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. [1] Most stock SUVs have RTI values from 400 to 550; [1] vehicles modified for off-road competition have the ability to exceed 1000. [2]
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 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.
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 [1] ) ramp before any wheels leave the ground and r is the calculated ramp travel index.
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, then [3]
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
Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both road holding/handling and ride quality, which are at odds with each other. The tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different.
Automobile handling and vehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly during cornering, acceleration, and braking as well as on the vehicle's directional stability when moving in steady state condition.
The GMC Envoy is a mid-size SUV manufactured and marketed by General Motors for the 1998-2009 model years over two generations. Adopting a nameplate used by GM Canada, the Envoy was a rebadged variant of the Chevrolet TrailBlazer, Oldsmobile Bravada, Buick Rainier, Isuzu Ascender, and Saab 9-7X.
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, the wheelbase is the distance between the steering (front) axle and the centerpoint of the driving axle group. In the case of a tri-axle truck, the wheelbase would be the distance between the steering axle and a point midway between the two rear axles.
Weight transfer and load transfer are two expressions used somewhat confusingly to describe two distinct effects:
The Ford Bronco is a model line of SUVs manufactured and marketed by Ford. The first SUV model developed by the company, five generations of the Bronco were sold from the 1966 to 1996 model years. A sixth generation of the model line was introduced for the 2021 model year. The nameplate has been used on other Ford SUVs, namely the 1984–1990 Bronco II compact SUV and the 2021 Bronco Sport compact crossover.
Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy needed for deformation of the wheel, roadbed, etc., is recovered when the pressure is removed. Two forms of this are hysteresis losses, and permanent (plastic) deformation of the object or the surface. Note that the slippage between the wheel and the surface also results in energy dissipation. Although some researchers have included this term in rolling resistance, some suggest that this dissipation term should be treated separately from rolling resistance because it is due to the applied torque to the wheel and the resultant slip between the wheel and ground, which is called slip loss or slip resistance. In addition, only the so-called slip resistance involves friction, therefore the name "rolling friction" is to an extent a misnomer.
Ride height or ground clearance is the amount of space between the base of an automobile tire and the lowest point of the automobile ; or, more properly, to the shortest distance between a flat, level surface, and the lowest part of a vehicle other than those parts designed to contact the ground. Ground clearance is measured with standard vehicle equipment, and for cars, is usually given with no cargo or passengers.
A glossary of terms relating to automotive design.
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 also been used as front axles in four-wheel-drive vehicles. In most automobiles, beam axles have been replaced with front and rear independent suspensions.
Hunting oscillation is a self-oscillation, usually unwanted, about an equilibrium. The expression came into use in the 19th century and describes how a system "hunts" for equilibrium. The expression is used to describe phenomena in such diverse fields as electronics, aviation, biology, and railway engineering.
Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics falls under a branch of physics known as classical mechanics. Bike motions of interest include balancing, steering, braking, accelerating, suspension activation, and vibration. The study of these motions began in the late 19th century and continues today.
The turning radius of a vehicle defines the minimum dimension of available space required for that vehicle to make a semi-circular U-turn without skidding. The Oxford English Dictionary describes turning circle as "the smallest circle within which a ship, motor vehicle, etc., can be turned round completely". The term thus refers to a theoretical minimal circle in which for example an aeroplane, a ground vehicle or a watercraft can be turned around.
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Eight-wheel drive, often notated as 8WD or 8×8, is a drivetrain configuration that allows all eight wheels of an eight-wheeled vehicle to be drive wheels simultaneously. Unlike four-wheel drive drivetrains, the configuration is largely confined to heavy-duty off-road and military vehicles, such as armored vehicles, tractor units or all-terrain vehicles such as the Argo Avenger.
Overhangs are the lengths of a road vehicle which extend beyond the wheelbase at the front and rear. They are normally described as front overhang and rear overhang. Practicality, style, and performance are affected by the size and weight of overhangs.
In vehicle acrobatics, a wheelie, or wheelstand, is a vehicle maneuver in which the front wheel or wheels come off the ground due to sufficient torque being applied to the rear wheel or wheels, or rider motion relative to the vehicle. Wheelies are usually associated with bicycles and motorcycles, but can be done with other vehicles such as cars, especially in drag racing and tractor pulling.
Driveline windup is also known as "axle binding" or "driveline binding".
Breakover angle or rampover angle is the maximum possible supplementary angle that a vehicle, with at least one forward wheel and one rear wheel, can drive over without the apex of that angle touching any point of the vehicle other than the wheels. This definition is contingent upon the wheels being in continuous contact with the supporting surface(s). Breakover angle differs from ground clearance, which is the shortest distance between the ground and lowest point on the vehicle.
This glossary of automotive terms is a list of definitions of terms and concepts related to automobiles, including their parts, operation, and manufacture, as well as automotive engineering, auto repair, and the automotive industry in general. For more specific terminology regarding the design and classification of various automobile styles, see Glossary of automotive design; for terms related to transportation by road, see Glossary of road transport terms; for competitive auto racing, see Glossary of motorsport terms.