Speed

[Pelicanbill]

We turned on ye olde Sat Nav and it went 'Quack!' (or whatever) to announce an impending speed camera. According to the speedo on Surf, 29mph = 30mph on Sat Nav

When driving my Mitsubishi Spacestar ... 27mph= 30mpg on Sat Nav and at 70mph we actually doing 65!

I assume the satellite thingy accurate. The Surf calibration seems remarkably accurate ..... I like my Surf, it seems nothing fazes it (apart from my driving) and it is exceedingly generous when it comes to flinging oil all over the place


My Surf is in the menders at the moment

[Tallyman]

I found mine to be very accurate at 30 mph as against the satnav. After that it's about 10% fast, showing about 76 on the speedo when the satnav says I'm doing 70. It will be interesting to see what difference a new set of tyres will make, as mine are down to about 5mm all round.

[puddlesurfer]

I drove Dixie to pick up his wheels a while back and my speedo was reading about 70 but his satnav said 65

[Calos]

Sat nav would be the most accurate for speed... so I'm told by the police.


peace
cal

[markp2]

Same % error with my Gen 3. Satnav 70mph is about 75 on the speedo at the moment.
I have noticed on other cars that tyre choice and tread depth makes quiite a difference to the speedo error.
My Alfa 156 speedo read completely accurately on new BF Goodrich tyres but over read by 5 mph at 70 when on worn Michelins. The rolling circumference of the tyre gets smaller as the tread wears and more revolutions per mile are needed.

Given the greater circumference of a Surf tyre and the greater tread depth when new there is likely to be even bigger difference in accuracy.
Who's going to do some maths to work out the changes?
Cheers,
Mark

[dieselboy]

Doesn't sat nav encounter more error % when you are travelling on a slope, e.g up / incline or down / decline a hill?

[lord_flashart]

Mine's the opposite, when the speedo says 65 I'm doing 70!
When I put the 33's on it'll be worse but I'm going to change the speedo face over to the 115mph one from the 105mph one I have and all will line up properly!

Thanks,

Ray.

[yoshie]

Mine's the opposite, when the speedo says 65 I'm doing 70!
When I put the 33's on it'll be worse but I'm going to change the speedo face over to the 115mph one from the 105mph one I have and all will line up properly!

Thanks,

Ray.

In a 2.4 even 65 is a lie, fit a vespa speedo that should do

[markp2]

Dieselboy. Interesting comment about the slopes. My Garmin Quest seems to compensate for this, but it is not a 'car' type one. It is designed for multi activities and I use it on off road motorbike, boat and horseback as well as for general road navigation.
I don't know how this sort of thing is programmed, but mine appears to have the mapping loaded in a 3D format.
Thanks,
Mark

[TFB]

The GPS transmissions let you locate yourself in 3 dimensions, so the sat nav should be able to compensate for uphill/downhill etc. The Sat nav also does a bit of averaging with the signals and positions and there is a bit of a delay before the displayed speed catches up with your real speed.

Still, a sat nav is going to be far more accurate than your speedo, especially when travelling at a constant speed. Though with 265/70/16's my speedo is pretty much spot on.

Regards

TFB

[Albannach]

Boring... I thought this was an ampheramines thread.