I've heard some people say that Selec-Trac is better in ice and snow. Other people say that's only if you don't know what you're doing.
There are 2 different types of Selec-Trac. There is Selec-Trac and Selec-Trac II. The original Selec-Trac had 2H, 4H Part Time, 4H Full Time, N, and 4L Part Time. Really, you can't go wrong with this 4WD system because it has pretty much every option.
Selec-Trac II on the other hand only has 2H, 4WD Auto, and 4L. 4WD Auto is basically a full time 4WD, but it can transfer up to 100% torque to the axle with the most traction if need be.
The only reason I explained this is because there is no real answer whether Selec-Trac is better or worse than Rock-Trac. A better question to ask would be whether 4H Full Time or Part Time is better, since that is the main difference between Selec-Trac II and Rock-Trac.
"Other people say that's only if you don't know what you're doing." This is correct. A Part Time system will always have more traction than a Full Time system because the front and rear axles are locked. It is the same with differential lockers; a locked diff will always provide more traction. However, whenever you lock a diff, you lose some maneuverability. The same is true with 4H Part Time.
To an inexperienced driver, a 4H Full Time system will behave pretty similarly to a 2WD system, except the vehicle will have better traction. The Part Time system behaves slightly differently since the axles are locked together.
In my experience, there has never been a time that I felt that my maneuverability was limited by the Part Time system, except maybe trying to make a tight turn at slow speeds. At higher speeds, I don't push the vehicle far enough to where my turning ability is limited because I feel like if I have to turn that quickly, I am driving too fast to begin with.
One disadvantage of Part Time is for roads with only patches of snow/ice. While it probably isn't necessary, I disengage 4WD whenever I am on pavement, wet or not. So there could be situations where you are constantly going back and forth between 4H and 2H if you have a Part Time system. Shift-on-the-fly makes this process relatively painless, but some people don't like having to shift at all, so they prefer a 4H Full Time system that can be driven on pavement so they don't have to shift at all.
If I had to choose between having either 4H Part Time or Full Time, I would choose Part Time in a heartbeat. It gives you more capability. However, the original Selec-Trac offered both 4H Part Time and Full Time, so that would be ideal since you have both options.
Correct me if I'm wrong, but my understanding is that with Selec-Trac, the centre differential doesn't lock. So all wheels can spin at different speeds. The system can apply more torque to the front or back axles depending on what's needed. Also there may be an option for a rear Limited Slip Differential (LSD). How does this affect things?
For Selec-Trac II, you are pretty much correct. Selec-Trac II does allow you to lock the center diff if you put it in 4L, but then your speed is limited, and I would not recommend that for extended driving in the snow. The original Selec-Trac did have a 4H Part Time option in addition to 4H Full Time option.
LSD will give you better traction 100% of the time without affecting your handling ability as opposed to a locker which will affect your handling ability. However, it again comes down to driver experience.
If you manage to get your tires spinning in the snow with LSD, you are more likely to slide around because both tires on the axle are spinning. If just one tire was spinning like in an open diff, the other tire would still have grip on the road, so you retain some side-to-side stability. In other words, donuts are much easier with LSD. The good news is that you can still control the vehicle if you know what you are doing.
LSD in the rear will cause the rear end to kick out more if you give it to much gas, and LSD in the front will cause more understeer if you give it too much gas.
I have LSD in both the front and the rear. The easiest way to regain control is to let off the gas. However, sometimes that is not enough. As an example, I was driving in the snow in 2WD with LSD. I was doing some fishtails, but I was too aggressive with it and ended up fishtailing back and forth (an inexperienced driver would have crashed easily). I let off the gas, but it still took some time to regain traction. What I realized is that because I drive a manual, letting off the gas was not enough because the engine was still connected to the wheels, and the engine did not slow down fast enough. If I had hit the clutch sooner, the wheels would have slowed down much more rapidly, and I would have regained control sooner. Lesson learned.
On the other hand, with Rock-Trac the centre differential locks in 4H, so that the front axles and rear axles have to spin at the same speed always(?). I'm not quite understanding this since the front and rear differentials are open in 4H, so the left and right wheels can still spin at different speeds? Does the sum of the back and front have to be the same? I'm so confused.
This is probably just semantics, but there is no center diff in the Rock-Trac. It is just as transfer case.
Yes, the front/rear driveshafts are locked together and will always spin at the same speed. There is sort of a sum game. In an open diff, the driveshaft will spin at a speed proportional to the sum of the speed of each wheel on the axle. If you jack up both wheels and spin one of them, the other wheel should spin in the opposite direction, and the driveshaft should remain still because the sum of each wheel (a positive and a negative) cancels each other out. That is why the left/right wheels can still spin at different speeds in 4H.
Also my main concern is how Electronic Stability Control (ESC), Traction Control (TC) and Anti-Lock Brakes (ABS) work when in Rock-Trac's 4H. Some things I've read on the internet seem to imply that these can't work when the axles are locked together. Are these features disabled when in 4H on Rock-Trac? That concerns me a lot because I drive a lot in ice and snow and need the added safety of ESC and ABS especially.
From experience, ESC and TC absolutely work. In fact, they work so well that I intentionally disable them when driving in adverse weather because they are so unpredictable. I feel much more comfortable driving my own vehicle than to have it drive for me because it always catches me by surprise and does something that I don't want it to do. It works exactly as intended; I just don't like it.
As for ABS, I never really thought about it, but the concept does make sense. The front brakes can control both the front and rear tire speeds in 4H, so while the front ABS is trying to control the front wheels only, it is inadvertently controlling the rear wheels as well, but the rear brakes are doing the same thing. I could see how the computer could get confused. I am not saying it is true, but it wouldn't surprise me.
However, whether ABS works in 4H Part Time or not is a moot point. If you are using 4H, you don't want ABS. It is a proven fact that on low traction surfaces such as snow, dirt, etc., ABS actually increases, not decreases, stopping distance, and it doesn't even give you improved control either. If you slam the brakes on a 2WD car with ABS in the snow, it will behave almost identically to the same car with no ABS. When you are stopping that quickly in low traction terrain, no computer system in the world can prevent the wheels from sliding. Since you only use 4H Part Time on these types of surfaces, it is actually beneficial to you if the ABS does not work.
