RE: [alfa] Another Old Wives Tale...

[James Montebello <jamesm@xxxxxxxxxxxx>]

On Thu, 4 Sep 2003, Richard Arnold wrote:
> Richard wrote:
>
> > just don't do this with unidirectional tires (unless you have special
> > knowledge. it was possible, for example, to rotate Yokohama A008R?
> tires
> > arbitrarily after you got the first couple of heat cycles into them,
> but
> > you needed to obey the arrows until you broke them in.)
>
> Most unidirectional tires I've seen are unidirectional for a specific
> reason.  Some have less tread cuts on the outer edge, sort of a slick,
> for better cornering grip while others have a "V" tread pattern designed
> to force water out.  This type of "rain" tread could be dangerous in the
> wet if rotating backward, thus forcing the water in.

The A008R? tires Richard mentioned are just such tires, having an
asymmetric tread pattern with a near slick on the outer third, progressing
to an intermediate on the inner third (more or less, depending on the
exact value of ?).  They were intended as dry weather racing tires for
classes that required DOT "street" tires.  Their unidirectional nature,
however, was not due to the tread pattern, but the carcass construction.
Until they heat cycled, the tread could come apart if subjected to high
loads in the wrong direction.  Once the rubber had stabilized, however,
you could run them either way with no problems.

You could even swap the tires around on the rims so the slick bit was on
the inside, rather than the outside.  They seemed to grip just as well
when the slick part was on the inside, at least at the level I was racing,
on cars that didn't suffer from terminal body roll.  Many competitors
did this, since the outer third would often chunk slightly long before
the rest of the tire was worn out, and swapping the tire around extended
the life of the tire for several more events.

All of this was based on repeated advice from Yokohama tire reps, which
was the special knowledge everyone needed to ignore the arrows (once
the tire was broken in).  For competition use, the advice is frequently
different from advice given to the "general public", who usually can't
even be trusted to maintain adequate tire pressures.
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