Tyres is a subject which often comes up on the forum. Many will have some idea as to how they are manufactured but I thought this video might be of interest:
Now a days, as you can see in the video, standard road tyres are produced with a minimum of human intervention but back in the Late 60s, when I worked out of the Firestone factory in Brentford, the tyres were all layed up by hand. It was a very dangerous place to work with heavy rolling mills for mixing the rubber and sharp knives for cutting the stock to length as it was applied to the building drum. That's before you started dodging the spiders and snakes which occasionally came in with the bales of natural rubber!
Now to the reason for me posting all this "drivel". If you've watched the video above you'll now understand that the tyre is built up in layers. The last of these layers to be added is the tread rubber. If you look at this picture I took recently of one of the tyres from the Mazda you can clearly see where the tread rubber and sidewall rubber join. Look at the edge of the tread pattern at around 1.00 o'clock to 2.30 o'clock in this picture:
Because of the way the light is falling on this image, you should be able to see quite clearly the delineating line between the tread rubber which is a completely different compound to the sidewall rubber. You can see this on most tyres and once you know this it gives you something else to look for when out shopping with the wife and bored out of your mind! Ha, Ha! But seriously, there is a point to this which is: Tread rubber is very tough and clever stuff, having to be able to provide grip in differing road conditions whilst at the same time providing resistance to wear so the tyre will last. The sidewall uses a very different compound as it has to be both tough - to protect the casing construction and "super flexible" to withstand the 3D flexing as the weight of the vehicle deforms it with every revolution but it doesn't need much abrasion resistance. When the tyre cures in the mould the casing rubber and tread rubber bond chemically and physically together. In fact this is a big quality control area as any imperfection introduced during building between the case and tread might well result in them failing to bond with the serious consequence that the tread may well separate in service and throw bits of tread off. (in racing, back in the day, we called it "chunking"). Even touching this interface was taboo as the sweat on your finger could cause the raw rubber to fail to bond. - Raw rubber, before it's cured is very "sticky" the surface is not unlike when you put the glue on an innertube before you stick the patch on.
So here's the "thought for the day" The tread rubber band is roughly the same thickness as the depth of the tread pattern, wee bit more on some. When the curing takes place a "mingling" layer is produced at the interface between the tread and casing rubber - this is everywhere under the tread rubber - so, if you think about it in cross section, starting off with the casing rubber, you then have a thin layer of intermingled casing and tread rubber and finally on the outside, the tread rubber. Tread rubber is designed to resist wear and abrasion whilst casing rubber is not. What does this mean? Well, when your tyres get well worn they might get into the area where this "mingled" layer is. If that happens the wear rate will become very rapid and can easily catch you out. If you look out for your tyres and check them regularly there's little risk of you experiencing this because you'll be checking pressures and looking at the tread depth right across the full width of the tyre. In my experience it's not unusual to find tyres wearing more on the inner shoulder and this is easy to miss as the tyre often looks fine from the outside. - turn your steering wheel full lock when checking to see both outside and inside shoulders of the tread. If you notice wear like this on your tyres it may just be that it needs checked for suspension wear and get the toe reset but also often it's a pointer to the rubber bushings on the suspension arms getting soft and allowing the front wheels to splay out a bit under braking. As most people know, the legal limit in our country is 1.6mm. Keep a regular check on your tyres, as most manufacturers now mould wear indicators into the tread - illegal when the indicator is flush with the surface of the tread. Many have little TWI letters on their sidewalls to help you find them - but remember if it's flush it's actually illegal right now, so we used to recommend changing at 2mm and I see some manufacturers are now recommending you think about renewing a tyre when it's showing 3mm. I find that particularly interesting as I got involved in doing testing tyre wet weather performance and we found that a tyre with anything under 2mm, on a properly wet road, not talking standing puddles here though, might as well be bald for all the difference it made to braking distances.
I think there are a number of factors in play with older worn tyres. Probably the biggest one affecting wet weather is the tread depth because if the tyre can't displace the water it's going to ride up on it, like a surfer, and then you're aquaplaning so have no grip at all! A big factor which few think about is that rubber oxidizes, becomes hard with age and grips a lot less well - one of the biggest reasons why your car seems to "feel" and handle better on new tyres - It's worth considering though, that if you run your treads really low and end up running on the "mingled" layer of rubber then not only will the wear rate greatly increase but also grip will be substantially compromised.
So, next time you're wandering down the street, add tyre watching to your activities, there's a bewildering number of tread pattern designs and defects to amuse yourself looking out for. If I ever get a "smart 'phone" I think I'll start a picture library of what I see.
Edit: If you're still reading you might like this: https://www.bathwicktyres.co.uk/tyr...egal limit of 1.6,the inner, centre and outer.
