New Tyre Sizing

[Muzza]

Well It's not new but for me It's new and I'll be honest, I'm confused.

We used to always state our tyre sizes as 33" x 10 1/2" x 15"

Now I'm seeing 285/65/r16 (assuming r16 = Rim size 16") (285mm is tyre width???) Whats the 65 for???

So we are now mixing imperial with metric are we?

Sorry for the basic question for most of you but for an old bloke It's confusing as hell. haha

Thanks for your replies, just curious?

Muzza

[Maxhead]

Size Coding - this might help
A tyre is referenced as "185/60R/15H", here is an explanation.
185=A, 60=B, 15=C


A = Width of Tyre (mm)
In this example it shows that the tyre is 185mm wide.
B = Profile as a % of width.
(i.e. profile is 60% of width)
In this example the ratio is 60%. This works out as 111mm.
C = Diameter of inner rim.
In this example it shows that the rim is 15" in diameter.

From this you can also work out your rolling circumference.

e.g. (2 x B) + C = diameter = d

therefore (2 x 111 = 222) + (15" x 25.4 = 381) = 603mm

circumference = pi x d = 3.142 x 603 = 1895mm

[YNOT]

65 (or the number that appears between the tread width and the rim diameter) refers to the side wall height as a percentage of the tread width. So using your example, the side wall height would be 65 percent of 285mm, what ever that works out to be.

Tony

Edit; beaten by 1 minute!

[Maxhead]

And yes, some smartarse thought it would be good to mix metric and imperial. I think just to confuse everyone.
Or maybe the tyre manufactures have moved on in time and rim makers are still stuck in the dark ages. GO FIGURE

[Muzza]

I know, thats just confusing.

mixing inches/mm as well as needing to calculate the percentage of width to work out your profile is just mad.

Is there any logic behind all this?

Cheers.

[Maxhead]

Not wrong about confusing.

Used to be easy. 33x12.5x16 where 33 is your diameter, 12.5 is width and 16 is rim

Now you have to calculate percentages, add, subtract and work out square root of pie to the power of 6 just to get the diameter.

[Mark]

Don't worry Muzza, I'm with you and to this day I still talk old school,

Old dog new tricks kind...lol

[Finly Owner]

Size Coding - this might help
A tyre is referenced as "185/60R/15H", here is an explanation.
185=A, 60=B, 15=C


A = Width of Tyre (mm)
In this example it shows that the tyre is 185mm wide.
B = Profile as a % of width.
(i.e. profile is 60% of width)
In this example the ratio is 60%. This works out as 111mm.
C = Diameter of inner rim.
In this example it shows that the rim is 15" in diameter.

From this you can also work out your rolling circumference.

e.g. (2 x B) + C = diameter = d

therefore (2 x 111 = 222) + (15" x 25.4 = 381) = 603mm

circumference = pi x d = 3.142 x 603 = 1895mm

another one for the index file

[ripper]

Just found a useful write up on Tyre sizes, Load ratings, Speed ratings, and more.
http://www.carbonblack.com.au/car-tyres/tyre-information.aspx

This could help too.
http://www.1010tires.com/tiresizecalculator.asp

[MudRunnerTD]

Here guys, here is a very good resource for instant conversions.

Plug in what you want and it will tell you what to order or the equivalent is

http://www.dakota-truck.net/TIRECALC/tirecalc.html