Average Speed Cameras - What's the trick?
Discussion
streaky said:
jondude said:
I can't remember exactly how it works, but isn't there something about changing the tyre sizes from the official recommended is also liable to change the speedo readings?
Smaller diameter wheels and lower profile tyres have a lesser rolling radius than the standard wheels and tyres for which the fitted speedometer is 'calibrated'. Larger diameter wheels and higher profile tyres have a greater rolling radius.The first will have the effect of making the speedometer read higher than the actual speed because the wheels travel a shorter distance in a set time, the second will make the speedometer read lower than the actual speed, as the wheels travel a longer distance in a set time.
The above is true for speedometers that are driven from the gearbox/hub. If the speedometer is driven from a sender on the wheel rim, it will read correctly.
Streaky
streaky said:
jondude said:
I can't remember exactly how it works, but isn't there something about changing the tyre sizes from the official recommended is also liable to change the speedo readings?
Smaller diameter wheels and lower profile tyres have a lesser rolling radius than the standard wheels and tyres for which the fitted speedometer is 'calibrated'. Larger diameter wheels and higher profile tyres have a greater rolling radius.The first will have the effect of making the speedometer read higher than the actual speed because the wheels travel a shorter distance in a set time, the second will make the speedometer read lower than the actual speed, as the wheels travel a longer distance in a set time.
The above is true for speedometers that are driven from the gearbox/hub. If the speedometer is driven from a sender on the wheel rim, it will read correctly.
Streaky
Both methods (link to gearbox and sender on the wheel) simply count revolutions of the wheel and then using an assumed wheel circumference derive a speed.
If the real circumference is larger than the assumed circumference then the vehicle will travel further per revolution than is assumed and the speed will be underestimated.
I could be wrong if the transducer that sends the wheel revolutions to the speedo is intelligent and can recognise different diameter wheels and thus compensate - but this still leaves the problem of tyre ratio.
I once fitted a cycle speedometer and was required to set the wheel size for accurate speed indication.
Russ
E Ponym said:
streaky said:
jondude said:
I can't remember exactly how it works, but isn't there something about changing the tyre sizes from the official recommended is also liable to change the speedo readings?
Smaller diameter wheels and lower profile tyres have a lesser rolling radius than the standard wheels and tyres for which the fitted speedometer is 'calibrated'. Larger diameter wheels and higher profile tyres have a greater rolling radius.The first will have the effect of making the speedometer read higher than the actual speed because the wheels travel a shorter distance in a set time, the second will make the speedometer read lower than the actual speed, as the wheels travel a longer distance in a set time.
The above is true for speedometers that are driven from the gearbox/hub. If the speedometer is driven from a sender on the wheel rim, it will read correctly.
Streaky
Both methods (link to gearbox and sender on the wheel) simply count revolutions of the wheel and then using an assumed wheel circumference derive a speed.
If the real circumference is larger than the assumed circumference then the vehicle will travel further per revolution than is assumed and the speed will be underestimated.
I could be wrong if the transducer that sends the wheel revolutions to the speedo is intelligent and can recognise different diameter wheels and thus compensate - but this still leaves the problem of tyre ratio.
I once fitted a cycle speedometer and was required to set the wheel size for accurate speed indication.
Russ
hora said:
I'm under the view that its like the 'follow the sheep' mentality..
After a while of seeing what seems like 'everyone' else driving quicker, you too pick up your speed. Its a group/tribal mentality thing that probably goes back to primeval thinking.
So these people that do sail through average cam's- do you ever hear from them? Do you get a note from them saying 'ah nuts I did get 3points you know when I passed you the other week'?
No.
What about hearing from friends etc who were stung? No, TBH if I picked up 3 points I'd hardly brag or boast about it. Normal people don't.
I just hit the cruise control and sit it out. Unfortunately a work colleague did that on the M1 works a while ago and set to 50. Forgot about the drop to 40 part way in and received a fine.After a while of seeing what seems like 'everyone' else driving quicker, you too pick up your speed. Its a group/tribal mentality thing that probably goes back to primeval thinking.
So these people that do sail through average cam's- do you ever hear from them? Do you get a note from them saying 'ah nuts I did get 3points you know when I passed you the other week'?
No.
What about hearing from friends etc who were stung? No, TBH if I picked up 3 points I'd hardly brag or boast about it. Normal people don't.
Since limiters have been fitted to several of our vans I find that lack of time and rushing has disappeared. It is almost enlightening. We cannot get anywhere faster (not that we broke any laws....). Plan ahead, leave in plenty of time and we get there cool calm and collected.
In the car, cruise control 70 (or 50 as dictated) and as its an older car it only has the time/distance thingy and a stop or two for the usual only adds a few minutes to the arrival time (I don't personally have a sat nav and never will). I still get there within minutes of my estimate when starting out.
