Man, you know it! Over 2/3 of motorcycle/car accidents are the fault of the car driver. We just need to clear the road of all the boxes on wheels! Motosafety

Yep, the helmet is not a fashion accessory and not a place to cut costs. My rule is that the degree of protection you put on your head is directly proportionate to the value of what you have in your head. Based on that simple rule, I see bare headed riders and must conclude that they have you-know-what for brains!

I have seen what happens to a cyclist wearing one of those stupid half shell fashion "helmets" after he did a face plant like I did. Not a pretty sight! In fact I did just that myself once in the dirt on my mountain bike landing a jump badly. Not a pretty sight. And being a lifelong bicyclist as well as motorcyclist (anything on two wheels! Wahoo!) I can testify to the value of bicycle helmets.

Tom

Bravus and Tom, I recommend you both trade in you motor- for bi- cycles - the kind you pedal. They are very healthy for one and I rarely hear of one getting hit by a car (it does happen of course.)

The power/weight ratio is variable and will increase more and more the more one pedals. ;)

Sound advise! As I said I have been a life long peddler.

But being safer should not necessarily be presumed. Until this most recent accident on my motorcycle, my bicycling injuries far outnumbered and surpassed in severity any I had had with motorcycles. Thousands of miles of bicycling do increase that probability. And I have hit and been hit by cars while bicycling. My collection of cracked bicycle helmets testify to the value and importance of a good bicycle helmet, even for, if not especially for, the weekend bike path warriors. Years ago I encountered an incident on a bike path involving only two bicycles that persuaded me to go out and immediately buy a good bicycle helmet. Two bicycles on a bike path collided at a combined speed of less than 20 mph - one man dead at the scene from severe head trauma, the other transported to hospital for treatment.

Bravus, to stay with the Algebra theme, my motorcycle slid about 35-40 feet on level dry pavement. How fast was I going?

Tom

Hmm, hard to say without knowing the frictional coefficient. It might be possible to figure out making some assumptions...

The accident reconstruction people would be able to make an estimate, but the calculation goes like this.

The normal force is m*g, where m is the mass of the bike and g is 10 metres/second/second.

The sliding frictional coeff of steel against concrete is about 0.5 - so the tangential force is half the normal force - and hence the tangential acceleration is about 5 m/s2

So what initial v, decelerated at 5 m/s2, has the object travelling 12 metres?

0.5 * 5 m/s2 * t * t = 12 m, so
t = 2.2 seconds, so v = 5 m/s2 * 2.2 s = 11 m/s

11 m/s is about 20 miles an hour

Am I even close?

/Bevin

That was a question I had when I was doing a bit of reading on accident reconstruction. There are basic formula for determining speed based on tire skid marks, but I wasn't able to find anything that suggested the degree of variation of friction coefficient for metal vs. rubber. The variable that is built into some simple skid calculator formula distinguish wet and dry pavement and degree of incline. So my assumption when I did the calculation was that motorcycle sliding on its side, metal on pavement, would be close to the same frictional coefficient as tires skidding on pavement, at least close enough for a rough speed calculation. While one would think that sheet metal parts would have less friction than rubber, some of the metal parts are ridged and angular digging into and gouging the pavement which would result in much higher friction. On balance I think the difference would be insufficient to skew the results significantly.

Tom