RTI stands for Ramp Travel Index. RTI is just a method of measuring articulation. The standard was 20 degree ramps, however with the advances in off-road suspension, 30 degree ramps are quickly becoming the standard. Basically you drive your vehicle up the ramp until your rear tire tries to leave the ground. The score is calculated by dividing the distance traveled up the ramp by your wheelbase , multiple that number by 1000. So if a stock Wrangler (93" wheelbase) travels up the ramp 45" you'd have: (45/93)*1000 = 483. 1000 is a perfect score, meaning your rear tire started up the ramp before a tire lifted. Scores greater than a 1000 are possible if you approach the ramp at an angle. Just keep in mind the score means nothing unless you include the ramp angle, 500 on a 20 degree ramp is very different than a 500 on a 30 degree ramp. Just for reference, 500 on a 30 degree ramp is 731 on a 20 degree ramp.