How to obtain the correct PSOM Constant

STEP 1:

        Convert tread width into inches.    TW (in centimeters)  .3937 = TW (in inches)

STEP 2:

        Find sidewall height.                     TW (in inches) X %TW = SW (in inches) 

STEP 3:

        Find tire height.                            SW (in inches) X 2 + Rim size = TH (in inches) 

STEP 4:

        Find Tire Circumference.             TH (in inches)  X 3.14 = TC (in inches) 

STEP 5:

        Find Revs per Mile.                     63360 / TC (in inches)  = Revs Per Mile

        NOTE: Revs per Mile can also be found by locating your tire manufactures web site.  This is the preferred method.

STEP 6:

        Find PSOM Constant.                   (Revs Per Mile X Tone Ring Teeth) / 8000 = PSOM Constant

NOTE:  Tone Ring Teeth is 108 for Broncos and F150s.  Ford used a 120 tooth tone ring in heavy duty apps.  Check your local Ford Dealer for proper size.