Selec-Trac ............... Simple explanation, PLEASE!

[AnthologyCT]

OK guys, I have Select-Trac on my vehicle ............

Does that mean that I can drive in 4-Wheel Drive, just like one would with an AWD car?

And, what's the purpose of Part-Time 4x4? Does that mean that when the front wheel's start to slip, then they would be locked? And if so, when does the vehicle return to 2WD?

Can I run Part time and 4x4 all the time with Selec-Trac, and not worry about bending?

 

[-=JoN=-]

yeah...4 full time acts like an awd...dont know the torque split (probably 50/50)

in theory you can generally leave it on all time, but that will also eat up some mpg's.

it wont return to 2wd unless you put it back to 2wd..it's not like the awd systems on other cars...where it's computer controlled

selec-trac only gives u the option of 4 full time.
if u put it in 4 part time, it's still gonna give you binding on dry surfaces..

command trac does not have 4 FT, only 4 PT/4LO

urs should have 4 full time as the first option after 2-hi

 

[JeepJeepster]

Click on select trac below the picture and listen to what the guy says:

http://www.jeep.com/liberty/4wd_capability.html

O

 

[stratjb]

For what it's worth, on the Select Trac (242) the 4 full time splits the power 48% front / 52% rear and eliminates *MOST* driveline binding on dry pavement. The 4 part time splits 50/50 and will bind a bunch making turns on dry pavement.

 

[AnthologyCT]

Selec-Trac

Click on select trac below the picture and listen to what the guy says:

http://www.jeep.com/liberty/4wd_capability.html

O

THANK YOU man!!!!!!!!!!!!!!!!!!!

That's the explanation I've been looking for.

 

[kjpilot]

in theory you can generally leave it on all time, but that will also eat up some mpg's.

I've actually seen an improvement (1-1.5) in MPG with full-time 4WD engaged. While it's true that turning all 4 wheels requires more energy from the engine than only turning 2 wheels, this does not take friction & drag into consideration.

While in 2wd, only 2 wheels are applying energy to the road, & the front wheels are just dead rolling weight, & the tires provide nothing but friction & drag. This retards movement. When all 4 wheels are transfering energy to the pavement, this friction is & drag is overcome more effeciently.

So even though it's harder for the engine to turn all 4 wheels, it's easier for the engine to move your KJ across pavement with all 4 wheels pulling their own weight.

 

[jfortier777]

in theory you can generally leave it on all time, but that will also eat up some mpg's.

I've actually seen an improvement (1-1.5) in MPG with full-time 4WD engaged. While it's true that turning all 4 wheels requires more energy from the engine than only turning 2 wheels, this does not take friction & drag into consideration.

While in 2wd, only 2 wheels are applying energy to the road, & the front wheels are just dead rolling weight, & the tires provide nothing but friction & drag. This retards movement. When all 4 wheels are transfering energy to the pavement, this friction is & drag is overcome more effeciently.

So even though it's harder for the engine to turn all 4 wheels, it's easier for the engine to move your KJ across pavement with all 4 wheels pulling their own weight.

This does make sense since regardless of Tcase position we have the front end drivetrain spinning at all times, so really the 4WD FT is just relocation of power to a system that functions in the vehicle's 2WD movement.

Of course so many calculations would have to be done to prove it either way.

 

[Dave]

That's an interesting thought about running full-time and actually getting better mileage. I will try it for a couple of weeks and see what develops. I'm sure it would be hard to tell though unless I did 2 identical trips - one in 2wd and one in 4wd full time.

 

[Gatorator]

I spend most of the time on Gravel Roads and the Full time 4x4 is a wonder. No more chattering around the corners on washboard and it feels under total control at all times.

Not so in 2wd. \/

 

[thecause17]

in theory you can generally leave it on all time, but that will also eat up some mpg's.

I've actually seen an improvement (1-1.5) in MPG with full-time 4WD engaged. While it's true that turning all 4 wheels requires more energy from the engine than only turning 2 wheels, this does not take friction & drag into consideration.

While in 2wd, only 2 wheels are applying energy to the road, & the front wheels are just dead rolling weight, & the tires provide nothing but friction & drag. This retards movement. When all 4 wheels are transfering energy to the pavement, this friction is & drag is overcome more effeciently.

So even though it's harder for the engine to turn all 4 wheels, it's easier for the engine to move your KJ across pavement with all 4 wheels pulling their own weight.

Of course so many calculations would have to be done to prove it either way.

Very true, especially when in the past it's been proven that AWD cars exhibit a higher amount of drivetrain loss than both RWD or FWD vehicles.

