With 285 tires, will the average fuel mileage on the DIC read more or less then you are actually getting?

Thanks

Less

How much less??

4 mpg or so

How could it read less? When the dic is reading off the fuel sender in the tank??It calculates off how much fuel you burn.

With the 265 tires I have the DIC reads better MPG than I actually get. It's about 1 MPG more than actual.

How could it read less? When the dic is reading off the fuel sender in the tank??It calculates off how much fuel you burn.
Because the different tire size throws off your speedometer/odometer readings. So yes, it is measuring the fuel used, but the fuel used per mile driven is off, since the actual mile vs. the odometer reading is wrong.

With 285 tires, will the average fuel mileage on the DIC read more or less then you are actually getting?

Thanks

What is the size (diameter, not width) of your tires? Assuming 285/75/16 the DIC will display your actual mpg as before but since you have driven further your actual mpg will be higher by the difference in tire diameter (new/old) as a percentage.

My 285s are not too far from stock and I think the mpg is more correct than before...:ro)

How much would it throw off speedometer from stock? 4 mph?

How much would it throw off speedometer from stock? 4 mph?
It won't throw it off a set amount, it will be a percentage. So, the faster you drive, the more it will be off. The best thing to do is to figure out much it's off. Interco tires has a neat and helpful calculator that will help you figure out how much it's off.
If you divide the old height by the new height, then you will see how what percentage it's off. In my case, it' s 7%. So I multiply my mileage by 1.07 to get actual miles traveled and then divide by gallons used to get my mpg.
Here is a link.
http://www.intercotire.com/site41.php

Another option for determining Speedometer Error - Find someone with a handheld GPS receiver (they are pretty cheep now and common), and drive your truck comparing actual speed (GPS) and indicated speed (speedometer).

I had the MPG off on my old HD when I changed to 285's. Going from memory, the 285 75 16's were about a inch and a half taller than the stock 245's. This meant that each tire would travel about 3 inches more per wheel revolution. Doesn't sounds like much- but that adds up at 80 miles and hour. I was about 8-10 miles and hour off at 75. This all added up for a loss of about 1.5 to 2 miles per gallon. I got a hypertech programmer and fixed the tire size difference. This brought it back closer to stock settings. Still had a slight loss, but i figured that was due to the more agressive tread design- hope this helps some... :beerchug: