John
Cannot contribute to your specific standards
In Australia the limit was 1/16 inch which converted to 1.5 mm on
metrication in the 1960's.
The current standards are of the form:
54. Tyre tread (1) A tyre on a motor vehicle must not have cleats or other
gripping devices that could damage road surfaces.
(2) Except at tread wear indicators, a tyre fitted to the vehicle must have
a tread pattern at least 1·5 millimetres deep in a band that runs
continuously--
(a) across--
(I) for a vehicle with a GVM over 4·5 tonnes net least 75% of the
tyre width that normally comes into contact with the road; or
(ii) for another vehicle the tyre width that normally comes into
contact with the road; and
(b) around the whole circumference of the tyre.
(3) A vehicle must not be fitted with a tyre that has been treated by
recutting or regrooving the tread rubber, unless the tyre was--
(a) constructed with an extra thickness of rubber designed for recutting
or regrooving; and
(b) labelled to indicate the construction.
I have never seen any research supporting this limit.
It is of course well recognised that slick tyres and a wet road are a safety
problem because a wedge of water builds up in front and causes loss of
traction.
But as the water film on the road builds with flatter roads and/or heavier
rain and/or the degree to which the road surface is self draining, the size
of the drainage slots through the tread must increase in order that the
rubber maintains contact with the road surface.
At 1.5 mm and limited numbers of grooves, the tyres ability to handle films
of water would be limited. More open tyre tread designs will perform better.
Regards
John Lambert
----- Original Message -----
From: "Bullas, John C" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, November 02, 2002 2:35 AM
Subject: New arrival to list
Fellow "listers"
I am researching (amongst other things) the reasoning behind the choice of
1.0mm and then 1.6mm
minimum tread depth for tyres for cars (PLG) in the UK
If anyone can shed any light on the "how & why" these tread depths were
selected is more than welcome to
contribute!
Regards
John
winchester UK
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