Accurate Speed of Golf

[PhilMart]

I know that there is a way that you can get the actual speed of your car using the Climate Control, but this stops after 100km/h.

As I was driving to Melbourne the other day I had time to wonder about how fast I was actually going and came across this .. sorry of posted before.

While going the speed you want, set cruise control and then reset the MFD by holding down the OK button on the steering wheel (for GTI - not sure about the others). This will reset your fuel, time engine running etc AND the average speed you are going. About two seconds later the average speed will be calculated and as you have not changed speed it will be your actual speed.

In my case the speedo was a tad under 120km/h on 110km/h speed zone and the MFD average speed was showing 111km/h. By way of a check, coming in from Adelaide on the freeway it shows you your speed and at the same speed as above I displayed at 108km/h.

Hope this can help someone fine tune their higher speeds to know "reasonably well" what speed they are doing. I expect but haven't tested that this speed correlates with the Climate Control speed but expect it would.

[idaho]

The climate display still works above 100 but it displays the digits alternately. The single 1 is for the 100 part of the speed and the 2 digits are for the rest.

[Maverick]

The error can be corrected to a certain extent. I have to do some more testing now with the 18's on but I suspect at the moment with the full correction applied that I'm about 4km/h out.

Info on the fix (requires vagcom/vcds) is here.

http://www.my-gti.com/140/volkswagen-speedometer-error-correction

As idaho pointed out the climate control speed still works above 100, the CAN bus speed is used everywhere except for the speedo readout so the speeds will all match up.

More info on the AC readout here.

http://www.my-gti.com/224/volkswagen-climatronic-diagnostics

[bazzle]

You need to use a GPS (Navman, in car unit etc ) to see your real speed.
None of the displays mentioned above are accurate. They only read corrected and canbus pulses.

The speedo error can be made less using VCDS and by moving needle.

Bazzle

[85turbo]

i would have to agree with bazzle on this one.

the best way to get accurate speed reading is with a GPS.
these will (in most cases) be much more accurate than any car's OEM speedo.

Jason.

[Maverick]

You need to use a GPS (Navman, in car unit etc ) to see your real speed.
None of the displays mentioned above are accurate. They only read corrected and canbus pulses.

I found that the GPS speed and the CAN bus speed were pretty well spot on with the 17" wheels, I haven't tested with the 18" wheels but it should be pretty accurate still.

GPS isn't always accurate, especially going up and down hills, turning corners, in the CBD etc. What is can do is allow you know what your needle is on 92 that you're actually doing 90 for example and it's useful for measuring under those circumstances where you can set the cruise control and read the GPS speed at the same time. Most GPS units are only 1Hz as well which makes them useless when changing speeds as it takes time for the GPS to catch up or slow down.

[85turbo]

GPS isn't always accurate, especially going up and down hills, turning corners, in the CBD etc. What is can do is allow you know what your needle is on 92 that you're actually doing 90 for example and it's useful for measuring under those circumstances where you can set the cruise control and read the GPS speed at the same time. Most GPS units are only 1Hz as well which makes them useless when changing speeds as it takes time for the GPS to catch up or slow down.

i agree completely, but on a freeway / highway, if you use vcds to calibrate the speedo to the GPS, it should then be very accurate ?
i mean, a km or two is not too bad, but as mine stands now the speedo reads 100, the gps is at about 92. that's a big discrepancy,
and i intend to have it corrected as soon as i get my hands on VCDS.

Jason.

[Maverick]

i agree completely, but on a freeway / highway, if you use vcds to calibrate the speedo to the GPS, it should then be very accurate ?
i mean, a km or two is not too bad, but as mine stands now the speedo reads 100, the gps is at about 92. that's a big discrepancy,
and i intend to have it corrected as soon as i get my hands on VCDS.

Jason.

You can only correct it so far, you'll probably get it to within 3-4km. I think Bazzle did the needle off trick to get it more accurate? But be stuffed if I'm pulling my cluster apart!

Look at the chart on the link I posted and it shows the accuracy of the CAN bus speed, gps speed, speedo speed before and speedo speed after the vcds fix.

[85turbo]

even 3 or 4km would be nice.
im not taking mine apart either !

Jason.

[bazzle]

17:, 18" , rim size makes do diff as long as rolling radius of tyre is the same.

http://www.miata.net/garage/tirecalc.html

They should all be ~25"

225/45/17 or 225/40/18 preeety close

Bazzle

[Creniac]

I've been testing lately and found this......

Speed limit 110km/h between Loftus - Wollongong.

I set the cruise at 120km/h on the dash Speedo, the speed through Climate control read 112km/h and the GPS read 111km/h

While driving that stretch of road there are the electronic speed signs telling you if you're over speed..... none of these picked me up until I set the cruise at 122km/h on the dash speedo.....

it seems the 10% incremental error programmed into our cars is about right.

[maca]

I'm sick of the way the speedo's out, I'm doing an indicated 100 while everyone's going 10k's faster than me!
I've also found that the AC speed is almost identical to the indicated GPS speed.

[scotty1991]

Use the GPS speed then, ignore the speedo

[85turbo]

Use the GPS speed then, ignore the speedo

That's exactly what i do.

Jason

[EUS GTIMK5]

Just had a long trip up country and agree that at about 120 on speedo equals about 110 on GPS. Also went through speed chacker and same result.
Does any one know is it is a constant 10% (i.e. accross all speeds)?