I know there has been a lot on this subject even today, but here's my situation. In-line six with a 3.55 rear end, manual 4-speed with TRUE granny gear so essentially it's a 3-speed. I've got 235/75 tires. At 65 mph on the interstate, I'm pushing 3000 rpms. I'm getting 15.1 mpg 50% highway 50% city. No towing or hauling to speak of except for an occasional trip to Lowe's or Home Depot. It has 113k original miles. I think bigger tires will hurt the look, can I put in 3.08 (or even a taller gear ratio) in the rear end or who has any ideas?

 

I have 3.08s in my 94 single cab short bed, stock 235/75 tires. I get about 18 highway 14 city, the gears are way too high for my liking as it is hard to get the truck rolling. tends to put a little more strain on the clutch. Great for highway driving or any driving where you don't have to start and stop frequently.

 

Also have the inline 6

 

Suggest the cost of conversion will take a whole friggin' lot of miles to just even out with fuel savings, especially if shop labor is involved. Swapping in a junkyard equivalent is a cheaper option - but playing the odds that the axle will be in good shape.

Consider the next time you need tires - look at the 31x10.50 or even the 30x9.50.

Still recommend that the biggest gains are with the driving habits - try 5mph slower on the interstates, taking it easier on the gas, etc. Nothing will be an OMG where have you been all my life finding, just incrementally help out a bit on economy.

 

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Bout summed it up. Would you see gas mpg savings? Yes. How much? Very little. You will affect your mpg more by keeping your tires properly inflated and how you drive.

 

I wish I had a little more get up and go without the effort, but I can readily get the truck up to speed pretty quickly with my stock 273's, M5OD and I6. It's not the same get up and go that my '94 5.0 has with the 355's and auto trans, but it is my daily driver for the 42 mile trip to work. I'll take my 21mpg interstate over the 15-16 interstate with the 5.0 all day long. I also have to say, my 2nd gear and most of the way through 3rd is pretty awesome with the 5 speed. Pulling a trailer though........it's like being tied to a stump. You just can't pull with the 273's and even the 5.0 with the 355's doesn't pull as easy as I'd like.

 

I'm with you on that. Pulling a trailer with 2.73s is no fun. Honestly I'd rather have a truck that can perform than save me gas. This is why I'll be running 3.55s in my very near future.

 

I always pull my trailer. I played around with gears and tire sizes to optimize fuel economy and power. '87 4.9 5 speed, pulling the trailer I don't use overdrive. I figured with my 3.55s I needed 32 or 33 inch tires. I swapped to 3.08s and 235/75s.

 

With the four-speed tranny I would drop to the 273 gear ratio. That will drop your RPM about 500 which should be a lot better at 65 mph. I would bet you'd get about 2 to 3 miles per gallon.