4x4 Technical Terms - Explained


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Re: 4x4 Technical Terms

kudos for amazing compliation buddy! [clap] i agree post all of them directly here!
 
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Re: 4x4 Technical Terms

Had posted the Doc file so that those interested could download it and share it with others freely. But here goes:

4x4 - This general term is used to describe a vehicle with four-wheel drive. The first figure is the number of wheels, and the second is the number of powered wheels. Another term for four-wheel drive.

4x2 - This term refers to a two-wheel drive vehicle with four wheels, two of which receive power. Another term for two-wheel drive.

All-Wheel Drive (AWD) - All-wheel drive is a passenger-car-based four wheel-drive system that has no two-speed transfer gearbox. It operates similarly to full-time or permanent 4WD, but does not offer Low Range capability for off-road use. This system is more typically available in passenger cars, such as those from Audi and Subaru. Now, however, AWD is cross ing over into sport-utility vehicles, and is used in the BMW X5, Oldsmobile Bravada, Ford Explorer V8 and Mercury Mountaineer V8.

Angle Of Approach - When viewed from the side, this is the angle between the ground and a line running from a front tire to the lowest-hanging com ponent directly ahead, usually the front bumper. This angle gives an indication of how steep a ramp a vehicle can negotiate without damage. It also allows the driver to judge a vehicle's ability to climb over rocks and logs without hitting -and potentially damaging the front part of the vehicles body or chassis.

Angle Of Departure
- In side view, this is the angle between the ground and a line running from a rear tire to the low est-hanging component directly behind it, usually the rear bumper or trailer hitch. Similar to the approach angle, the departure angle indicates a vehicle's ability to drive off a ramp or obstacle without damaging the rear of the SUV.
Anti-lock Braking System - This braking system senses any significant difference in wheel speed from one wheel to another, when a vehicle is braking hard. When any of the wheels begin to lock up (completely stop rotating), ABS automatically reduces the braking forces to that wheel or wheels in order to keep all the wheels rolling -to prevent brake-induced skidding. ABS can control all four wheels (most cars and SUV’s have this system) or only two (this is found on some pickup trucks and SUV’s). The system can group wheels together in "channels" of operation (i.e., a three channel system on a four-wheeled vehicle) or have one channel for each wheel (four-channel ABS).
Axle Articulation - This term indi cates the ability of one axle to move vertically relative to the chassis or its fellow axle -left wheel up, right wheel down (or vice-versa). It is the measure of the ease with which wheels stay in contact with the ground (and retain traction) on a very bumpy, uneven trail.

Box-Section Frame - This term refers to the characteristics of a frame when viewed in cross section. A box-section frame is constructed using four sides of steel to create a box, as opposed to a C-section or even I-section frame (which would look like those letters in cross section).

Brake Fade - As brakes heat up with hard or repeated use, their effectiveness usually diminishes. This is called brake fade.

Brake Lockup - In braking, lockup describes the point at which a tire starts to skid (stops rotating while the vehicle is in motion) in an emergency-stopping situation. A tire's maximum braking force is developed when it is on the verge of lockup, so a car's shortest stopping distances are produced when its front and rear tires are held just short of lockup. Anti lock brakes (ABS) prevent wheel lockup, giving the advantage of simultaneous steering and braking ability (a locked wheel cannot be steered).

Center Differential - Rear-wheel drive cars need a rear differential to power the right and left rear wheels and let them turn at different rates of speed when cornering. Front-wheel-drive cars need a front differ ential for the same reasons. Vehicles with full-time or permanent four-wheel drive require a center differential (or similar device, such as a viscous coupling). In a tight turn, all four wheels travel at different speeds. A center differential receives power (or, more correctly, torque) from the transmission (or transfer box) and sends this torque to the front and rear dif ferentials, while allowing the front and rear wheels to travel at different rates. (See "Differential" and "VISCOUS Coupling.")

Chassis - This term can describe a vehicle's structural elements or the collection of mechanical components attached to its frame. In vehicles with unitized or "unibody" construction, the chassis comprises everything but the bolted-on body panels of the car. In vehicles with a separate frame, chassis usually refers to the frame.

Coil Spring -Used in a suspension system, a coil spring consists of a bar of resilient metal (usually a steel alloy) wound into a spiral form. It can be compressed repeatedly or extended without permanent deformation.

Constant-Velocity joint - A "CV" joint is a type of universal joint, usually used between the front half-shafts and front spindles/wheels in a front-wheel-drive or four-wheel-drive vehicle. CV joints are engineered to transmit power more smoothly (compared with universal joints) as they move through two planes. They are also less prone to driveline vibrations.

