0-100 KM/H times as reported by Dragy far off Audi's official claimed times

[Techniec]

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Dear fellow A8 drivers,

With reference to the topic matter, please allow me to quickly introduce myself and provide some background info. 

My name is Pieter, and in 2019 I became the lucky owner of a mint 2018 A8 50 TDI Pro-Line Plus (more or less full option). A couple of months after purchase, I took the car to ABT, who installed their tuning box, upping horsepower to 330 HP and torque to 650 NM. Now recently, I got myself this Dragy GPS device, which supposedly can measure 0-100 times (a.o) quite accurately. This weekend, I performed several runs, but was unable to clock a time faster than 7,1 seconds, which is quite a bit removed from Audi's claimed time of 5,9 seconds, and keep in mind that's the quoted time for the standard, non ABT-tuned vehicle ! Now granted, the A8 sits on winter tires (Goodyear Ultra Grip M+S), so I would assume that this could be the culprit, but would that really make that much of a difference ? If so, how much do you reckon it could (on or about) go faster on quality summer tires, like Pirellis ?

Looking forward to your replies, and many thanks in advance !

Best,


Pieter