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nomolosddot t1_jdjmmc7 wrote

Reply to comment by wenestvedt in Family, friends mourn 2 killed in Cranston dirt bike crash by Addicted2GravyTears

The length of a skid mark left by a dirt bike depends on several factors, including the speed of the bike, the type of surface it is skidding on, and the condition of the bike's tires.

Assuming a dry dirt surface, a reasonable estimate for the coefficient of friction between the tires and the ground is around 0.5. To calculate the required speed, we can use the following equation:

v^2 = 2μgd

where v is the initial velocity of the dirt bike, μ is the coefficient of friction, g is the acceleration due to gravity (32.2 ft/s^2), and d is the length of the skid mark (50 ft). Solving for v, we get:

v = sqrt(2μgd) = sqrt(2 * 0.5 * 32.2 * 50) ≈ 40.3 ft/s ≈ 27.5 mph

Therefore, the dirt bike would need to be going approximately 27.5 mph in order to leave a skid mark that is 50 feet long on a dry dirt surface with a coefficient of friction of 0.5.

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wenestvedt t1_jdkfy08 wrote

I would have figured faster than 25-20 -- but when you're headed right for the wide of an SVU, you can't argue with the math.

A friend of mine laid down his bike in Boston like 20 years ago when someone turned in front of him next to the trolley tracks. He was wearing leathers and was fine, but our friend riding behind him was really ripped up -- and she was lucky he was already going so slow and knew what to do. There's often no good outcome when a bike meets a car.

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