Re: Tire diameter

[Mike Norman <mike.norman@cubic.com>]

Robert Houk - WorkGroup Server Firmware wrote:
> 
>    Hi group,
>      Tire diameter is easy:
> 
>           td = ((tire width*aspect ratio*2) / 2540) + wheel dia in inches
> 
>    circumference = td * pi                              77.55
>    circ (in feet) = circumference / 12           6.4625
>    wheel revolution/ mile = 5280 / circ                817.021
> 
>    anybody with programming abilities can make a small program in qbasic, c
>    or whatever to automatically check out any tire size, and how that
>    tire/wheel combo will be to stock.
> 
> However, bear in mind that there can be a *lot* of variation from
> brand and model to another model and brand. It's more or less what-
> ever the manufacturer wants to call it.
> 
> As I recall, it was Yokohama A-001Rs that were about half-an-inch
> bigger diameter, and actually rubbed (ever so slightly, mostly just
> "kissing") the inside fender well . . . so don't place *too* much
> faith in idealistic calculations. (In particular, calculating to
> 4 decimal places is hopelessly optimistic)
> 
>                                         -RDH
Thanks for the return.  

  I realize that the decimal places are "HO".  I just copied them off of
the calculator.  One could round each calc to 1 place and still not be
far enough off to matter. 

  And, yes, mfr's do play fast and loose with the "standard"
dimensions.  There is also the difference between a tire's "new" dia and
well used, probably a 1/4".  

  Another variable is the dia of the wheel.  A 225 wide tire on a 17" is
actually wider that a 225 tire on a 16".  Or maybe it's the wheel width
and how it affects the shape.  

  Anyway, many variables.  Just have to do the calc's and take your best
shot.  The final authority is, of course:  "Do they fit!"