Differentials fall in one of three main categories; open, locking, or limited slip differentials. A differential transmits power to the wheels, allowing them to rotate at different speeds. The type of differential a vehicle has determines how good it is for driving on different terrains.
With the differentials in place, the tires will rotate at different speeds, allowing you to make a turn and to drive off-road. Is a limited slip differential good for off-road driving?
Is Limited Slip Good For Off Road?
A limited-slip differential is good for off-road driving as it transmits power to the wheels that still have traction and limits power to the slipping wheels. The wheel that still has traction will spin and steer the vehicle while the wheel that is slipping will stop. This way, you will not be stuck with your vehicle spinning in place.
This is unlike an open differential that still sends power to the wheels that are losing traction. If you are driving on a slippery ground, the open differential makes the wheels on the slippery side of the road slip more.
The locking and limited slip differentials are also known as traction aiding differential.
How Does a Limited Slip Differential Work?
A limited slip diff attaches to the drive axle of your vehicle. Its main function is to distribute engine power to the wheels. It also ensures the vehicle does not lose traction when driving.
During normal operation in an open road, the wheels are allowed to have the same power and spin at independent rates. When you are making a turn, the wheels will spin at different rates, allowing you to take a turn. When you drive on a path where one side is slippery, the limited slip differential transfers power to the wheels away from the slippery side so that you have enough traction to keep moving.
When driving off road in a rough terrain, one wheel might not be touching the ground while others are on the ground. With an open differential, the hanging wheel might get more power and only ends up spinning without the vehicle moving. With a limited slip differential, the wheels on the ground will get more torque, and this is how you drive on uneven ground.
LSD offers the best of open and locking differentials. The open differential allows wheels to spin separately while a locked differential allows the wheels to spin at the same time.
When driving on open roads, the limited slip differentials acts like an open differential where the wheels turn at different rates. When your vehicle needs more traction for one wheel, the LSD acts like a locking differential by allowing the wheels to turn at the same rate. The wheels with traction will place more torque on the ground and the vehicle keeps moving even on slippery or uneven grounds.
What are the Types of LSDs?
Differential comprise of two axle halves each with a gear on one end. The two are connected with a third gear, which makes up the third side of a square. To complete the square, there is a fourth gear that adds strength to the setup.
Further, the differential has a ring gear in its case and this additional gear holds the core gears together. The ring gear ensures the wheel receive power when connected to a drive shaft through a pinion.
These gear components and setup form the most common differential, the locking different. It is from this setup that the limited slip differential and other more complicated differentials are derived. From it, you can have the following types of limited slip differentials:
Mechanical Clutch LSD
Mechanical clutch LSD encloses the basic gearing setup as in the locking differential above. However, it has a pair of pressure rings that exert pressure to two clutch plates positioned near the gears. The exerted pressure limits the independent rotation of the wheels and this changes the differential from open to locking.
The pressure rings surround the core gears. The gears, on the other hand, are forced apart by the central gear pins, and they push against angled surfaces when the gears rotate. This movement forces the pressure rings onto clutch packs and generate resistance to change the behavior of the axle.
Mechanical clutch LSD is available in three sub-types. Each of these sub-types behave differently when you apply pressure on the pressure rings, and they push the clutch plates.
• One-Way LSD exerts pressure under acceleration. In this type, the differential behaves as an open type differential where the wheels turn independently. When under acceleration, the forced differential rotation creates friction on the clutch plates and locks them in place for added traction.
• Two-way LSD only exerts pressure on the clutch plates when under deceleration. This improves the stability of the vehicle, especially when you are driving off-road.
• One and half way offers the best of one-way and two-way LSDs. This differential exerts more pressure when you are accelerating and lesser pressure when decelerating.
While mechanical LSDs are adaptable and allow you to drive off the road, they require regular maintenance to keep them operating optimally. They are also susceptible to wear and tear, and you may have to replace the entire differential after a few years.
