Barmyclown

Don`t know where i read it they did a test using the proper measuring equipment when they were on about the zero tolerance at 30 mph, am pretty sure it was a policeman that said it, and it,s only 1 or 2 mph. And before you go on about if it underreads at 30 it must do at 60, I,ve seen mechanical test equipment underread low down the scale and over read further up then under read again further up the scale, while testing the accuracy of the scale. At the end of the day a speedo is driven by some sort of mechanical device so is prone to the same problems.

brihoppy

this could develop into quite an interesting debate, i accept your point but please consider this...as of 20 Oct 01 average GPS accuracy was:

PPS (Precise Positioning Service) <21m (Y code fix-military only)
SPS (Standard Positioning Service) <33m (C/A code-civilian access)

as you can see, even with PPS there is still quite an error in accuracy...readings upto a few centimeters can be acieved using a system call DGPS (Differential GPS), where several units are connected together...using SPS to measure speed is not the most accurate method when an error that great my be encountered...a laser can give a reading with better than 0.1 mph accuracy...

im not saying by that im the world authority on GPS, not by any means, but my training and information come from the Defence Hand Held GPS manual, and i am one of only approximately 150 trained GPS instructors in the whole of HM Forces...our accuracy is quite an issue when it comes to dropping bombs on people, well, usually...

good to see there are more GPS geeks out there, i look forward to your reply mate...

N1 SPAN

If GPS isn't accurate then how can it be used so accurately for data logging?? All the car mags are now using GPS rather than laser or trundel wheels behind the cars!

brihoppy

the thing with GPS is that although its a fantastic aid to navigation, it still has its limits, as described above...the facts about the system ive described arent exactly set in stone, but they are the figures quoted by Rockwell-Collins who make the military units...and they should know, they make space shuttles (even though they do blow-up occassionally), and all kinds of gucci stuff...so i would assume that given these errors, a speed reading might be quite innacurate...its not going to be a million miles away by any stretch of the imagination, but im just applying a bit of logic...!? thats not to say that your GPS receiver wont ever give you a very accurate reading as you can estimate the error from the Dilution Of Position and Estimated Positional Error readings on the units...the only reason i brought it up is if you want to quote speeds, i guess you want them to be as accurate as possible...? its just a point of interest thats all

Slick555

Have a standard MY00... and has clocked 146 and was still pulling hard. Then got a road angel 2 and at 100 it reads 94. Not so impressive.

And now for the maths...

Tire o/d x rpm x .002976 divide by your final drive ratio will give you your top speed.

Trust me. Having raced at Bonneville it works. Though on 4 wd scoobys I;m not sure... If you know your fdr you'll be accurate

fuz

bugeyes have the limiter set to 160
which makes sense as the speedo goes to 160
with 300lbs/ft this is achievable in mile 1 1/4
with the limiter removed the car should go to 198 with a 6 speed
any production/warranty prodrive car unfortunetly would be way short of these figures without a tek 3 or non oem ecu

bluepolarbear

A scoob will never go to 198 due to drag

billythekid

GPS can be an amazingly accurate system, for battlefield users the most important use of GPS is for an accurate position, thus a robust receiver in terms of build and processing is required.

However GPS can be used for much more interesting things, I have worked with it for some years (DGPS since about 97). I cant really comment in detail here but for civilian users of GPS their handsets will give more than accurate speed readings when all 12 channels are in use. Positional fix is still not going to be 100% accurate but it should be +/- 10m at worst. Over the next 5 or 10 years there are going to be some very very interesting developments in the system but it will probably be 2015 before its all working.

Regarding laser, it can be hugely accurate, but also hugely expensive and bulky. The lasers that are used by the police are quite cheap and are accurate by +/- 1mph. But laser is going to be the best if cost / size is not the problem.

brihoppy

yeah, i accept you point...it is the geographical position that is mostly affected, as stated above upto 33m for SPS, and you are right that when tracking 12 SVs, accuracy is better...i would still say that speed/distance measurement is possibly less accurate than other methods, but it is the most available to the general public...

im interested in what experience you have with GPS...i dont meet many people with knowledge of it...

virgin

anyone know what a blob 04 wrx with ppp would get as top speed ?

fuz

drag only comes into it if time is a factor

even quicker then if the runway in question has a cliff at the end of it as the newage cars are so heavey

lightning101

An audi RS6 plus - avant is the fastest unlimited speed estate car - 196mph, they only have limiters in mainland europe although 174mph on the plus.


I know this for a fact.

bluepolarbear

What?

Drag has nothing to do with time, it is a function of speed / aerodynamics and air density

Even dropped vertically of a cliff - drag will determine the speed - its why raindrops don't kill you.

Weight has nothing to do with speed of object when dropped - google search on Galileo