What’s actually happening when tyres go ‘off’ ?

So, why do tyres go ‘off’ and whats actually happening when they do, does anyone know?

I’ve been using Avon Roadriders on the Commando on track days and have just changed them. I forget how old they were, but they were definitely not past their date. And there was plenty of tread left.

Of course, they were kinda chewed up as happens on the track. But as I say, not old and plenty of tread.

But, even though I’m certainly no Peter Williams, they were definitely giving me plenty of feedback that they were well past their best.

I know it’s a known phenomenon, the posh teams have always passed their ‘scrubs’ onto the less posh teams, in order to have the best tyre condition. But to be honest, I had previously always thought this was unnecessary.

I never suffered this when racing, but tended to change the tyres every winter, so that must have been enough to avoid this issue.

Why do tyres go ‘off’? What’s actually happening to the rubber / tyre to make them ‘off’? And are there some rules of thumb that tell you when to change tyres to ensure best tyre performance?

I've noticed the fronts wearing into a triangular profile sometimes. The handling becomes very difficult. It takes more effort than it should to start the turn and then the bike finally falls too far into the turn. That requires a quick correction in the other direction. Smooth turns are not possible with this type of wear.
Most often this wear pattern occurs after considerable mileage, but not always.

Glen

It's not a matter of tread. The composition of the rubber itself degrades over time. I have to replace all 4 of the winter tires on my truck this year. They have lots of tread but last year they just stopped gripping. They where great the first few years.

Google is your friend, I think....
From a brief glance it would seem that heat/light/age all conspire to reverse the processes used to make this natural raw material into something with a reasonable durability....
Molecular chains appears to be the buzzword !!

Once they go off I find they taste foul.

I had a Shinko being used on a sprint bike, it was new, within date, and yet wouldn’t do anything apart from spin up Despite being fully warmed at the start line and only run at 10psi. It was as if it was made from hard plastic and not rubber. I’m told the rubberisers or something had gone from the tread, and so effectively they’d gone off as if it was old age.

My truck tire went "off" this morning...

Wow Pete. Not quite the definition of ‘off’ I was referring too!

Glad you’re ok.

worntorn said:

I've noticed the fronts wearing into a triangular profile sometimes. The handling becomes very difficult. It takes more effort than it should to start the turn and then the bike finally falls too far into the turn. That requires a quick correction in the other direction. Smooth turns are not possible with this type of wear.
Most often this wear pattern occurs after considerable mileage, but not always.

Glen

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Interesting. I'm seeing a scalloped effect across the front K70 tire after nearly 11k miles. And the bike has recently developed the turn in 'oversteer" effect you describe. I had thought this was due to isolastics being out of ideal adjustment, giving the 'hinge' effect, feeling like rear wheel is steering the bike at times.

Tornado said:

Interesting. I'm seeing a scalloped effect across the front K70 tire after nearly 11k miles. And the bike has recently developed the turn in 'oversteer" effect you describe. I had thought this was due to isolastics being out of ideal adjustment, giving the 'hinge' effect, feeling like rear wheel is steering the bike at times.

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At 11k I’d say the tyre has passed its useful life expectancy anyway.

worntorn said:

I've noticed the fronts wearing into a triangular profile sometimes. The handling becomes very difficult. It takes more effort than it should to start the turn and then the bike finally falls too far into the turn. That requires a quick correction in the other direction. Smooth turns are not possible with this type of wear.
Most often this wear pattern occurs after considerable mileage, but not always.

Glen

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I have that going on with my FJR (Angel GT's). The guys in that sandbox seem to believe it has to do with dual compound tire construction. Still plenty of rubber left and handles OK, about 5K on the set. Should last me the rest of the summer. I doubt anyone has a definitive answer. Unlike Norton issues, where there is always only ONE answer.

Pete

I been off for long time lol, I always get the most out of my tyres on everything, on the bike I replace the 2x rear to 1x front and even when the front tyre still has good tread but still clock up a lot of miles on the tyres before replacing them, I check air regularly with the same gauge, don't trust service station gauges as they get knocked about to much, but if any tyre have signs of cracking in the side wall they get replaced but that has only happened on my old trailer, new trailers with second hand tyres fitted from the factory.