Crossmember - This component of a frame (or sub frame), placed transversely, connects to and strengthens longitudinal frame rails.

Differential -A differential transfers power (more accurately, torque) from the transmission or transfer gearbox to the axles/wheels, and allows the axles and wheels to turn at different speeds (so the vehicle can turn corners without drive train wind-up -the wheels on the outside of a curve turn faster and travel a greater distance than the inside wheels). While most differentials are mechanical gear-driven devices, sometimes a viscous coupling (VCU) or a multi-plate transfer clutch pack (MPT) can act in place of a differential.

Differential Lock - The main disadvantage of an "open" differential is that the usable torque is restricted by the wheel with the least traction. A differential lock literally locks out the differential action and forces torque to be split equally between each wheel (or each axle) for maximum traction. In a rear wheel drive vehicle, for instance, locking the rear differential locks the left and right rear wheels together so that both receive equal torque. In a full-time or permanent 4WD vehicle, locking the center differential locks the front and rear driveshafts together, sending equal torque to the front and rear axles. While locking a differential helps increase traction, it makes steering more difficult on high-traction surfaces because it tends to force the vehicle to travel in a straight line.

Disc Brakes - This type of braking system consists of a disc or rotor that rotates at the same speed as the wheel to which it is attached, straddled by a caliper. The caliper contains brake pads, operated by small pistons, that squeeze against the surface of the disc to slow it down or stop it. Disc brakes operate more efficiently at high temperatures and wet conditions than drum brakes.

Drive shaft - The drive shaft transmits power from the transmission or transfer gearbox to the differential. A four-wheel drive vehicle has at least two drive shafts -one running to the front differential and one to the rear. Also known as propeller shafts or prop shafts.

Drive train - Also called a powertrain, this term describes all of a vehicle's components that produce power and transmit power to the wheels -the engine, transmission, transfer case, drive shafts, differentials, axle shafts and wheel hubs.

Drum Brakes - A drum brake uses a drum-shaped (cylindrical) housing, usually made of cast iron, that is attached to the wheel and rotates with it. Inside the drum are curved brake shoes that are forced into contact with the inner drum to provide braking. Drum brakes are simple and generally effective, but less efficient than disc brakes under heavy use or when wet.

Engine Braking - This term describes the driving technique of slowing a vehicle by taking your foot off the throttle, particularly in a lower gear (such as first gear/Low Range). Engine braking uses the compression of the engine and the low gearing of the trans mission/transfer gearbox to slow the vehicle.

Final-Drive Ratio - This is the ratio of the gear set (usually the differential) that is farthest from the engine. A ratio of 3.90:1 means the drive shaft turns 3.90 times for every one turn of the wheels. Generally speaking, the higher the number, the better the vehicle's initial acceleration and pulling power. The lower the number, the better the vehicle's fuel economy:

Full-Time 4WD - This drive system offers both a 2WD and 4WD mode. Four-wheel drive can be engaged on dry pavement for normal on-road driving because this system uses some type of center differential. A typical full-time 4WD system offers 2WD, 4WD "Auto" and 4WD Low. Virtually all full-time 4WD systems also have a two-speed transfer gearbox.


Remaining terms in next post.....
 

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Re: 4x4 Technical Terms

....continued from previous post

GVWR - Gross Vehicle Weight Rating is the combination of curb weight plus payload (including driver and fuel). It is the maximum rated (by the manufacturer) amount the vehicle can weigh and safely operate. GCWR is Gross Combined Weight Rating, the maximum weight of the vehicle plus any trailer and load it is carrying.

Gear Ratio - This is a numerical ratio of a series of gears in relation to each other, based on the number of turns of the input shaft, compared to turns of the output shaft. Gear ratios are determined by the number of teeth on each gear (and therefore the size of each gear). For instance, a gear with 36 teeth meshed with a gear with 12 teeth gives a 36/12 or 3/1 ratio. This is usually expressed as 3.00:1.

Ground Clearance - With the vehicle stationary, ground clearance is the measurement from the lowest-hanging point under the vehicle (usually a differential or the exhaust system) to the ground. A high ground clearance allows a vehicle to more easily drive off road or through heavy snow without damaging under-body components.
Half-Shaft -A half-shaft is an articulating, rotating shaft used in independent-suspension systems to transmit power from a differential to a wheel. The term is also used to describe a non-articulating axle shaft.

Independent Suspension -This describes a suspension system wherein each wheel on an axle is sprung separately and can react independently to bumps. A non-independent suspen sion uses a solid, beam or rigid axle to "connect" the suspension of two wheels. Both systems have advantages and disadvantages.

