OT: Biodiesel

On Mon, 21 Jan 2008 20:02:01 -0000, "Kim Siddorn"
Almost certainly they will work well into the infra red so will pick
up the number plate. In about 1968 my father was in the home office when they were testing materials for reflective plates, it was well before digital cameras so they were considering film, and one of the reasons for the bright yellow rear plate was for better contrast for the cameras they were intending to use.

From what I've read it was more to do with how they presented the system for some sort of legal compliance. The cameras cover multiple lanes but are only compliant if they catch the same car in the same lane, so shifting lanes between cameras made it impossible to prosecute, I expect they've resubmitted the system for multiple lanes by now.
Andrew Heggie
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Surely the speedo/tacho assumes you know the rolling radius of the tyre. That varies from unloaded to fully loaded, worn tyre to new tyre, and drift in the tyre pressure (yes I suppose we should all adjust tyre pressures for the load). I would have thought you could get 1/4" to 1/2" difference on a 12" radius, which would be 2 to 4%. Presuming it is calibrated when new, unladen, with the correct tyre pressures, then I would have thought that most of the error is skewed towards the speedo/tacho reading slightly high when running under 'real' conditions. The GPS does not suffer from this, so maybe someone should try laden and unladen and see if they can measure the difference - you only need a mile of straight road. Steve
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ISTR that early puncture warning systems worked by comparing wheel speeds. If one was consistently lower than the others, it was assumed it's radius had reduced due to lower tyre pressure. I'm not sure what the current sensing systems detect.
As for sat nav speeds, my speedo v sat nav reads about 10% low up to 50 the a steady 5mph low until my nerve runs out. The speedo is electronically driven analogue with 100,000 miles on it should that make a difference. The sat nav takes a couple of seconds to catch up when the speed changes. This is especially noticable when my enthusiasm is at work. As for bends however, 2 seconds makes very little difference. If the speed is high, the car cannot rotate through an arc small enough to make any real difference and if I'm driving like that the speedo is the last thing I'm looking at. If the speed is lower, the error due to resolution exceeds that of the speedo and, anyway, who cares how accurate these things are at 10mph. Much more useful are the warnings I get of speed camera locations. Not that I exceed the speed limit of course but they're only placed at accident black spots. Of course there is the theory that most of these accidents are due to drivers braking hard when they see the camera.
John
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John,
If you obeyed the speed limits you would not worry about the information of where the cameras are :-))
My Sat-Nav and speedo appear to change in unison, I see no delay.
Martin P

ISTR that early puncture warning systems worked by comparing wheel speeds. If one was consistently lower than the others, it was assumed it's radius had reduced due to lower tyre pressure. I'm not sure what the current sensing systems detect.
As for sat nav speeds, my speedo v sat nav reads about 10% low up to 50 the a steady 5mph low until my nerve runs out. The speedo is electronically driven analogue with 100,000 miles on it should that make a difference. The sat nav takes a couple of seconds to catch up when the speed changes. This is especially noticable when my enthusiasm is at work. As for bends however, 2 seconds makes very little difference. If the speed is high, the car cannot rotate through an arc small enough to make any real difference and if I'm driving like that the speedo is the last thing I'm looking at. If the speed is lower, the error due to resolution exceeds that of the speedo and, anyway, who cares how accurate these things are at 10mph. Much more useful are the warnings I get of speed camera locations. Not that I exceed the speed limit of course but they're only placed at accident black spots. Of course there is the theory that most of these accidents are due to drivers braking hard when they see the camera.
John
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wrote:

You know me Martin, I always obey the speed limits. The warnings are to alert me to areas of great danger so I can slow down even more.
I've noticed that my speedo and sat nav change in unison when I'm in a slow van as well.
John
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You obviously do not drive the sort of van I drive then :-)) I have yet to see whether technology and a 60's hot hatch go together.
Martin P
wrote:

You know me Martin, I always obey the speed limits. The warnings are to alert me to areas of great danger so I can slow down even more.
I've noticed that my speedo and sat nav change in unison when I'm in a slow van as well.
John
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wrote:

There ain't nothin' slow about the new vans....
Peter -- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk http://www.oldengine.org/members/diesel http://www.stationary-engine.co.uk
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Peter,
What you have to realise about John is that as he gets older its his perception of speed that slows down and as it was slow in his younger years it is now stopped relatively speaking. :-))
Martin P

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Well since this is a group for stationary engine enthusiasts, I suppose anything that moves must seem quick :-)
John
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