Charlie writes:
>
> Durometer is not reliable. Do you durometer a full tread tire or one
> that
> is shaved? One with heat cycles or not. At what temperature? A tire
> can
> durometer fairly high (the higher the number, the harder the rubber) at
> 60
> degrees but change to a soft tire when heated, and another tire will not
> respond
> the same. Durometer has been bandied about as a measurement device in
> SCCA
> for 20 years but no one has shown it to work.
In addition to all the variables Charlie mentions, just the variation in
specific measuring devices and technique(s) used in making measurements can
both contribute to significantly different readings on the same tire.
However there are some conditions where the use of a Durometer is practical.
I've used a Shore brand Durometer Hardness meter for many years. And as
Charlie mentions, I've done measurements on the same/same condition tire(s)
over several days and, with only moderate garage temperature changes (10-15
degrees), have gotten significantly different readings. Also a tire that
hasn't been used for some time will yield marginally higher measurements
before an event compared with measurements on the same tire shortly after an
event even if all other conditions/techniques are the same.
However, there are situations where comparative measurements of different
age/tread depth same-size/model tires are useful in predicting which will
work better or, in determining why your competition is "killing" you on a
particular day.
Finally, there is some physic value in having the results of measurements
taken before and after the application of tire softeners. In a perverse way,
the measurement differences validate the time and effort spent in doing the
softening:-) And, the tires usually DO work better after the treatment, but
only for a few runs. I once put in nine runs on some softened tires on a hot
Sacto/Mcclellan practice course. By about the fifth or sixth run the
traction was beginning to fall off and by the ninth run the traction was
definitely inferior compared with early runs. BTW, I was water-cooling
between runs to minimize the loss of volitiles. And, of course, for each
subsequent use, even if there is no noticeable degradation during an event,
once-treated tires need to be softened again ---- unless you want to go
slow:-)
Don
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