I'm a grave menace to society

[Mekk]

By ????

I may be wrong, but it looks as if barnett is saying that people defending the law or system in this argument are scared of living, scared of taking risks etc. That does not reflect my attitude towards biking and thus the feeling of misrepresentation.

Que? Care to explain how those two statements go together?

I don't really understand the confusion.

I'm saying this is about accepting responsibility for being caught when knowingly travelling over the limit. As opposed to not taking risks due to being scared of the consequences.

[MSTRS:Me]

Reads to me like you are saying you do runners when pinged AND yet take responsibility when pinged. Can't do both...

[Mekk]

Oh I see, sorry.

Nah I didn't mean evade as in doing runners. I meant avoiding them in the first place and keeping under the limit around them because I do exceed it at times too. What I'm saying is that getting caught is a risk we know of and take anyway...which means there's no point in creating a big fuss when we are caught.

[MSTRS:Me]

.... no point in creating a big fuss when we are caught.

Wot? This is KB, ffs. It's wot we do. Mostly.

[Mekk]

I know, it's what most bike forums do which was a point further up. SHRUG.

[rwh]

The basic speed from slide to stop calculation: v = the square root of (2*g*d*f)

v = velocity (metres per second)
g = gravity, which is represented by the figure 9.81 (don't ask me why, it just is)
d = skidded distance
f = drag factor or co-efficient of friction. (the typical NZ road has a drag factor of 0.6 - 0.65)

Example:

A vehicle skids to a stop leaving 29.5 metres of skid marks and the road surface has a friction value of 0.7g.

Initial velocity = the square root of (2*9.81*29.5*0.7) = 20.13m/s

To convert metres per second to kilometres per hour you multiply it by 3.6.

20.13 * 3.6 = 72.4kph initial speed.

This is the most basic formula used. There are many variations to it and you can add in other factors such as gradients plus or minus, whether all four wheels are locked up or only three etc etc. There are also calculations for factoring in ABS and for impact velocity based upon crumple damage etc.

Cool.

A couple of points I'd like to note, which no doubt crash investigators are also well aware of:

If the vehicle skidded to a stop, that implies it didn't hit anything - that would have slowed it down faster. So there's presumably a more complex formula which involves speed at impact, as estimated from damage to the vehicles etc.

This example also assumes the vehicle was skidding, right from the first moment of deceleration - I'm guessing it's much harder to see where braking started if it didn't immediately result in a skid. And judging the rate of deceleration without skidmarks must be really hard too - you don't know how hard the driver was pushing the pedal.

Merely defining what you mean by 'initial velocity' is tricky.

One of my nastiest close encounters was several years ago:
I was driving down the Ngauranga Gorge in Wellington at about midnight, in the wet, with hardly anyone else on the road. As I came round one of the corners, I saw a car way ahead near the next corner - no problem. The lights were bright - must be brake lights - ok, but back off a bit. That car is not moving very fast - start braking. That car is nearly stopped - brake hard. I ended up locking the wheels and releasing several times before coming to a stop, maybe 5-10m back from the car (which had stopped behind a truck that had rolled onto its side).

So what counts as my initial velocity? I was probably doing around 100, maybe a bit more, before all this started. By the time I started braking hard, I was probably doing around 70. By the time I locked my wheels and started leaving evidence, maybe 50. Of course in the end I didn't hit, so there was nothing to investigate (on my part; I don't know whether the cops were involved for the truck). Anyway - what counts as my initial velocity? 100-120? 70? 50?

What I do know is that I don't drive down the Gorge at 100 any more - especially not in the left lane, with its reduced visibility round the corners.

Richard

[swbarnett]

He was proven to be over the speed limit, which under legislation is illegal and thus he was guilty.

Technically you are correct. That's how the right to innocence is subjugated. I was extrapolating and saying that a speeding ticket is in essence an accusation that you are a "grave menace to society".

I haven't abused anyone your post was crap though.

Sorry if I over-reacted. I appreciate that this type of argument can be frustrating from both sides. It felt like a knee-jerk reaction with no substance.

