34MPG in a GIANT truck

[comptiger5000]

I wish my Jeep was geared that tall. I turn 2k RPM at 67 mph, so about 1500 at 50. It could do less, as it'll pull well at 1100 - 1200 in OD with the TC locked.

[JasonG]

Or,
I know its against the "slow down" philosophy, but our vans get better MPG at 70MPH than 60MPH........
I guess the V8s settle into a sweet spot in their fuel curve?
I'm thinking of putting a scangage on one to get realtime feedback. I can tell from fill to fill.

[comptiger5000]

That's entirely possible. Depending on gearing, the engine may settle into its optimal load/rpm point at a higher speed, possibly allowing the increase in engine efficiency to outweigh the extra aero drag, giving better mpg.

[bandit86]

why dont you guys buy taller tires? go form a 25 inch tire to a 27 inch tire, should fit, instant 8% gear reduction. I know they're heavier but might work better. my old chevy tracker loved 70-80km on sideroads with 33s. those were 25% bigger then stock, I barely touched the gaspedal. Also had a snorkle

[Christ]

Tire changes are usually bad for stop and go driving, and might work out great for highway driving... it depends on what kind of driving you do if you'll ever see a gain from it.

[JeepNmpg2]

Originally Posted by Christ

Tire changes are usually bad for stop and go driving, and might work out great for highway driving... it depends on what kind of driving you do if you'll ever see a gain from it.

Definately agree with you Christ, I went up 6% in size (28.5's to 30's) and I can barely break epa for city stop and go (17 is better than 14), even with a lot of neutral coasting. However on the highway between 62 and 70, MPG's seem to stay steadily between 23 and 26 (instead of 19), depending on the grade and wind conditions, which is 20-25% better than epa.

Note: I did gain about an inch in tread width too, but I don't really have any FE estimates of the old tires, I only had them for about 2k miles after I bought the rig.

[ShadeTreeMech]

Bad thing about bigger tires is having to mentally recalculate your speed/miles on a tank due to the speedo expected stock tire size. I think on newer vehicles you can have the ECU reprogrammed to adjust for the tire size, but on an older manual speedo, you're kinda stuck with what you got. Mind you, it's not that difficult to add x% all the time but it can be misleading if you forget and start to speed by going with the readout on the speedo.

[comptiger5000]

On some vehicles with mechanical speedos (Jeeps, most other 4wd vehicles, some cars), you can change out the speedo gear in the tranny or transfer case to correct the speedo. For others with electronic speedos, it can be done in the computer.

[Frank Lee]

I've run oversized tires on the F150 in the hopes of improving fe and it's been a fail. It already has the "tallest" axle ratios so the net result was that the a/t downshifted for every little rise in the road. Stock size 235-75R15; tried 265-75R15 and 245-75R15.

[orange4boy]

I've run oversized tires on the F150 in the hopes of improving fe and it's been a fail. It already has the "tallest" axle ratios so the net result was that the a/t downshifted for every little rise in the road.

Did you look into the TCC lockup switch? Mine took all of 10 minutes to wire up and gave me an excellent FE boost.

I have not looked into it but I'll bet these new trucks have better TCC lockup specs.