stopping distances

[mamie]

does anyone know a formula for working out stopping distances?

[ugly_bob]

Thinking distance (in metres) is

Speed (in mph) x 0.3

Braking distance is

Speed x Speed x 0.015

Total stopping distance is

Speed x 0.3 + Speed x Speed x 0.015

Or, take S as Speed / 10

Then it is

(S + (S x S)/2) x 3

[JudgeJ]

Speed (in mph) squared, divided by 20. Then add speed in mph. This gives you the stopping distance in feet.

For example, from 70mph:

70 x 70 = 4900

Divided by 20 = 245

Plus 70 = 315 feet.

The mph squared part of the formula represents the braking distance and the additional bit (the plus 70 in my example) is the "thinking" distance.

[Toureman]

The two examples above are very interesting but do not take into account the efficiency of braking systems, tyres, suspension systems, drivers skill including reaction time, weight of vehicle or road surfaces.

[ugly_bob]

Sorry, should have mentioned, these both give the recomended minimum stopping distances according to the highway code

[ianess]

Speed in mph, divided by 20 gives you the "multiplier" for braking distance in feet.
Speed times 1 equals the thinking distance in feet.
eg at 70mph the total overall stopping distance under ideal conditions is 315ft. [70 x 3.5]+70

[jake-the-peg]

In feet!?

If I get a fine I wonder if they'll let me pay in groats?

[ianess]

Ouch! Am I that old?

[Zulu]

Try this one,

Speed i.e 50mph x 5 (or 7 if is 70 mph or 3 if it's 30mph etc) = 250......divide this figure by 2....= 125, then add the original speed + 50 = 175 feet.

Double it for wet or damp conditions.

That's probably the simplest way to do it.

[northstar]

rule of thumb assuming dry firm road surface and tyres and brakes up to spec allow one yard for every mph double this in wet