RAV4 tires are delivered in one of two sizes, depending on the 
option packages that were ordered.  Most RAV4s are delivered with 
tires with a size designation of P215/70R16.  The alternate size 
is P235/60R16.  You can easily determine the size of your tire by
reading the size code stamped into the sidewall.

The first number in the size code is the width of the tire, 
measured from sidewall to sidewall, in millimeters.  To convert 
to inches, divide by 25.4.  For example, the width of 215mm is 
equal to 8.46". 

The second number is the aspect ratio, or the ratio of sidewall
height to width. For the RAV4, the 70 indicate that the height
of the sidewall is .70 of the width.  So, the height of the tire
sidewall is 215mm X .70 = 150.5mm or 8.46" X .70 = 5.93".

The "R" indicates a Radial tire design.  Virtually all tires 
available today are of this design.

The last number is the diameter of the wheel in inches.

For more details of other markings on the sidewalls of tires, see:

<http://www.tirerack.com/tires/tiretech/sidewall.htm>

Often, tires and wheels are replaced as a set for various reasons.
When a "plus 1" wheel is used, the driver wants better handling 
characteristics.  A wheel one inch larger than stock is installed,
and tire with a correspondingly smaller sidewall height is chosen
to retain the same diameter of the tire.  Maintaining tire diameter
is important to keep speedometer and odometer readings accurate.

In the same way, a "minus 1" tire and wheel package may be 
installed, often for a snow tire package.  A wheel one inch 
smaller is installed with a tire with a correspondingly larger
sidewall height.  A taller, skinnier tire performs better in 
the snow.

To calculate the differences in wheel and tire size, use this
tire size calculator: <http://www.powerdog.com/tiresize.cgi>