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What is Corner Travel Index?

Corner Travel Index or CTI measures a vehicle's maximum axle/wheel articulation at the four corners of the vehicle, often referred to as “flex”. The CTI is used in the off-roading industry to quantify the axle/wheel articulation in order to compare the performance potential of a wide variety of vehicles and vehicle builds. CTI totals the articulated wheel travel of each individual tire on the vehicle (in inches) and multiplies that total by 10 (ten).

Significance of CTI and Axle/Wheel Articulation

A vehicle with a higher CTI offers greater axle/wheel articulation and therefore greater potential off-road performance over extreme terrain and obstacles. A vehicle with a higher CTI will maintain more constant wheel contact with the ground while traveling over extreme terrain and obstacles. This ensures that all wheels deliver torque or traction to the ground surface maintaining the vehicle’s ability to move.

Measuring and Calculating CTI

CTI can be measured two ways, the two wheel method (Estimated) and the four wheel method (Certified). Estimated is the easier value to generate as it only requires lifting the vehicle once. Certified is required and preferred for a truly accurate measurement of the CTI.

Calculations use the following tire positions:

Procedure

1. Set all tire pressures to 15 psi. This sets a standard for consistent measurement across a wide variety of vehicles and builds.

2. Simultaneously lift the Front Passenger Tire (FPT) and the Rear Driver Tire (RDT) off the ground and STOP lifting when the first tire not being lifted is just about to leave the ground (two tires must be touching the ground). This can be done with forklifts or with a CTI platform lift system.

Measure the vertical clearance, in inches, between the ground and the lowest point of the Front Passenger Tire. Measure the vertical clearance, in inches between the ground and the lowest point of the Rear Driver Tire.

Measurement must be taken from the lowest point of the tire. Record the values:

• Clearance under the Front Passenger Tire (FPT) = 19 ½” (example)
  
• Clearance under the Rear Driver Tire (RDT) = 18 ¾” (example)
  
• (Values need not be the same, just similar, to get an accurate CTI calculation)

3. The two wheel method or Estimate of CTI can be calculated at this time:

• CTI = (FPT + RDT) x 10 x 2
• (19 ½ + 18 ¾) x 10 x 2 = 765 CTI (estimated)

4. Simultaneously lift the Front Driver Tire (FDT) and the Rear Passenger Tire (RPT) off the ground and STOP lifting when the first tire not being lifted is just about to leave the ground (two tires must be touching the ground). This can be done with forklifts or with a CTI platform lift system. Measure the vertical clearance, in inches, between the ground and the lowest point of the Front Driver Tire (FDT).

Measure the vertical clearance, in inches, between the ground and the lowest point of the Rear Passenger Tire (RPT).

Measurement must be taken from the lowest point of the tire. Record the values:

• Clearance under the Front Driver Tire (FDT) = 19 ¼” (example)
  
• Clearance under the Rear Passenger Tire (RPT) = 18½” (example)
  
• (Values need not be the same, just similar, to get an accurate CTI calculation)

5. The four wheel method or Complete CTI is calculated as follows:

• CTI = (FPT + RDT + FDT + RPT) x 10
• [ 19 ½ + 18 ¾ + 19 ¼ + 18 ½] x 10 = 760 CTI (Complete)

Corner Travel Index (CTI) vs Ramp Travel Index (RTI)

The Corner Travel Index (CTI) originated as an alternative to the complex, confusing and inconsistent system known as the Ramp travel index. As off-road enthusiasts looked for better and more consistent ways of measuring axle/wheel articulation it became clear that the CTI was far superior to RTI for the reasons outlined in the side by side comparison below.