I recently changed my front tyres from 195/55R15 ro 195/50R15. Not a massive change, but I tried adjusting the speedometer calibration in Forscan. Altered the wheel circumference setting and the one where you specify the tyre size. No effect, speedo is showing me about 10% faster than the GPS

I read on this forum and others about this procedure and needing to run "PCM  - Module initialization/relearn vehicle data" and "TCM - Module initialization/relearn vehicle data" but these dont appear, nor anything similar.

How do you do the equivalent for the Fiesta Mk7.5?

I tested another setting to turn off, DRL, but that didnt work either. All settings show my new values if I disconnect the laptop and reconnect so they are stored somewhere, presumably.

See the following thread which you may find useful:

https://www.fordownersclub.com/forums/topic/125865-change-size-size-currently-ford-focus-cc-has-205-50-17-can-i-replace-with-new-205-55-17/?tab=comments#comment-880200

 

The error of +10% seems very high for a car so new. The change of tyre size will have increased the error but only by typically 3%.

In order to get the error down to something more sensible it might be worth putting the wrong tyre size in to get the speedo more accurate.

This is a list of the errors induced by changing the tyres:-

Speedometer Difference

Speedo Reading	Actual Speed
20 mph (32.19 km/h)	19.35 mph (31.13 km/h)
25 mph (40.23 km/h)	24.18 mph (38.92 km/h)
30 mph (48.28 km/h)	29.02 mph (46.7 km/h)
35 mph (56.33 km/h)	33.85 mph (54.48 km/h)
40 mph (64.37 km/h)	38.69 mph (62.27 km/h)
45 mph (72.42 km/h)	43.53 mph (70.05 km/h)
50 mph (80.47 km/h)	48.36 mph (77.83 km/h)
55 mph (88.51 km/h)	53.2 mph (85.62 km/h)
60 mph (96.56 km/h)	58.04 mph (93.4 km/h)
65 mph (104.61 km/h)	62.87 mph (101.18 km/h)
70 mph (112.65 km/h)	67.71 mph (108.97 km/h)
75 mph (120.7 km/h)	72.54 mph (116.75 km/h)
80 mph (128.75 km/h)	77.38 mph (124.53 km/h)
85 mph (136.79 km/h)	82.22 mph (132.32 km/h)
90 mph (144.84 km/h)	87.05 mph (140.1 km/h)
95 mph (152.89 km/h)	91.89 mph (147.88 km/h)
100 mph (160.93 km/h)	96.73 mph (155.66 km/h)

Thanks, unofix.

Interesting, but doesnt relate to what I think is more of a forscan question that speedo accuracy. I have set the forscan to show my car is on the smallest diameter 14" wheels & tyres and the biggest 17" but the speedo shows the same discrepancy from the GPS. Also, I cant get other options to stick - such as the removal of daytime running lights.

There seems to be a process to force changes made in forscan to the TCM and PCM, (below), but those dont appear on mine.

https://forscan.org/forum/viewtopic.php?t=15994 

I see your problem. There is a guy on here who is very good at sorting ForScan issues called 'colinmcg71' normally you find in posts to do with Sync it might be worth asking him.

Thanks, unofix.

On 6/7/2021 at 2:48 PM, BeerJammer said:

I recently changed my front tyres from 195/55R15 ro 195/50R15. Not a massive change, but I tried adjusting the speedometer calibration in Forscan. Altered the wheel circumference setting and the one where you specify the tyre size. No effect, speedo is showing me about 10% faster than the GPS

I read on this forum and others about this procedure and needing to run "PCM  - Module initialization/relearn vehicle data" and "TCM - Module initialization/relearn vehicle data" but these dont appear, nor anything similar.

How do you do the equivalent for the Fiesta Mk7.5?

I tested another setting to turn off, DRL, but that didnt work either. All settings show my new values if I disconnect the laptop and reconnect so they are stored somewhere, presumably.

What are you using to connect your car to your laptop, I have found that trying to do it with the basic no switch for HS/ms can OBD2 interface won't work and any wireless one will cause this type of issue

Hi neb.

Using a switched USB cable, bought from ebay. Follow the instructions in Forscan to flip the switch.

I have read elsewhere about needing to disconnect the battery for 10 mins?