Jounce - Jounce is the motion of a wheel that compresses its suspension. Full jounce refers to a wheel that is at the upper limits of its travel. A jounce bumper or jounce stop is an elastic "cushion" used to stiffen the suspension gradually as it approaches the end of its jounce travel.

Ladder Frame - A ladder frame, shaped like a large ladder, is used in body-on-frame construction. Two long "rails" run along the sides, with cross members connecting the two. This type of frame is used in most pickup trucks and sport utilities. However, differences exist in the shape, structure and thick ness of the various frame elements.
Leaf Spring - A leaf spring is a long, flat, flexible piece of steel (or a composite material) curved into an arc that bends when forces act upon it. Leaf springs, most often used in pickup trucks, usually mount a solid axle to a vehicle.

Limited-Slip Differential - This differential has a mechanism to limit the speed differences between its two outputs (generally; between the two wheels on the same axle). A limited-slip differential ensures that some torque is always distributed to both wheels, even when one has very little traction. (See "Differential.")

Live Axle - A live axle is a solid axle that transmits power to a pair of wheels. It is composed of a rigid axle with a differential and axle shafts to power two wheels. It is called "live" because it has engine power flowing through it. A solid axle that does not transmit power is called a beam axle.

Multi-Plate Transfer (MPT) - A component that can act as a differential or a slip-limiting device, a multi-plate transfer is a set of several hydraulic clutches that are progressively engaged and disengaged to limit slip and/or allow differential action of the wheels. Most MPT’s are computer-controlled, with wheel-speed sensors to determine when to engage/disengage the clutches. Some Ford Explorers and Chevrolet Tahoes, for example, use an MPT in place of a center differential.

On-Demand - While this was originally a name marketed by Subaru for its part-time 4WD system, it is now used to describe the action of full-time 4WD. Power is sent to the rear wheels until the front wheels "demand" more because the rear wheels are spinning.

Part-Time 4WD - The most basic type of four-wheel-drive system, part-time 4WD operates in two-wheel-drive mode (usually rear-wheel drive) all of the time on dry pavement. Four-wheel drive can be engaged only off-road or when the pavement is very slippery because this system forces the front and rear wheels to travel at the same speed. Using 4WD on dry pavement can damage the drive train and cause extreme tire wear. Virtually all pan-time 4WD systems also employ a two-speed transfer gearbox.

Permanent 4WD - As the name suggests, permanent 4WD sends torque to all four wheels "permanently" (con tinuously), on- or off-pavement. There is no 2WD mode, and the driver does not need to determine when to engage 4WD mode. Drive selections typically include 4WD High and 4WD Low. Most permanent four-wheel-drive systems also have a locking center differential or a limited-slip center differential, plus a two-speed transfer case. All Land Rover vehicles have permanent 4WD.

continued in next post......
 
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Re: 4x4 Technical Terms

...continued

Powertrain - This term describes an engine and transmission combination. (See "Drivetrain.")

Push-Button 4WD - Both pan-time and full-time 4WD systems can be engaged electronically via a push button on the instrument panel. While this is convenient, it does not change the limitations and abilities of the basic system.

Ramp Break over Angle
- This is a measure of a vehicle's ability to drive over a sharp ridge or ramp without touching its underside. The "included" angle measures the angle inside the ramp; the "excluded" angle measures the combined angles outside the ramp to the horizontal. A short-wheelbase vehicle with large tires will have the best (largest) ramp break over angle.

Rebound - Rebound is the vertical motion of a wheel that extends the suspension. When a wheel is in full rebound, it is fully extended to the limits of its travel. Rebound is the opposite of jounce.
Recovery Strap - A recovery strap is a strap made of elastic nylon with loops on both ends. Unlike a simple rope or chain, a recovery strap uses kinetic energy (like a rubber band) to help free a stuck vehicle using another vehicle.

Shift-On-The-Fly - Older-style part- time 4WD systems sometimes required drivers to stop and lock the front hubs before engaging four-wheel drive. Most SUVs now have automatic locking front hubs and the ability to shift-on-the-fly (at speed) from two-wheel drive to four-wheel drive. However, many limit the speed at which this can be done (usually less than 50 mph and some times as low as 15 mph), and many still require the driver to stop and back up to fully disengage four-wheel drive.

Skid plate - This term refers to a protective cover or "plate" under a vehicle that covers vulnerable compo nents, such as the transmission/ transfer gearbox, engine oil pan or fuel tank.

Strut - A strut is a suspension element in which a reinforced shock absorber is used as one of the wheel's locating members, typically by bolting the wheel hub to the bottom end of the strut.

