clarkson used some old car with drums all round, more modern than the braking distances, and a Ford Focus, 1.4, nothing special, small front discs and rear drums etc, the older car (cant remember what it was) took a much greater distance to stop from the same speed. Even modifying your own brakes on your car will lessen your stopping distances, or at least lessen the fade, never mind manufactureres brakign systems after over 60 years of development.

As for the thinking distances, I wouldnt think a more hectic lifestyle will have affected these much, at very best they are an average anyway, everyone will have varying reaction times.

I would have said that perhaps an average from a selection of cars from 10-15 years ago should be used, and the braking distances revised, after all using cars from the last 2 or 3 years would be silly, there are a lot older cars out there. Thinking distances should remain the same. At best the whole thing is a guide anyway, and common sense and experience will tell you how far it will take you to stop, which is much further than you probably think. The run off at Crail is down a slight slope, and looks a long way if you stand at the finish line, but hitting the line flat out at almost 100 mph (or more in the case of some folk I know) and then trying to stop for the right angle bend at the bottom, you have to apply a fair bit of braking effort to do it in the faster cars. One guy came with an Amercian car of some description, ran an 11 second 1/4 in the RWD class, then couldnt stop and had to bail into the potatoe field to stop. Brakes were standard apparently, one a highly tuned car, which is never a good idea.

not a good idea vaughan ,it would only give that moron driving two feet off your back end more excuses, plus i dont think the human brain has evolved that much in sixty odd years to affect reaction times to any significant degree.

Talkng about braking distances, does any one know the formula for calculating the distance covered by a car travelling at a set speed, i.e how many feet would a car travelling at 30 mph cover in 1 second or conversely a car travelling at 40 kph cover in 1 second.

[sarge]

It's simple ratios. 30 mph is 30 miles in one hour or 30 miles in 3600 seconds, so at constant speed in 1 second it travels 3600ths of 30 miles. I don't know how many feet are in a mile (call it Y for now), but your car would travel that distance (Y) x 30 and divided by 3600 (which would be the same as Y divided by 120). I think that's right!

Sarge
'99 V70 AWD

Sarge

1760 yards = 5280 feet in a mile!

You have to be over forty to know stuff like this now as they stopped teaching it in schools in 1973.

So 5280 / 120 = 44 feet in a second.

Incidentally, the "thinking" times are the time it takes you to get the brakes applied after the hazard requiring them becomes apparent: therfore it involves observation, thinking, and the longest part: getting your foot from the accelerator to the brake and pressing the pedal!

John & Christina
340 CVT 1991
340 1.4 1988

Actually it is not braking distances I am after. I own a S80 automatic which has up to a 3 second delay when changing gear on acceleration from a speed of about 10-15 mph, for example if slowing down for a T junction to turn left and then accelerating as you deem you have enough time before the car approaching from your left is on top of you. 3 seconds is a long time if that is car is approaching at about 30 mph. Excuse my ignorance, but I am not sure about the 120 that you are dividing into the feet. What does the 120 represent?

[migrator]

Andy1,

We could agree to agree on this one!! :D :D

[doorman]

Here is the formula for remembering overall stopping distance;
thinking distance always same as mph, even figure has multiple of 1at20, 2at40 3at60 uneven would be 1.5 at 30 2.5 at 50 3.5 at 70.
So example, 50mph = 2.5 x 50 = 125 + 50'thinking =175' overall stopping.
Hope that makes it easy, also check out the following thread 'Taking your driving test'
Dave
V70 'R' AWD

why not? make a nice change!