Adding weight to a vehicle

Put the weight directly over the rear axle or closer to the center of gravity. Weight in the extreme rear increases the “polar moment of inertia”, and as mentioned, this pendulum affect is bad for spinning out of control. The Corvair had its engine hanging way out and spun out easily.


Doc–Just imagine if the Tucker 48 had gone into series production, with its massive H-6 engine (372 ft lbs of torque!) hanging out behind the rear wheels.

A skilled driver would have probably been able to deal with its handling, once he got used to its very pronounced oversteer, but imagine if a little old lady had to suddenly deal with the rear end of that big sedan swinging out on her. That car would have been a bear to deal with in low-traction situations.

In the years just before WW II, Mercedes, Alfa Romeo, and Auto Union were the top 3 contenders on European racing circuits. While the Mercedes & Alfa racers were conventional front engine/RWD cars, the Auto Union racers were rear engine/RWD, and the rear placement of their TRULY massive (V-12, IIRC) engines gave them awful weight distribution and oversteer that was–literally–deadly.

After losing a lot of their drivers to one-car accidents resulting from that oversteer, Auto Union decided to hire only motorcycle race drivers, and to retrain them to drive the unconventional Auto Union race cars.

It seems that even very experienced race car drivers who had always driven conventional cars couldn’t be retrained sufficiently to stay alive in the AU cars, but if the factory people began from square one with motorcycle drivers, those men were able to deal with the incredible oversteer of the AU cars and not be killed by them.

Alternatively, you could just get 4WD pickup and not worry about this sort of thing :slight_smile:

A couple of things. Real good points about the weight behind the rear axle increasing the yaw rate to extreme by going too much outside the axis and lightening the front.

The idea of adding weight correctly is two fold. First, to gain traction in the rear wheels which even 4 wd needs and secondly to balance handling, which a 4 wd pick needs as well. Getting weight 50 / 50 is better for handling but I have always strived for near 45/55 to the rear with weight just forward of the rear axle. The handling is still good and the tendency to loose the rear end is lessened. You can’t drift through a corner as fast, but that is never the intent of a truck.

A slight bias ( not as much as VDC interestingly described) to the rear i feel is safest and gives you better traction overall for acceleration, climbing and taking corners with the power on up hills. Living on steep hills even with 4wd Is made easier. So 4 wd trucks need added weight in the rear nearly as much as 2 wd. It’s a fallacy that they don’t. Even in the summer, when unloaded, I still kept a 70 lb bag of tube sand or two in he back, then removed them when carrying loads.
So, unofficially, because I see it was in jest, I will disagree with @fodaddy. ;=) Think of the added front diffential alone adding too much weight to an unloaded 4wd pick up when the 2 wd version is poor in front weight bias to begin with.

Pickup trucks–whether RWD or 4WD–tend to have very light rear ends when unladen.
So, adding some weight above the rear axle is a good idea in the winter with any pickup truck.

Even in good weather, unladen 4 wd pick ups can handle very poorly with rwd and so much front bias. Traction and stability control help, but there is nothing like a balanced chassis to begin with. It may hurt mileage a little, but it’s always helpful both in ride and handling to have a little extra weight added back there.

I agree with the physics involved here. When I was 16 I drove a 2WD 1974 F-100 with a 4bbl 390 through unplowed roads during the blizzard of 1996 (blizzard being somewhat relative as I’m in central VA), and while I didn’t get stuck or anything, it wasn’t the ideal vehicle to drive in such conditions. These days, I have an old 1997 F-150 4WD that sees maybe 500 miles a year of use. When it snows I don’t even bother putting anything in the back, the 4WD and BFG A/T tires are enough to get me through anything I’ve encountered since owning the trying. Adding some weight to the back probably wouldn’t be bad thing, but it’s unnecessary in my experiences.

Around here, every rwd vehicle is enhanced by adding weight and wearing snow tires. I tried an experiment some years ago. I drove my Suzuki Sidekick to pick up tube sand in 70 lb bags for my pick up truck. At the VIP store, I loaded over 400 lbs in the back. It squatted some, but I drove back in 2wd with AT tires without spinning a tire. When I drove out I needed 4 wd engaged. I drove in 2 wd back out to the end of our mile and a half road just to check the differnce again. 2wd with all that weight, went as well, easier in some areas, as 4 wd without. Now, my Zuki wouldn’t like that diet every day, but the extra weight was surprisingly effective . Any one who experiments with added weight, sees immediate advantages…in rwd, 4 wd.
I even throw a bag or two in the back of my wife’s RAV Awd, and it helps when it’s really bad.

You add the weight above the rear axle or slightly forward.

Weight that’s added to the rear of the axle can and does cause a whipping of the rear end. I’ve experienced it a couple of times. Yes…adding weight to the rear of the axle will add more overall weight to the axle…but it can cause whipping. So just add MORE weight right over the axle instead.

