jeepoch
Well-Known Member
- First Name
- Jay
- Joined
- Nov 13, 2019
- Threads
- 1
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- 951
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- 2,687
- Location
- Longmont, CO
- Vehicle(s)
- 2019 JL Wrangler Sport S 3.6L Auto 2 door, 2.5" lift, 35s
Lay,
[Edited from peer review feedback.]
One thing not really well understood about 4wd is that it depends on the type of axle, or rather the locking differentials, and whether (or not) you have them. Rubicon's have full lockers on both axles. Most (or probably the majority) of Sahara's have a Limited Slip Differential (LSD) on the rear, which isn't a true full locker. But in some ways it's even better. However like the Sport, the Sahara has an open differential (non-locking) in the front. Finally, most Sports come from the factory with only open diffs on both front and rear axles. Of course there are always some variations, but that's the general rule of thumb when thinking about the various Jeep trims.
Regardless of the trim level however, all axle types are pretty much always open diffs when 'unlocked'. The LSD is the only exception. It's potentially always partially 'locked' or possibly slipping all the time. For the locking diffs, they can only be locked in 4Lo (unless you have special overrides to very specific software calibrations via various third party programmers).
When 'unlocked' or with open diffs one and only one wheel on a particular axle, is getting power (when traction is lost). In fact the power is generally reduced to both wheels during 'slip' such that the overall contribution to motive effort from that particular axle is marginal.
So for every Jeep trim in 2Hi only one wheel (not two) is essentially getting power at the instant when either wheel starts slipping. Either can be powered but only the wheel with the least resistance is the one getting the most energy from the powertrain.
Noting that an open diff axle will distribute power to each wheel equally (50%) but ONLY with adequate traction. Once any wheel starts slipping, power is reduced to both wheels with the slipping wheel getting the most torque. Certainly not advantageous. That is exactly why lockers are so much better.
Also for every trim package when in 4Hi, potentially only two wheels are powered. One wheel in the front and one wheel in the back (if both axles are slipping). Again either wheel on each axle will be powered but only one per axle. So both 2Hi and 4Hi are misconceptions and named improperly. They should be named 1Hi or 2Hi respectively (while slipping). But since either wheel can be powered at any instant it's still considered 2 or 4wd respectively.
Only when in 4Lo do more 'powered' wheels potentially come into play. Only (ONLY) the Rubi's with the full lockers can have all 4 wheels powered (all the time) independent of any slipping wheels. When 'locked' all 4 wheels spin at exactly the same rate and the available torque is equally divided to all four wheels. This makes the Rubicon the only truly possible 4 wheel drive Jeep.
The Sahara with the LSD in the rear and an open diff up front when in 4Lo will have at least 3 powered wheels (during slip). The power to either rear wheels will be variable depending on the clutching action of it's LSD diff. So both rear wheels will have some fraction of the total available torque. However, they will both still be powered. In many situations, the LSD is far superior to the full locker because it will better adapt to give the most power to the non-slipping wheel. However, the Sahara's front axle is exactly like the Sport with an open diff.
With the Sport due to the open diffs both front and back, when in 4Lo it can have a potential of just two powered wheels, one on each axle if they're each slipping. So for the Sport it really can only ever achieve at best 3 but sometimes just 2wd, depending on which wheels on which axle are slipping. Again because either wheel on both axles can potentially be powered it's still considered 4wd.
So in summary (during wheel slip):
Sport:
2Hi -> 1 powered wheel (rear)
4Hi/Lo -> 2 powered wheels, 1 front 1 rear
Noting that most typically only one axle is experiencing slip so effectively there are 3 powered wheels.
Sahara with the LSD:
2Hi -> 2 variably powered wheels (rear)
4Hi/Lo -> 3 powered wheels, 1 front 2 rear
Note that with the LSD, it will always have at least 3 powered wheels during slip.
Rubicon:
2Hi -> 1 powered wheel rear
4Hi -> 2 or 3 powered wheels, same as the Sport
4Lo:
unlocked -> 2 or 3 powered wheels, same as the Sport
locked -> 4 powered wheels, 2 front 2 rear all the time
So advantage Rubicon. It is the only Jeep trim that can have all 4 wheels powered all the time independent of any slip.
I drive a lifted 2019 Sport with 35s. There are fortunately ways to compete with the Rubi's. I've done many trails successfully where some Rubicon's (almost all stock) had to be assisted. The secret is TRACTION. I've added a Sway Bar Quick Disconnect kit for added articulation and I've got a particularly light foot to keep from spinning any wheel. I also invested in really great 35" A/T tires. Regardless of your Jeep, independent of your 4wd selection mode TRACTION is always your best friend!
