1. Contact patch is determined by a combination of tire shape, pressure and rider weight.

Imagine a tire that is presurized high enough to "not deform" under a static rider load. Now image a squared off tire in that situation. The entire width of the squared section of the tread is in contact with the road. If it is a round tire (remember that the pressure is high enough in this example to prevent deformation under rider load) the contact patch will be smaller.

Think of Area Moment of Inertia and the difference between an I-Beam and a flat bar wiehgt bearing capability differences when thinking of the impact of shape on loading....

As the pressure decreases in this example from the "max theoretical" in my example to a real world riding pressure...the tire will deform, but think....botht the rounded and the squared will deform at the same rate if pressures and weight are held constant. Net result is a larger contact patch in with the squared tire.

That being said...the differences have got to be so small that they are not only non-noticeable by the rider, but negligible. I mean we're talking about small area differences in mm2 with large weight. It's like talking about how landing a fly on an aircraft car will change the vessel's handling.

So to answer your question it is possible to acquire the same increase in contact patch by either having a squared tire, or by decreasing the pressure in a rounded tire...they aren't different...in a straight line. I don't wish to begin to tackle cornering.

2. I agree with what has been written about this one. I find the rear skids more, probably due to the higher lateral forces a tire sees in the rear while conering due to the higher percentage of rider weight it is bearing.

Its theoretically possible to fail in doing the required correction (on rear tire skid) too :(

So then, some tires are pointier (rounder) than others. I know there's a wide range in 27 x 1 1/4 tires, but my impression was that they just had differences in real widths compared to the label. Overall though, if pointiness is important, won't you get the same result with a narrower tire?

A few comments in this thread suggest that a tire gets squarer with age/wear?

I'm not sure I follow what you're asking, but narrower tires are used to reduce rolling resistance (I KNOW THIS IS A BLANKET GENERALIZATION AND THAT THERE ARE INSTANCES WHERE THIS DOESN"T HOLD TRUE - DON'T FLAME ME).

BTW - "Pointy" is part of it, but sidewall properties/stiffness, casing stiffness, etc play a much larger role than unloaded shape.

And for your last statement...yes tires will develop w flat "squared off" section in the center of the tread as they wear. This wear is the basis of this thread.

Again, I am not a physicist, but this doesn't make sense when viewed from your position that the contact patch on a squared off tire is larger... I am happy to learn here, and I am presenting a few items that I don't understand in hopes of getting an explanation. I would hate to keep presenting false statements.

How is deformation measured to make this true? The only reasonable measurement I can imagine for deformation is contact patch size. How is deformation actually measured?

How does a bicycle tire not follow the general rule that the contact patch times pressure is equal to the weight being supported?

BTW starting with your assumption at zero deformation doesn't seem valid in explaining what happens in the real world. I could easily prove that heavier riders don't descend faster than lighter riders by presenting theoreticals about what happens in a vacuum... and then showing that as wind speed increases the forces, it has the same effect on the rider regardless of body weight... but the real world evidence proves otherwise.

Ah-Ha! - you missed the point where I said theoretical...this means it bears no resemblence to the real world. :D

You have percieved a clear flaw in my initial theoretical model. The load the tire carries and the pressure the tire is inflated to will always lead to the exact same contact patch size as long as the casing and sidewall are free to deform and the pressure is low enough (any practical pressure) to allows for deformation (READ:"Under Real World Conditions").

I had a feeling I was missing something simple, but not this simple. My embarassment is compounded by the fact that I work in the Hydraulics field where this basic idea is the principle that my entire product offering works off of.

I was so wrong I could work for the government.:D

EDIT: This should also bring a close to this debate because using this basic reasoning there is no difference in contact patch between a squared or rounded tire. Handling changes is something I know little about though, but I assume that there is little ot no difference in that area either.

Can you then say that as a tire wears, it rides like a wider version of the tire? It might even improve handling?

Well...I guess you could say that as the tire wears the contact patch remains exactly the same (straight line - again I don't want to guess about the deformation changes seen in cornering). In essence then you could say that it doesn't ride like a wider version of the tire, but rather it rides just like it always did.

As for improving handling I would expect no handling change (riding straight) - again I can not speak for cornering.