 

[kjpilot]

Very true, especially when in the past it's been proven that AWD cars exhibit a higher amount of drivetrain loss than both RWD or FWD vehicles.

AHHH, but remember in most AWD cars you cannot switch off AWD. that means you cannot do a true comparasion! An AWD version will weigh significantly more than a FWD or RWD only model of any given car. In the KJ, When you switch between AWD & RWD, all other variables remain the same.

 

[thecause17]

Very true, especially when in the past it's been proven that AWD cars exhibit a higher amount of drivetrain loss than both RWD or FWD vehicles.

AHHH, but remember in most AWD cars you cannot switch off AWD. that means you cannot do a true comparasion! An AWD version will weigh significantly more than a FWD or RWD only model of any given car. In the KJ, When you switch between AWD & RWD, all other variables remain the same.

I'm talking about dynoed power, showing the loss through the drivetrain. When the Jeep is in Full Time 4WD, it is essentially AWD, making use of a center differential, weight has nothing to do with it. If you want a true comparison, then you should find an AWD dyno, which there only a handfull in the country, and do runs on that.

 

[kjpilot]

I'm talking about dynoed power, showing the loss through the drivetrain.

I've already said that there is more power required to turn all 4 wheels at the same output level (ie, At the same power level, output is lower), in an AWD car due to the added work of moving all 4 wheels (drive train loss). This drivetrain ineffecency is overcome by the added effecency of all 4 wheels applying power to the pavement.

A Dyno can't tell you much about fuel effiecncy, at least not directly.

 

[JeepMonkey1965]

Hi Guys

Just to split hairs, the split in 4-FULL TIME is 48% FRONT & 52% REAR :-#

I must confess that I don't see an increase in consumption in Full-Time on mine and it beats being hauled out of a ditch 8-[

Anyway, guys if you really want to bitch about fuel consumption then just move to the UK where fuel is currently £1 per litre or in old money $7.20 per Gallon (US) .......... yes I'm sorry for those of you that now need therapy 8-[

 

[thecause17]

I'm talking about dynoed power, showing the loss through the drivetrain.

I've already said that there is more power required to turn all 4 wheels at the same output level (ie, At the same power level, output is lower), in an AWD car due to the added work of moving all 4 wheels (drive train loss). This drivetrain ineffecency is overcome by the added effecency of all 4 wheels applying power to the pavement.

A Dyno can't tell you much about fuel effiecncy, at least not directly.

You can speculate all you want, like I said, if you want a true comparison, dyno in both 2WD and Full Time....less total power hitting the pavement is what you should be concerned with...thats what will show the inefficiency. Until someone can actually document whether or not there is no more loss, with charts, filling up at the same gas station, same pump, with identical temp/humidty conditions, and driving patterns, it is all just speculation.

Show some facts about how you say that works, thats what i want to see, not an opinion. I'm not trying to be ass, but back it up with fact about how applying power to something for something other than rolling resistance is going to approve fuel economy when your increasing the drivetrain loss by doing so. In effect, less total power to the pavement, with the same vehicle, more efficient?

 

[AnthologyCT]

AWD vs. 4WD

ALL WHEEL DRIVE vs. 4WD


ALL WHEEL DRIVE:
Definition: A vehicle where all four wheels are driven, but there's no transfer case like a four-wheel drive rig. Most AWD setups are full time systems for year-round driving, and use a viscous fluid coupling center differential instead of a transfer case to route drive torque to all four wheels. This allows the front and rear wheels to turn at slightly different speeds when turning on dry pavement. Most folks do not consider this the same as four-wheel drive. It can be useful (and more fuel economical) in pavement driving where you're mainly negotiating bad weather conditions.


FOUR WHEEL DRIVE:
Definition: A method of driving a vehicle by applying engine torque to all four wheels thru the use of a transfer case, differentials and hubs. Various schemes are used for 4WD including part-time, full-time and variable four-wheel drive. To help cut the drive train drag (and reduced fuel economy) that most 4WD's have, a transfer case is included that allows the driver to select either two- or four-wheel drive depending on driving conditions. Some performance cars have full-time variable four-wheel drive and use a computer-controlled transfer case to route power between the wheels.



It's important to note that even in 4WD, you still have only two driving wheels; one front; one rear. A normal passenger car is essentially one wheel drive, because the other one can slip. So a 4WD rig, with the front axle engaged, now has two wheels driving. Then if you add a locker to the rear, you've added one more wheel, to make your rig three-wheel drive. Add a locker to the front, so no tires can spin, and you have TRUE, 4-wheel drive, all four wheels driving.