Car Center of Mass Calculator
Locate a vehicle's center of mass from scale readings and a simple lift test, and see how its height sets the rollover limit.
🚗 What is a Car's Center of Mass?
The center of mass of a car is the single point where its whole mass can be treated as concentrated, the mass-weighted average of the position of the engine, body, passengers, fuel and everything else. Near the ground, gravity is uniform enough that this point is also the center of gravity. Where it sits decides how the car handles: a CG far forward loads the front tires and tends toward understeer, a CG far back does the opposite, and a high CG makes the car lean more and transfer more weight to the outside wheels in a corner. Wikipedia's article on the center of mass gives the general definition, and this page applies it to the three directions that matter for a vehicle.
Each direction needs a different measurement. The front to rear position follows from weighing the two axles on a level surface and using the wheelbase: the CG lies closer to the heavier axle, in inverse proportion to the load. The left to right position comes from the same idea with side scales and the track width. The height is harder, because level scale readings contain no information about vertical position. The classic fix is to lift one axle, which tips the car and moves the CG horizontally by an amount that depends on its height, and then to measure the change in axle load.
Typical users are owners balancing a track car, builders of kit cars and karts, engineers checking a design against a target, and students of statics. The same numbers also feed the rollover estimate. The static stability factor, track width divided by twice the CG height, tells you the sideways acceleration at which a rigid vehicle begins to lift its inside wheels. It is a screening number, not a prediction. Tires usually slide before a normal car tips, and suspension roll, tire deflection and dynamic effects all lower the real threshold, which is why researchers working with national road-safety data treat it as an indicator, not a guarantee.
Common mistakes are mixing units across the two scale readings, measuring with a half-full tank one time and a full tank the next, and taking the height test on a car whose suspension compressed during the lift. Weights can be in any unit as long as they are consistent, but lengths must be in metres. For the turning forces that act at the CG, see the centripetal force calculator and the angle of banking calculator, and for adding up several forces on the car use the net force calculator.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — Front to Rear Position
A 2.7 m wheelbase car with 780 kg on the front axle and 620 kg on the rear
Example 2 — Left to Right Position
690 kg on the left side, 710 kg on the right side, track width 1.55 m
Example 3 — CG Height from a Lift Test
Same car with a tire radius of 0.33 m. Raising the rear axle 0.5 m increases the front reading from 780 kg to 805 kg
Example 4 — Rollover Threshold of a Passenger Car
Track width 1.55 m, CG height 0.55 m, tested on a curve of radius 50 m
Example 5 — A Tall SUV
Track width 1.70 m, CG height 0.75 m, curve radius 80 m
❓ Frequently Asked Questions
🔗 Related Calculators
How do you find the center of mass of a car?
Weigh the front and rear axles to get the longitudinal position: the CG is a = Wr x L / W behind the front axle. Raise one axle and weigh again to get its height. Side scales give the left to right position.
What is the center of gravity of a typical car?
Most passenger cars have the CG about 0.5 to 0.6 m above the ground, roughly 40 to 55 percent of the wheelbase behind the front axle. Sports cars are lower and SUVs and vans are higher.
How is front to rear weight distribution calculated?
Front percent = front axle weight divided by total weight, times 100. A car with 780 kg on the front and 620 kg on the rear has 55.7 percent of its weight on the front axle.
How does the lift test give CG height?
Raising the rear axle by H tilts the car and moves the CG forward over the front axle, so the front scale reads more. The size of that increase, with the wheelbase and tilt, fixes the height: h = (L x dW / W) x sqrt(L squared - H squared) / H.
What is the static stability factor?
SSF = T / (2 h), where T is the track width and h the CG height. Dividing it into g gives the sideways acceleration at which a rigid vehicle begins to tip. Typical cars have values from about 1.3 to 1.5 and tall SUVs sit near 1.0 to 1.2.
Why does a lower CG make a car safer?
A lower CG raises SSF, so a larger lateral acceleration is needed to tip the car. It also reduces the weight transferred from inside to outside wheels in a corner, which keeps the tires evenly loaded.
Will my car actually roll over at the calculated acceleration?
Usually not on a flat road. Tires slide at around 0.8 to 1.0 g, below the threshold of most cars. Rollover usually needs tripping on a curb or soft shoulder, and suspension roll lowers the real threshold.
Does adding passengers or cargo move the center of mass?
Yes. Every added mass shifts the CG toward itself. Roof loads raise it quickly because height is weighted by mass. Enter the loaded axle weights to see the new position.
What units should I use?
Weights can be in kg, lb or N because only their ratio matters, as long as all readings use the same unit. Lengths must be in metres in this calculator.
What is the difference between center of mass and center of gravity?
The center of mass is the mass-weighted average position. The center of gravity is the point where gravity effectively acts. In the uniform gravity near the ground they are the same point, so the terms are used interchangeably for vehicles.
Can I find CG height without lifting the car?
Not from axle weights alone on a level surface, because level scale readings only fix the horizontal position. You need a tilt, a lift or a measured weight transfer under braking or cornering.