Hello Everyone I have a 1986 f250 with a 6.9 with a four speed cruising around town isnt bad but highway cruising kills fuel mileage I have stock tires 235/85/16's on there does anyone know if I switch to a 285/75/16 will this help with highway driving or really wont make a difference. any suggestions would be appreciated I was thinking about putting in a 5sp or a automatic but dont have the time to get involved with that

 

i went from a 265 75 16 which is same height as 235 85, to a 285 75 i lost like 250rpm on the highway, i think youd have to go like 35 inches high to see a big difference, thats just my opinion though

 

wat if you change your gears.that should help it

 

Highway travel isn't really efficient for these trucks at all. They get there best mpg when kept under 2k rpm. Changing gears is the easiest way to change that. With the right combination of gear/tire, some guys can cruise at 70mph at 1500rpm. My 86(with a 4spd) has 3:55 gears and 235/85 tires and I hit 2k rpm at 55mph.

 

How do you figure out what gears you have? And how do you change the ratio? Just a new rear end or what? Cause I have a 93 7.3 and it runs around 2500 at 70. And goin to Monroe from my town on the interstate I'll use 3/4 of a tank there and back and it's around 65 miles round trip. Terrible gas mileage. So I stay off the interstate and out of Monroe.

 

2500 at 70. i am going to say u have 3.54 gears. they are the better ones for mileage. motor might not be in tip top condition in the fuel system, restulting in bad mileage.

 

My rig only has 100,000 miles on it though. At what point do I need new injectors and lines and pump?

 

around now. stock injection systems are only good for 100000 miles or so. putting a good reman pump and new injectors in it will help alot! oregon fuel injection is a good place to get them. stay away from pensocola and dieselcare.

 

agreed now if you are just looking at tires and nothing else to help you mpg smaller tires bigger rims less sidewall IMO now thats just for tires... keep that in mind

 

Thanks diesel crawler. Around how much does that cost?