Roger wrote:

I can't find a single copy of The Highway Code atm (I have 3 stretching

Here's one:

http://www.highwaycode.gov.uk/

This would be the (in)famous page:

http://www.highwaycode.gov.uk/09.htm#105

back over the later half of my driving experience) but ISTR that the
formula is 0.5 seconds thinking distance plus retardation at two thirds
g. I wouldn't doubt halving the thinking distance but retardation well
in excess of g from an ordinary road car seems a little suspect to me.
IIRC brake efficiency for cars only needs to be 50% so was it that that
was doubled?

Many modern cars can pull over 0.6g in a corner, they can usually stop
much better than that.

Most bods who tried found they could stop in the dry within 55m
including thinking time. If you accept the highway code thinking
distance at 70mph (31m/sec) being 21m, then that only leaves 32m to
actually stop in.

In g terms that gives us:

v^2 = u^2 - 2as

a = (v^2 - u^2) / -2s

a = (0 - 31^2) / -64

15 m/sec^2 or about 1.5g

(It maybe that their thinking time in these tests was less than in real
life because they were anticipating the event).

--
Cheers,

John.

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