Find a Tyre Dealer or Tyre Dealers in hampshire based in aldershot, andover, basingstoke, brockenhurst,
eastleigh, fareham, farnborough, lyndhurst, portsmouth,romsey, southampton and winchester. |
|
Tread Depth Law
Current tread depth legislation requires that car tyres must have a minimum of 1.6mm
of tread in a continuous band throughout the central ¾ of the tread width and over
the whole circumference of the tyre.
However, despite the law, it is generally recognised in the tyre industry that the
legal limit is an extreme. Many tyre manufacturers state that they design tyres
to function as well at 1.6mm as they do at 9mm (the accepted normal tread depth
when new). That is a surprising statement for any tyre company to make, but some
have said just that.
So, if a tyre performs as well at 1.6mm as it does at 9mm, what happens at 1.5mm?
Is there a sudden drop in performance? Actually there isn't, because industry testing
has shown that when a tyre reaches around 3.5mm in tread depth, the level of performance
in the wet, in particular, starts to deteriorate, as does its dry handling characteristics.
The recommended point for change is accepted Europe-wide as being 3mm. So much so
that ministerial cars in the UK have their tyres changed at, you guessed it, 3mm.
Why then the current legal limit of 1.6mm? There are several arguments against the
change, some of which you may question. One is that the sudden change from 1.6mm
to 3mm would have a serious impact on the pockets of hundreds of thousands of motorists
who are already struggling to keep their cars on the road. Another is that it would
require changing all the tyre moulds in use to increase the tyre wear indicator
depth to 3mm. And of course Europe plays a part, as there would not be universal
implementation of 3mm tread depth, requiring double standards in production and
possibly in policing.
The reality is that since tyres are now a global commodity it would almost require
a global adoption of 3mm as a minimum. It doesn't take an Einstein to counter the
arguments against 3mm, but until the legislation is in place you can make up your
own mind, scrape by on 1.6mm, or be safe on 3mm. Your choice.
Truck tyres currently have a 1mm legal minimum tread depth - which many are trying
to drive up to 1.6mm - for exactly the same reasons as they want to see 3mm for
car tyres.
Incidentally - you may wonder why the normal new tread depth is generally around
9mm. This is to do with the slip, ie distortion in a tyre block, and its level of
hysteresis. If you take an eraser and holding it vertically, draw it across a desk,
you will see that it distorts before it loses grip - that is what we call "slip".
If you increase or decrease the length of rubber you are flexing, the slip increases
or decreases. It becomes obvious that too much slip would make a vehicle unstable.
Remember that the compound is a compromise too and the ratio of slip to tread block
and the compound used is all finely tuned. The industry norm is for car, van and
SUV treads, 9mm.
|