Wow, Dave, very cool information. I wish I could see these tires in
person before I buy to do that. But maybe the seller will do it for
me. Either way, very cool to know this!
-- Andrew
On Jan 26, 2006, at 4:33 PM, Dave & M wrote:
> Hi Andrew,
>
> Factory tire compounds vary considerably in the beginning, & also
> harden
> a lot with age. The harder the tread the less traction. When tires are
> made, the vulcanizing process cures, hardens, the soft rubber. This
> process continues at a slower rate throughout the life of the tire due
> to heat & exposure to ultraviolet light & ozone. Tires that sit on a
> dealers shelf for years, that are stored in a hot location, exposed to
> sunlight, near ozone generating devices, (anything that makes sparks)
> may have hardened to less than half of their useful life before ever
> being installed on a car.
>
> It's not hard to tell if a tire is age hardened or just plain was made
> that way. You use a tire durometer. A device that measures the tread
> hardness on the "Shore A" scale. You can see one here. Durometers are
> found in the tool boxes of most serious racers.
> http://www.hrpworld.com/index.cfm?
> form_prod_id=815,363_3955&action=product
>
> For reference, a fairly sticky street tire may measure somewhere
> around
> 60. After five years of exposure to heat, UV light from the sun, &
> atmospheric ozone, it may measure 85 or 90. This represents a large
> loss
> of traction. Tires designed for high mileage as a primary
> consideration
> may measure 85 or 90 from the start. Sticky, competition only, tires
> could run from 30 to 50.
>
> Another effect of age hardening is that the tire may become brittle &
> experience tread separation. Thus the "safety" discussiouns about
> maximum tire life limits.
>
> When you go to buy tires, check the durometer readings & look for
> something in the range of 60.
>
> Regards,
> Dave Russell
>
> Andrew K wrote:
> > Hi Michael,
> >
> > That is an excellent point. The Avons I bought for the other car
> must
> > have been fresh because the rubber is very soft and the adhesion to
> > the road is spectacular. It breaks away very smoothly and
> > predictably when you exceed it's limits in a corner. I have been
> > looking at XAS at Coker or Longstone (UK) and perhaps I need to
> check
> > on the manufacture date for the stock that they carry? Old stock
> > could explain some peoples experiences with either tire.
> >
> > Magnus indicated that his Avons were much harder than his XAS, but I
> > don't know if he meant the rubber or the ride. IF the XAS is at
> > least as soft as the Avons I purchased, I imagine they will be a
> > fantastic tire, as they appear to be a much more advanced design and
> > during the sixties and early seventies were chosen by many
> > manufacturers for their top performance cars. IF however they have
> > been sitting for five years, they may be hard and all bets are off.
> >
> > This is all conjecture at this point of course. If only there was a
> > place you could go and spend the day trying different tires on your
> > car. Or wouldn't it be cool if someone tried them all and tested
> > them the way one of the car mags would, for adhesion, stability etc.
> >
> > Not likely to happen though, so I will surely be basing my decision
> > on anecdotal evidence and conjecture. Ahhh, but I have made
> > decisions based on less than that!
> >
> > -- Andrew
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