Car weight applied to a speed bump while driving over it

[jHoeplinger]

Hello All,

 

Long time reader, first time poster. Not an engineer.

 

Problem:

 

A car drives over a speed bump. How much weight rolls over the speed bump per axle?

 

Assumptions:

1. Normal sedan, suspension, tires, etc.; weighs 3000lbs
2. Assume 50/50 weight distribution (I know it's not)
3. Driving 10mph
4. Speed bump is 1ft long, 1in high (I know, small)

Questions:

1. What would your thought process be? Please be detailed.
2. What's the right unit of measurement? lbs/square inch?
3. Considerations / missing information? Thinking the suspension might come into play... anything else? What would some good assumptions be?

Note:

This is not a work or academic related problem-- Just something I'm curious about.

 

Thanks,

 

John

[Greg H.]

If you take the weight of the car, and a 50/50 weight distribution, you would get 1500 pounds per axle (roughly - 50/50 is rarely exactly equal down to the ounce except maybe in very high performance cars where that kind of precision really matters).

 

You also have to take into account the load inside the vehicle, which could throw off your weight distribution, depending on how that load is distributed.

 

If what you really want to know is how much impact force is delivered to the tires/speed bump, you're looking at a much more complex scenario.

 

Edit to add:

If you want to know how many lbs/in², you need to know the area of the contact patch (the part that's in contact witht he road at any given time) for the tires - so that formula would be:

 

[math]W_{lb/in^2} = \frac{1500lbs} {2(CP_{t}in^2)}[/math]

Edited January 13, 2015 by Greg H.

[jHoeplinger]

Thanks for your response, Greg.

 

Correct-- I'd like to know the impact force delivery to the speed bump. How would you go about this calculation? Please be detailed.

 

Note: Not an engineer, but moderately quantitative.

Assumptions:

1. Normal sedan, suspension, tires, etc.; weighs 3000lbs
2. Assume 50/50 weight distribution (I know it's not)
3. Driving 10mph
4. Speed bump is 1ft long, 1in high (I know, small)
5. **Assume each tire has a 100in² contact patch (10x10in).

Questions:

1. What would your thought process be? Please be detailed.
2. What's the right unit of measurement? lbs/square inch?
3. Considerations / missing information? Thinking the suspension might come into play... anything else? What would some good assumptions be?