Calculate speed bump load, mass, time, or velocity from any four inputs with units in kg, lb, m/s, ft/s, mph, seconds, minutes, N, or lbf.
Speed Bump Load Formula
The calculator uses the impulse-momentum relationship. It treats the speed bump load as the average force needed to change the vehicle or wheel mass from an initial velocity to a final velocity over the contact time.
F = \frac{m*(v_i - v_f)}{t}Rearranged forms used when a different field is left blank:
m = \frac{F*t}{v_i - v_f}v_i = \frac{F*t}{m} + v_fv_f = v_i - \frac{F*t}{m}t = \frac{m*(v_i - v_f)}{F}- F = bump load, or average force during contact with the bump
- m = mass
- vi = initial velocity before the speed change
- vf = final velocity after the speed change
- t = time in contact with the bump
The calculator converts all inputs to base SI units before calculating: kilograms for mass, meters per second for velocity, seconds for time, and newtons for load. It then converts the answer back to the unit you selected.
If you leave bump load blank, it calculates the average force from the change in velocity. If you leave mass, initial velocity, final velocity, or time blank, it solves the same equation for that missing value.
Speed Bump Load Units and Result Checks
Use these tables to check units and interpret the sign of the result.
| Quantity | Supported units | Base unit used in formula | Conversion to base unit |
|---|---|---|---|
| Mass | kg, lb | kg | 1 lb = 0.453592 kg |
| Velocity | m/s, ft/s, mph | m/s | 1 ft/s = 0.3048 m/s; 1 mph = 0.44704 m/s |
| Time | seconds, minutes | seconds | 1 min = 60 s |
| Bump load | N, lbf | N | 1 lbf = 4.44822 N |
| Condition | What it means |
|---|---|
| Initial velocity is greater than final velocity | The result is a positive load from slowing down over the bump. |
| Initial velocity equals final velocity | The calculated speed-change load is zero. The calculator cannot solve for bump load from velocity change if there is no velocity change. |
| Final velocity is greater than initial velocity | The result becomes negative because the object speeds up instead of slowing down. |
| Shorter contact time | For the same mass and speed change, the calculated average load increases. |
Speed Bump Load Example Problems
Example 1: Calculate bump load
A 1500 kg vehicle slows from 5 m/s to 3 m/s while contacting a speed bump for 0.25 s.
F = \frac{1500*(5 - 3)}{0.25}F = 12000\ N
The average bump load is 12,000 N, which is about 2,698 lbf.
Example 2: Calculate contact time
A 2000 lb mass slows from 10 mph to 7 mph under a bump load of 900 lbf. First, convert internally to SI units:
- 2000 lb = 907.184 kg
- 10 mph = 4.4704 m/s
- 7 mph = 3.12928 m/s
- 900 lbf = 4003.398 N
t = \frac{907.184*(4.4704 - 3.12928)}{4003.398}t = 0.3039\ s
The contact time is about 0.3039 seconds.
Speed Bump Load FAQ
Is the bump load the same as the vehicle weight?
No. Vehicle weight is the gravitational force on the vehicle. This calculator estimates an average dynamic load from a change in velocity over time. A vehicle can have a speed bump load that is different from its static weight because acceleration and contact time affect the force.
Why does a shorter contact time increase the load?
The same change in momentum must happen in less time. Since force equals change in momentum divided by time, reducing the contact time increases the average force when mass and velocity change stay the same.
Should you use total vehicle mass or wheel mass?
Use the mass that matches the situation you are modeling. If you are estimating the load on the whole vehicle from a speed change, use total vehicle mass. If you are estimating the load at one wheel or axle, use the portion of the mass supported by that wheel or axle. The result is only as specific as the mass value you enter.
