Speedo Calibration

Does anyone know if the 500's speedo is calibrated accurately and/or does anyone have the facilities to test such a thing? The ACPO guildelines say that a speed camera should be calibrated to the speed limit plus 10% plus 2 mph, meaning that on a 70mph motorway you'd need to do 79mph to get snapped. Anyone had any experience with this?

cheers
J

Most car's over read by 5-10% (depending upon wheather origional wheels are fitted) to allow for this. A Sat Nav or GPS locator is the best was to check how accurate a speedo is. Sit at a steady speed, say 70MPH, and Sat Nav will probably read something like 61MPH.

And don't take the speed cam guidelines for gospel, as thats exactly what they car, guidelines, do 31 in a 30, and you've broken the speed limit and the law

Hope this helps. Jon.

Remember that anything relying on a satellite hundreds of miles out in space is going to get confused by gradient.

Cheers

PD

I always wondered this. But I doubt it will affect it that greatly as it know's how high/low you are surly?

Soon speed cams wont exist neways

explain! ! !

because we'll all have trackers for road pricing

hmmm, tell me about it I hate the idea

The sats triangulate your position. When you are travelling up a hill the sats will only see you moving across the ground.

If you think back to Mr Pythagoras, you are travelling up the long side when the sats think you are travelling along the middle sized side.

Cheers

PD

Mine shows my height above sea level at any given time. I thought that this was always true as long as 3 or more satellites were used to determine your position.

Also remember that all GPS satellites are owned and run by the US Military and they dictate how accurate they are for civilian use.

In military use they are accurate to within 5m, civilian use not better then 25m, but more likely 50-100m.

This is partly why in aviation they are still not authorised for position reports say over the Atlantic where there is no radar and the info would be useful, therefore transatlantic flights are still controlled on old methods based on time, this will change as the need to put more air craft into the available airspace is needed.

You will find the often banded around thumb rule of 10% out is really urban myth. When testing accuracy of speedo's you find that if its 3-4mpg out at 50mph, its pretty much the same inaccuracy to 100mph. The speedometers are set up to always over read slightly to ensure roads suers are kept within speedlimits, hence why if caught you have pretty much no defense as the speedo would have been reading way over limit.

One way of checking is when on motorways you see all the HGV's are pretty much the same speed as each other on the straights, only generally annoying us normal road users when a hill comes up and they try and overtake with there 1-2mph advantage. Its because they are all limited to 56mph, and are all calibrated regulary therefore if you draw level with one check your speedo and GPS if available and see how close all the figures are.

We have an illuminated sign near us that flashes your speed at you when you aproach if your travelling over 30mph (some bodies silly idea to try and get you to slow down)
I dont know how accurate it is but at whatever speed i pass it my speedo's always reading 2mph slower.

I think you'll find it's nearer to 5m for civilian's also. How comes it knows when I'm at the end of a road and then tells me to left when I'm 20m away, what you say indicates it would need to say it atleast 75m away to make sure it tells me in time.

Jon.

In a word NO.

As stated already ALL GPS satellites are owned and run by US Military, they can and do move the satellites to areas they want to look at more closely when they want ie the are in conflict with someone like Iraq, they can also switch them off to civilians when they want, they did on 9/11 as possibility of remote detonation devices was suspected, think laptop, mobile phone, and GPS device linked together do you want them to be really accurate

There is a Russian system called Glonas which uses less satellites than US system but in many ways in more accurate as satellites have fixed paths.

Because of the reliance on US Military hardware Europe has considered setting up its own system now for a while, if it happens is anyones guess.

As yet GPS approaches (aircraft landing) have been trailed in UK but are known as NON PRECISION APPROACHES, unlike ILS (Instrument landing systems) or MLS (microwave landing systems) which are PRECISION APPROACHES, this is due to GPS not being accurate enough.

So if they were accurate to within 5m aviation would have made more use of this because aviation uses things way before the man in the street ever will.

They do use lots of trick software to try and overcome the deficiencies and these do work well to a certain extent, but this can sometime slow down the rate of information, I know if you accelerate fast or brake hard the GPS lags behind by someway, or if you approach say a slip road roundabout off a motorway you can get round the bend before its knows where you are.