Re: copyright, that mythical concept - tyre diameters

["Eric Renneisen" <renneie@hlthsrc.com>]

Dave Easton wrote:
>> changing tyre sizes does *not* change the *size* of the 
>> contact patch, only it's shape.

then Stephen Bigelow responded:
> I'm _so_ glad I'm not the only one who sees that too.....
> The "balloon" analogy in one of the mags worked for me.

Yeah, that's what I thought, too. We had something of a 
broo-ha-ha on the 20V list about this some time back. With the 
design of today's tires, the contact patch area is different 
for different tire sizes (even at the same pressure). Now, the 
change is minimal, but it's surely there. Think about run-flat 
tires, or low-profile stiff-sidewall tires. Even when fully 
inflated, some of the weight is still supported by the 
structure of the tire (e.g., sidewall, resistance to 
deformation of the tread area), and that structure varies from 
tire to tire, even within different sizes of the same model, 
so the area of the contact patch is more complicated than 
weight divided by pressure.

Now, my argument through the whole thing was (and still is) 
that these effects are so small as to be insignificant (our 
discussion was about going from 205 to 225 width, presumably 
the same brand and model of tire), but I was forced to think 
about these other factors which I hadn't considered before. 
So, I now say that the area of the contact patch doesn't 
change *noticeably*.

Eric Renneisen
'90 CQ 20V  -  my 'racing-iron'  ;^)
Chattanooga, TN