Ramp Travel Index (RTI)
Ramp Travel Index (RTI) is for measuring how flexible your suspension is. There are two ways to accomplish this (one more accurate than the other).
The most common method is to use a ramp. You may have seen these before at various off-road events. Even though it looks like fun just to drive up the ramp, it also serves as a valuable tool in determining your flexibility, looking at shock length, etc. Most ramps are typically at a 20 degree angle. To compute your RTI, drive up the ramp until one or more wheels comes off the ground. At that point, measure the distance from the start of the ramp to the middle of you hub. Take that distance (in inches), divide it by your wheelbase (in inches) and multiply that percentage by 1000. That is your RTI. For example, a 88" wheelbase travels up the ramp 30". The RTI is 341 ( (30 / 88) * 1000). You use the wheelbase in the formula so that you can get a fair comparison across the different types of vehicles.
If you do not have a ramp handy, there is another way to calculate your RTI but it is not as accurate (but pretty close). Remember, you are measuring how far you can lift a tire vertically before another tire gets lifted. There are various ways to do this such as a fork lift or jack. Just place a tire on either and start lifting (be careful - I am not going to go over all the security measures on jacking it up). When another tire begins to lift, measure the distance (in inches) from the bottom of the lifted tire to the floor. With this measurement, we can calculate the RTI as if you were on a ramp. A 20 degree ramp rises 0.345 inches per 1 inch of travel. Divide the height of the tire by 0.345 (or 20 degrees). Now divide that number by your wheelbase (in inches) and multiply by 1000. Again, this is not perfect but close.
Now for those really hard core folks, here are some diagrams that show you how to build your own backyard ramp (compliments of Four Wheeler Magazine - April 1997).
