RPM/speedo don't match... (more)
 

Taner posted this reply earlier. I checked my RPM/speedo matchup and lunch and mine does not match.
gear 1: 3kRPM=15mph, 4kRPM=20mph, 5kRPM=25mph, 7100RPM=36mph [6700=34]
gear 2: 3kRPM=28mph, 4kRPM=37mph, 5kRPM=47mph, 7100RPM=66mph [6700=63]
gear 3: 3kRPM=43mph, 4kRPM=57mph, 5kRPM=72mph, 7100RPM=102mph [6700=96]
gear 4: 3kRPM=55mph, 4kRPM=73mph, 5kRPM=91mph, 7100RPM=130mph [6700=122]
gear 5: 3kRPM=66mph, 4kRPM=88mph, 5kRPM=110mph, 7100RPM=156mph [6700=147]
gear 6: 3kRPM=77mph, 4kRPM=103mph, 5kRPM=129mph, 7100RPM=183mph [6700=173]

I had noticed this before too, but figured I was seeing things. I had experienced twice on a roadtrip, driving with friends in other cars, that my speedo was about 6mph LOWER than theirs (i.e., mine said 70, theirs said 76). I am running stock Blowtenzas, checked my air pressure recently, no balance or alignment problems, everything seems fine.

This is really bugging me now because I don't want to be going 70 in a 65, thinking I'm ok, when I'm really going 76 in a 65 (and thus in ticket-land).

Anyone else have this problem? Thanks in advance,

Wow, and you're on stock tires?
 

I guess there is always the possibility of needing to re-calibrate your speedo -- should be "simple" since it's all electronic

Might want to ask your dealer?

-Taner

Re: Wow, and you're on stock tires?
 

I mentioned it to the dealer before and they looked at me like I had two heads. I have had this problem since day 1 of ownership and I've got almost 8k miles on it now. It doesn't seem like a "serious" problem so I keep forgetting to harrass the dealer more about it..

And yeah, stock Blowtenzas. Tried pressures between 37/37 and 40/40 with same results.

Thanks,

if you're 6mph TOO LOW, that's kinda bad.. I'd rahter my speedo read fast :-/

Instruments wouldn't know any difference between what tires you're on, but this is sounding familiar
 

...since both Don P and I had our speed displayed by a radar trailer out on a highway in the 70-something MPH range to be about 6-7mph higher than our speedometers showed, and we both assumed the trailer was inaccurate. I've passed a radar trailer in my neighborhood that was accurate within 1mph with my speedometer around 35-40mph.

If you have VAG tool
 

Output the Speedometer on the cluster, should read 62MPH. Also check the speed as per the ECU and the Speed as per the Instrument. If they are off, I'd check the coding of both. followed by going to a new dealer

You might also want to try a GPS for yet another opinion.

Does it effect the odometer? If so, then your miles will roll off faster. ;(

This is exciting!! You must have a setting out of whack.
 

I've been hunting down where in the ECU the tire size calibration is done... You should meet up with someone local w/ a car that is giving good numbers and compare all the settings in the engine settings and instrument cluster settings.

(I'm starting to believe the tire size information is in the ECU not in the instrument cluster, because it has data blocks for your current speed on it...)

I really want to track down where the setting is so I can fix the speedo for my slightly smaller tire diameter.

Good idea. Anyone in Tampa Bay area have a VAG tool? we could get together and check ECU settings.
 

So you think that it contains some "default" tire size setting and determines speed by that? Funky-monkey man..