Well, it’s snowy season again, and those of us driving pickups are considering adding weight to aid in traction/handling.
The conventional wisdom is to add weight directly over the drive axle. However, my experience in physics class, doing “weight and balance” calculations for flying, and time on a seesaw tell me that’s bull.
Basically, changing the CG of a vehicle is like a seesaw: you can balance a big weight with a small one, provided the small weight is sufficiently far from the pivot point.
To relate this to a vehicle, say you’ve got a 4000# vehicle with a 60/40 weight distribution that you’d like to get to 50/50. You could put 800# right on the axle, which leaves the front axle unchanged, and and ups the rear to a matching 2400. Alternatively, you could put 267# one wheelbase BEHIND the rear axle (granted you’d need a big bed!) which would transfer 267# rearward, to balance at 2133# on each axle…saving you 533# of dead weight. (Heck, construct an infinietly strong, infinitely light boom and place one pound a half mile back…)
So, what’s the downside? The only thing I can think of is polar moment of inertia, which would make it minimally harder to enter a spin (and minimally harder to recover if you did manage it). I’m not sold that PMI is relevant outside the race track; heck, if we gave two hoots about it, we’d all be driving mid-engined rides. (It should be noted that in aviation, where spins are a BFD, ballast is still added as far forward or aft as practical.)
Heck, I think the sloshing effect of half a tank of fuel is about a realistic safety issuse as PMI variances!
So, what do you think: ballast over the axle, or as far back as it’ll comfotably fit?