Sub frame -A sub frame is a small, separate frame usually attached to a unitized body vehicle. A front sub frame might be used to "cradle" the engine and transmission, while a rear sub frame would attach the rear suspension to the unibody structure.

Suspension Travel
- This term refers to the amount of vertical wheel move ment allowed by the suspension, from full jounce to full rebound.

Sway Bar - Also called an anti-roll bar or stabilizer bar, this suspension element is a long torsion bar (essentially a rod that can twist) mounted across the vehicle from one wheel to the wheel on the opposite side. By transferring movement and force from one side of the vehicle to the other, a sway bar can restrict body lean (or sway) during cornering. Vehicles may have sway bars in the front, rear or both.

Torsion Bar - This is a type of spring made of a long solid or tubular rod with one end fixed to the chassis and the other twisted by a lever connected to the suspension.
Traction Control System - Traction control is like ABS for acceleration. If a wheel starts to spin, traction control may cut engine power or pulse the brake on the spinning wheel (or both) to help transfer some of the engines power across the axle to the wheel with more grip. Expert off-road drivers sometimes pump the brake pedal on vehicles without traction control to try to accomplish the same thing.

Transfer Gearbox - A transfer box (or transfer case) is a system of gears or an auxiliary transmission, used in four wheel drive vehicles, which transfers torque from the transmission to the front and rear drive shafts. Transfer gearboxes typically have two gear ranges, High and Low. High Range is used for typical on-highway or light off- road use. Low Range is used for serious off-road conditions. Putting a transfer gearbox in "Neutral" disconnects the transmission from the wheels. Unless the brakes are applied (foot brake or hand brake), a vehicle can roll when the transfer gearbox is in "Neutral," even if the transmission is in "Park" (automatic) or a forward/reverse gear (manual).

Transmission - A transmission is a gearbox (either manual or automatic) with a number of different ratios to match the engine's rpm and torque to various driving situations.

Unitized Construction - This is a type of body construction that does not require a separate frame to provide structural strength or support for the cars mechanical components. A unitized body (or unibody) uses many strong but light structural elements as an integral part of its construction.

Universal joint - A U-joint "connects" two moving shafts that aren't in a straight line. Depending on its design, a universal joint can accommodate a large variation between the angle of the input shaft and that of the output shaft.

Viscous Coupling -This complex device, also called a VCU, relies on the characteristics of a special fluid inside it. It can act as a differential, as a means to restrict wheel spin or both. It consists of a small sealed canister filled with silicon fluid. Inside are two sets of slotted metal plates -one connected to a front shaft, the other to a rear shaft. When there is a significant speed difference between the shafts, the silicon fluid heats up and becomes thicker (more viscous), limit ing the speed difference and thereby the slippage right-to-left or front-to-rear. In effect, it "locks" the shafts together (although not mechanically, as in a locking differential). When there is lit tle or no speed difference between the shafts, the viscous coupling does no work. Range Rover, for example, uses a VCU as a slip-limiting device in con¬junction with its center differential. Lexus RX 300 uses a VCU in place of a center differential.

Winch - A winch is an externally mounted mechanical device consisting of a cable spooled onto a drum. It is used to pull heavy or bulky objects or to retrieve a vehicle that is stuck. The drum can be driven by the engine, by hydraulic power or electrically.
 
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Re: 4x4 Technical Terms

Thanks @ Sam Dinkar.

It is very helpful as i am using Scorpio VLX 4WD

once again -- Thanks for sharing.
 
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Re: 4x4 Technical Terms

Thanks for sharing Sam Dinkar , extremely useful for beginners like me!


BTW one doubt can you explain the difference between Independent and non-independent suspension? Their advantage and disadvantages?
 
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Re: 4x4 Technical Terms

Thanks for sharing Sam Dinkar , extremely useful for beginners like me!


BTW one doubt can you explain the difference between Independent and non-independent suspension? Their advantage and disadvantages?
Sure. I will try not go get too technical.These two terms refer to the ability/inability of opposite wheels in a car/suv etc to move independently of each other.

Consider our two legs. We can move our left leg up/down/left/right irrespective of what our right leg is doing.

So if you fall in a ditch, you can put one of your legs at the wall of the ditch while using the other leg to support your body weight and hence climb out of it. Another simpler example could be climbing a staircase - one leg is on the next stair while the other one supports the body weight.

That's independent suspension for you. Two wheels moving independently of each other. If the left front wheel goes in a pothole, the right front wheel is not bothered by it and just keeps moving smoothly without any encumbrance.

