This calculator estimates the Ramp Travel Index (RTI) without having access to a "real" ramp.

Ramp Travel Index is based on climbing a 20 degree ramp with one tire while keeping the trailing
tire in line. At the point where any tire begins to lift into the air is where it's calculated.
Measure from the bottom of the ramp to the center of the bottom of the tire
(use a plumb from the hub to find center). This distance traveled in inches is divided by
the wheelbase in inches and multiplied by 1000. What this gives you is a percentage of travel
up the ramp in relation to your wheelbase. Basically if your wheelbase is 100 inches, and you
travel 75 inches your RTI will be 750 (75% or .75 X 1000).

Since this is based on math we can use a formula to estimate your RTI.
The trick is to get one tire off the ground while the other three remain touching the ground. Then
measure from the bottom of the lifted tire to ground.
I've seen forklifts being used, climbing up a steep rock face, even climbing stairs.
I suppose you could climb different things and use the calculator to find the RTIs.
Then take the average of all. In any event, if you're curious I've provided a calculator
that will get you an idea of your RTI. Anything above a 500 is great, there are a few rigs
out there that can do perfect 1000's or better. How will you do?