Just to add to the thread. I use 4wd on my truck mainly when it's snowy here. Last winter, I had different brand (although the same size) tires in the front and back. Worked great in the snow, but as soon as I hit a dry patch, there was a drag on the truck. It wasn't bad enough to cause the hopping, but it would prevent 4wd from disengaging when I hit the button to turn it off, I would have to get out and unlock my hubs. I replaced the tires over the summer (all the same this time), so I'm ready for winter.
Oh, and 4wd helps a lot in the snow and ice, but it's still easy to slide off the road, so be careful in 4wd still.
It was once explained to me that 4wd just allows one to get stuck further from the road.
Coming from someone who moved to a snowier climate with a large and heavy 2WD Suburban with a open differential in the rear... 4x4 makes a hell of a difference. Even limited slip in the rear makes a hell of a difference. Last winter was my first time driving in snow and also my first time using a 4x4 vehicle. My mind was blown. I was driving on icy/hardpack surfaces that I wouldn't feel comfortable walking on. That was with balding 8 year old cheap Les Schwab made in China all-season tires.
For this upcoming winter, I've purchased a used set of quick-fit diamond style chains and will be purchasing some Cooper Discoverer AT/3 tires. I think short of high-centering, I'll have the confidence in going anywhere I need to.
Back to the topic at hand, basically, all 4 tires NEED to spin at the same exact rate. This will likely never happen. Bad alignment, bad joints/bushings, slightly different tire wear, sloppy steering gearbox, slight turn of the wheel... many things can work against you. Something has to give when the driveline binds up from different rotation rates, usually that's the low traction surface you're on, dirt, gravel, snow, etc.
Take a look at this video:
https://www.youtube.com/watch?v=gIGvhvOhLHU
While the average 4x4 owner won't have a locking differential in the front/rear, the important thing to remember is that the binding occurs because the front and rear axles need to spin at the same rate, regardless of what the differential is doing. The binding can be released if one tire on either axle loses traction.
(this is all how I understand it, feel free to correct me if I'm wrong)
