| Word |
Definition |
| Approach Angle |
The angle at which a line drawn from the leading part of the vehicle's bodywork and touching the front tire meets the ground. It gives an indication of the steepness of a step-up that a 4x4 can approach without its nose digging in. The bigger the angle, the closer it is to 90 degrees the better for offroad work.
See also departure angle.
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| Articulation |
The suspension's ability to follow varying terrain keeping all four wheels on the ground in a cross-axle situation. |
| Axle Wrap |
Referred to as both rear spring and rear axle wrap-up. As power is applied, torque load causes the rear pinion to pivot upward. Once this load reaches a certain point the leaf springs begin to deform, which stresses numerous driveline components. The "fix" is to increase spring strength, via add-a-leafs, or install Super-trac traction bars. |
| Bump Steer |
The tendency of a vehicle to suddenly veer or swerve to one side when hitting a bump or dip in the road. The condition is caused by uneven toe changes that occur as a result of the steering linkage or rack not being parallel with the road surface. This causes the wheels to change toe unevenly as the suspension undergoes jounce and rebound. |
| Departure Angle |
The angle at which a line drawn from a vehicle's rearmost bodywork and touching a rear tire meets the ground. It gives an indication of the maximum steepness of a step-down that a vehicle can negotiate without dragging the rear bodywork. Long body overhangs reduce the departure angle. The closer the angle is to 90 degrees the better for offroad work. See also approach angle.
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| Ramp Travel Index (RTI) |
A vehicles RTI or ramp travel index is a measurement of a vehicles suspension (and frame) flexibility. There are several factors that make up the RTI score. First the ramp. In most cases the ramp is on a 20 degree angle. Some events measure the extremely flexible vehicles with a ramp of greater angle like the 23 degree ramp. The vehicle attempts to climb the ramp as high as possible without lifting a wheel off the ground. The distance the vehicle can travel up the ramp without losing contact with the ground is measured from the leading edge of the ramp to the center of the hub on the ramp. That number is then divided by the vehicles wheelbase (the distance between the vehicles centerline of the front axle and the centerline of the rear axle) and then multiplied by 1000 to calculate the average. For instance, if a vehicle with a wheelbase of 94 inches travels 62 inches up the 20 degree ramp then the RTI would be calculated as: 62" divided by 94" x 1000 resulting in a score of 659. This method of multipling by the vehicles wheelbase allows one vehicle to compete with another vehicle like a CJ-5 to an F-250 Crew Cab on the same ramp test.
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| Spring Over Axle (SOA) |
Axle and spring setup where the springs (typically leaf springs) are mounted over the top of the axle tubes. See also Spring Under Axle (SUA). |
| Spring Under Axle (SUA) |
Axle and spring setup where the springs (typically leaf springs) are mounted underneath the axle tubes. See also Spring Over Axle (SOA). |
| Wheel Travel |
A measurement of the total amount of available suspension travel; from full compression to full extension. |
