Tirerack says the OE tire for my truck is a 235/70-16 (29")

Google says the OE tire for my truck is a 255/65-16 (29")

I've got 265/70-16's on it now (30.6") 105.5%

I'm about to put 265/75-16's on it. (31.65") 109%

Geared to 4.10 from 3.55 (115.5%) (a 33.5" tire will return my effective ratio)

Sean's "can tune" for mid-grade gas. I run 87 right now but will be switching to 89 once I put the 1.7 rockers on.

Right now my speedometer is off about 8%. I figure my odometer is off the same.

If I keep my foot out of it, I get 13.75-14mpg on the fuel receipt, otherwise, it's 12.5-13, city. Highway at 65mph on cruise I get about 18 on the fuel receipt. Do the 105% correction factor and it's 13.1-13.6 to 14.5-14.7 city and 19 highway.

Ditching the clutch fan I'm hoping will free up 1/2mpg city and 1 mpg highway. Put me at 13.6-14.1 to 15-15.2 city and 20 highway. Not so bad.

Then putting on the 1.7 rockers from Harland. John Mercedes said they're worth 1-1.5mpg depending on the foot and 15-24hp on the dyno depending on supporting mods. Didn't say if that's city or highway mpg. Figure they can get me another 1/2 mpg city and 1mpg highway, I'm at 14.1-14.6 to 15.5-15.7 city and 21 highway.

I wouldn't complain about that, but I'm still wondering if there might be something else out there to snag at?

I've also been tracking minutes per gallon. Pretty much consistently between 36 and 38 minutes per gallon regardless of city or highway.

My commute is all of 13 miles per google earth, all city. Takes me 30 minutes (about 0.8 of a gallon) to go those 13 miles. I'll let you figure out that average speed. Two commutes per day, 1.6 gallons per day, 20 gallons per tank, 12 days per tank. Alot of the time, of course, is spent idling at red lights.

I'm not so concerned about highway MPG since i don't highway very often, but if I can pick up a few points in the city, that would be great.

I just counted on google earth. 22 stoplights and 3 stop signs in 13 miles. I think that counts as city driving.

 

You have to realize how much these things are costing you and how long the return on investment is. If you're going to be doing gears and 1.7's, you're looking at a good chunk of change. I'm sure if you're doing either instal yourself but if not, these mods will not pay for themselves for a very long time, perhaps not as long as your own the truck.

When you only drive 26 miles a day, gaining 1 mpg is not noticeable. If you were putting on 500+ miles a week, then you might start seeing the savings.

One thing that shouldn't be over looked is the current conditions of truck. How long has it been since you did the cap, rotor, plugs, plug wires, etc? Other things like your air filter, cats, O2's, MAP sensor, and tire pressure should all be addressed too. I would look into these things before I started looking into modifications.

Getting 19 on the highway @ 65 is about right but might be a little low for a 3.9. I could get 21 at 65 when I had a 3.9. So I would look into the pieces I just mentioned to make sure they're all working correctly. The basics will affect how the modifications perform as well.

Just trying to make sure the truck is running well to begin with is important and often over looked. People jump right on things that claim you will increase your gas mileage by 15% or whatever but they don't realize they could do that just by taking care of routine maintenance.

 

I did the 4.10's last year. All numbers are current sans 1.7's and E-fan. Also have to factor how screwed up my front suspension was (about to pick it up). In a 232 highway mile trip, I went from 4/32nds of tread to no tread on the front tire outside edge.

 

Seems to me if I pick up 1mpg city and 2 highway, yes they're small gains, but they are gains.

14 mpg city = 280 per tank
15 mpg city = 300 per tank (gets me 2/3 of a day's commute back)

19 mpg hwy = 380 per tank
21 mpg hwy = 420 per tank

Highway aside since I don't drive it often,

320 or so commutes per year = 8,320 miles.

8,320 / 14 = 594.28 gals
8,320 / 15 = 554.66 gals

594.28 - 554.66 = 39.62 gals saved per year @ $3.30/gal = $130.75 per year saved.

The rockers were $269 and figure the E-fan will be $60 or so, it'll take 3 years to make that back, yes. But the performance (what they were really bought for) side says who cares. Who knows, now that I'm not scrubbing the hell out of the tires, that HAS to be worth something. So I might pick up even more than I'm predicting.

 

Yeah, I mean, if you're doing it for the performance, then price really isn't a factor. There is no payback on performance. You pay what you're willing to. I think you're safe saying you will pick up 2 mpg highway. I wouldn't expect to see too much more than that, but you never know...

 

well between those mods and no having tires scrubbing anymore, I think 1 city and 2 highway is reasonable if not low-balled. But yes, parts are for performance...fuel mileage gains are just a positive side effect.