Not exactly Subaru related but thought someone might be able to answer my question quicker, here!
Most tyres sizes are expressd like, 235/75/15 for example so what the hell is this size- 31.10.50R15??? Obviously 15inch radius but whats the rest all about and how come they list some tyres in this format??

 

31 is the height of the tyre from ground level to the top of the tyre (when fitted on a vehicle), 10.50 is the width of the tyre in inches

They are American sizes, I have them on my Pajero

 

Makes sense now. Cheers Nate!

 

Basically, off-road tyres.

It's due to the high profile sidewall. As off road tyres have tall side walls; the taller, the better. Road tyres are generally the opposite.

Normal road-going radial tyres have a sidewall height proportional to the the tyre width: 100 profile is as tall as is wide (100%), 80 less so (sidewall is 80% of the width). 35 is like rubber bands (sidewall is 35% of the width).

Thus the denotation 215/45/18 --> 215 = Tyre width in mm. 45 =profile ratio. 18=rim size (in inches).


With off-road tyres. Say 31 x 10.5 R15 is --> 31= Overall Diameter (inches). 10.5 Tyre width (inches) R = Radial. 15 = Rim size (inches).

Hope that makes sense

 

As the others have already said it's just a different way of measuring it.

A 31x10.5R15 will be roughly equivalent to a 265/75R15 tyre.