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View Full Version : Rubber=Rubber? That is the question!



t0daY
27-09-2016, 17:07
Why would worn tyres equal worse grip? Unless all rubber has been completely removed, rubber=rubber and hence there's still grip. The only real difference is that tyres with less rubber heat up and cool down quicker, which may affect lap times positively or negatively, not just negatively per-se.


You do realise that the case was: worn tires = better grip and not equal grip. Give me one example were worn tires are 1sec faster than a brand new tire set.

The initial thread was closed but I am still curious about the answer here. Also I do not think it is correct that rubber=rubber and you have the same grip even when the tires worn out. What do others think?

AbeWoz
27-09-2016, 17:09
i think that, yes, rubber=rubber. But the first quoted posts answers the question. It has to do with the heating and cooling of the tire, as well as how much actual material is in contact with the road surface.

t0daY
27-09-2016, 17:12
i think that, yes, rubber=rubber. But the first quoted posts answers the question. It has to do with the heating and cooling of the tire, as well as how much actual material is in contact with the road surface.

I get that point but the case was "Worn Tires = More grip not Equal grip". Also you suffering more from worn tires than just heating and cooling issues...

miagi
27-09-2016, 17:44
I had a look in the R&D Department of Continental. They have all kinds of machines and devices to analyse the chemical, mechanical, thermal ... characteristics of rubber. Rubber is never just rubber.

The way a tires is vulcanized and the way it cooles down, the outer rubber on the tire is less vulcanized than the inner rubber. Leading to different compounds. A tire that is pushed around the track at 90 maybe even 120C is further vulcanized. Means towards the end of a stint, when some of the rubber is left back on track, the compound is harder than with fresh tires.
It depends on the carcass, but there are tires where the thread rubber adds significantly to the stiffness of the contact patch. That can have influence on the mechanical characteristic of the contact patch for example on the standing wave phenomenon that happens when a tires run at too high travel speed and/or too high wheel load (than it's classified).
Tires usually change shape when Camber is used. They were a bit more on the inside than on the outside. That changes the shape of the contact patch and also the pressure distribution.

And knowing tires a bit, probably half a dozen other effects I couldn't think off right now.

Jussi Viljami Karjalainen
29-09-2016, 17:37
Yup, rubber is a real bastard. And IRL there's stuff like heat cycles (even if a tyre isn't worn down significantly, a tyre that has heated and cooled down a number of times behaves differently, often the tyres are at their absolute best during the first heat cycle) which can really affect things, especially when you consider that a GT3 team usually has around 4-5 sets of tyres for the whole race weekend.

And there are multiple types of wear, you could wear one edge out more than the other, changing how the contact patch pressure distribution behaves, you can get graining on the surface of the tyre (this is actually modeled in pCARS), you can get blistering, the diameter of the tyre changes slightly, and with that again you can get an effect in contact patch size/shape/pressure, various things can happen to the tyre that would throw it out of whack while it wears down.

miagi
29-09-2016, 22:29
About heat cycle. Very difficult to understand what the hack is going on with the rubber, but easy to test. For our formula student tire that is the softest compound that is processable. It is important to heat it up once, let it rest and then use it, than it will wear in a sensible speed(still influenced by temps, tarmac and so on). If not, wear rate will be huge. It's like the rubber needs to be activated, maybe "exhale" surplus resin(s).

Jussi Viljami Karjalainen
02-10-2016, 00:38
About heat cycle. Very difficult to understand what the hack is going on with the rubber, but easy to test. For our formula student tire that is the softest compound that is processable. It is important to heat it up once, let it rest and then use it, than it will wear in a sensible speed(still influenced by temps, tarmac and so on). If not, wear rate will be huge. It's like the rubber needs to be activated, maybe "exhale" surplus resin(s).Interesting! Have you noticed differences in grip before and after the first heat cycle? Would be interesting if you got more grip but horrible wear during the first cycle... =)

hkraft300
02-10-2016, 03:53
Interesting stuff.
I wonder if that heat cycle is having an effect somewhat like stress relieving of metals.

miagi
02-10-2016, 17:07
Interesting! Have you noticed differences in grip before and after the first heat cycle? Would be interesting if you got more grip but horrible wear during the first cycle... =)
Afair it's not that significant esp. compared to how much the wear rate is exaggerated. When we were in spain, when the sun was burning on the tires before the disciplines, the tire became really sticky. Wasn't like that at Hockenheim or Redbull Ring.