I did the same thing with my MK6 TDI Jetta and my car came with 225/45R17 as well. Are there any other way to improve this further. Please help. Thank you in advance.
When I got my 2010 TDI I discovered the speedometer read up to 10% high. With the help of this website and the speedometer fix page, I used VCDS to adjust the "distance impulse number". Unfortunately it could only correct 2-3%. I'm not sure what to do? I'm considering getting bigger tires when I get snow tires this fall. This is the common with BMW owners since BMW has the worst error of all manufacturer.
At 66kph my GPS showed 60kph. At 120kph, it was off by 9km. I used VCDS, but the default "distance impulse number" was 7. Unfortunately the largest value was 8. This did reduce the error at 120kph to 7.
In Canada the car comes with 205/55R16 tires. In the USA it's 225/45R17. This could account for a bit, but less than 4%.
I just cannot believe the European regulations are up to 10% of the true speed PLUS 4kph. Wow! This would allow a speed as high as 126kph instead of the real 111kph.