Ramp travel index
Encyclopedia
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.
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
and finally multiplied by 1000 to give a final RTI score. Most stock SUVs have RTI values from 400 to 550; vehicles modified for off-road competition have the ability to exceed 1000.
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
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
(beam axle
). Independent suspensions have tended to have reduced articulation while offering better on-road comfort, and are becoming increasingly popular in road-oriented SUVs.
Where b is the wheelbase of the vehicle, d is the distance travelled along a (usually 20 degree) ramp before any wheels leave the ground and r is the calculated ramp travel index.
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
Off-roading
Off-roading is a term for driving a vehicle on unsurfaced roads or tracks, made of materials such as sand, gravel, riverbeds, mud, snow, rocks, and other natural terrain.-Off-road vehicle:...
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
Wheelbase
In both road and rail vehicles, the wheelbase is the distance between the centers of the front and rear wheels.- Road :In automobiles, the wheelbase is the horizontal distance between the center of the front wheel and the center of the rear wheel...
and finally multiplied by 1000 to give a final RTI score. Most stock SUVs have RTI values from 400 to 550; vehicles modified for off-road competition have the ability to exceed 1000.
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 tractionTraction
- Engineering :*Forces:** Traction , adhesive friction or force in the context of vehicle** Traction vector, in mechanics, the force per unit area on a surface, including normal and shear components...
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
AWD
AWD may refer to:* AWD Holding, , a German company* Acute Watery Diarrhoea, a symptom associated with cholera* Afghan War Diary, a collection of thousands of US military documents that were leaked to the public via Wikileaks in July, 2010* Agency Worker Directive * Air Warfare Destroyer* All-wheel...
systems and chassis
Chassis
A chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...
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
Live axle
A live axle, sometimes called a solid axle, is a type of beam axle suspension system that uses the driveshafts that transmit power to the wheels to connect the wheels laterally so that they move together as a unit....
(beam axle
Beam axle
A beam axle is a suspension system, also called a solid axle, in which one set of wheels is connected laterally by a single beam or shaft...
). Independent suspensions have tended to have reduced articulation while offering better on-road comfort, and are becoming increasingly popular in road-oriented SUVs.
With a ramp
The formula for calculating RTI using a ramp as pictured above isWhere b is the wheelbase of the vehicle, d is the distance travelled along a (usually 20 degree) ramp before any wheels leave the ground and r is the calculated ramp travel index.
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, thenAlthough 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 vehicleOff-road vehicleAn off-road 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 deep, open treads, a flexible suspension, or even caterpillar tracks...
- Four-wheel driveFour-wheel driveFour-wheel drive, 4WD, or 4×4 is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine simultaneously...
- Mini SUVMini SUVMini SUV is a class of small sport utility vehicles with a length under . This class should not be confused with compact SUV, which refers to slightly larger vehicles, from ....
- Compact SUVCompact SUVCompact SUV is a class of small sport utility vehicles with a length roughly between . This class should not be confused with mini SUV, which refers to smaller vehicles.- Background :...
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