RTI stands for Radical Tire Inclination.....just kidding, it stands for Ramp Travel Index. It's a way of measuring your vehicals ability to flex. But instead of measureing how high you can get one tire, it takes into account the vehicals wheelbase. So really, it's a percentage of your wheelbase. The first people to do it, that I know of, was Four Wheeler Magazine. The original ramp, and the standard for now, is at 20 degrees. But now-a-days we are starting to see steeper ramps for the big players.
The way its measured is simple, if you can divide in your head, but a calculator can be helpfull. You drive one wheel of your truck straight up a ramp, keeping your front and back wheels inline with the ramp. Go up the ramp as far as you can, until you start to lift a wheel off the ground. Measure from the the center of the front tire to the base of the ramp, along the incline. The center of the front tire is where the tire comes in contact with the ramp, directly below the center of the wheel. You then divide the distance up the ramp by your wheelbase. Then, multiply that by 1000. So in my case, my Jeep can travel up a 20 deg. ramp 72". My wheelbase is 93". When I divide that it's .774, I then multiply that by 1000 and I get 774.
If I was on a steeper ramp, I would have scored lower, because I wouldn't have been able to travel up the ramp as far, eventhough my tire would come off the ground the same distance. So when you measure you score, you must also state you ramp incline.
The reason I called this a percentage, is because the number is realy a percentage of your wheelbase. In my case, 72" is 77.4% of my wheelbase, hence 774 as a score. The "perfect" 1000 score means you can travel 100% of your wheelbase up the ramp, to the point where your back tires touch the base of the ramp. A score over 1000 puts your back tire up the ramp some distance. (Editorial: I think they should've just had people multiply by 100, and state the percentage, instead of a score. This is much easier to grasp.)
A 20 degree ramp increases in height roughly .345" per inch of travel up the ramp. So you don't really need an exactly 20 deg. ramp to figure out your score. Say you have a loading dock near you (like my pic above) that's really only 15 degrees or so. Drive up it WITHOUT putting you back tire on it. Measure the distance between the ground, and the point where your tire makes contact with the ramp, directly below the center of the wheel. Take that number and divide it by .345, and you have how far you would have traveled up that ramp, if it was 20 degrees. You can then apply that number in the formula used above to figue your score.
For example: Say you drive up a ramp, of almost any angle, as far as you can before you lift another tire off of the ground. Measure the distance between the ground and the center oflifted tire, at the point it makes contact with the ramp . Say it 24" off of the ground. Take 24" and divide it by .345. That equals 69.6". This would be the distance you would have traveled up a 20 degree ramp. Divide that 69.6" by your wheelbase, lets say it 96" this esample. It would come out to .725. Multiply that by 1000 and you get a final score of 725! Who needs a stinking RTI ramp anyways? Now this is not exact, but it close enough for bragging.
Now I'm a dumb-ass, so don't go driving your dad's pickup over your neigbors
Corvette because you saw something on my web site that "made you do it"! See my
opinion on Law Suits.
Soon, I will include how I built my ramp, and some pics.