Your explanation of the skid/speed formula was very interesting. I've managed to do a full emergency stop from 50km/h in the cage with the wheels only losing traction for the last metre or so. According to the skid marks I would only have been travelling at 3.7km/h on the same road in your example. This is what leads me to believe that skid marks aren't always a good indicator of the initial speed of the vehicle. I run stickier tyres than most with standard brakes so they don't skid too easily.

[spudchucka]

If the vehicle skidded to a stop, that implies it didn't hit anything - that would have slowed it down faster. So there's presumably a more complex formula which involves speed at impact, as estimated from damage to the vehicles etc.

Yes, that calculation gives you the speed from the start of the skid to the stop. Where that eventual safe stop has been brought forward by the vehicle hitting another object the crash investigator will take into consideration many more factors, including damage to vehicles.

However if you look at the skid to stop calculation as a bench mark figure that says the initial speed of that vehicle was "no less than", then that gives you a starting point.

The experts use all sorts of flash as gear and science to work these things out, forensic mapping, computer programmes that analyse the surveyed skid marks and location of each vehicle post crash and can reconstruct the pre crash circumstances etc etc.

[spudchucka]

Your explanation of the skid/speed formula was very interesting. I've managed to do a full emergency stop from 50km/h in the cage with the wheels only losing traction for the last metre or so. According to the skid marks I would only have been travelling at 3.7km/h on the same road in your example. This is what leads me to believe that skid marks aren't always a good indicator of the initial speed of the vehicle. I run stickier tyres than most with standard brakes so they don't skid too easily.

When the crash guys are doing their sums they will test the drag factor for the road surface in a similar vehicle and with similar tyres fitted in order to get the most accurate figures for that particular road surface and vehicle type.

[boomer]

When the crash guys are doing their sums they will test the drag factor for the road surface in a similar vehicle and with similar tyres fitted in order to get the most accurate figures for that particular road surface and vehicle type.

you mean he licks his fingers and holds it in the air?

[swbarnett]

I may be wrong, but it looks as if barnett is saying that people defending the law or system in this argument are scared of living, scared of taking risks etc. That does not reflect my attitude towards biking and thus the feeling of misrepresentation.

Indeed I can see were you're coming from in this. I did have the impression that you were more on the fearful side than the last couple of post would suggest. My apologies. It seems that you are somewhere nearer the middle.

[scumdog]

Indeed I can see were you're coming from in this. I did have the impression that you were more on the fearful side than the last couple of post would suggest. My apologies. It seems that you are somewhere nearer the middle.

It goes both ways - at times I think YOU (among others)are totally on the other side.

And at times it's hard to tell trolls from real curiosity/lack of knowledge, for that reason (and a bit of experience with KB) I tend to err on the 'ah, probably a troll' side of things.

[spudchucka]

you mean he licks his fingers and holds it in the air?

Or:

Pick a number and double it, divide by 3, add 47, multiply by your age, stand on your head, scratch your arse, have a cold pie and warm beer, run three kilometres, turn around five times and then multiply your answer by the number of peas and carrots your throw up.

[rwh]

And at times it's hard to tell trolls from real curiosity/lack of knowledge, for that reason (and a bit of experience with KB) I tend to err on the 'ah, probably a troll' side of things.

One also needs to be open to the possibility that the other person is actually right - or at least arguing rationally ... I may have been reminded of this recently ...

And when one is trying to work out whether the person who has just pulled one over for speed in exess of the posted limit is a troll or just ignorant, displaying either attitude seems likely to result in less favourable discretion being used ...

Richard

[Patrick]

Roughly half the drivers on our road would be of an above average skill

We wish it was as high as that... Funny.... Roughly half wouldn't even make average, let alone above average...

Or:

Pick a number and double it, divide by 3, add 47, multiply by your age, stand on your head, scratch your arse, have a cold pie and warm beer, run three kilometres, turn around five times and then multiply your answer by the number of peas and carrots your throw up.

Ummm.. show me the formula?????