Speedo accuracy - GPS test!

[rt172]

Just been out to find out how accurate my speedo is once and for all using one of those handhelp GPS systems. I was expecting major inaccuracies and I was expecting it to get progressively more inaccurate the faster I went. I was suprised by the results:

Car Speedo GPS

30mph 27.5mph

40mph 37.5mph

50mph 48mph

60mph 57.5mph

70mph 68mph

80mph 77.5mph

90mph 88mph

And it followed through that at say 50mph on the car speedo, it would show 52/53 mph on the clock. No matter what speed the speedo said I was doing, it was always over reading by 2 to 2.5mph.

Didnt get a chance to try faster, but it did look like it was sticking to 2.5mph out all the way. Dunno about anyone else, but I find that quite interesting...! Itll also allow me to properly calibrate my AP22 now.

Rhys

 

[paddymph]

nice one, wonder how far out mine is?

 

[Ben j]

yep sounds right.. my digi screen readouts like that too

 

[Nice Try Good Bye!!]

Now thats srange as my mate had a GPS with him the other day, and my results were very accurate, 100mph was 100mph on the GPS, I dont know a lot about GPS but it gives the same reading as the speedo, maybe there both out!

 

[rt172]

Nope, if youre speedo and GPS read the same, youve probably got an accurate speedo. Remember that my car is 8 years old....needle is a bit shaky below 30mph!

Its bound to differ from car to car, but its interesting to see that it it fairly accurate on my car, just consantly out by the same amount.

 

[BRUN]

its the same on my RT.... about 2 or 3 mph out all the way...

 

[aaronc]

Interesting stuff rhys.

It looks as if its pretty consistent all the way.

 

[007]

Mine are about 4-5mph all the way

 

[rt172]

Carlos, out of interest have you checked yours with GPS too? Im going to go and play with the AP22 in a bit to try and calibrate it properly to the speedo now i know what the speedo is actually reading.

 

[Rich-D]

Quote: Originally posted by paddymph on 08 June 2003

nice one, wonder how far out mine is?

Ive got one Paddy, so you can try that...

 

[Tom_16v]

Interesting.

 

[007]

No GPS for me im afraid! - ive used two very unscientific methods

1st measured against my cousins RX7 (his speedo was calibrated) hard to tell but we knew it was at least 4 mph out from 30mph upwards - the needle wobbles like your Rhys below that!

2nd I have 2 Laser Guided signs LOL at each end of the estate that tell me my speed everyday!!

My speedo was 3-4mph now with the new tyres its 4-5mph! I thought it was supposed to be the other way about

I have only checked to 70mph as its a 30 zone the signs are in



Oh and while I have the autocar tests out heres their williams 1 accuracy differences:

Real MPH - Speedo

30 - 32

60 - 62

80 - 83

100 - 104

110 - 114

 

[BozVanDam]

My speedo must be waaayyyy out - it says Im doing 70 when I know for a fact I must be doing at least 120

 

[Nick Read]

Well my GPS lags a little behind the actual speed so you need to cruise at each test speed for a few seconds to let the GPS settle down. But mines a definite percentage, about 3%. Ive tested it at every speed up to about 120 but unlike factory standard cars which will read higher than actual speed if theres any error, because Im running 17s (and a different gearbox) the speedo is 3% slower than the actual speed. So on that almost top speed run in Germany with 140mph on the clock, that was in reality around 144-145mph.