Viewing a single comment thread. View all comments

wenestvedt t1_jdiaf3q wrote

> "It appeared the driver of the motorcycle attempted to brake; there was over 50 feet of skid marks."

Just how fast are you going -- when the vehicle plus two passengers weighs under 500 pounds -- that you skid for fifty feet?

Out here in the 'burbs I see quads and dirtbikes on state roads and residential streets, and it makes me so mad because they are all, always, driven stupidly.

66

FailingComic t1_jdimueq wrote

Not very fast. You can lock up the rear incredibly easily and once its locked it doesnt slow you down well at all. Odds are if they managed to skid that far, their front brake didn't work. A lot of these dirt bike/atv guys bikes barely function.

20

fishythepete t1_jdj4ojk wrote

I mean there’s a reason you need to take a class to get a motorcycle license - it’s not the same as driving a car. Possible the front brake didn’t work, but also easily possible he grabbed a handful of clutch instead of brake in a panic, or that he was relying on back brake because front brake can be “scary” in an emergency stop if you don’t have practice with threshold braking.

23

wenestvedt t1_jdin34k wrote

The article also says that he got it, what, the day before or the weekend before? So probably inexperienced.

14

str8dwn t1_jdlstxf wrote

80-85% of stopping power (on bikes) is from the front brake....

2

FailingComic t1_jdlw4qc wrote

Yes it is. Which is why if you don't have one on your dumpster find dirtbike, you'd be likely to skid 50ft after locking your rear panic braking.

3

foolproofphilosophy t1_jdj21fi wrote

Small tire contact patch to start with plus off-road lugs that further reduce the contact area leads to poor breaking performance on pavement.

9

wenestvedt t1_jdkfods wrote

Ah, right: a small area of contact with those new, pointy tires, right? Makes sense.

2

foolproofphilosophy t1_jdklxqw wrote

Yes. And the rubber compound. Tires made for dirt are very different than tires made for pavement.

6

nomolosddot t1_jdjmmc7 wrote

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.

7

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.

1

moreobviousthings t1_jdknvg9 wrote

Tires made for dirt have big knobs of rubber, so not much touches the pavement at any given time. So skid marks are easy to make, but the bike won't slow down much.

3

wenestvedt t1_jdkprif wrote

Now that you mention it, I remember a book where they said a car has four big contact points but a motorcycle has two small ones "the size of your tongue."

2

str8dwn t1_jdlsq27 wrote

Ever hear of "knobbies"? They're dirt bike tires that don't do well on pavement. And you may have meant over 500 lbs. Not judging, just trying to provide accurate info...

Peace.

3