I know this is not the most advanced explanation but bear with me..
I believe it to be like reverse heat cycling, the rubber molecules still
generate heat as they work, but the tire contacts the cold ground, or is
suddenly splashed through a <0 degree puddle.
instead of giving the rubber time to set it is being heated and cooled in
rapid succession. with no time for the bonds to realign..
now we should take a winter hardened street tire "rehydrate" it with some
formula V and heat cycle it or even use this on our race tires after we V
them they seem to become "Addicted" to the stuff, if we treat them I picture
it as Rehydrating or restoring them to factory new condition, give them a
gentle heat cycle and they should not need a retreat for a longer time..
rambling
Jeff
-----Original Message-----
From: owner-autox@autox.team.net [mailto:owner-autox@autox.team.net]On
Behalf Of Ian
Sent: Thursday, July 27, 2000 9:50 PM
To: Jeff Lloyd; Otto Crosser; autox@autox.team.net
Subject: RE: Heat cycle for the DOT Race tires, needed or not?
After seeing plenty of empirical evidence for cold weather ruining
performance tires, I still haven't found a good explanation. I presume that
it has something to do with cold work, as the tires are rolled while very
cold. What I'm not sure about is how this affects the structure of the
tire.
My first guess would be that the rubber molecules cannot flex when cold, so
some of the sulfur bonds formed during vulcanization are broken. The
problem is, this would seem to make the tire softer because there are now
less crosslinks. However, the empirical data shows that the tire harden.
Try again. Assuming that the tire compound is composed of different
molecular weight chains that are crosslinked by sulfur during vulcanization,
then the molecular weight distribution and crosslink density affect the
hardness of the rubber. Perhaps, the energy from the cold work causes some
of the weaker molecular weight chains to break, leaving a greater ratio of
higher molecular weight chains. This might cause the rubber to harden and
form cracks. This would support the empirical data that cold weather makes
a tire harder.
I guess I could apply this to explain heat cycling and ozone damage, but
I'll stop here in case I am WAY off base. :-) Any tire engineers out
there? Anyone want to debunk or support my guess?
Ian
92GSX Philly ESP, retired to commuter duties
97GSX Philly Region's Street Modified!
> -----Original Message-----
> From: owner-autox@autox.team.net [mailto:owner-autox@autox.team.net]On
> Behalf Of Jeff Lloyd
> Sent: Thursday, July 27, 2000 9:03 PM
> To: Otto Crosser; autox@autox.team.net
> Subject: RE: Heat cycle for the DOT Race tires, needed or not?
>
>
> ever have a set of Really Good street tires Get "slippery" after
> using them
> for a winter.. there you go. I remember my dunlop SP 8000's were
> the worst,
> before the winter they were a good tire. after a winter they were like
> rocks..
>
> Jeff Lloyd
>
>
>
> -----Original Message-----
> From: owner-autox@autox.team.net [mailto:owner-autox@autox.team.net]On
> Behalf Of Otto Crosser
> Sent: Thursday, July 27, 2000 5:01 PM
> To: autox@autox.team.net
> Subject: Re: Heat cycle for the DOT Race tires, needed or not?
>
>
> Ok, Heat cycling helps. What about Cryogenically freezing them?
>
> Otto Crosser
>
>
> >From: Alan Pozner <AlanP@identicard.com>
> >Reply-To: Alan Pozner <AlanP@identicard.com>
> >To: "'autox@autox.team.net'" <autox@autox.team.net>
> >CC: "'kevin_stevens@hotmail.com'" <kevin_stevens@hotmail.com>
> >Subject: Re: Heat cycle for the DOT Race tires, needed or not?
> >Date: Thu, 27 Jul 2000 15:02:16 -0400
> >
> >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
>
> ________________________________________________________________________
>
>
>
|