[EMAIL PROTECTED] wrote:
>
> This past weekend we traveled up and down 6,7,8% grades. My question is, % of
> what? Why not use 20 deg. 30 deg. or what ever. I know going up that 8% grade
> would have been better described as, oh....i don't know a 40. Can anyone help
> me see the "height"?
>
> J.L.Dietz #4361 S.E.PA
>
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.
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