I was wondering what those numbers on tires mean:

180 = millimeters I assume in width of the tire

(For Example) what does 160 /70 mean?

What does a 21 inch tire mean: I also assume this is the height of the tire.

Don't like to assume...you know what that does...

 

I run a 180/55/18 which means 180 width, 55 height(sidewall) and 18 as in rim size.

 

18 rim size refers to what dimension?

 

My rear rim size is 18x5.5 which means 18" in height and 5.5" wide.

 

160 / 70 / 21

160, as you say width of the tyre in mm

70, the profile height of the tyre as a percentage of the width

21, fits a 21" diameter wheel

 

Cool...I got it now.

Tires are in mm
Rims are in inches

180/60 60 refers to the sidewall height. That was the one that was confusing me

Thats guys..as always HD Forum help comes through

 

Not quite,

The 60 represents the aspect ratio of the tire width, ie., 60% of the180mm width.
In other words the 180/60 actually refers to a tire 180mm wide and 108mm tall.

I'm pretty sure someone will correct me if I'm wrong.

 

I believe you are correct. I read that somewhere, I can not remember where or I would have posted the link.

 

They would, but you're not.

 

The writing on tyre sidewalls is getting close to a novel! For even more info on what it all means google 'tyre markings' or if you prefer 'tire markings'!