I found mother nature the perfect solution. With an open bed because if the wind patterns my bed would fill up with snow, Enough weight to provide decent traction. In town driving the snow would eventually be gone by the time I did not need the weight.

I always add weight in the form of tube sand, between the axle and seat or cab at in the 4Runner, same for the RAV and trucks but stacked vertically so it stretches to the axle area. That said, the 4 Runner is so good in snow anyway with the cab weight, I stopped doing that… Throw a tarp over it and just throw loads on top of everything. Always had a cap or cover on trucks so the snow idea never appealed to me. Letting it fill with snow just gives you a two passenger car that gets 18 miles per gallon.

If you tow any thing substantial with a heavy tung weight, it’s worth adding more weight up by the cab, as far forward as possible to help handling if it’s not a load distribution hitch.

I’ve not bothered trying to add weight in my car in the 3 years I’ve had it; mostly because it’s an FWD biased part-time AWD setup. Though, I can get the rear to “kick out” a bit if I apply enough throttle as I’m going around a corner. I only do that when I feel understeer kicking in so I’m not heading straight when I want to turn; a bit of opposite lock and I can get her righted.

The snow in the truck bed idea is nice, if you get enough snow to fill the bed up good enough. I think the worst we got in my area was maybe 6~8 inches one day. I know the drift in my old driveway going to the garage was up to my knees, but that part of the driveway was essentially a wind tunnel(my house, detached garage and neighbor’s house were really close together). A few occasions the unplowed parts of town had me scraping the top of the snow with the bottom of my Civic. Since I’ve bought my CX-7 I’ve not had to even shovel my (current)driveway because it has much more ground clearance.

I had good luck with four wheels and tires, three pallets and two bags of sand in back of my 1974 Ford 150 with 8 ft. bed. It was about as evenly distributed as you could get with four wheels… I never got stuck.

Hear something scary ? At work several years ago after the first snow storm a lady who was a fellow teacher made this comment in the teacher’s room. I heard you guys talking about adding weight to the back of your trucks so I tried it in my car. It didn’t help at all. It was terrible. After a little questioning, we forund out she had all season tires and…fwd.

@bscar2 yes, adding weight to the rear of any Awd, even with fwd bias, helps. In the new ones, as much as 50 to 90 percent of the torque can be shifted to the rear. At that point, balance weight distribution really helps. Like I said. Wife’s car is that way in her RAV. It helps a lot. We just do it selectively when our road is iced up or deep snow and leave the bags at the end of the garage normally.

“a lady who was a fellow teacher made this comment in the teacher’s room. I heard you guys talking about adding weight to the back of your trucks so I tried it in my car. It didn’t help at all. It was terrible. After a little questioning, we found out she had all season tires and…fwd.”

I think that I may have encountered her cousin several decades ago.
After a very heavy snow storm, as I was walking to a grocery store, I saw a woman who was throwing traction grit under the rear tires of her new-ish Toronado, which was in the middle of a large snow drift.

Thinking that I was being helpful, I stopped to point out to her that, if she was having traction problems, she should be throwing the traction grit under the front tires. Her angry response was, “Listen sonny, those front wheels are turning just fine. It’s the rear wheels that I can’t get to move!”

I said something along the lines of…Of course…How silly of me…and continued on my walk to the grocery store.

The bad thing about adding weight behind the rear axle is that it destabilizes a vehicle causing oversteer. You might be able to mitigate this by slightly underinflating the front tires and slightly overinflating the rear tires.
Make a vehicle tail heavy enough and it starts having the handling charactoristics of a taxiing taildragger airplane, these are infamous for ground looping and being a handful to keep going straight at high taxiing speeds. This is because the center of mass is behind the main wheels and the g-forces of a turn acting on the center of mass causes the turn to become tighter and can go to the point of no return, a ground loop, which often causes a wingtip to scrape the runway.

I made it through a couple of Alaskan winters with a 2WD Jeep pickup by adding weight to my bed. I put a large plastic sheet in the bed of the pickup when freezing weather arrived. I filled up the bed with water and let it sit overnight to freeze. I trimmed the plastic sheet and was good to go. Fuel economy plummeted but the truck handled very well on the frozen Alaskan highways…as long as you drove slowly. You could always tell who drove fast because you could see them in the ditches on the right and the left…usually facing the wrong direction.

I believe there are just too many factors to expect a rule of thumb to provide a reliable answer to this one.

There are many factors.

I have to ask how many of those asking have winter tyres on their car?

That’s hilarious !
You are absolutely right about the variables. But generally speaking, if adding weight balances the distribution in a rwd4wd car or truck, and is done correctly , there is no down side. That is not to say you throw 500 lbs in the back of a delicately suspended BMW and leave it all winter.
But , one thing must be noted. Adding weight anywhere to a fwd car, other then on the front seat as you back up a slippery steep hill, does nothing to help and often hurts traction.