Isn't it because the solvents evaporate, and this happens faster if the tire / tyre is cooked . Don't the go-cart boys paint on that tire softening chemical to keep tires softer .

Most elastomers will undergo significant changes over time when exposed to heat, light, or oxygen (ozone). These changes can have a dramatic effect on the service life and properties of the elastomers and can only be prevented or slowed down by the addition of UV stabilizers, antiozonates, and antioxidants.

Depending on the microstructure of the diene elastomer, oxidative degradation will either cause hardening or softening. For example, polybutadiene usually undergoes oxidative hardening whereas polyisoprene softens when exposed to heat and oxygen. Hardening is much more common because free radicals produced when rubber is exposed to heat, oxygen and/or light rapidly combine and in this process form new crosslinks. This drastically reduces the flexibility of the rubber.

1. Store vehicles out of the sun
2. Keep them cool
3. Use Nitrogen to preserve tire life
4. Don't store them in a shop with tools, fridges, compressors, etc.

Shelby-Right said:

Isn't it because the solvents evaporate, and this happens faster if the tire / tyre is cooked . Don't the go-cart boys paint on that tire softening chemical to keep tires softer .

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Well there’s a thought, I used to use a tyre softener product when I was racing, and as posted earlier, never had this problem when racing. I know it’s only correlation, but it’s got me wondrin’…

NPeteN said:

My truck tire went "off" this morning...

View attachment 98785

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Pete,
How did this happen?Glad you are safe
Mike

I think what happens with tyres depends on what is in the compound. My tyres are Battlax, When I ride the bike hard, they do not feel as though they have deteriorated. In the 1960s two-strokes arrived. The first thing which was very noticeable was their increased angle of lean in corners when compared with Manx Nortons. It is due to the difference in steering geometry. If you have more trail, the bike oversteers slightly more than it does with neutral steering. In short with an old bike you do not need the best tyres, but if you have the best tyres, you can get away with being a less proficient rider. The problem is this - the rider leans to ride from the bike. If the bike sends the wrong messages, you don't become proficient.
When Mike Haileood was learning to race, his daddy bought him a 250 Mondial - not some piece of shit. It had been developed to it's peak by other riders
With a Manx Norton good tyres were never so essential. However on modern bikes, when you are out wide in a corner at full lean and applying more power, you need all the grip you can get. But the old bikes did not handle like that They were more nimble. When you get your bike to oversteer when you gas it and the back goes down , it will turn in the correct direction due to the angle of lean, and stay more vertical.
You will notice in MotoGP, most races are processions, and nobody has a distinct handling advantage. Passing usually happens when someone makes a mistake under pressure.
In about1993 John Kocinsky won a World Championship on the Honda RVF750, by powering through the corners. There are a couple of videos of him doing it, on Youtube.

YING said:

Pete,
How did this happen?Glad you are safe
Mike

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I'm fine. Complete 360 degree separation from the sidewall at highway speed. Never seen anything like it.

Beware old tires no matter how good they look. I had a trailer tire given to me that had been a never used spare, always stored under cover. It still had the little nubs on it. I needed a tire for my wood chipper and admittedly the tire was a load range E when an F should have been fitted but the chipper never leaves the yard. One day my wife heard a shot and it wasn't hunting season and it seemed too close to the house. The sidewall blew out. I checked the date code and it was over 20 years old.

I had another tire blow out while sitting. It was on my bucket truck - a yard truck only. This time I heard the shot and couldn't identify it. I was wondering what kind of gun my neighbor was shooting. Several days later I found the blown out tire. The piece that left had hit the barn leaving a considerable mark; glad I wasn't near! I couldn't decipher the code on that one but it was an 11:00-20 14 ply rating which I believe is G. The fact that it didn't say G means it was very old.

At any rate this is a timely discussion as I should be replacing my Commando's tires due age as it just doesn't get all that many miles.

Fast Eddie said:

Well there’s a thought, I used to use a tyre softener product when I was racing, and as posted earlier, never had this problem when racing. I know it’s only correlation, but it’s got me wondrin’…

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I am an industrial chemist and I would not do that. Some chemicals unlock the bonds in polymers. If you ever drive your car through spilled gearbox oil, you can end up with a bulge in your tyre.