who has GPS speedometer? what R the actual speeds

[DucatiGary]

yes ive been bored over the past few days touring the country, sticking to ALL speedlimits everywhere.

I was curious as to how acurate the speedo was in the 911 so set my GPS system to just show speed.

32mph on speedo is 30mph on Sat Nav
43/44mph on speedo is 40mph on Sat Nav
54mph on speedo is 50mph on Sat Nav
75mph on speedo is 70mph on sat nav

I use Tom Tom Navigator and it is bluetoothed to my PDA/Mobile phone (XDA2s) just so you know :)

I was just wondering if there is anyone else sad enough to have done this in their porker and if these differences are the same across the board?

I tried it in the LandRover and at top end (on closed roads of course) speedo says 125mph! so this is what made me first try it as I dident believe the speedo, FYI sat nav showed 108mph when speedo showed 125mph.

Ducati - this was a little difficult, I had to set the sat nave up in my pocket (using battery powered bluetooth unit in other pocket) and put it on record ;) so I could see the outcome later.

speedo shown 178mph and sat nav shown max speed of 157mph.

bike and car test where both carried out on closed roads.

has anyone else been this bored before? or is this much of a geek?

Flame away should you choose to.

[DanH]

There was an article about speed accuracy in car and driver that refers to Porsche & BMW. Here you go :

www.caranddriver.com/article.asp?section_id=4&article_id=1906&page_number=1

[sundeep]

based on my GPS, the digital speedo in the trip computer is about 4% over reading

but the actual speedo over reads by 7%

[DucatiGary]

im gonna go take it to our german office as soon as possible as I havent visited them yet.

ill take the 911 over and see what top end it has mabe visit the ring? then ill post the results that are higher than legally alowed in UK as I am now a converted law breaker and I have learnt my mistakes

prolly wont be until sept but i will do it.

[flemke]

GT3 (II) Indicated 203; Actual 190
Carrera GT Indicated 217; Actual 206

[mutt k]

Not done it scientifically, but generally find speedo reads 5mph lower at most sppeds than Road Angel in my 911

[mightydquinn]

Every car I have tryed my tom tom in has done the same.
in the shogun 77 = 70mph
landcruiser 75 =70mph
RS 75 = 70mph
I didnt have tom tom when I had the boxster.
my land speed record is 131mph gps with over 145 on dash in my current car.

[verysideways]

I have checked mine and it reads a little over - when it shows 170km/h on the speedo it's actually doing 100mph (160km/h).

Amazingly, this is fairly consistent. Fastest i have been in the car was 176mph on the GPS, which was showing about 295km/h. 176mph = 281km/h

vs

[GuyR]

Varies from car to car as VMax events proves.

At last but one VMax, my Ruf GT2 indicated 201mph was actual 196mph (timing beam and GPS), so only 2.5% over-read. Hits the rev-limiter hard on longer autobahn stretches at indicated 212mph (so probably actual 207mph), because I could not see the point in paying for the longer 6th gear.

Wifes BMW 545i I ran at last VMax was showing 158mph on speedo (steady as at limiter) and timing gear showed 154mph - so also a co-incidental 2.5% error.

Skyline GTR R34 did 180mph on GPS whilst showing 180mph on speedo - utterly accurate.

However I have also been in cars with well over 10% speedo error.

>> Edited by GuyR on Wednesday 17th August 09:58

>> Edited by GuyR on Wednesday 17th August 09:58

>> Edited by GuyR on Wednesday 17th August 09:59

[GregE240]

At VMAX an indicated 153 in the SL was.....

153mph on the boards.....

Not sure if thats a good or a bad thing.

[DucatiGary]

I only performed the test to make sure I was getting to where i wanted to be, when on open roads, at the maximum speed.

therfore not holding up any other well to do road users as I am actually driving at the required speed.

and driving too slow is more dangerous than driving 10% over the speed limit.

thanks