Are you all seeing a speedo reading 2-3 mph higher than actual (stock tire/wheel size)? I checked mine against the GPS yesterday and it reads 77-8 when car speedo is directly centered on 80 (2011 v6 pony pkg - 18 in wheels)

Not a big deal, but good to know

 

I find that a bit unusual. The more common complaint is the speedometer is giving a reading higher than actual speed.

 

My GT's speedometer is off by about 1.5-2 MPH high with my 275/40/18's. Close enough for government work. It keeps me a tad more... "honest".

 

Doubletap - yes, that is what I am seeing.

The GPS reads 77-8 when car speedo is directly centered on 80

 

Same here - seeing a 2-3 MPH difference on stock wheels/tires, seem to be common in my other cars as well

 

So if the speedo is reading fast does that necessarily mean the odometer is also clocking quicker than it should? So I am NOT getting 30 mpg?

 

Correct, however the difference is negligible unless you are an **** compulsive engineer ;-)

 

I...Uh... I think the word you were looking for was retentive. Your sentence means something entirely different haha.

 

I guess my attempt a humor did not cut it I was attempting to combine the traits of an **** retentive: A mild form of obsessive-compulsive disorder. A collection of very irritating personality traits that include stubbornness, orderliness, and a desire to control others and their surroundings. It makes a person meticulous or fixated about little things, nit-picking or paying extreme attention to detail, and trying to control his or her environment and other people. Plus the traits of an obsessive person: Obsessive-compulsive disorder is an anxiety disorder in which people have unwanted and repeated thoughts, feelings, ideas, sensations (obsessions), or behaviors that make them feel driven to do something (compulsions). Such as checking their gas millage every time they fill up.

Often the person carries out the behaviors to get rid of the obsessive thoughts, but this only provides temporary relief. Not performing the obsessive rituals can cause great anxiety.

So many engineers I know have both characteristics, therefore I classify them as ****-compulsive.

As we say in the rural part of southern NYC "That joke don't laugh"

 

Back to the OP...

The onboards are not very accurate as I mentioned earlier. If you want to get a true idea of your average fuel mileage, begin hand calculating at each fill-up. I keep a cheap pocket planner (1 month per 2 pages) from WalMart in the glove box just for that and I also use it to log whatever I do to the car. You can go back and average each month for your best value for average fuel mileage. When I lived in the north, I would plot each vehicles monthly mileage and it was interesting to note the swings from summer to winter.

Yeah, I'm one of those **** engineers. Compulsive? Depends on the chick... or whatever.