Yes - mostly

If the pressure is equal across the contact area, then load=pressure*area, so the area will be equal regardless of the tyre size.
In practice, however, pressure on the road will transition from zero at the very edge of the contact area, to the loaded tyre pressure towards the center of the contact patch. So the contact area may vary slightly due to shape and suppleness of the tyre but in general you are correct - Contact patch area is primarily a function of load and tyre pressure, not tyre size.

Yes, the area is generally the same. In simplest terms, pressure is pounds per square inch. So, if the pressure is the same, then the square inches must also be the same for the tire to exert the same pounds of force against the road.

And as you note, the shape of the contact patch would be different. A narrow tire would have a longer and skinnier contact patch, while a wider tire might have a rounder shaped contact patch.

Are you all confusing pressure internally in the tube and tyre with pressure (Force/Area) on the ground contact patch.

These are surely different, (although correlated)

For the purpose of my illustration, no. I led with the phrase "in simplest terms."

As per my earlier post, they are the same except for the impact of tyre deformation forces on the uniformity of the pressure.

You could test this yourself with a latex party balloon if you were to stick a pressure gauge in the neck of it and balance a flat bottomed object of known weight on top. You'd find the area of the balloon flattened against the bottom of the object multiplied by the gauge pressure in the balloon would give you the weight of the object.

Pressure is a measure of force per unit area. The only way the above is not true is if something is interfering with the uniformity of the pressure exerted across the contact area. That can surely only be the balloon (or tyre) material.

thank you so much everyone.......a cheeky follow up....anyone any idea how much tyre pressure goes up when the rider (eg 70kg) sits on the bike (tire-wiz users maybe would know??)

Hi,

For once I can answer something on here.

I work in this industry, in R&D.

The answer is no - a lot depends on the construction of the tire, which can vary greatly depending on what kind of footprint is needed for what kind of performance.

You can have a really strong tire that deflects very little under x psi pressure, or a very weak one that deflects much more under the same x psi.

Having said that, there are fewer differences in cycling tires as for car or truck.

HTH