[VAC] Re: Grade %

["Fred Coldwell" <agrijeep@xxxxxxxxx>]

Percent grades can be thought of as number of feet in
elevation gained over a given horizontal distance.  As Rich
mentions, using 100 feet horizontal as the base makes
comparing percentage to elevation easy.  A gain of 1 foot in
elevation over 100 feet horizontal distance is a 1% grade. 
A gain or loss of 5 feet over 100 feet distance is a 5%
grade.  It is easy to compute when the base horizontal
distance is a multiple of 100 feet.  

  A gain/loss of 1 foot in elevation over a 1 foot distance
is a 100% grade.  It is also a 45 degree angle.  

  Since this is America, and one gets higher numerical
results using percent grades than angles (100% vs. 45
degrees, which would you rather have?), the larger number
(percentage) is used.   I have not plotted the relationship
of angle to percent grade (I'll leave that to Dr. G), but it
is a bit under half (45 degrees is a bit less than 100% / 2
= 50%). 

  I leave my protractor at home on trips, but someone more
ingenious than I could probably program their Palm Pilot or
onboard computer to convert percent grades into angles in a
flash of the ole chip.  In my old trucks, I know the
downgrade angle is getting too steep when the 
Big Mac slides off the seat onto the floor.  

Fred Coldwell
Denver, CO.