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
Off-roading is the activity of driving or riding in a vehicle on unpaved surfaces such as sand, gravel, riverbeds, mud, snow, rocks, and other natural terrain. Types of off-roading range in intensity, from leisure drives with unmodified vehicl ...
industry to test and describe chassis limits of modified vehicles.
The ramps vary between 15 and 30 degrees of angle for the vehicle to ride up. "Ramping" a vehicle involves putting one front tire on the ramp and driving up slowly until one of the other three tires (usually the rear one on the same side as the tire driving the ramp) begins to leave the ground. The measurement is only taken when the other three tires are still on the ground. The distance traveled up the ramp is then measured and is divided by the vehicle's
wheelbase
In both road and rail vehicles, the wheelbase is the horizontal distance between the centers of the front and rear wheels. For road vehicles with more than two axles (e.g. some trucks), the wheelbase is the distance between the steering (front ...
and finally multiplied by 1000 to give a final RTI score.
[RTI Ramp - Ramp Travel Index Score - What is it, what does it tell you?](_blank)
/ref> Most stock SUVs have RTI values from 400 to 550;
Significance of RTI and Axle Articulation
A high RTI or good axle articulation is essential for good off road performance on severe routes. A vehicle that has good axle articulation can keep all wheels in contact with the ground while traversing obstacles, which ensures that all wheels can deliver their torque to the surface with less risk of losing traction on any given wheel. 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.
Over a given obstacle, vehicles with simple AWD systems and chassis
A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of an artificial object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpa ...
designs that restrict their RTI—i.e. 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 tends to make uninterrupted (safer) progress as all wheels remain in contact with the ground during the maneuver. One chassis concept that often allows comparatively high RTI is the live axle
A beam axle, rigid axle or solid axle is a dependent suspension design in which a set of wheels is connected laterally by a single beam or shaft. Beam axles were once commonly used at the rear wheels of a vehicle, but historically they have als ...
(beam axle
A beam axle, rigid axle or solid axle is a dependent suspension design in which a set of wheels is connected laterally by a single beam or shaft. Beam axles were once commonly used at the rear wheels of a vehicle, but historically they have als ...
). Independent suspensions have tended to have reduced articulation while offering better on-road comfort, and are becoming increasingly popular in road-oriented SUVs.
Calculating RTI
With a ramp
The formula for calculating RTI using a ramp as pictured above is
Where ''b'' is the wheelbase of the vehicle, ''d'' is the distance travelled along a (usually 20 degree
Without a ramp
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. Using the diagram below, if ''h'' is the maximum distance from the bottom of the tire to the ground, thenRight Triangle Trigonometry
/ref>
Although ''d'' is not an available measurement, we can use the relationship between ''h'' and ''d'' to express ''d'' in terms of ''h'':
Substituting this into the RTI formula produces:
This yields a convenient formula for calculating a 20° RTI value when no ramp is available. If ''b'' is the vehicle's wheelbase and ''h'' is the maximum distance from the ground to the bottom of the wheel without allowing any other wheel to leave the ground, then
See also
*Off-road vehicle
An off-road vehicle, sometimes referred to as an overland or adventure vehicle, is considered to be any type of vehicle which is capable of driving on and off paved or gravel surface. It is generally characterized by having large tires with d ...
*Four-wheel drive
Four-wheel drive, also called 4×4 ("four by four") or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer ca ...
*Mini SUV
A sport utility vehicle (SUV) is a car classification that combines elements of road-going passenger cars with features from off-road vehicles, such as raised ground clearance and four-wheel drive.
There is no commonly agreed-upon definit ...
*Compact SUV
Compact as used in politics may refer broadly to a pact or treaty; in more specific cases it may refer to:
* Interstate compact
* Blood compact, an ancient ritual of the Philippines
* Compact government, a type of colonial rule utilized in Briti ...
*Crossover SUV
A crossover, crossover SUV, or crossover utility vehicle (CUV) is a type of automobile with an increased ride height that is built on unibody chassis construction shared with passenger cars, as opposed to traditional sport utility vehicles ...
* Luxury SUV
References
{{DEFAULTSORT:Ramp Travel Index
Off-road racing