RAMP TRAVEL INDEX / RTI

The term RTI stands for Ramp Travel Index.  Ramp Travel index is a measurement of a vehicles suspension, frame and tire compression and the resulting flexibility of all components of the vehicle to achieve a score.  This standardized test uses a ramp to find the extreme flex point of the vehicle.

The RTI test is a good indicator of how well a vehicle will do in many situations offroad while traveling over an obstacle.  Ideally a vehicle will do better if it is able to keep all wheels on the ground for maximum traction.  If a vehicle's suspension is too stiff (less flex), it generally will lift a wheel or possibly two wheels while attempting to get over an object resulting in a loss of contact and traction at those lifted wheels.  Loss of traction is especially apparent with vehicles equipped with open differentials.  In situations requiring a lot of flex locking differentials and some limited slip differentials will help maintain momentum with the opposite wheel of the axle (front or rear), however good flexibility results in more wheels on the ground, better traction and better stability of the vehicle as the suspension conforms to the terrain.
  

At many shows and offroad events, you may have seen 4x4's taking a shot at the ramp.  While the ramp itself is fun to challenge, it does have it's useful points as a valid test.  The ramp can tell you a lot about your overall flex and is very useful in evaluating suspension, examining the length of your shocks and finding contact and interference points of components and other things all of which can give you insight into a vehicles capabilities on the trail under extreme flex.   Several factors make up the score on the RTI ramp.  These factors include the ramp itself, the length of the vehicle's wheelbase measured centerline of front axle to centerline of rear axle, and the distance traveled up the ramp without lifting a tire off the ground.  In most cases the ramp used is a 20 degree ramp.  Some events use a ramp with a more extreme angle such as a 23 degree ramp.  The test proceeds as the vehicle attempts to climb the ramp as high as possible with a single front or rear tire without lifting a wheel off the ground.  The distance the vehicle can travel up the ramp without loosing contact with the ground is measured from the leading edge of the ramp itself to the point on the ramp just below the center of the hub of the wheel on the ramp.  The distance is measured up the ramp and on the ramp, not to the actual hub of the wheel.  That number is the divided by the vehicles wheelbase and then multiplied by 1000 to calculate the average.  For example if a vehicle with a 81 inch wheelbase traveled 59 inches up a 20 degree ramp then the RTI would be calculated as: 59 divided by 81 x 1000 = 728 (rounded down).  This method of multiplying by the vehicle's wheelbase allows vehicles of different wheelbases to compete with each other on the same ramp.

Although you can't "cheat" on the ramp, you can optimize your score on the ramp and in the process improve your vehicles ability to flex and maximize traction over terrain.  One of the easiest things that you can to do to improve your score somewhat, which translates into improved traction offroad, is to air down your tires.  Airing down means to reduce the air pressure in the tires to the point where the tire is more likely to conform to the terrain.  Airing down to approximately half the recommended maximum PSI of the tire will allow a small gain on the ramp.  More noticeably, "airing down" will improve offroad driving in the form of better traction, a smoother ride over harsh bumps and allowing the tires to conform over obstacles resulting in better grip.  How much you air down may depend of several factors.  Some people air down as low as into the single digits however this can result in bead separation.  As a result bead locks are sometimes used to secure the tire bead to the rim.  Also smaller tires with a short profile aired down too low can suffer damage to the tire and rim such as tire pinch on the rim or a bent wheel rim.  Generally speaking extreme low pressures are usually reserved for large tires equipped with bead locks and in many cases bias ply tires are the preferred tire as they are more durable at low pressures.  Another factor for how low you go is whether you are equipped to air back up when you leave the trail ... or the ramp.  Obviously if you are not able air up, don't air down.  It is important to always bring your tire pressure back up to the recommended PSI for highway driving to avoid damage to the tire or loss of control while driving. 

Another factor that can improve your ramp score and improve the offroad ride with leaf sprung suspensions is to grease between the leafs in the leaf spring pack.  Without grease leaf springs in the pack tend to bind together and resist flexing.  Vehicles equipped with sway bars can greatly improve ramp travel by disconnecting the swaybar from the axle or suspension.  The swaybar is designed to limit wheel travel from one side to the other.  Most vehicles have a front swaybar, some have one in the front and in the back.  Many aftermarket vendors sell swaybar quick disconnects.  Disconnecting the swaybar will again, not only improve your ramp travel index score but also improve your articulation off-road resulting in better traction and a better ride offroad.  Always be sure to re-connect your swaybar(s) before hitting the road again.  With leaf sprung suspension, another aftermarket product designed to improve articulation is compound shackles such as the Revolver Shackles and obviously better suspension all together will improve RTI as well as off-road performance.
  

Measuring your RTI Score
Without a Ramp

If you want to find out your RTI score but you don't have a ramp, you can find out what your RTI would be if you were on the ramp.  Given that the RTI score is simply mathematics it can therefore be measured and calculated without a ramp.  At it's core the RTI score is a measurement of how high a tire can travel vertically before another tire is lifted off the ground.  The challenge is to safely raise one of the tires until one of the other tires almost comes off the ground but still has contact with the ground.  How the tire is safely raised depends on your resources but some people use a forklift with the tire resting on a strong pallet or they use a floor jack with the tire resting on a flat surface on the jack. Be sure to do this safely.  Placing jack stands under the vehicle as it is jacked is one way people secure the raised vehicle.  The main objective is to raise one wheel as high as possible before lifting a tire off the ground. Once the vehicle is raised to that point, measure the distance between the bottom of the tire and the ground. 

If using a fork lift you would measure where the tire meets the pallet to the floor.  With this measurement you calculate the score like this:  Since a 20 degree ramp rises at .345 inches per inch of travel, divide the height of the lifted tire by .345 (for 20 degrees).   Then divide that number by your vehicles wheelbase.  Multiply that number by 1000.  The result is your RTI score on a 20 degree ramp.  While the ramp is a true measurement of your RTI this calculated method is pretty close.  The calculator below does the math for you and allows for different ramp angles.