At 70 the gps shows 71 and at 85 my gps is 90mph !!!!!!!



[Edited by sammyh - 12/3/2002 12:07:18 PM]

In theory, a gps obtained speed is more accurate than a speedo...

So, in the interests of interest, I compared my indicated speedo in PTMW! against my GPS

GPS --- Speedo

30 ----- 34
40 ----- 44
50 ----- 54
60 ----- 66
70 ----- 76

Now please don't use this as a guideline as all speedos vary in accuracy & I won't be held responsible for anyone getting a nicking on my "advice" but this is particular to PTMW!

However, it is quite interesting that when you "think" you're doing 70, you're probably only doing 64/65 or something like that. At an indicted 80, like as not 72/73, 85 for 77 ish etc etc.

So people that get knicked for 100 are likely to be @ 110+ indicated...

Next time I go to a trackday, I'll bring my GPS along & people can get a true idea of the speed they can get down the main straight ;)

:)

I have not got the balls to look at the GPS when the speedo is showing 150 ;) (private road etc etc)

That's why I have little sympathy for people who get nicked for speeding in or around town. Given the margin for error the police usually allow (speed limit + 10% + 3mph) combined with inaccuracy of the speedometer, there is no way anyone can seriously argue they didn't realise they were speeding.......

Found your charger then Puff :D

Ian

Is that a speed-trap one?

They don't want people getting caught when being a defense against cameras, so I would imagine err on the side of caution...

Ian

Always had it at home - just forgot to charge the night before :rolleyes:

Wot GPS have you got? I'm thinking of getting one myself.

That's not the case in West Yorkshire. Their tolerance is 10% +2mph.

APCO is 10% + 2 but that is just a "guideline" so anything above a speed limit is a potential nicking.

Carl

My BT GPS thingy & an iPaq :D

:)

sorry for being picky ;)

My StreetPilot showed that my old STI Type-R was doing 85mph at an indicated 100. :eek:

The Jag is better, only under-reading by about 4-5mph @ 100mph. Our Pug 306 is about the same, maybe slightly more accurate.

James,

sorry I disappeared at bedford whilst you were hunting for a charger for your GPS gizmo. As you can imagine we had a fair bit on our plates on Saturday.

Maybe next time eh ???

Ian

PS: I think we are going to take the Westi to donington on sunday - if you are up I'll try take you out for a quick spin (hopefully not literally ;) )

I think speedos (not the trunks ;)) are supposed to only over read and never under read. So if you get caught for speeding you are going way way faster than the limit ??

The rules on speedometer accuracy are +/- 10% of actual speed so they are allowed to read low. Hence the +10% when getting nicked for speeding, if the police nicked you for a speed in that 10% tolerance band then they'd have much more trouble proving your guilt in court.

James, those figures are very close to mine with a Road Angel and 17in wheels. Road Angel claim their speeds are accurate, but I previously had an Origin Blue-i and that was much closer to the speedo reading.

Also remember that 215/40x17in tyres are 1% or so smaller than 205/50x16in.

When I was at Bruntingthorpe recently ;) an indicated 130 was an actual 122.

Cheers,

Richard.

Hoppy

As I was blasting down the back straight @ BA @ an indicated 130, I was thinking to myself it was probably only 115-120!!! (Had ran out of battery when I was playing) Sometimes you don't want to know!

Puff, that's close to mine with Road Angel too. Std 16's on MY00.

F

Reffro,

I don't think speedos are allowed to underead. IIRC, the rule is usually stated as:

"+/- 10% but are not allowed to underead"

Which basically is a contradiction as it should really read "+10%" :rolleyes:

Matt :)

My Blue-i reads 2 mph slower than speedo all through range even up to 130 ish couldn't look much after that.
Gaz

when i was at power engineering having a tech2 fitted mervin had the deltadash connected to my car and according to him the deltadash was saying at 100mph my speedo was reading 104mph which apparently with 18"wheels (the bigger the wheels the less speedo inaccuracy) is about right

when i was at santa pod last i looked at my speedo as i passed the finnishing line and it read app. 107mph when i got the readout it said i was doing 103 so going with the 4% theory

My Origin Blue tallys exactly with my speedo, down to a single mph. Guess we're allowed +/-10% but it can still be dead on sometimes.

Watch out with the Street Pilot. Don't forget that it holds your highest speed in memory, so don't forget to reset after a blast in case plod takes a look :-)

Mike

Mike,

In the unlikely event of them getting the chance to check this, you would tell them that was the fastest you got up to last time you were on track. ;);):D:D

Matt :)

I have a streetpilot V - very good device. The warning above is not all - yes, it holds your fastest speed but, it also hold data every 4 seconds for your trip.

you can get this out using a computer - the data shows the elevation, start point co-ords and the end point co-ords as well as the average speed over that few seconds. so a quick overtaking manouvre on a motorway where you've been doing 70mph all the way shows up!!!

this is enough evidence for a conviction...

given that insurance companies are trying to move to a model whereby customers will have GPS units attached to the car for pay-as-you-drive insurance... this may even be mandatory for young drivers in years to come...

rd
wrx wagon

Hmm, I think that the Street Pilot allows you to not record doesn't it? I'll have to check my manual now!

BTW, is there a database of Gatso's / Black Spots etc for the Street Pilot? Seems such a shame to have to buy another GPS device too. How many gadgets does one have to lock in the boot these days? :-)

Cheers!

Mike

PS. Just got a 128Mb datacard on eBay at half price this week!

BuRR,

Not being picky either but I have been made to understand that in Northamptonshire its plus 2mph only. The 10% bit does not exist.

If true, be afraid, be very afraid...

WB

I have read that the standard speedos can read anything upto 10% higher, but they cannot by law be allowed to read lower than the actual speed you are traveling.

Remember that your speed is a factor of the rolling circumference of your (driven) wheels. Therefore, brand new tyres (with deep tread) running at higher pressures will give a higher speed for a given engine speed etc. This could be furhter exagerated if aftermarket wheels/tyres are fitted that have a slighty different (and by that I mean larger) rolling circumference. It is concievable that as speed increases rolling circumference increases too (look at a video of a top-fuel dragster if can't figure this one out!).

In summary, mechanical speedometers are never going to be accurate (all the time) and speed limits are gay (but you knew that already!).