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Discussion Starter · #1 ·
When I bought my turck it had 315's on it so i dont know the fuel mileage difference between the two. Anybody help me with differences in fuel mileage gained by putting 265's back on? Also, what do most of you guys get for highway mpgs with 7.3?

Thanks
 

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TDG MAFIA #101
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I have reached 16 with mine, about half on interstate and half in town driving per tank. That is with 265's. My last 7.3 had 315's and it never got above 13. The last truck was a 1 ton with a small lift. My new one is a 3/4 ton no lift. The last truck did have more extras than this one does. For now :sly:
 

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265 smaller more rpm=less mpg in most cases
315 less rpm more mpg
 

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camojeeper said:
265 smaller more rpm=less mpg in most cases
315 less rpm more mpg
My thought too, but there is also the issue of aerodynamics from being lifted, rolling resistace, rolling mass, takes more to get em goin...

My conclusion....... Who the heck knows!!! too many variables, like driving style, how much lift, gearing, trans type. It is near impossible to have a universal answer.:2cents
 

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MAFIA MEMBER 106
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:whs there are a lot of varyables likr tread type air psi drag on the truck you will probably be the same mpg with both i run a 285 m/t and am happy w/14 mpg but i drive hard
just my .02 worth
 

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I get anywhere from 16.5-18 HWY with my 305s. Depending on traffic, speed, wind, and other variables.
 

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Discussion Starter · #7 ·
Whats best cruising speed.....

I'm making trip to Texas thats why im asking all specifics because Ive never drivin a tank in my truck thatwas straight highway for the whole tank(use it on my dads farm and lot of snow/fourwheel drive). What is best cruising speed on the highway for mpg that you guys see. I wanna be above 65mph

:smoke
 

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the right question would be, what is the best cruising RPM's...
and I believe that to be around 2000. The speed is another thing that changes depending on tires and other variables.
 

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jkdank said:
I'm making trip to Texas thats why im asking all specifics because Ive never drivin a tank in my truck thatwas straight highway for the whole tank(use it on my dads farm and lot of snow/fourwheel drive). What is best cruising speed on the highway for mpg that you guys see. I wanna be above 65mph

:smoke

It depends on weather....windy, raining....if you are against the wind on if the wind is with you. I made a trip to FL a couple of months ago. I got 17mpg on the way there running 72mph (2000 RPMs). On the way back, I ran 76 mph (2200 RPMs) and I got 18 mpg.:shrug: I don't know what to think about that. :damnit
 

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Discussion Starter · #10 ·
Cool, just getting some opinions. Thanks guys. I'm just going to leave my 35's on for the trip, too much hastle swapping them and truck will probably look ridiculous with the leveling kit i put in and 265's anyways. Now if anybody knows some good towns with sweet country bars i can stop at on the way down please let me know! Im gonna take my time and see some of our country
 

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My truck has run stock 265's, 315's, and now 325's. Going from 265's to 315's dropped fuel mileage by 2 mpg's on the highway, partly due to the lift that was put on at the same time.

Yes you are turning lower RPM's with larger tires, but it's not enough to compensate for the huge increase in drag and rolling resistance. Physics works against you every time in this case.
 

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I have made two trips from Michigan to Florida. One in October and another in January. The worst MPG's was 18.2 and the best was 20.5. Now with that said I have been running at 67mph to 68mph at about 2100 rpm's. A friend gave me some brand new tires (245 x 75 x 16) which came off his brand new GMC 2500. There's a formula (I left at home) which tells exactly the difference the size tires make in mpg. I wished I had it with me to share. Also, I don't have a chip but I do have a Hypertech 3 and I have change the tire size in order for my speedo to be accurate. I compare it to my GPS and they both are the same, so I am pretty confident my mileage numbers are accurate.
Sorry, I went on too long. Good Luck.
 

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jkdank said:
Cool, just getting some opinions. Thanks guys. I'm just going to leave my 35's on for the trip, too much hastle swapping them and truck will probably look ridiculous with the leveling kit i put in and 265's anyways. Now if anybody knows some good towns with sweet country bars i can stop at on the way down please let me know! Im gonna take my time and see some of our country
billy bobs in dallas/fort worth a good time to be had by all:eek:wned
 

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Pocket said:
My truck has run stock 265's, 315's, and now 325's. Going from 265's to 315's dropped fuel mileage by 2 mpg's on the highway, partly due to the lift that was put on at the same time.

Yes you are turning lower RPM's with larger tires, but it's not enough to compensate for the huge increase in drag and rolling resistance. Physics works against you every time in this case.
hey curtis u r right on but i think you can go from 265 to285's with out any lift and get a little more mpg(safe bet) but with any lift you loose. and a gear change won't allways make it better with lift and tires
 

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bluovaltruk01 said:
When I went from a 265 to a 285 my mileage increased by about .4 Mpg
Was that before or after other mods?

It seems to me that mods, if driven correctly, would help with not losing a lot of mileage when stepping up in tire size.

the other thing I wonder is how to figure out the actual effect of gearing since they can hurt or help depending on exactly what the change is.
 

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That was before the mods. The straight piped exhaust helped too, but I haven't done any numbers with it. It just seems like its helped out.
 

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