Auto weight distribution


#1

Hello everybody,



Lets say you have an automobile that weighs 4,000 pounds, and it’s sitting on four tires. Are those four tires each supporting 4,000 pounds? Or are they each supporting 1,000 pounds? Is the total weight shared by all four tires? Equally?



Thanks,



Brad


#2

They’re splitting up the 4000, could be evenly, but likely one end carries more than the other, so could be 1200 each up front and 800 each for the rear, for example.


#3

First, you need to know how much of the total car weight is on the 2 front wheels and what % is on the rear wheels. If it is 50% front and 50% rear, you have 2000 lbs on the 2 front wheels, so 1000 lbs on EACH wheel. Similarly for the rear wheels. If you have 75% on the front wheels, which is more common, you have 3000 lbs on the 2 front wheels, and 1500 lbs on EACH front wheel.

Trust this answers you question.


#4

Most cars have between 50% and 60% of the weight on the front tires. 50% is usually considered ideal for handling. BMW is usually right at that 50% mark.


#5

Typical FWD sedans have about a 60:40 weight distribution, 60% in the front.

That means that 2,400 pounds would be supported by the front two wheels (1200 ponds each) and 1600 pounds the rear two wheels (800 pounds each).

So, if we assume that each front wheel has 32psi pressure, we can even now calculate that each front tire has about 37.5 square inches of tread in contact with the ground. If the car has a tread 8 inches wide, we can even know from this that the contact patch on each front tire is about 8" wide by 4.6" long.

Cool, huh?


#6

To make it simple: your second choice, 1000 pounds each is the one that’s possible.


#7

If you take a look at the car tests in magazines like Car & Driver or Road & Track, they always list the percentage of weight on the front wheels and the percentage of weight on the rear wheels (weight distribution).

The old rule of thumb was that a vehicle that was “heavy” in the front would be prone to understeering, and one that was heavy in the back would be prone to oversteering. While modern suspension design has helped somewhat to overcome those tendencies, that old rule of thumb is still valid to a very great extent.

In general, you want your car to have weight distribution as close to 50/50 as possible for optimum handling. Typically, a FWD vehicle will be “nose heavy”, which is why they tend to understeer. The old VWs and Corvairs were “tail heavy”, and that is why they tended to want to put their rear ends in front of the car on sharp curves if the driver was not aware of their unique handling . Some RWD cars–BMWs come to mind–have a weight distribution fairly close to 50/50.


#8

It is not appropriate to assume that each rear tire carries the same weight; same applies to each front tire. Go to a truck stop and get weighed; only costs a couple of dollars. Who will say that you can’t put one wheel on the scale?

Motorhomes typically do not have the same weight on each corner; why should cars be different especially if there is a driver and no passengers.


#9

Tire inflation also affects over/under steer. underinflated front tires and/or overinflated rear tires = understeer (front wheels skid in a turn)

overinflated front tires and/or underinflated rear tires = oversteer.

Power delivered to the rear wheels also has an effect, a coasting car will understeer but when you step on the gas, it will switch to oversteer. Dirt track sprint car racers use the throttle to steer the car in the turns.