Thread: Replacement of older tyres?

Is totally true - tyres may look OK and are probably safe but they will have started to go hard and no longer perform as specified. What is the best before date - 5-6-10years - is not actually specified but is in that order.

There is a code on the tyre giving its build date.

Garry

the rubber will harden and so will not perform as well. This in turn will affect things like sidewalls with a risk of blow out as the tyre flexes, and loss of traction due to hardening of the compound.

Having said that I ran a set of BFG all terains until they were worn out. Probably about 12 years old or so.

The 6 year rule is a manufacturer's reccommendation. From the info I have found it is not law.

So it is up to you to decide if the tyres are still fit for service of not.

How old is too old?

This is a subject of much debate within the tyre industry and no tyre expert can tell exactly how long a tyre will last. However, on the results of experience many tyre companies, including Bridgestone, warrant their tyres against manufacturing and material defects for five years from the date of manufacture. Based on their understanding a number of vehicle manufacturers are now advising against the use of tyres that are more than six years old due to the effects of ageing.
Tyre Ageing Mechanism

There are three main mechanisms of tyre ageing. The first involves rubber becoming more brittle. Sulphur is used to link rubber molecules together during vulcanisation with the application of heat and pressure, giving the rubber its useful elastic properties and strength. As the tyre absorbs energy in the form of light, heat or movement the tyre continues to vulcanise. This ongoing vulcanisation causes the rubber to become stiffer and more brittle.

The second mechanism of tyre ageing is oxidation involving oxygen and ozone from the air compromising the strength and elasticity of the rubber and the integrity of the rubber to steel bond. Basically heat and oxygen cause cross linking between polymer chains (causing the rubber to harden) and scission of polymer chains (leading to reduced elasticity).

Thirdly, breakdown of the rubber to steel-belt bond will occur due to water permeating through a tyre and bonding with the brass plate coating on steel belts. This causes the steel to rubber bond to weaken leading to reduced tyre strength and reduced heat resistance. If compressed air used for inflation is not completely dry, tyre strength will be affected over time. Even unused tyres will become more brittle, weaker and less elastic with exposure to water, air, heat and sunlight.
Warning signs

Regardless of their age tyres should be replaced if they show significant crazing or cracking in the tread grooves or sidewall (Figure 3&4) and or bulging of the tread face or sidewall. All tyres, especially unused spare tyres, should be inspected periodically to determine their suitability for service. If there is any question about a tyre's suitability please consult your local Bridgestone Tyre Centre expert.

I had a set of 9 year old HanKooks and just last month 3 of them let go internally developing large eggs in the tread, all within a week of each other. Up til then, I thought they were great tyres, got more than 100k out of them, might be something in what that tyre mob says

Tyres will undoubtedly deteriorate from the day they are made - the question is, at what rate? And howbad do they have to get before this deterioration means they should be replaced?

Despite what the tyre manufacturers (and sellers) have to say, the answer to these questions will not be a neat, simple number - whether it is 6,8,10 years or whatever. The answer to the first question will depend on the temperatures encountered, the exposure to UV, etc. And how much deterioration is acceptable will depend on another set of variables, including how much the original spec is above what is needed, and what the usage of the tyres will be.

I know that I would be very careful if I was told that my tyres need to be replaced after six years by someone who stands to make a lot of money by selling me the replacement tyres! On the other hand, if he pointed out cracks, chipped treads, bulges etc, I would be much more receptive. In over fifty years of driving, I cannot recall a single case of a tyre failure that could in any way be attributed directly to age, although I suspect that the ease with which I staked a tractor tyre may have had something to do with this (tyre was probably forty years old!). On the other hand, I have had tyres fail with as little as 1000km and less than a month age (developed sidewall blisters, had never been run except at specified pressure - all five tyres on a new car, including spare!).

John

John,

It was on both A Current Affair and Today Tonight about two years ago - so it must be true - you cannot dispute respected sources like these programs .

Garry

I think you should take it "with a pinch of salt"
I ran a set of TA Kos over the Oodnadatta Strezlecki and then the Savannah Way at 9 years old .

When I returned from the 8k trip, I noticed the rears had some very fine cracks around the raised line on the sidewall and I then replaced them.
They probably got hotter than the fronts as I reduced pressures for the dirt.
I bought a set of cheap Japanese Bridgestones for my car then noticed they were 6 years old. They performed AFAIK perfectly and didn't seem any different to a fresh tyre. They had been stored in the dark and in their protective wrapping though, and I think the exposure to sunlight may be a big ageing factor.
Regards Philip A

My BFG M/T's are now 11 years old and show no visible defects. I have lost a lug or two on some rocky tracks but consider them still serviceable with about 8mm tread depth remaining. They are stored in the shade - I've seen younger tyres which are in the sun all day develop sidewall cracking.