Tyre life...

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Tyre life...

Postby BrettZZR » Sun Dec 31, 2017 9:27 am

I saw this post in the GPX resurrection thread, so I thought I give my 5c worth here rather than jacking that thread:

The_Fixer wrote:Tyres have a use life of 5 years, no matter how they look. I think this is also a roadworthy rule too, but not sure about different states rules.

Tyres may also be prone to catastrophic failure past this time frame, something not very desirable particularly a front one on a bike.

My bike (GPZ 750) has been sitting for over 5 years and the tyres still look okay, but I will be replacing them.

Catastrophic failure?! You don't really believe that shit do you?!

There are so many variables that any "age" picked is totally arbitrary. You can pick 5 years as your personal standard, and that is fine, but to suggest that there is any probability of catastrophic failure (let alone a likelihood or "prone") is just bullshit.

The vulcanising reaction in rubber is triggered by the addition of zinc oxide in the rubber compound, but along with silicon, carbon black, and a multitude of other additives mean the compound will have differing target mechanical properties once it is cured. This vulcanising reaction works a bit like a "half-life" - ie the reaction slows down naturally over time. This is why new tires are soft and seemingly sticky. It is an easy mistake to make to assume that the new "softer" rubber means that there is more grip, and with track/performance oriented compounds this is mainly true. But a lack of "hardness" can also cause peeling or rolling rubber off at the point of contact, reducing ultimate grip. Heat/sunlight speeds the reaction, while cold/being wrapped in plastic slows it.

But either way the reaction goes ever slower over time, so from a vulcanising reaction point of view there is a difference between a new, 3 month and 6 month old tyre, but no difference between a 5 year old tyre and an 8 year old tyre.

The only other variable is "abuse". Ignoring the obviously stupid ones (like prolonged exposure to solvents) there are two factors both of which only really are an issue for tyres that are "in storage":
Sunlight - the combination of prolonged UV and temperature cycling causes deterioration of the compounds. Often resulting in surface cracking etc (Que Burt Munro's boot polish fix!)
Cold spots - if a tyre is stored standing up on the garage floor, the bit on the floor will always be colder than the rest resulting in differing cure rates/ properties etc at that localised spot - no brainer in the not good department. Store tyre off the floor, or on wood.

So tyres on your bike that has any reasonable amount of use and is parked mostly in the garage/carport are good till the tread is gone - only then do they "need" replacing.

Not picking on Mr_Fixer, just sharing my 5c.

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Re: Tyre life...

Postby Mister_T » Mon Jan 01, 2018 4:24 pm

I hadn't heard of the tyre shelf life debate until I searched around for tyre DOT code translation.
Maybe those with connections to the classic bike or car scenes would care to comment.
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