Hope this helps.
Jay
[Edited from peer review feedback.]
One thing not really well understood about 4wd is that it depends on the type of axle, or rather the locking differentials, and whether (or not) you have them. Rubicon's have full lockers on both axles. Most (or probably the majority) of Sahara's have a Limited Slip Differential (LSD) on the rear, which isn't a true full locker. But in some ways it's even better. However like the Sport, the Sahara has an open differential (non-locking) in the front. Finally, most Sports come from the factory with only open diffs on both front and rear axles. Of course there are always some variations, but that's the general rule of thumb when thinking about the various Jeep trims.
Regardless of the trim level however, all axle types are pretty much always open diffs when 'unlocked'. The LSD is the only exception. It's potentially always partially 'locked' or possibly slipping all the time. For the locking diffs, they can only be locked in 4Lo (unless you have special overrides to very specific software calibrations via various third party programmers).
When 'unlocked' or with open diffs one and only one wheel on a particular axle, is getting power (when traction is lost). In fact the power is generally reduced to both wheels during 'slip' such that the overall contribution to motive effort from that particular axle is marginal.
So for every Jeep trim in 2Hi only one wheel (not two) is essentially getting power at the instant when either wheel starts slipping. Either can be powered but only the wheel with the least resistance is the one getting the most energy from the powertrain.
Noting that an open diff axle will distribute power to each wheel equally (50%) but ONLY with adequate traction. Once any wheel starts slipping, power is reduced to both wheels with the slipping wheel getting the most torque. Certainly not advantageous. That is exactly why lockers are so much better.
Also for every trim package when in 4Hi, potentially only two wheels are powered. One wheel in the front and one wheel in the back (if both axles are slipping). Again either wheel on each axle will be powered but only one per axle. So both 2Hi and 4Hi are misconceptions and named improperly. They should be named 1Hi or 2Hi respectively (while slipping). But since either wheel can be powered at any instant it's still considered 2 or 4wd respectively.
Only when in 4Lo do more 'powered' wheels potentially come into play. Only (ONLY) the Rubi's with the full lockers can have all 4 wheels powered (all the time) independent of any slipping wheels. When 'locked' all 4 wheels spin at exactly the same rate and the available torque is equally divided to all four wheels. This makes the Rubicon the only truly possible 4 wheel drive Jeep.
The Sahara with the LSD in the rear and an open diff up front when in 4Lo will have at least 3 powered wheels (during slip). The power to either rear wheels will be variable depending on the clutching action of it's LSD diff. So both rear wheels will have some fraction of the total available torque. However, they will both still be powered. In many situations, the LSD is far superior to the full locker because it will better adapt to give the most power to the non-slipping wheel. However, the Sahara's front axle is exactly like the Sport with an open diff.
With the Sport due to the open diffs both front and back, when in 4Lo it can have a potential of just two powered wheels, one on each axle if they're each slipping. So for the Sport it really can only ever achieve at best 3 but sometimes just 2wd, depending on which wheels on which axle are slipping. Again because either wheel on both axles can potentially be powered it's still considered 4wd.
So in summary (during wheel slip):
Sport:
2Hi -> 1 powered wheel (rear)
4Hi/Lo -> 2 powered wheels, 1 front 1 rear
Noting that most typically only one axle is experiencing slip so effectively there are 3 powered wheels.
Sahara with the LSD:
2Hi -> 2 variably powered wheels (rear)
4Hi/Lo -> 3 powered wheels, 1 front 2 rear
Note that with the LSD, it will always have at least 3 powered wheels during slip.
Rubicon:
2Hi -> 1 powered wheel rear
4Hi -> 2 or 3 powered wheels, same as the Sport
4Lo:
unlocked -> 2 or 3 powered wheels, same as the Sport
locked -> 4 powered wheels, 2 front 2 rear all the time
So advantage Rubicon. It is the only Jeep trim that can have all 4 wheels powered all the time independent of any slip.
I drive a lifted 2019 Sport with 35s. There are fortunately ways to compete with the Rubi's. I've done many trails successfully where some Rubicon's (almost all stock) had to be assisted. The secret is TRACTION. I've added a Sway Bar Quick Disconnect kit for added articulation and I've got a particularly light foot to keep from spinning any wheel. I also invested in really great 35" A/T tires. Regardless of your Jeep, independent of your 4wd selection mode TRACTION is always your best friend!
Hope this helps.
Jay
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