Re: alfa-digest V7 #1352 - Tire Size Conversions

[AlfaNeely@domain.elided]

In a message dated 02/14/2000 9:43:42 AM Central Standard Time, 
owner-alfa-digest@domain.elided writes:
<< 
 Date: Mon, 14 Feb 2000 04:12:02 -0500
 From: ascher@domain.elided
 Subject: 164S tire choice
 
<snip>
 also, i am assuming this 205-55-16 size is closest to stock.  can i
 expect no speedo deviation from the factory 195-65-15? 
 <snip> 
 thanks in advance,
 ascher
 91 164S
 91 164L auto
 78 spider >>


    It is very easy to get an approximate method of conversion between tire 
sizes.  The tread width in mm times the aspect ratio divided by 25.4 mm per 
inch will give the tire side wall height.  Add the tire side wall height 
twice and the rim diameter once and you get the diameter or height of the 
tire.
    195-65-15 is 195 x .65 / 25.4 = 4.99 inches.  4.99 x 2 + 15 = 24.98 
inches tall
    205-55-16 is 205 x .55 /25.4 = 4.44 inches.  4.44 x 2 + 16 = 24.88 inches 
tall
Thus, it appears your conversion is quite close and should work fine.
    A word of caution: Manufacturers do not all read the specifications and 
apply them exactly as they are supposed to.  Therefore, the math I just gave 
you may not work in every case.  Or as some like to say, "Your actual mileage 
may vary."
Ciao,
Russ Neely
Oklahoma City

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