XK Fuel Economy

[NeilSmith]

I keep telling myself it is the tire size skewing the numbers .

What size tires are you running ? I went up to a 245/75 and the odometer readout is about 20 miles different from the gps with a full tank( if I remember right ) . That is definitely enough to skew your mileage if you're using the dash display. If I want to check the mileage, which I never really do, I use my GPS.

[Matt]

^^ I was going to say the same thing because if you're running a 31" tall tire, that would make his MPG of 16 go up to 17.1.

But i checked one of this threads and i believe his tires are only 1/2" taller than stock.. a 245/65/17 if i remember correctly.

[wookie]

The Wife averages 14Mpg with mixed highway/ city. She drives like she stole it. If the ECO comes on she just goes faster. I have milked 21.8Mpg on the highway doing 60ish, bone stock and no roof rails.

[Sal-XK]

She drives like she stole it.

LMAO that's hilarious!

[wookie]

She drives like she stole it

I picked the Commander out for me as a tour gift..........She rarely drove the 06. So she did "steal" it from me.....

[Adondo]

When I first bought it, mine was at or around the 20's on the highway. I once posted a photo of the computer showing 20.8 MPG after a day trip.

Now? With a lift kit, 265/70 M/T's and roof rack catching the air? It's doing fantastic to get 14.5 on the highway, and 10 in town. BTW, the tire guys said those M/T's would "negativity impact the MPG." They weren't kidding.

On edit: I've reset the speedo with the Hyperchips programmer, so it matches the GPS. That means it REALLY DOES get as crappy of MPG as the computer shows.

[Matt]

On edit: I've reset the speedo with the Hyperchips programmer, so it matches the GPS. That means it REALLY DOES get as crappy of MPG as the computer shows.

Yeah I've noticed that I always have to put in a smaller tire size to get the speedometer accurate since the tire flexes with the vehicle weight.... so for my 245/75/17 that are supposed to be 31.5" tall I had to put in 30.5 to get my computer to read accurately. That works out being right too if you follow most programmers instructions; they say to measure from the center of the hub to the ground to get the true "effective" radius of the tire and double that for the programmed diameter.

A lot of people just put in the tire diameter based on size... always makes me wonder if their reported mpgs are a bit inflated because of that... (though its only about .5 difference in most cases. Still food for thought)

[Lt_JWS]

Well guess i shouldn't complain.... I get around 15mpg driving the on the roads around here, on the highway I get 18(without roof racks), I just ordered a AEM intake for $172US shipped(new/amazon!) that should get me another MPG and my ported Throttle body should breath easier!

[Adondo]

A roof rack and its catching the air profile does make a difference.

As for the tire diameter, I just went for a road trip, and "messed" with the tire size a bit at a time until it matched the GPS in speed and distance. The programmed value is written down somewhere, and isn't a match to the actual tire size. It's black magic to get perfect I guess.

[TrialByFire]

I'm getting 14-17 MPG highway--corresponding to 80 mph and 60 mph respectively.
In town, it's more like 10-12. My Fuelly average (including off-roading) has dropped to about 13.5 with all the mods.