Re: RTI Calculations

["Bill Thebert" <bthebert@domain.elided>]

> Date: Thu, 06 Aug 1998 17:50:21 -0600
> From: Darrel Kline <darrelk@domain.elided>
> Subject: RMIHR
> 
> What's the formula for the ramp test? I went 83 inches up the 25 degree
> ramp. Any spectulation on what this would be on a "standard" 20 degree
ramp?

Darrel:

The "standard" calculation is (ramp distance / wheelbase) x 1000 = RTI

Example:  a 100" Scout II travels 50" (half its wheelbase) up the ramp.  50
/ 100 = .500, but like a batting average, we say "he's hitting '500' this
year".  That's the only reason for the multiplication by 1000.

As for converting to a 20-degree ramp, the key here is the raw "vertical
lift" of the tire, I think.  And the pertinent math is:  sinX = O / H,
where "O" = the side of a right triangle "opposite" of angle X, and "H" =
the hypotenuse of said triangle.

To clarify:

You drove 83" up the hypotenuse of a 25-degree right triangle.  We wish to
solve for the "short" or "vertical" side of said triangle.

sin(25 degrees) = O / 83

.4226 = O / 83

.4226 (83) = O

O = 35.077 inches of vertical wheel lift.

Now you're asking "how far would I have had to drive up a TWENTY-degree
ramp to achieve the same vertical lift?"  Same math, but solve for "H" this
time, and use the sin(20 degrees) and the now known value for "O".

sin(20 degrees) = 35.077 / H

.3420 = 35.077 / H

.3420(H) = 35.077

H = 35.077 / .3420

H = 102.558

If your wheelbase is still a perfectly stock 100", your RTI would be (102.6
/ 100) x 1000, or a whopping 1026.

I did this same math for my rig on the RMIHR pages that I posted on the
Binder Bulletin web site yesterday
(http://www.binderbulletin.org/travel/rmihr98).

Bill Thebert
The Binder Bulletin