Re: Heat cycle for the DOT Race tires, needed or not?

[Alan Pozner <AlanP@identicard.com>]

Kevin wrote in part:
>Allow 24-48 hours mininum time before using or don't bother
>heatcycling at all.

>>One aspect of heat-cycling I've never understood is the above.  If the
tires 
aren't good to go as soon as they cool, then there must be some bonding 
transitions still going on - that's clear.  What's not clear is how.  Once 
they have cooled any chemical reactions are going to be happening at a 
glacial rate compared to what goes on when they're heated up.<<

First off plenty of chemical reactions occur at room temp. The difference
between 130 deg Fahrenheit and 70 degrees Fahrenheit is really small when
referenced to absolute zero ( -273.15 deg Celsius ). 

Second what is it that really takes place? My understanding is that the long
chains of molecules in the rubber compound are unaligned and of various
sizes before the first heat cycle. After heating the molecular chains are
shorter and unattached. By letting them cool gradually they can align and
form similar length long chains making the compound stronger. Did you ever
do the "grow a purple or blue crystal experiment" in school? Where you heat
some salt in water with a string dangling from a popsicle stick. The crystal
starts growing as the mixture cools but continues to grow for several
hours/days after the liquid is back to room temp. I suspect that the rubber
is going through an analogous process. The chains continue to grow for a
period after cooling. Experience has shown that most of the growth has
stopped in 24 - 48 hours hence the waiting period. If you heat the tire up
before the 24 hours is up you break the chains. After the 24 hours the
chains are stronger and longer and better resist heat cycle breakdown.

Regards,
Alan "yes, I do have a Chemistry degree, among others" Pozner