Incorrect Speedometer - Golf mkVII?

[GolfVII]

I wonder if when calibrating the Mk7 speedo they used a wheel size ?225?/40 R18?

That is what is run on my Mk7.

Be interesting to know if anyone with a GTI, R-line pack or optioned a 18" rim on a Mk7 find their speedo to be correct?

[brad]

Almost without exception though they all drop back to an indicated 100 when the fixed speed camera comes up. So much for confidence in speedo recalibrating and sat nav readouts, heh? It seems like when speed really matters that the speedo readout is what really counts to most of us.

I pass a minimum of 4 HWP cars & a 2-way speed camera most work days. So many idiots that are at legal speed and they jam their brakes on when they see the HWP car or go through the 60kmh fixed speed camera doing 40kmh.

[par2]

I wonder if when calibrating the Mk7 speedo they used a wheel size ?225?/40 R18?

That is what is run on my Mk7.

Be interesting to know if anyone with a GTI, R-line pack or optioned a 18" rim on a Mk7 find their speedo to be correct?

I am checking this out today. I have GTI with 225/40 R18 tyres, only 4,500km on the odo. I have been using the same GPS (a Tom Tom) for 4 years, setting cruise control speed based on it. I see at least one fixed and two mobile revenue cameras each way to work every day, and have never been fined. Hence, I assume the GPS is accurate. Will post up the results when I have checked.

[MGV]

Yeah, i reckon the GPS speed is pretty good. I've been checking my Tom Tom against a free phone application called SpeedView with identical results (within +/- 1kph). Setting my cruise to 118 (110 on GPS) on the M1, been past plenty of coppers with radar with not an issue.

[Mountainman]

I have had a chance to check my speedo against my Garmin now over a much wider range of speeds and have found that it is not consistently 5% fast over the whole speed range. At speeds up to 110km/h it is 5% optimistic but over that it just reads 6km/h fast, all the way through to 160km/h. So 60=57, 80=76, 100=95, 120=114, 140=134 and 160=154.

[par2]

OK, checked this out over a range of speeds this morning. The base data is 2015 model Mk7 GTI DSG, 4,500 km (tyres are new), correctly inflated to manufacturer recommended pressures. Wheel 18 x 7.5, tyres 225/40 R 18. GPS is a Tom Tom Xl. At a steady 80 km/h on car, GPS showed 77 km/h. 90 = 87, 100 = 97, 110 = 106. This indicates an under read by the car speedometer of about 3.5% to nearly 4%. Trying the reverse, Car cruise set to 83, GPS showed 80/81. Car set at 93, GPS 90/91. Car set to 103, GPS 100 exactly. Car set to 114, GPS 110 exactly. So, a general "plus 4km/h" rule is what I will use from now onwards.
For interest, I did the same with my 2010 Mk6 Golf, with 17 x 7 wheels and 225/45 R 17 tyres, manual 118 TSI. It has a cosistent under read of about 5%. That is, car at 80, GPS 76, 90 = 86, 100 = 96, 110 = 105. This was using the same Tom Tom GPS. I ended up with a general "plus 5" rule for it. This has kept me "off the Radar", literally, for four years now.....

[knightsy]

Just got my new Mk7 110 Tdi Highline on Friday. Decided to check the speedo. I used the following advices from this thread:

"As for checking the speedo itself - if you don't have a GPS handy this works well at getting the uncorrected speed out of the car..

- Set the cruise control to the speed you want to check, say 100km/h
- With the vehicle at speed reset the trip computer
- Select the average speed readout
- Initially it will show dashes but after a few seconds the average speed is shown which is the uncorrected speed and actually quite close to GPS speed..

For cruise control at 100km/h I get 94km/h"

and

"On the touchscreen, press car, go to settings (the cog wheels in the bottom right corner) scroll to multifunction display, scroll to second bottom option to reset "since start". I have never tried it while the car is in motion though."

I did a check on the weekend and with cruise at 105kph I pressed OK in "since start" and got 105kph avg. Thought I must have done something wrong. I did it again today, twice. The first time I got 105 and so pulled over into a lay-by. Naturally the avg slowly dropped and when the road was clear I set off again with the avg at about 49kph. Up to 105kph cruise and when I pressed OK on "since start" it immediately changed to 105kph avg.

Is it possible that my speedo is accurate? Has anyone else got this result? Or did I do something wrong?

[lambertia]

Have you got a smart phone? Download a speed app. My car indicates 104 at a gps indicated 100.

[knightsy]

So I downloaded a speedo app (Speedview) and went out with a mate today. The results are: speedo 115, gps 110; speedo 105, gps 100; speedo 85, gps 80. All while using cruise. This last was done without cruise in traffic and we got speedo 63-64, gps 60.

All of which leaves me thinking that the average speed function is sampling the speedo, not the odometer. Unless of course I was doing the original checks incorrectly.

At least I know now how to proceed on my trip to Melbourne in a couple of weeks.

[popcorn]

I know the mk5 climatronic had a diagnostic function built in and one setting would show uncorrected speed. Unsure if the mk7 air conditioning system has a diagnostic function in it though