Viscous LSD uses a thick liquid instead of clutches. The liquid offers the resistance needed to change the differential from open to locked. Viscous LSDs have fewer moving parts and this makes them simpler than mechanical LSDs.
Unlike mechanical LSDs, Viscous LSDs provide a smoother operation as the resistance builds in unison with the speed of the wheels. The VLSD is also able to channel more torque to the wheel that has traction more effectively.
The fluid in the differential offers more resistance when the wheel is under speed. If a wheel loses traction and starts spinning faster, the high speed of that wheel creates more resistance on the wheel that moves slower and this is how the wheel with traction receives more torque from the drive shaft.
The viscous LSD is less effective after a prolonged use. Its fluid heats and loses its viscosity thereby providing less resistance. The fluid is also less effective when you need to lock as with mechanical LSD as the fluid cannot give absolute resistance.
Both viscous and mechanical LSDs do not transmit torque effectively when you need to corner at high speed. When you are cornering, the system might view the outer wheel as losing traction and send power to the inner cornering wheel. This can generate over or understeer when you are cornering.
Limited Slip Differential vs. Torsen Differential: Which is Better for Off-Road?
Torsen is short for torque-sensing differential. This system employs advanced gearing systems to give the same effect as a limited slip, but you do not need a clutch or a fluid to create the effect.
The Torsen differential achieves resistance through addition of worm gears to the open differential setup. These worms act on the axle to offer the needed resistance for torque transfer. For that to happen, the worm gears need to be in a constant mesh through connected spur gears.
The mesh created by the two sides of the differential allows smooth transfer of torque immediately to the wheel that has more traction. This makes the torsen differential better when you are driving off the road as it offers fast transfer of torque to the wheels that need it.
While an open differential can share power to all wheels equally, the torsen differential directs more power to one wheel, depending on the gear ratio. This ensures there is no limitation of power that is witnessed with open differentials.
Automakers can also engineer the gearing so that there is a different ratio of resistance when you accelerate to decelerate as with the one-way and two way mechanical LSD. Instead of electronics and friction on parts, torsen achieves different resistance levels mechanically.
Torsen is more effective variant of the limited slip differential. Both systems allow you to drive off the road, but the Torsen diff is more responsive and faster than the limited slip differential.
LSD vs. Active Differential for Off-Road Driving
Active differential has an almost similar mechanism to the limited slip differential. This type also relies on resistance to transfer torque from one side to the next. It has clutches that rely on electronic activation rather than mechanical force.
The system uses electronics to alter the mechanical forces your vehicle experiences when you drive in different conditions. This way, you can control your differential more or even program it as you need. The system works through a range of sensors and your computer will detect the wheels that need power and direct it to them.
Think of an active differential as an advanced form of limited slip differential or LSD that you can actively control. When you are driving off road on rugged terrain, this differential offers you a smooth driving experience.
Which Vehicles Have Limited Slip Differentials?
LSD is not common with most automakers. It is only available on some models of performance vehicles. For instance, rally drivers may prefer limited slip differential as they drive on changing road conditions.
LSD is available in off-road vehicles such as the Jeep Wrangler. These off-road trucks and SUVs may have a more advanced version of the LSD, such as active differential, to help them navigate the changing road conditions amicably.
You may also come across limited slip differential in performance cars such as BMWs, Dodge, Lexus, Audi, and Cadillacs. Some inexpensive performance cars such as the Ford Mustang and the Subaru BR-Z also have LSDs.
Vehicles with a limited-slip differential are ideal for driving off the road. However, most purpose-built offroad vehicles have locking differentials. The advancements in technology have made it possible for automakers to use advanced forms of the limited-slip and locking differentials.
The use of active, torsen, and torque vectoring differentials is now more common for vehicles that need performance. Other vehicles use software-based alternatives to LSD. These software-based alternatives have the same effects as the original LSD to a point that most drivers cannot tell whether their car has LSD or a software option.
The Ford torque vectoring control is one of the more advanced forms of LSD that modern vehicles use.