We have sometime or the other all negotiated speed breakers in our cars in a way when we allow only one side of the car to mount the speed breaker while keeping the other side of the car on the shoulder of the road - what happens in such cases? The side of the car on the shoulder of the road remains unaffected (no up/down movement because the suspension on that side does not get affected by the movement of the suspension on the opposite side) while the other side of the car that goes over the speed breaker moves up/down.

Now try doing the above in an old Mahindra Jeep or a Gypsy (both have a solid axle i.e a non-independent suspensions) and you would find that irrespective of which side of the Jeep/Gypsy goes over the speed breaker, the impact would be felt on the opposite side as well (though it won't be that harsh as it would be on the side that has negotiated the speed breaker).

Now let's get a bit technical without going fully over trhe top. An axle is a central beam/shaft for a rotating wheel (see pic). A non-independent suspension normally has an axle that holds wheels parallel to each other and perpendicular to the axle. When the camber (the angle made by the wheels of a vehicle - see pic) of one wheel changes, the camber of the opposite wheel changes in the same way in a car fitted with non-independent suspension.

An independent suspension, on the other hand allows wheels to rise and fall on their own without affecting the opposite wheel. Most Indian cars (like your Verna) come with a 'fully independent double wishbone/McPherson struts' front suspension.

Within these two types of suspensions, there are many other sub-types (live axles, swing axles, semi elliptical leaf springs, wishbones, McPherson struts, multi-link, trailing arms, Panhard rod, semi-dependent suspension etc.) but explaining all of them here would be a mammoth task.

Coming to advantages and disadvantages, a non-independent suspension is an extremely simple and tough(er) design that is easier and cheaper to manufacture and repair while a independent suspension system is more complex , may or may not be as tough, and costs more to manufacture and repair.

Non -independent suspension ensures constant camber and that is why it is used in heavy commercial vehicles.

Independent suspension allows more control over the suspension geometry and provides a more comfortable ride but at a higher price than non-independent suspension and that is why it is used in passenger cars.

Look at the pictures of the Land Cruiser and the Gypsy below. The LC has an independent suspension (notice how one wheel is fully compressed while the other is completely horizontal to the ground) while the Gypsy has a solid axle (non-independent suspension) - notice how one wheel is on the boulder while the other is in the air.

Non-independent suspension also offers greater wheel articulation (articulation is the measurement of how far the wheels can travel, which translates into the ability to keep your wheels in contact with uneven terrain) and that is why many off roaders still prefer vehicles fitted with solid axles.

Some easy reading could be found here:

Suspension | The suspension is killing me | Drive Out
 

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Re: 4x4 Technical Terms

Really informative thread. Thanks for sharing this wonderful information, Sam. Thread marked sticky.

Drive Safe,
350Z
 
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Thanks for the explanation Sam , cleared most of my doubts!


So for off-roading i assume non-independent suspension setup is the best?


If possible can you name some SUV'S with both the suspension setups? Starting from our Gypsy till Q7 , if possible?
 
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Thanks for the explanation Sam , cleared most of my doubts!


So for off-roading i assume non-independent suspension setup is the best?


If possible can you name some SUV'S with both the suspension setups? Starting from our Gypsy till Q7 , if possible?
Whether non-independent suspension is best for off roading or not depends on a lot of factors and it is a huge task to list all of them here. There are various off roading situations that require various types of suspension settings. But one thing is for sure, a solid axle is always tougher and easier to repair than an independent suspension set up.

At present, apart from the Gypsy and the Mahindra Thar DI, all other 4x4 vehicles available in India (including the Thar CRDe) are fitted with independent front suspension.
 
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What will happen if Nomenclature is changed, by auto industy as follow s,?

4X 4 changed to 4/4 i.e. 4 wheels out of 4 wheels,
4X2 changed to 2/4 i.e. 2 wheels out of 4 wheels,

Any benefits to layman ¿
 
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What will happen if Nomenclature is changed, by auto industy as follow s,?

4X 4 changed to 4/4 i.e. 4 wheels out of 4 wheels,
4X2 changed to 2/4 i.e. 2 wheels out of 4 wheels,

Any benefits to layman ¿
Hi, i see no difference ? 4 by 4 is traditional names, they cannot change.
 
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Nomenclature

What will happen if Nomenclature is changed, by auto industy as follow s,?

Any benefits to layman ¿
First thing, it will not change because the nomenclature is practiced world over.

4X 4 changed to 4/4 i.e. 4 wheels out of 4 wheels,
4X2 changed to 2/4 i.e. 2 wheels out of 4 wheels,
I think for the layman this is much easier to understand. First digit denotes the total no. of wheels (on ground) and the successive digit denotes the no. of wheels which can be driven (live wheels). Hope this helps.

Spike[:)]
 
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