I know it's strange and twisted, but some people do it! Here's my current motorbike:



Here's one I almost bought last weekend, but now won't be buying for various reasons:



The yellow one is 1/3 heavier than the red one, but 3 times as powerful. Can you express the power to weight ratio of the yellow one as a number, relative to the power to weight ratio of the red one?

The red one is better designed, more artistic.

How far off is this answer: 2.30769(yellow):1(red)?

a quick try gave me 9:4 which, if you want reduces down to 2.25:1

Ambulance people love organ donors....

You should have seen the cool injury I dealt with this weekend - I didn't know feet could point that direction.

/Bevin

Oh, yeah- my dad has a great story about a motorcyclist from when he worked at the Motor Vehicle Branch in Vancouver. Kinda along the same line as Bevin's

I was going to say to Bravus- more power to you! But somehow that expression turned into a pun or something LOL

Ed D has the correct answer, nice work. Yours is close, D. Allan, but a little high (and I agree, I love my little red bike, and it's a great looking machine).

Just as a quick explanation, the power to weight ratio is found by dividing the power by the weight. We could lay it out neatly in algebra and get 3p/1.333w (where p is the power of the red one and w is its weight), but doing it in fractions is more accurate because there's no rounding error (a third is a funny fraction that has an infinite number of terms if we make it into a decimal).

So it ends up being 3 divided by 4/3. An easy way of dividing with fractions is to 'invert and multiply' - turn one fraction upside down and multiply instead of dividing. So that gives us 3 times 3/4, which as Ed said is 9/4 or 2.25 or 2 1/4.

{ominous voice}there will be more of these{/ominous voice} ;)

And yeah, I've sustained one or two spectacular bike injuries myself. I know I'm by no means invulnerable, but I *am* significantly older and a fraction wiser, and now how to ride to beat the stats...

Yes, but that is the wrong calculation.

You CARE ABOUT the power-to-weight ratio of the bike+rider.

So - what is your weight measured in red-bikes(not kilograms) ?

/Bevin

not kg? :(

Heh, I think I'm about 0.68 red-bikes, plus or minus (and incidentally me and the Mrs together are more than one red-bike, which is one reason to upgrade to something bigger - the little one struggles two-up). That makes me about 0.5 yellow-bikes.

(and Gail, a little research would give you a number in kg, if you cared enough to do it)

nevertheless, for the purposes of our little calculation, your weight is a constant, and would have no effect on the original question.

True, although because it's added to the weight of the bike, and is a different proportion of the total weight in each case, it might change the answer if the question asked for the power-to-weight ratio of the bike+rider package...

Instead of the bike-only 9:4, you get a bike+rider 10:4, which makes the Yellow look even more likely to turn you into a donor :-)

/Bevin

All true, if power and weight were the only variables in the comparison... It appears that even if engine size and weight were the same between the two bikes, the yellow bike would likely outrun the red bike. Slightly better aerodynamics with cowling and fairing and although I can't tell for sure just from these pictures, slightly better geometry and rider position possible.

And some of the donor-cycle commentary comes a bit close for personal comfort at this point in time for me. I am recovering from dumping my bike almost 6 weeks ago. Not quite back 100% but much better. Broken collar bone, seriously bruised and torn ribs, and bruised hip. Full face helmet sacrificed itself doing its job, so I avoided any head, neck and face trauma. (I went down face first and slid on my head about 30-40 feet.)

Ride safe!

Tom

All the gear all the time, Tom: nice work, and best wishes on the recovery.

We do love the ambulance guys very much, and forgive them their teasing and occasional scolding... the stuff they have to see and deal with I would hate. And considering that the yellow bike does sub-11 second quarter miles standard from the shop, and I almost bought it for under 6 grand, there is plenty of potential for young guys to do themselves harm. Heck, there's potential for us old guys to do ourselves harm too, but we're a bit better at riding defensively and riding to the conditions. Stuff still happens though, as your spill shows.

What a terrible spill Tom. Hope you are doing well. We are privileged to still have you here on CA.

Unfortunately it isn't just the skill of the biker - there are some pretty stupid car drivers out there...

Tom - great choice of helmet! One of the first questions out of the ER doc's mouths is "were they wearing a helmet?"

/Bevin

Who cares about the math, the yellow bike is way more awesome looking dude.

The old vs young thing is so true! I had my motorcycle license when I was 16 before I had a car drivers license. Luckily I didn't have a fast street bike like the kids now run. I got myself in quite enough trouble back then with 200cc. As I recall all my spills back then were all due to my own stupidity, lack of experience, judgment, testosterone overload, or whatever. As an old guy, this is my second major spills in last 7 years, both due to car drivers' fault.

And the right gear saved a lot of skin for me and much more. At least one of the EMT's that came for me was a biker, so they were sympathetic.

And Redwood, thanks. It really is good to be around for awhile longer!

Tom

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