No 4H

[ROBERT BONNER]

Open or unlocked differentials split torque evenly to all 4 wheels, so when you aren’t applying power (like in a slow down situation) brake force should be distributed pretty evenly. At least that’s my understanding. Even open diffs are technically “matching” power to all 4 wheels. It’s just that it only takes a few lb ft of torque to spin one side when it has no traction, so that’s all the other side gets sent to it (not enough to spin that sides wheel). This is what causes the one wheel peel effect you see commonly. On an open diff the tire with least traction on each axle determines the power both wheels on that axle gets. That’s the Achilles heel. This is where lockers and limited slips come in handy and fix the issues of open diffs, because they allow torque to differ between wheels on the same axle to get them to spin at the same rate in these situations where even torque doesn’t cut the mustard. But alas in braking, whether you are locked up via a locker or open and not locked a 50/50 locked transfer case is going to slice some distance off your stop. The testing I watched they did were on Jeeps with open diffs and ABS. The difference was quite large between 2WD and 4WD stopping distances.

I used to call BS when people said 4WD helps you stop, but then people sent me some videos and independent tests and I was proven wrong and surprised. I tried to lay it out to the best of my understanding, but I was a finance major not an engineer haha.

Yes, but having driven on frozen pads at Ford with different vehicles in different modes, and under different conditions, it is more complicated than that. If you are on a relatively frictionless surface, ABS will work much better with unlocked differentials, this is due to 2 things: 1) The brakes have to stop not only the vehicle; but, the rotating inertia attached to the wheels. 4x4's have a lot more rotating inertia especially on the critical front wheels. 2) It's difficult to keep the ABS from fighting itself wheel to wheel through the drivetrain, there are fairly complicated algorithms involved in fighting this, most of which end up reducing the frequency and effectiveness of the ABS when a vehicle is in 4wd. Where things change is in snow, sand, mud conditions which are not as frictionless as ice. ABS doesn't allow as much net force to be applied to the brakes (duh) when active. When in deeper, colder snow all vehicles can stop in shorter distances without ABS than with it at moderate speeds, this is because, abs doesn't allow mass to "pile up" in front of the tire and doesn't allow the tire to "sink down" to a higher friction surface. Those same ABS algorithms that cause 4x4's to take longer stopping distances on ice, cut the other direction in heavy snow.

Disclaimers: All that being said, my experience in this area is about 15 years old now and I'm sure improvements continue to be made in both hardware and software on all fronts. All vehicles and all surfaces are different, it's difficult to replicate real world conditions on an experimental basis, the friction of various snow and ice conditions can be radically different when only a few parameters are changed by small amounts. Drive Safe!