Since I went to 265's I have noticed a 2-3 mpg drop in mileage. Is this normal? How would I convert the miles shown on the tip odemeter to "actual" miles for mpg calcs?

Thanks!http://www.dieselplace.com/forum/smileys/Embarrased.gif

My 265s threw my odometer off by 4 percent. In other words, if I reset my tripmeter in the DIC & the tripmeter in my GPS at the same time, when the DIC says 100 miles, my GPS will say 104 miles.

2-3 sounds a bit excessive, but since your odometer is now "off" you'll need to compensate for that when you do your calculations.

You know I never really gave it much thought. I have 265's also. My mileage runs about 16.5 (except this last time it was 15.5 - I was playin' with the juice.) I had the dealer reflash the TCM this week for the ODLO switch. While the truck was there, I also had them reflash the (ECM??) for the 265 tires. So maybe now I will have the correct MPG. Guess time will tell if it really makes any difference.Edited by: Lakedaisy

I got a best of 21.6 mpg with 265s and a 90 HP Juice box set on the 90 HP setting. I added the 3.8% correction factor.


Also, realize that we all lose a couple mpg when we run into winter fuel. It is entirely possible to still find winter fuel in some of the stations that don't do a lot of diesel sales.


When I had my '02 reflashed for 265s, all it did was correct the ABS--speedo was not corrected.

I just got back from a trip to Ohio and averaged 22.67 mpg. That was crossing some realy big hills or small mountains (depending on who you talk to) on Rt 322 and I 80. Other than 265s, I run a stock truck.

afp1- Correction factor should be 3.9%.

[QUOTE=afp1]

I got a best of 21.6 mpg with 265s and a 90 HP Juice box set on the 90 HP setting. I added the 3.8% correction factor.

Actually, when you do the math to six decimal places, it comes out to 3.73181%. The nominal diameter of a 245/75R16 is 30.468503, and the nominal diameter of a 265/75R16 is 31.649606. When you divide the diamter of the 245 by the 265, the 245 works out to being 96.26819% of the height of the 265, which is a 3.73181% difference.

Ya better check your tread depth & your tire pressure to the sixth decimal point first before you use that figure to calculate your MPG, though.http://www.dieselplace.com/forum/smileys/Wink.gif

AFP1, don't forget the BFG AT are 31.800001" OAH.


That will change your ### too.


3.7-4% isn't going to affect it much anyway.

If you want a real shocker, measure your tire's diameter with a tape. Off the truck, my 285s--which are supposed to be 32.830708" tall, actually measure around 32.3" tall.

I stand corrected http://www.dieselplace.com/forum/smileys/Clown.gif
The tire size calculator on the web said 3.9 but I guess it doesn't do the math to 6 decimal places.

I have been a bit suspicious about the online calcultors............Anyway, all they, and the math formula do is calculate nominal tire size. The actual size is often a bit smaller........