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Discussion Starter #1
anyone know the mileage difference between the two?
 

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I went from 285's to 35's, and my milage dropped about 1.5-2 MPG's. The milage doesn't actually drop all that amount cause everything else is thrown off as well.
Also speedo will be off about 4-5 mph at 70, 2-3 mph at 55mph, and for every 18 miles registered on your odo., you've actually gone 20 miles, for every 90 miles your odo. reads you've gone 100, and so on....

I've done this all based on gps readings
 

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so in all reality just go with 35s? its not that big of a difference then? huh...i thought maybe it was because i was gettin like 12mpg with my truck with 35s and i had one with the stock 265s and got 17mpg
 

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:bump::bump:
 

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Well the truck is spending a little more fuel to push the bigger tires, but it's hard to say exactly how much cause the values you are using to determine the MPG have changed. That is if you're hand calcing, which is the way you should be IMO.

Think about it like this. Say you make a trip that is 200 miles long. On a truck with stock tires the odo. will read 200 miles. Lets say you fill up at the end of the trip and you pump 12 gals. That works out to 200miles ÷ 12 gals = 16.7 MPG.

Now put 35's on the same truck and make the same trip. Your odo. will read 180 instead of 200. You're going to calculate your mileage based on a 180 mile trip, when the truck actually drove 200 miles. It's hard to say how much more fuel the truck will need, but just for sake of discussion well say it took 12 gallons again. Now 180 miles ÷ 12 gals. = 15 MPG.

The truck will probably take a little more than 12 gallons this time though, because it is harder on the truck to push the bigger tires(especially if you're putting mud tires on it), and that will make the MPG reading even lower.

My point is, you can't really tell how much more fuel the truck is using until you get the speedo and the odo corrected for the tires that are on the truck.

Until then, it's just not comparing apples to apples.
Hope that rediculous argument helped :hehe:
I know it confused me :dunce:
 

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woops, let me finish my thought :doh:

I meant to say, so when you get the odo fixed for 35's it will read 200 miles for the same trip and then you will know how much extra fuel you needed and thus the milage drop.

200 miles ÷ say 13 gallons = 15.4 MPG

IN that case you lost 1.5 MPGs going to 35's. But until you get the odo fixed/calibrated, you think you're only getting like 13.8 MPG(180 miles ÷ 13 gallons = 13.8)

Am I beating a dead horse?

Am I even making sense?

:lol:

I'm done
 

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Believe it or not I know exactly what your saying haha.

But you're right...the mileage difference is so small its hardly worth worrying about. I know I actually get better mileage with bigger tires. Because after you figure in 10% more miles(ie odom says 200, but you really went 220) its pretty easy to figure out. With 35's and a 4inch lift I consistantly get 18+mpg. Now I drive 28miles one way to work basically highway at 60mph. If this was stop and go driving or interstate at 70+mph my mpg would pry be closer to 16. But as far as I can tell the bigger tires keep
your RPM's down and even out the loss from having to turn those bigger tires.
 

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I know the Q was pretty much answered, but I wanted to add a little as I've seen similar questions before. And I've included a nifty calculator at the bottom from a guy on another forum. I suggest you save it.

Will you get better fuel economy going to a bigger tire? yes, but it's all about the drivetrain/gear combo. If you go TOO big your truck will be dogging trying to turn the bigger heavier tires. Gearing generally fixes this problem. The goal being trying to retain as close to stock ratio as possible. I don't know squat about diesels, but I've messed with a few Jeeps.

When I went to 33's on my waggy I noticed lower revs on the highway and increased freeway speeds with stock gearing. Cruising on the highway I got better fuel economy(I have a V8), but I didn't feel all the torque as before getting to the tires. When I went to 4.10's which is a lot lower than stock (3.31) but closer to stock ratio with new tires, I lost all the cruise (screaming at 65) but have lots of low grunt now where it matters for a Jeep.

With the drive train in these big trucks you aren't going to notice too much of a loss in performance until you start lifting and getting some real big meats on there. My .02

Here's a cool calculator to mess with if you want.Gear Ratio Calculator
 
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