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 at 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.
>
> R... The "R" refers to radial construction, which has been the
> industry standard in passenger car tires for more than twenty
> years. Prior to radial tires, most cars came with bias-ply tires
> which had a crude construction that made for poor handling.
> Bias-ply tires are still used for certain truck applications.
>
> 16.... This is the rim diameter, in inches, for which the tire
> was sized. Pay particular attention to this number if you plan
> on upgrading your wheel size. If your wheel diameter
> changes, you'll have to purchase a new set of tires that match
> this new diameter.
>
> 89... A tire's load index is a measurement of how much weight
> each tire is designed to support. To find out what "89" means,
> it must be looked up on the official Maximum Load-Carrying
> Capacity Per Tire chart.
>
> In this case, the 89 indicates a maximum weight of 1,260
> pounds. Remember that this is per tire, which means you have
> to multiply by four to get the total capacity for a complete set
> of tires.
>
> V... The speed rating is a measurement of what speed the tire
> is designed to run at for extended periods. A "V" speed rating
> signifies that this tire can be run safely at speeds of up to 149
> mph for extended periods.
>
> Will it explode if it goes, say, to 155? No, not immediately...
> but it might if it is run at that speed for several minutes.
>
> Here is a complete list of the various tire speed ratings, and
> their associated letters:
>
> S 112 mph
> T 118 mph
> U 124 mph
> H 130 mph
> V 149 mph
> *W 168 mph
> *Y 186 mph
>
> * For tires having a maximum speed capability of more than
> 149 mph, a ZR may appear in the size designation.
>
> * For tires having a maximum speed capability greater than
> 186 mph, a ZR must appear in the size designation ...and a
> radar detector had better be on your dashboard!
>
> In addition to these basic tire specifications, you might find a
> DOT number that is used by the Department of Transportation
> to track tire production.
>
> The DOT uses this information for recall purposes. If a
> certain tire produced by a certain manufacturer on a certain
> day at a certain plant proves to be defective, this number helps
> keep track of where these tires ended up so that buyers can be
> notified of the problem.
>
> There is also a traction rating found on the sidewall of all
> modern tires that can be represented as an A, B, or C.
>
> This is a rating of a tire's traction when tested for straight line
> braking on a wet surface. For this rating A signifies the best
> traction performance and C indicates the worst.
>
> Finally, you might find the word TREADWEAR on the
> sidewall followed by a number like 120 or 180. This is a
> rating of the tread's durability, as tested against an industry
> standard.
>
> The reference number is 100 (like 100%) so a tire with a
> treadwear rating of 180 has an 80 percent longer predicted
> tread life while a rating of 80 means a predicted tread life only
> 80 percent as long as the industry standard.
>
> There's also a newer version of the treadwear rating that
> ranges from 20 to 620. Once again, the higher the number, the
> longer a tire's useable tread life will be.
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