# Deceleration of Vehicle off pavement

How would I calculate the deceleration of a vehicle (ATV), wheels locked, on dirt? How long would it take to halt? How fast is it decelerating?

I used this calculator, but it seems incorrect for a light vehicle.

• ^I might add that our vehicle is under 700lbs, and a max speed of 35mph. Also, according to that calculator, no matter what the mass, a vehicle going 35mph will stop in about 62 feet (.7 COF)...does that mean a train will stop in 62 feet as well? Commented Mar 26, 2012 at 20:24
• Commented Mar 26, 2012 at 20:46

## 1 Answer

The calculator assumes a constant coefficient of friction which is probably a good approximation within a certain range of weights for rubber tires on a hard surface. For a train, metal on dirt would probably have a very different coefficient of friction, and also the weight of the train would likely deform the surface, so this analysis would not apply. Likewise, for a vehicle stopping wheels locked on a soft dirt surface, there will be a digging in effect which will be different than stopping on asphalt.

• Before we start fights over this again, perhaps it would be better to call it the coefficient of rolling friction? Commented Mar 27, 2012 at 6:27
• @AlanSE: The wheels are locked. Commented May 26, 2012 at 3:26
• I don't see why the coefficient of friction model should work for dirt. You need to measure, it might be strongly velocity dependent. Commented May 26, 2012 at 3:28