How stiff are F1 tyres?

[marekk]

... the engineers announced that the reason the tyre stiffness had changed so dramatically was because they had adjusted the pressure split of the tyres. Then I discovered the car was fitted with inner liners (which explained, incidentally, why the wheels had 2 schrader valves).

Now ,as wee all know that stiffnes of the tyre doesn't depend on volume change (air is there just to preload the structure at inflation time), how could the tyre stiffness change so dramatically without (i suppose) changing the pressure of main tyre, just by introducing a inner liner not connected with main tyre by any means (air dosn't count, as we know) ?

Ciro ? Tom ? Dave ? Anyone ?

[DaveW]

The obvious possibility is usually the correct one.... The inner liner was in contact with (& supporting) the tyre.

[marekk]

The obvious possibility is usually the correct one.... The inner liner was in contact with (& supporting) the tyre.

[AWF]

I think what most are forgetting except for Dave, is that in F1 tyres if you increase the pressure, you also induce a crowning effect on the contact patch of the said tyre. What happens when you reduce contact but keep the same load.... the force will act on a smaller area thus creating a higher pressure which pushes the crowned tyre down thus giving a bigger deflection for the same load resulting in a measured reduction in tyre stiffness, however this becomes rather non linear and can be an issue.
The lateral stiffness will increase as the wall stiffness is higher and cannot deform to the same extent causing other issues.

these phenomenon are not as pronounced in low profile LeMans spec tyres but it is noticable at low pressures as the majority of the load runs more directly through the exceedingly stiff shoulders which arch into the tread section.

It is a very miss understood idea that presssure merely increases tyre stiffness but does stant up in some cases, but in F1 style tyres I am afraid DaveW is very correct!

[Jersey Tom]

I think what most are forgetting except for Dave, is that in F1 tyres if you increase the pressure, you also induce a crowning effect on the contact patch of the said tyre. What happens when you reduce contact but keep the same load.... the force will act on a smaller area thus creating a higher pressure which pushes the crowned tyre down thus giving a bigger deflection for the same load resulting in a measured reduction in tyre stiffness, however this becomes rather non linear and can be an issue.
The lateral stiffness will increase as the wall stiffness is higher and cannot deform to the same extent causing other issues.

these phenomenon are not as pronounced in low profile LeMans spec tyres but it is noticable at low pressures as the majority of the load runs more directly through the exceedingly stiff shoulders which arch into the tread section.

It is a very miss understood idea that presssure merely increases tyre stiffness but does stant up in some cases, but in F1 style tyres I am afraid DaveW is very correct!

I find this exceedingly hard to believe.

[riff_raff]

Increasing inflation pressure creates higher tensile preload in the tire structure, which changes its cross section profile and alters the deflection produced in the sidewall from lateral forces. Of course, the dynamic CF force produced on the tire structure at high speeds has a somewhat similar effect. The tire structure is able to handle tensile forces well due to the reinforcing fibers used, but the only capability it has to handle compression is that provided by the rubber materials.

[mertol]

measured reduction in tyre stiffness

But this measurement is false because the deflection is in the contact patch becoming flat and not the side walls bending. Whoever is taking care of the telemetry probably takes this into account.

[Smokes]

So, from this conversation we can conclude that the air pressure affects the tension of the ply and therefore affects the stiffness of the Tyre. Therefore can we conclude that the Tyre stiffness varies dependent on the Air temperature,and the ply temperature and the compressive force acting on the air inside the Tyre.
My only query Is how do you account for the tyre profile a and therefore tyre footprint as the car does a lap on the track?

Also how much downforce is absorbed by compressing the tyres air?

[Greg Locock]

Also how much downforce is absorbed by compressing the tyres air?

None.