Hi, I'm new to this forum. I have a early 2005 A4 Quattro 3.0 (same, I think, as the 2004 version) that I love and would buy again. No major problems, but I'be blown three taillights in just over a year. Anyone heard of a reason for this? The dealer says the bulbs are poor quality. Also, by setting the cruise control and then initilaizing the average speed display, I found out the the speedometer understates the true speed. At 60 kph, it's about 1 klph slow and at 120 kph it's about 5 kph slow. The dealer says the is for "legal liability reasons". Any thoughts on this?

 

Have you changed the size of your wheels?

Are you basing your speed off the "average" or off the analoge dial or off a radar gun?

Average is never going to be exact, too many factors come into play. Slopes, wind gusts etc etc etc so even with the cruise conrol on your speed varies slightly depending.

There is now way I could tell you exactly what my speed is based on the analog dial, maybe a rough estimate based on the needle position but that changes depending on your line of site, angle your looking at etc as well

 

Theres probably nothing wrong. If your tire size was incorrect itd be off by alot more. You speedo is incorrect by less than 5% at 100kph which is definatly acceptable. There was an article a while back in car and driver on speedo acuracy. I dont have the exact numbers but the americans were usally the closest with about 1% acurracy at 60 mph. The asians were in the middle with about 3% and the germans were way off at abou 4-5%.