Ice on hwy - use 4wd or not
 

Jeep Cherokee 2001 Sport - Advice/experience sought. Black ice on a very curvy mountain highway. Would you put in 4wd? Or 2wd? Does ABS cease in 4wd? I appreciate anyone who will share their opinion. Drive about 50 miles on the highway with curves and ice on a canyon road. (4wd has helped get up icy snow covered steep country roads. Wondering about hwy use.)

Slow down (most important) and use the modest additional braking advantage offered by 4wd in icy conditions. Jalopnik had a nice demonstration earlier in the year (https://jalopnik.com/this-should-set...ate-1822591648).

Thank you! Just what I needed to know.

There is no modest additional braking advantage offered by 4wd in icy conditions. The brakes work the same in or out of 4wd, wet or dry, even with an XJ equipped with ABS. ABS works the same either way, regardless of driving conditions. The only advantage being in 4wd is increased traction as you have two more tires fighting for traction as the transfer case sends engine power to all four corners instead of only two.

There is no difference in 2wd or 4wd when it comes to braking.

Thank you!

4wd does make a difference in braking, the reason is because most vehicles have front brake bias meaning most of the braking pressure goes to the front, so the front wheels will lock up before the rear does. However in 4x4 the front and rear axles are mechanically connected by the transfer case and driveshafts, so the front can not lock up without the rear locking up. The braking pressure is still the same as it is in 2wd but you also get braking from the drive line, even if you had no rear brakes at all you would still get braking in the rear when in 4x4, that is why in the tests you can stop quicker in 4x4.

the brakes are not hooked up to the transfer case. totally separate units.

but, i can see getting drive line bind slowing the rear axle due to front wheels locking up, thus binding up the transfer case and ultimately the rear drive shaft, and rear axle, bringing the rear wheels to stop turning.

but yes, engine braking will work the same way, therefor slowing down both axles in their rotational energy, while slowing down the vehicle easier than brakes alone.

I will run part time in really crummy weather. If I don't my wide tires will sometimes float and the rear will step out accelerating up hill, if I hit ice or slush.

But since it is shift on the fly, I usually pop it back in 2wd when I no longer need it.

Full time 4wd you can run year round 24/7 if you want, and definitely recommended if its icy out.

Full time will let the front wheels turn at differnet speeds, part-time the wheels will bind up and want to spin at the same speed which means low speed turns you are going to understeer a ton or it will bind and "pop" if there is too much traction and you are on the gas.

Makes sense, but ive never noticed a difference between 2wd and 4wd when the weather gets bad. Then again i dont drive as fast as they were for the test to find out. I just stick it into full-time 4wd and use common sense. Perhaps being in full-time is why i never noticed a difference between the two?

Full time won't have the same effect since the front and rear aren't locked together like they are in part time.

Keep this in mind also. In reality with open differentials, you only have one wheel driving on each end when traction is compromised, as in slippery conditions. In 2wd, you've only got one. I'd rather have 2, one on each end pulling in 4wd. I've found with my WJ in full time and sitting at a stop with all 4 wheels on ice, you hit the throttle and only one wheel will spin and you go nowhere. Shift to part time and you can take off, gently of course.

Funny how people hear 4x4 they think all 4 tires spin together.

Mine do that.

With lockers they would. Smartass.

LOL you have lockers

I'm talking a stock vehicle haha. Although SOME do come with lockers granted.