A little of both - the description is a little off. If you imagine cutting a
tire in half across its diameter, you'll get a revolved "U" shape. What the 205
measures is the maximum width of the "U". The tread with can be fairly close to
this (usually in low profile tires), or a little narrower, due to the bulge
that usually happens in the middle of the "U".
The 205 doesn't include the sidewall height (the sides of the "U"), that is
described by the "55". As stated below, it's a percentage of the 205, so in
this case 55% of 205 is 112.75mm.
Hope I haven't confused you more!
-=Chris
Chris King - cbking@alum.rpi.edu
http://mywebpages.comcast.net/kvcbk/
---------- Original Message ----------------------------------
From "Guy Weller" <guy at weller-lakes.freeserve.co.uk>
Date: Fri, 15 Nov 2002 08:10:13 -0000
>I think that the description of the first number is wrong.
>The example of 205 measures the tread width only, i.e. the width of
>rubber that contacts the road and with no element of the tyre wall
>height. 205 is about 8 inches and if you included the tyre wall
>height in this, say 2 X 3 inches, it dosn't leave much width of tyre
>for the road does it?!
>
>Or have I misunderstood your description?
>
>Guy
>
>----- Original Message -----
>From: "Bill Bryant" <bryant@sonic.net>
>To: <spridgets@autox.team.net>
>Sent: 15 November 2002 04:22
>Subject: rubberized hieroglyphics
>
>
>> Anyone with a little knowledge and a printed copy of this
>> article, can decode the rubberized hieroglyphics on the side of
>> tires!!
>>
>> The best way to understand tire markings is to take an
>> example and break it down. We'll start with the most
>> important numbers found on a sidewall.
>>
>> Take, for example, the numbers: 205/55R 16 89V
>>
>> 205.... The first number in this series, refers to the tire's
>> section width, or distance from sidewall edge to sidewall edge
>> (in millimeters) when measured up and over the tire's tread.
>> Generally speaking, the larger this number is, the taller and/or
>> wider the tire will be.
>>
>> 55.... This number is the tire's aspect ratio, or its section
>> height as compared to its section width. In this case, the
>> section (or sidewall) height is 55 percent of the section width.
>> This number can be very indicative of a tire's purpose. Lower
>> numbers, like 55 or less, mean a short sidewall for improved
>> steering response and better overall handling.
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