Friday, 19 February 2010

Buying new Tyres? What do Tyre Markings Mean?

Buying new tyres?

  1. If you live in Australia, spend $10 or go to a library and get the Choice test for tyres that your car uses (or something close).
  2. Look at the recommended tyres and decide what features you want more than others. 
In my case, I want best wet weather cornering and braking, followed by dry weather cornering and braking - then price.

I need 205/65R15, 215/60R15, or 225/60R15 tyres. I have 7" wide rims (15x7J) so I can use 8" to 9" tyres (205 - 225 and maybe 235).

You can change widths and profiles if your rims are the right width and you consider speedo errors.

For example  a 205/65R15 has the same circumference as these:

  • 215/60R15 (1.3% error),
  • 225/60R15 (0.5% error), and 
  • 235/55R15 (1.2% error). 

Here is my Math.

Circumference = pi * ( rim_size * 25.4 + 2 * ( profile / 100 ) * width )

A worked example might help.

For 225/60R15, C = pi * (15*25.4 + 2*60/100*225) = 2045mm

What to look for.

  • Tread Wear 300+ (3 time 'standard' tyre life) 
  • Traction (braking in the wet) AA or A 
  • Temperature A 
Other Markings

The tyre manufacture date is also on tyres. It seems to be stamped in rather than the other text which is raised. Look for something like 2309 - meaning 23rd week in 2009.

Here are photos of the Treadwear, Traction, Temperature, tyre size and date from one of my old tyres.

Treadwear 300
Traction A
Temperature A

Tread width 225mm
Profile 60% (of 225mm)
Tyre Radial (R)
Rim 15"
96V load and speed rating

Manufactured in the 49th week of 2007

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