Backspacing is the measurement from the wheels' mounting hub (the surface that bolts to the axle) to the outer edge of the wheel lip on the back side of the wheel.
You need less backspacing to move the wheel away from the wheel well.
On the back side of the wheel, throw a straight edge across the lip to span the whole wheel. Now take a tape measure and measure from the mounting hub, up to the straight edge (surface that is resting on the wheel). That's your present backspacing.

 

i got t273 35 and it fit awesome pictures coming soon