RE: Tire Size -Reply

From: Jon Steiger (stei0302@cs.fredonia.edu)
Date: Fri Mar 20 1998 - 11:47:26 EST


On Fri, 20 Mar 1998, Jack Snodgrass wrote:
> I don't know about that first link.
>
> If you put in 215/75/15 ( what I have on my stock 97 ) and
> 255/55/17 ( what shoud come on a new R/T )
>
> it tells you that the tires are about the same size in height
> but the R/T tires are going to be narrower by 1/2 inch or so. If
> the R/T tires are on 9 inch rims and the stock tires are on 7 inch
> rims... wouldn't the R/T tires be wider?
>

  Yep, absolutely. Tires are:

  width (mm)/sidewall height as a percentage of width/inner diameter (in)
                  
   Width and inner diameter require no computation; just read the
  number and that's what it is. In the tires above, 215mm and 255mm,
  for width, and 15 inches and 17 inches inner diameter, respectively.

   The second (middle) number which represents the sidewall height
  is a percentage of the width, so to find the sidewall, you just
  multiply by that percent. (move the decimal in two places and multiply)
 
    Incidentally, to convert mm to inches, divide by 25.4.

      The numbers I get for the above tires are:

    stock: 8.5" wide, 27.7" tall 87.01
      r/t: 10" wide, 28.0" tall 88.100

    So the R/T tires are a whole inch and a half wider, and about a
    quarter of an inch taller... (Which for all practical purposes
    is the same height.) If my calculations are right, if you put
    the the R/T tires on a stock 97, the speedometer would read
    .75 MPH low at 60mph. (I guess they must have a bug in
    their calculator somewhere...)

                                              -Jon-

  .--- stei0302@cs.fredonia.edu -- http://www.cs.fredonia.edu/~stei0302/ ---.
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