In the car, cruise control 70 (or 50 as dictated) and as its an older car it only has the time/distance thingy and a stop or two for the usual only adds a few minutes to the arrival time (I don't personally have a sat nav and never will). I still get there within minutes of my estimate when starting out.
Given the accuracy of most speedos and the general guidelines that have been published (10%+2) you should be able to pass a 50MPH SPECS zone at a GPS 57MPH without trouble. On a speedo this is likely to look around 65MPH or so. I would imagine that the tolerances for SPECS aren't that great so the margin for error for a reliable conviction is also high (possibly as high as another 10%). I wouldn't be surprised if you could pass most 50MPH SPECS zones at up to a real 65MPH without a problem. Remember it's an average so to secure a conviction you'd have to be going in excess of 65MPH (real) for the entire segment length. If you dropped to 60MPH for just a few seconds, this could buy you some time at 70MPH without pushing your average.
If you're travelling at a 50MPH (speedo) you're miles and miles away from the conviction limit. The average part works in your favour too.
There's a reason why hardly anybody has been convicted by SPECS, the limits are set high and it's actually hard to push an average higher than them on anything less than an empty road.
typed in instead of on...
If you're travelling at a 50MPH (speedo) you're miles and miles away from the conviction limit. The average part works in your favour too.
There's a reason why hardly anybody has been convicted by SPECS, the limits are set high and it's actually hard to push an average higher than them on anything less than an empty road.
typed in instead of on...
Edited by _rubinho_ on Monday 6th September 12:08
_rubinho_ said:
If you're travelling at a 50MPH (speedo) you're miles and miles away from the conviction limit. The average part works in your favour too.
There's a reason why hardly anybody has been convicted by SPECS, the limits are set high and it's actually hard to push an average higher than them on anything less than an empty road.
I would hate to put that to the test. A friend brought his sat nav along one day and my car is pretty bang on. The Mrs Festa is miles out when it was following one of our tacho vans at 70 (she was showing 85) and the tacho vans are bang on +/- 1mph.There's a reason why hardly anybody has been convicted by SPECS, the limits are set high and it's actually hard to push an average higher than them on anything less than an empty road.
People being done, see my link on page 1. People are being done. Link from page one
PS. Thinking about my collegue what got done in the 50 then 40 bit. Might have been a gatso?
jmorgan said:
_rubinho_ said:
If you're travelling at a 50MPH (speedo) you're miles and miles away from the conviction limit. The average part works in your favour too.
There's a reason why hardly anybody has been convicted by SPECS, the limits are set high and it's actually hard to push an average higher than them on anything less than an empty road.
I would hate to put that to the test. A friend brought his sat nav along one day and my car is pretty bang on. The Mrs Festa is miles out when it was following one of our tacho vans at 70 (she was showing 85) and the tacho vans are bang on +/- 1mph.There's a reason why hardly anybody has been convicted by SPECS, the limits are set high and it's actually hard to push an average higher than them on anything less than an empty road.
People being done, see my link on page 1. People are being done. Link from page one
PS. Thinking about my collegue what got done in the 50 then 40 bit. Might have been a gatso?
from link said:
When you consider that more than 21 million vehicles have passed through this stretch of road since the camera went live (approx 110,000 a day), this figure represents a tiny fraction of traffic driving through.
2379 NIPs have been issued out more than 21 million vehicles. The statistics themselves bear out that hardly anybody has been done. Those odds are longer than being struck by lightning! With the forward facing cameras on the A14 near Cambridge I watched a car tailgate someone past the first camera, disappear into the distance 20-30mph over the speed limit and tailgate someone past the second camera. 
So as well as not getting caught speeding the driver was also not caught driving dangerously.
Average speed cameras are as bad at Gatso's in the "drive at twice the speed limit and brake a hundred Yards before the camera then drive like a tw@ again as soon as you pass it stakes".
No camera will ever take the place of a Police officer on the roads.
So as well as not getting caught speeding the driver was also not caught driving dangerously.
Average speed cameras are as bad at Gatso's in the "drive at twice the speed limit and brake a hundred Yards before the camera then drive like a tw@ again as soon as you pass it stakes".
No camera will ever take the place of a Police officer on the roads.
hora said:
You need to get people into the mindset and keep it there for the duration IMO.
I wouldn't want to be surveying or planning a new section of tarmac with an idiot doing 100mph with a plastic cone between me and him.
The only mindset that gets people into is one of 'there are no roadworkers, I may as well do 100mph'.I wouldn't want to be surveying or planning a new section of tarmac with an idiot doing 100mph with a plastic cone between me and him.
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