Are you confused by your
car's tyres? Don't know your rolling radius from your radial? Then take
a good long look through this page where I hope to be able to shift some
of the mystery from it all for you. At the very least, you'll be able to
sound like you know what you're talking about the next time you go to
get some new tyres.
Tyre sizes and what they
mean.
Okay, so you look
at your car and discover that it is shod with a nice, but worn
set of 185-65HR13's. Any tyre mechanic will tell you that he can
replace them, and he will. You'll cough up and drive away safe
in the knowledge that he's just put some more rubber on each
corner of the car that has the same shamanic symbols on it as
those he took off. So what does it all mean?
185
65
H
R
13
This is the
width in mm of the tyre from sidewall to
sidewall when it's unstressed and you're looking
at it head on (or top-down).
This is the
height of the tyre sidewall, or section
height, expressed as a percentage of the
width. It is known as the aspect ratio.
In this case, 65% of 185mm is 120.25mm.
This is the
speed rating of the tyre.
This tells
you that the tyre is a radial construction.
Check out tyre construction if you want to know
what that means.
This is the
diameter in inches of the rim of the
wheel that the tyre has been designed to fit on.
Don't ask me why tyre sizes mix imperial
and metric measurements. They just do. Okay?
More
recently, there has been a move (especially in Europe)
to adjust tyre designations to conform to DIN (Deutsche
Industrie Normal). This means a slight change in the way
the information is presented to the following:
185
65
R
13
91
V
Tyre width
Sidewall
height %
Radial
Rim
diameter
load rating
speed
rating.
Decoding all that
information on the sidewall
It's
confusing isn't it? All numbers, letters, symbols,
mysterious codes. Actually, most of that information is
surplus to what you need to know. So here's the
important stuff:
Key
Description
A
Manufacturers
or brand name, and commercial name or identity.
B and J
Tyre size,
construction and speed rating designations.
Tubeless designates a tyre which requires no
inner tube. See tyre sizes and speed ratings
below.
C
Denotes type
of tyre construction.
D
M&S denotes a
tyre designed for mud and snow. Reinforced
marking only where applicable.
E
Load and
pressure marking requirement (not applicable in
the UK). These go from a load index of 60
(250kg) up to an index of 114 (1180kg).
F
ECE (not EEC)
type approval mark and number.
G
North
American Dept of Transport compliance symbols
and identification numbers.
H
Country of
manufacture.
Calculate the speed
difference
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Website design (c)2006 Ian Cattermole.
![[your tyre]](general_images/tyre/your_tyre.gif)