Tire softness/hardness questions

[adambrouillard]

I was wondering if anyone knew what made the rubber of some tires harder than others. Also why do tires get harder as they age and heat cycle. Also what is the deal with tire softener products, what are they actually doing to the rubber. I can't find any good info source on this and I would think a tire engineer would probably know this stuff, but I don't know any.

[GORDON STREETER]

I do know that the tyre softener liquid (its like cellulose thinners) does work on old tyres to get a bit more life out of them. However I thought it was illegal to use it and it even used to say it on the product container !! as it would give you an advantage in a close policed one make series.

[jerryk]

its all like electricity

MAGIC

[Jeff 8]

As far as I know the compound is made by a different mix of oils and either natural rubber or polymer. When tyres sit outside they get very hard but with use the oils move through the tyre and soften it again, you see this most on trailer tyres that sit for long periods.

Whilst illegal in some race series, tyre softener is used in many others. I remember reading an article in Circle Track about 'Tire softener' and they did tests finding it advantageous even on new tyres. Some competitors even built a jig with a bath to rotate the tyre through. They also showed the US series where it was not allowed they were using sniffer dogs to detect it.

Jeff

[dtype38]

Originally Posted by Jeff 8

... I remember reading an article in Circle Track about 'Tire softener' and they did tests finding it advantageous even on new tyres.

Would be interesting to know how much of that is true and how much "urban myth". In my own experience, tyre softner is ok for getting a bit more life out of some old tyres that have gone like lumps of bakelite, but no meaningful difference on newer tyres. I once jacked up my previous car in the paddock and soaked my tyres in softener overnight, retreating them regularly. When I went down to qualifying the next day the surface was so soft I left black streaks from where it was parked. Result? Great grip for all of about 1 lap then normal service was resumed!

[Andrei]

I have never used softeners, so I can not tell you anything about them.

Tyres are getting harder because the rubber is creating new bonds (process of vulcanisation) because of heat (when driving) and light. The process is ongoing, it can not be stoped.

[ubrben]

Most race compounds are SBR (Styrene-Butadiene-Rubber) and it is unlikely that much natural rubber is used.

The rubber will be reinforced with carbon black (slick) or silica (wets) or some combination of the two.

Softeners will be used (oil or other) along with various resins to alter the modulus and damping characteristics of the rubber

Rubber is cured (vulcanised) by the addition of sulphur that creates cross links between the polymer chains.

Other things will be included such as anti-ozonates and processing aids.

The ratio of all these ingredients can be altered to affect the two key parameters (performance-wise) in a compound, which are the dynamic modulus and the damping coefficient.

For grip you need low stiffness and lots of damping in the rubber, but both of these directions will general make the rubber wear more. This compromise keeps tyre engineers very busy :-)

Ben

[adambrouillard]

Originally Posted by ubrben

Most race compounds are SBR (Styrene-Butadiene-Rubber) and it is unlikely that much natural rubber is used.

The rubber will be reinforced with carbon black (slick) or silica (wets) or some combination of the two.

Softeners will be used (oil or other) along with various resins to alter the modulus and damping characteristics of the rubber

Rubber is cured (vulcanised) by the addition of sulphur that creates cross links between the polymer chains.

Other things will be included such as anti-ozonates and processing aids.

The ratio of all these ingredients can be altered to affect the two key parameters (performance-wise) in a compound, which are the dynamic modulus and the damping coefficient.

For grip you need low stiffness and lots of damping in the rubber, but both of these directions will general make the rubber wear more. This compromise keeps tyre engineers very busy :-)

Ben

You seem to really know your stuff, so what exactly causes tires to get harder as they age. Is it continuation of the vulcanization process? Do heat cycles speed this up? Also can this process be reversed, or is all tires softeners doing breaking down the rubber?

[MGDavid]

Originally Posted by adambrouillard

You seem to really know your stuff, so what exactly causes tires to get harder as they age. Is it continuation of the vulcanization process? Do heat cycles speed this up? Also can this process be reversed, or is all tires softeners doing breaking down the rubber?

I always thought it was the solvents evaporating off, and heat speeds up the process?

[dtype38]

I believe Andrei answered that about four posts up.

[GORDON STREETER]

http://www.energymanagertraining.com/tyre/tyre.htm
Now we can all be tyre experts, if you have time to read it !

[kjw]

I was thinking of buying a few sets of tyres pre season so I have them when needed. I this a bad idea because they may start to go hard before being used? Is it better to buy them as and when required. One assumes Dunlop store them in a dark temperature controlled environment.

[GORDON STREETER]

If I have brought (or been given) tyres that I wont use for a while I keep them in the workshop in bin liners .

[dtype38]

I've taken your advice on that one with a brand new set of R888's. I'll let you know in a few months if it works.

[Tim Falce]

Nice floor in your shed there dtype

[ubrben]

Originally Posted by adambrouillard

You seem to really know your stuff, so what exactly causes tires to get harder as they age. Is it continuation of the vulcanization process? Do heat cycles speed this up? Also can this process be reversed, or is all tires softeners doing breaking down the rubber?

I'm a race tyre designer...

Cross link density going up - i.e. continuation of the vulcanisation process is a lot of what causes a tyre to go off. The other is that as the tread wears the shear deflection in the tread reduces and makes it harder for the tyre to maintain the tread temperature required to generate decent grip.

If you have internal pressure/temp sensors in for a long run - e.g. 30 laps plus you'll see a build up of pressure to an equilibrium, then a decline as the tread wears down.

Ben

[kjw]

Ubrben That is interesting, what about tyre storage? Is there a shelf life for a race tyre. i.e from when the tyre is manufactured to before it is used. Do they become hard due to being stored for a period of time.

[Speedy1]

if this helps

bicycle connoisseurs store their high performance tires in a cool dark place with some humidity ... the wine cellar

[ubrben]

Originally Posted by kjw

Ubrben That is interesting, what about tyre storage? Is there a shelf life for a race tyre. i.e from when the tyre is manufactured to before it is used. Do they become hard due to being stored for a period of time.

If I'm honest I've not got any hard data. Most of my work is development tyres, which are used within a few weeks of manufacture and are generally used for a few heat cycles and then scrapped.

Direct sunlight, ozone, etc are obviously bad for the tyre and storage instructions should be followed, but I wouldn't want to quantify the effect on performance.

Ben

[dtype38]

Originally Posted by Speedy1

bicycle connoisseurs store their high performance tires in a cool dark place with some humidity ... the wine cellar

Not just connoisseurs of bicycles then

[DaveGT6]

Originally Posted by ubrben

I'm a race tyre designer...


If you have internal pressure/temp sensors in for a long run - e.g. 30 laps plus you'll see a build up of pressure to an equilibrium, then a decline as the tread wears down.

Ben

Ben - does this mean that as our tyres wear we should increase the cold pressure to maintain grip levels? If so what sort of increase?

[phoenix]

Originally Posted by ubrben

Most of my work is development tyres, which are used within a few weeks of manufacture and are generally used for a few heat cycles and then scrapped.

If you have any tyres that need testing, please put me at the top of your list!

Thanks

Martin