RE: The VW Jetta GLX Mailing List Digest V4 #60

["Belt, Stephen D" <stephen.d.belt@intel.com>]

Sundie sez>

> Yes, the contact patch is 10mm wider.  But the tyre will also be 10mm
taller.

> 205/50-15

> 205=width of contact patch
> 50=percentage of contact patch that the tyre is tall from the rim 
> (eg 205*.50=102.5, which means your total tire height > will be 15" 
> (rims) plus 102.5*2 (top and bottom))
> 15=size of rim.

Technically, you are correct, the tire will be 10mm taller, when measured
across the diameter.  However, since the tire should rub against the ground,

but not the fender, most people don't usually concern themselves with the 
diameter, but rather the radius, and how much closer to the fender we will 
get with a taller tire.


When the previous poster mentioned 5mm taller, I'm sure he was speaking of
radius, as that is what most people will be worried about.  Most people look

at the gap between the tire and the fender, with the wheel at full lock in 
both directions and the suspension compressed and in some way measure this 
gap (eye-balling it is the typical means).  Most people would then compare 
this with the estimate of how much larger the tire will be, to see if it
will 
fit.  If the change in total diameter were compared with the tightest fit 
location, that would be a radius vs. diameter comparison, and not accurate.

So to the original poster:  if the tire is exactly the size of its spec (and
most are actually smaller), the tire will have a radius of 5mm larger (which
is approximately the width of the cable leading to my mouse).  The tire will
also be 10mm wider.  Taking both aspects into consideration, I'd estimate 
that the tire will end up 7-8mm closer to the fender than before.  Should be

quite safe.

Steve Belt - Scotts, AZ
1998 VW Jetta GLX