Now a days, as you can see in the video, standard road tyres are produced with a minimum of human intervention but back in the Late 60s, when I worked out of the Firestone factory in Brentford, the tyres were all layed up by hand. It was a very dangerous place to work with heavy rolling mills for mixing the rubber and sharp knives for cutting the stock to length as it was applied to the building drum. That's before you started dodging the spiders and snakes which occasionally came in with the bales of natural rubber!
Now to the reason for me posting all this "drivel". If you've watched the video above you'll now understand that the tyre is built up in layers. The last of these layers to be added is the tread rubber. If you look at this picture I took recently of one of the tyres from the Mazda you can clearly see where the tread rubber and sidewall rubber join. Look at the edge of the tread pattern at around 1.00 o'clock to 2.30 o'clock in this picture:
Because of the way the light is falling on this image, you should be able to see quite clearly the delineating line between the tread rubber which is a completely different compound to the sidewall rubber. You can see this on most tyres and once you know this it gives you something else to look for when out shopping with the wife and bored out of your mind! Ha, Ha! But seriously, there is a point to this which is: Tread rubber is very tough and clever stuff, having to be able to provide grip in differing road conditions whilst at the same time providing resistance to wear so the tyre will last. The sidewall uses a very different compound as it has to be both tough - to protect the casing construction and "super flexible" to withstand the 3D flexing as the weight of the vehicle deforms it with every revolution but it doesn't need much abrasion resistance. When the tyre cures in the mould the casing rubber and tread rubber bond chemically and physically together. In fact this is a big quality control area as any imperfection introduced during building between the case and tread might well result in them failing to bond with the serious consequence that the tread may well separate in service and throw bits of tread off. (in racing, back in the day, we called it "chunking"). Even touching this interface was taboo as the sweat on your finger could cause the raw rubber to fail to bond. - Raw rubber, before it's cured is very "sticky" the surface is not unlike when you put the glue on an innertube before you stick the patch on.
So here's the "thought for the day" The tread rubber band is roughly the same thickness as the depth of the tread pattern, wee bit more on some. When the curing takes place a "mingling" layer is produced at the interface between the tread and casing rubber - this is everywhere under the tread rubber - so, if you think about it in cross section, starting off with the casing rubber, you then have a thin layer of intermingled casing and tread rubber and finally on the outside, the tread rubber. Tread rubber is designed to resist wear and abrasion whilst casing rubber is not. What does this mean? Well, when your tyres get well worn they might get into the area where this "mingled" layer is. If that happens the wear rate will become very rapid and can easily catch you out. If you look out for your tyres and check them regularly there's little risk of you experiencing this because you'll be checking pressures and looking at the tread depth right across the full width of the tyre. In my experience it's not unusual to find tyres wearing more on the inner shoulder and this is easy to miss as the tyre often looks fine from the outside. - turn your steering wheel full lock when checking to see both outside and inside shoulders of the tread. If you notice wear like this on your tyres it may just be that it needs checked for suspension wear and get the toe reset but also often it's a pointer to the rubber bushings on the suspension arms getting soft and allowing the front wheels to splay out a bit under braking. As most people know, the legal limit in our country is 1.6mm. Keep a regular check on your tyres, as most manufacturers now mould wear indicators into the tread - illegal when the indicator is flush with the surface of the tread. Many have little TWI letters on their sidewalls to help you find them - but remember if it's flush it's actually illegal right now, so we used to recommend changing at 2mm and I see some manufacturers are now recommending you think about renewing a tyre when it's showing 3mm. I find that particularly interesting as I got involved in doing testing tyre wet weather performance and we found that a tyre with anything under 2mm, on a properly wet road, not talking standing puddles here though, might as well be bald for all the difference it made to braking distances.
I think there are a number of factors in play with older worn tyres. Probably the biggest one affecting wet weather is the tread depth because if the tyre can't displace the water it's going to ride up on it, like a surfer, and then you're aquaplaning so have no grip at all! A big factor which few think about is that rubber oxidizes, becomes hard with age and grips a lot less well - one of the biggest reasons why your car seems to "feel" and handle better on new tyres - It's worth considering though, that if you run your treads really low and end up running on the "mingled" layer of rubber then not only will the wear rate greatly increase but also grip will be substantially compromised.
So, next time you're wandering down the street, add tyre watching to your activities, there's a bewildering number of tread pattern designs and defects to amuse yourself looking out for. If I ever get a "smart 'phone" I think I'll start a picture library of what I see.
Edit: If you're still reading you might like this: https://www.bathwicktyres.co.uk/tyr...egal limit of 1.6,the inner, centre and outer.
