new mpg

[05 1500HD]

I've got a 05 1500HD 4x4 with a 6.0L and 3.73 gears. Original tires were 245/75/16, and I put 285/75/16s on it a while back. I never got my speedometer recalibrated after the new tires. The other day I reset my indash MPG and after a couple of days its showing 11.2 mpg. I was wondering if anybody knew what I was really getting. I drive 3 miles to work, 3 miles to home for lunch, back to work, then back home. So really about 12 miles a day.

[TJay74]

Your new tire is bigger than your old one

 

245/75/16 = 30.47" rolling circumfrence

285/75/16 = 32.83" rolling circumfrence

 

That is going to throw your speedo and odometer off by a decent amount. Indicated 60mph will now be almost 65mph. You are adding an extra 77 miles to your odometer every 1000 miles or 770 miles every 10,000 miles. sadly without a programmer of some sort there is no way to program the ECM to correct for this.

 

Here is a nice site that lets you see the differance.

 

http://www.paspeedo.com/calculator.htm

[Silverado4x4]

Your new tire is bigger than your old one

 

245/75/16 = 30.47" rolling circumfrence

285/75/16 = 32.83" rolling circumfrence

 

That is going to throw your speedo and odometer off by a decent amount. Indicated 60mph will now be almost 65mph. You are adding an extra 77 miles to your odometer every 1000 miles or 770 miles every 10,000 miles. sadly without a programmer of some sort there is no way to program the ECM to correct for this.

 

Here is a nice site that lets you see the differance.

 

http://www.paspeedo.com/calculator.htm

 

 

No thats wrong, his truck will be doing 65 mph but the speedometer will show 60 mph so he will be adding less miles to the odmeter.

[AGT]

7.8% difference. So your MPGs should be up by 7.8%. Roughly you are looking at 12mpg

[1990ss]

Your new tire is bigger than your old one

 

245/75/16 = 30.47" rolling circumfrence

285/75/16 = 32.83" rolling circumfrence

 

That is going to throw your speedo and odometer off by a decent amount. Indicated 60mph will now be almost 65mph. You are adding an extra 77 miles to your odometer every 1000 miles or 770 miles every 10,000 miles. sadly without a programmer of some sort there is no way to program the ECM to correct for this.

 

Here is a nice site that lets you see the differance.

 

http://www.paspeedo.com/calculator.htm

 

 

No thats wrong, his truck will be doing 65 mph but the speedometer will show 60 mph so he will be adding less miles to the odmeter.

 

 

No, thats wrong. If his speedometer reads 60 mph, he will actually be traveling almost 65 mph.

[HEMICAT]

I think you guys just said the same thing?

[1990ss]

My bad. I wasn't awake yet. lol

[Spurshot]

Another way...If you have a Garmin or similar GPS, there's a dashboard feature with trip miles that you can use to compare real miles traveled against the odometer. That's what I used to calculate my mileage, along with actual fuel used fillup to fillup.

 

I found that tires aren't round and calculated radius is off by as much as an inch. There's squash factor of the contact with the ground.

[2016 Sierra Owner]

The 11.2 sounds about right for you. I had a 2001 6.0 25HD non 4x4 with 4.10 gearing on stock tires. My average was around 11.5 to 12.5. My commute to work is 3.3 miles one way and I mostly just drove around town with it.