Mary, I would guess that the F-150's advantage is simply weight
on the drive wheels, not the tire size. Weight = traction.
A limited-slip diff (LSD)
limits the amount one tire spins by partially locking the left and right sides of the axle
together - great if one tire has less traction (poorer surface, for instance) than the other. With a limited-slip, you aren't so limited by the worst-off tire, but if both tires
are working together and still don't have enough traction (both spin), the LSD isn't enough.
The problem is the backing up: with the rig facing downhill, the truck's front axle carries more load (and the rear axle less) than while level - that's load transfer
. This means less traction for the rear axle to drive with. I have had the corresponding front-wheel-drive problem: traction is reduced when going forward
uphill. Certainly, this is a practical limitation to the towing capacity of two-wheel drive vehicles: how much of the rig's total weight is on whatever tires
are being driven?
I find it interesting that weight-distributing hitches (WDH
) exist to transfer load away from the rear axle (onto the front axle and trailer axle), so with a rear-wheel-drive vehicle it makes drive traction worse; with a front-wheel-drive, the WDH would make drive traction better. If I had the backing problem with the Ranger, and was using a WDH, I would slack off the WDH as much as possible (without violating the rear axle rating) to improve traction in this situation.
I already had "I have no idea if Mary is using a WDH or not
" in this post, but now that Mary has responded I'll point out that since she doesn't use a WDH, this part is not relevant to her. (I also edited the formatting of this post for clarity).
In my case, when loaded, the front and rear axles of the van carry almost identical load, so it would not matter which end gets driven except
for the hill issue, and the fact that load transfers from front axle to rear when accelerating.