My experience is usually most VAG vehicles show excess speed. If you want more accurate speed, it is possible to adjust it using the RossTech tool.

 

I noted the speed by speedometer is consistently higher than measured by GPS/Waze by 8 -10%. First, I thought that winter tires I installed (Dunlop 245/45R19 instead of stock Pirellis 275/40ZR19) might be responsible...I guess not (the difference is negligible based on the tire size calculator). Is it too difficult to adjust the speedo using the RossTech tool?
Thanks very much in advance!

 

 

just fyi, my own gt and the 3 others I test drove ALL were 5 mph faster indicated speedometer readings than GPS (2 different external gps devices and 1 phone... One is garmin glo on my car, which I've updated the nav and added touchscreen, other 2 times were iphone 7+ gps and 3rd was a garmin nuvi the seller had velcroed just above the navi screen, lol)

Perhaps it's a safety or marketing thing but I found it odd they were all off the same amount. All cars on stock tires/rims.

 

Most all cars (if not all) read higher speed than actual. I remember back a few decades ago, one manufacturer (I think it was Audi or VW) displayed speed that was less than actual. But, as hundreds of people got speeding tickets because they were speeding, but sure they weren't because their speedometers (or cruise controls) read less, they began class action suits against the company.

Of course, experts were hired and verified that ALL the speedometers (calibrated at the factory that way) read lower than the actual speed. Since then, auto mfgrs are in a less litigious situation by going the other way and calibrating the speedometer to read a few mph higher than actual.

 

Speedo reads 6 mph faster than actual speed. Consistently.
2005 GT

 

 

So my GTC Speed is supposed to be good for 200 mph and since the speedo is reading faster than accurate (like they all do) maybe its not really a 200 mph car? If its not then they may have cheated me and I would be due compensation for lost bragging rights?

 

I hear ya man!

Maybe next time you're going 200 you can let us know if it reads 200 or 205?

 

 

So any ideas on how to solve for this?

I think I am having the issue, primarily evident by my spoiler deployment that should be at 95 mph. My spoiler deploys only at 100 MPH on my cluser

2007 Bentley GT

 

You can code it, need someone who did before.