You can't assume that equal pressures on tires will give them the same diameter/height. As tire molds wear the size of the tire changes. You may have two tires on your machine from different molds or production dates, thereby giving you different heights at the same tire pressures.
There are 2 Methods I use to overcome this:
1. Grab a level, and a rule taller than your tire. Lay the level across the tread of the tire and level it. Measure from the level to a flat surface you have parked the machine on. Suppose you got 14 inches on that tire and you know it is at the specified pressure. Now do the same for the other sides tire. Level across top of tread sticking out to the side, measure height. It will most likely vary a little. Now add or remove enough air to bring that tire to the same height as the other side. Take note of each tires pressure. Take a paint marker and mark each wheel with the respective air pressure that leads to the same height tires.
2. Take a piece of small coated wire cable or electrical wire (to avoid stretch) long enough to wrap the circumference of your tire and add a few inches to it. Wrap this around the tire and with a marker make a mark where one end meets up with the other end (near the end) of the cable. Now take that cable and wrap the other sides tire and match your one end to the mark you made. Adjust the inflation until that tire has the same circumference as the tire you previously measured. Take note of the air pressure of each tire and mark the wheels with a paint marker accordingly.
From then on fill your tires according to what you have marked on the rim. One tire may be 15 psi, and the other may be 13 psi or 17 psi to obtain the same height/diameter or circumference. Fairly regulary check against your level and rule or wire cable to verify your findings are accurate.
Last edited by 44DCNF; 10-21-2012 at 12:45 PM.