I've had my truck for four years and regularly take it long distance trips. I fully understand that it's a large 4WD, so I've been very happy with my average of 17+ mpg (even when I pull my pop-up camper).

I recently added a grill guard and changed from basic 265s, to a set of 285 Destination M/Ts. I'm in the middle of my first road trip since these changes and so far I've dropped down to about 13.5 mpg. That was all highway and running cruise at pretty nominal speeds.

My future plans call for duals with a hi-flow cat, and an intake system of some sort (suggestions??). Any chance I'll see an increase in my mpg with those changes, or will they further add to the problem?

I don't mind losing some mpg due to the new goodies, but on 1500+ mile plus trips, I'm going to feel this in the wallet more than ever before.

 

the duals and intake wont hurt your mileage. with the duals you will lose some low-end torque though. as far as a CAI goes, i would recommend just replacing the filter with a highflow filter like ones that come in the kits. i know air raid makes better flowing intake tubes to replace the stock ones. you can also try the Gotts intake mod.

you might get 1 to 1.5mpg from a CAI, depending on how dirty your filter is now, but your mileage wont change from the exhaust .

 

Just increasing tire size will cause your gas mileage to go down 3-5% because you are traveling farther for each turn of the wheel, but your spedometer doesn't register the added distance traveled.

 

He's right on. You're about 2mph slower with the bigger tires,throwing your mpg calculations off. Put your tire sizes in here and see the difference.

http://www.miata.net/garage/tirecalc.html

 

RIght, if you have not recallibrated your speedometer your MPG's are not as bad as you think.

 

After recalibration, I would guess you would lose about .5 mpg, if your truck is similar to mine. Then when I went to even larger, the 305/50/20s, I lost anothe 1.0 mpg.

 

Um, no. As long as the pipes are the proper size, the pipes will not hurt anything. But, if you have dynos to prove that point...