2014 tyre supplier decided ?

[timbo]

I don't think so. The grip depends of the area and not the length the area has in the direction of the force. Directional differences in grip are probably much more a consequence of construction and the deformation due to construction differences.

The degree of deformation would most certainly depend on tyre dimensions. Also I think that saying that grip depends only on area might be simplistic, it should not depend on area too if it were that simple .

[WhiteBlue]

I don't think so. The grip depends of the area and not the length the area has in the direction of the force. Directional differences in grip are probably much more a consequence of construction and the deformation due to construction differences.

The degree of deformation would most certainly depend on tyre dimensions. Also I think that saying that grip depends only on area might be simplistic, it should not depend on area too if it were that simple .

I wasn't saying it only depends on the area if you read it carefully. My point was more that it will not depend on the length of the contact patch that happens to be in the same direction as the force.

[dlstanf2]

I should hope this gets a much stronger investigation. Tyres have been a mess since Pirelli became the supplier. Either open the field of tire to other manufacturers with the same general rules now in use, or the one I prefer.

A mandatory pit stop of three(3), maybe(4) Stops. This will allow racing to again be the sport we love and give the teams a means to go all out. Competition on the track and in the pits.

This guarding the tires or cruising is not racing. The tires are the major talking points now. Aerodynamics is secondary to all. If this keeps on we might as well install left turns or right turns and rebrand the sport as "Fancy Cart Races".

[raymondu999]

I stand by my previous assertion that if the loads to be supported, and tyre pressures, etc were all identical, an increase in tyre width or diameter would NOT alter contact patch size

[xpensive]

I stand by my previous assertion that if the loads to be supported, and tyre pressures, etc were all identical, an increase in tyre width or diameter would NOT alter contact patch size

I agree, the vertical load on the tire will obviously be equaled by tire-pressure times contact-patch area.

[WhiteBlue]

I stand by my previous assertion that if the loads to be supported, and tyre pressures, etc were all identical, an increase in tyre width or diameter would NOT alter contact patch size

Huh, that sounds strange to me. Do you think the decreased deformation would compensate for an increase in tyre width? Can you elaborate particularly for the case the tyres are made wider. I hope you understand my question.
If there was no deformation flattening the tyre circumference at the contact line there would not be a contact patch. So that deformation is vital to create the patch. If we make the tyres wider the contact line becomes wider. In order to keep the contact patch the same size the deformation that produces the length of the patch had to go down exactly as much as the width increase contributes. How likely is that?

[Blanchimont]

I agree, the vertical load on the tire will obviously be equaled by tire-pressure times contact-patch area.

IMO this is only true for a very soft tyre. Imagine the tyre air valve is broken and the tyre itself is still OK. The pressure difference is set to zero in this example, but the tyre can still hold the car up (depends on how stiff it is and how heavy the car is).

[raymondu999]

I stand by my previous assertion that if the loads to be supported, and tyre pressures, etc were all identical, an increase in tyre width or diameter would NOT alter contact patch size

Huh, that sounds strange to me. Do you think the decreased deformation would compensate for an increase in tyre width? Can you elaborate particularly for the case the tyres are made wider.

I'm not a tyre expert, but logically thinking through the entire system as a tyre supporting a mass, you don't have to look far. From first principles, P = F/A. If P is the same and F is the same, then it stands to reason A cannot be different. P of course being tyre pressure and F being force to support (ie how much mass to support).

But as Blanchimont has added to this discussion - the tyre sidewall adds some. So instead of F = P x A, it becomes F = (P x A) + sidewall "force"

[xpensive]

I agree, the vertical load on the tire will obviously be equaled by tire-pressure times contact-patch area.

IMO this is only true for a very soft tyre. Imagine the tyre air valve is broken and the tyre itself is still OK. The pressure difference is set to zero in this example, but the tyre can still hold the car up (depends on how stiff it is and how heavy the car is).

With a vertical load of 5000 N (500 kg), I believe the load-bearing effect of the tire-carcass itself is negligible.

[WhiteBlue]

I stand by my previous assertion that if the loads to be supported, and tyre pressures, etc were all identical, an increase in tyre width or diameter would NOT alter contact patch size

Huh, that sounds strange to me. Do you think the decreased deformation would compensate for an increase in tyre width? Can you elaborate particularly for the case the tyres are made wider.

I'm not a tyre expert, but logically thinking through the entire system as a tyre supporting a mass, you don't have to look far. From first principles, P = F/A. If P is the same and F is the same, then it stands to reason A cannot be different. P of course being tyre pressure and F being force to support (ie how much mass to support)...

You are correlating different pressures with the force and the contact patch. The pressure that is described by your equation is not the tyre pressure - which is inside the tyre - but the pressure between the tyre and the track in the contact patch, basically outside of the tyre. When you talk about tyre pressure everybody will think you talk about the pressure inside the tyre.

[WhiteBlue]

I agree, the vertical load on the tire will obviously be equaled by tire-pressure times contact-patch area.

IMO this is only true for a very soft tyre. Imagine the tyre air valve is broken and the tyre itself is still OK. The pressure difference is set to zero in this example, but the tyre can still hold the car up (depends on how stiff it is and how heavy the car is).

With a vertical load of 5000 N (500 kg), I believe the load-bearing effect of the tire-carcass itself is negligible.

I think Blanchimont is right. It is impossible to balance the internal tyre pressure by weight and area because you have elastic effect from the overpressure. I think there is a misunderstanding about the pressure. The outside pressure is not the inside pressure.

[xpensive]

"The outside pressure"?

[WhiteBlue]

"The outside pressure"?

Do you deny that the contact pressure is not related to the tyre pressure? The equation given was not for tyre pressure as claimed but for contact pressure. And contact pressure will not be constant when you keep tyre pressure constant.
May I remind you of the issue on hand. The question was about changes caused by changes in tyre dimensions. Naturally the tyre width is crucial to the size of the contact patch. The contact patch typically grows if you increase the width of the tyres for a given application. Naturally the contact pressure will also decrease. Do you deny this?

[xpensive]

"The outside pressure"?

You could be a bit more polite. Do you deny that the contact pressure is not related to the tyre pressure? The equation given was not for tyre pressure as claimed but for contact pressure. And contact pressure will not be constant when you keep tyre pressure constant.
May I remind you of the issue on hand. The question was about changes caused by changes in tyre dimensions. Naturally the tyre width is crucial to the size of the contact patch. The contact patch typically grows if you increase the width of the tyres for a given application. Naturally the contact pressure will also decrease. Do you deny this?

Not that I believe it's leading anywhere to discuss mechanics with you, but I feel a certain responsibility toward other members, after all some of them have given you 98 votes. Again, at vertical loads in this range, 5000N, the stiffness of the tire itself is negligible, which makes the tire-pressure almost identical to the contact-patch pressure, which is load over area.

[WhiteBlue]

Again, at vertical loads in this range, 5000N, the stiffness of the tire itself is negligible, which makes the tire-pressure almost identical to the contact-patch pressure, which is load over area.

The tyre pressure is partly caused by the vertical load which you give at 5 kN. But it also depends of the initial inflation which can be considerably higher than the additional tyre pressure caused by vertical loads.
Even if I disregard that fact, the areas that are exposed to tyre pressure and contact pressure are not of the same size. So your assumption that tyre pressure and contact pressure are equal or near equal are simply false.