Ramp travel index

Ramp travel index or RTI, is a way of measuring a vehicle's ability to flex its suspension, a property also known as axle articulation.

The RTI rating is used mainly in the off-roading industry to test and describe chassis limits of modified vehicles.

[1] Most stock SUVs have RTI values from 400 to 550;[1] vehicles modified for off-road competition have the ability to exceed 1000.

All this can allow a very high level of off-road performance without the need for electronic chassis control systems that can be vulnerable and unreliable under extreme conditions.

that have poorer axle articulation—lift a wheel early which is then free to turn spinning away power unless differentials are able to be locked.

A vehicle with high RTI with open diffs tends to make uninterrupted (safer) progress as all wheels remain in contact with the ground during the maneuver.

Independent suspensions have tended to have reduced articulation while offering better on-road comfort, and are becoming increasingly popular in road-oriented SUVs.

Independent suspension can have similar or better articulation, handling, durability and/or payload capacity as solid axle, but it requires significantly more money and engineering[citation needed].

The wide availability of traction control and automatic diff locking means that RTI is not useful as a measurement of off road ability for modern vehicles, but is still used for bragging rights.

It is possible to calculate RTI without a ramp using basic trigonometry, provided a safe method is available to lift one wheel, say, using a forklift.

This yields a convenient formula for calculating a 20° RTI value when no ramp is available.