Speedometer/Odometer/MPG inaccuracy ?

I just went up from the stock 265's on my 2019 Off Road to 275/70R17. I know my speedometer will now be 2-3 mph slower than what my actual speed is but I've seen a couple people on here say that they automatically recalibrate (which I doubt). Any truth to that?
If not, has anyone had their speedometer recalibrated/is it worth it?
So does that mean my odometer is reading more miles than i'm traveling?

The second thing is that I was pretty stoked on averaging around 18-20 MPG on a road trip I took over the weekend until my buddy mentioned that my MPG's would not be accurate since I have larger tires now as well. True? How can I know what i'm averaging?

I might be overthinking it but I would like some peace of mind.

 

Here you go, installed in mine and all is good.

https://www.jegs.com/i/Hypertech/53...xSMLYLSZXQAioAQgh7CC0XREIL-aQ-4gaAqh3EALw_wcB

Edit: I’m running 285/75/16, still get about 17-18 with the taco.

 

How are you guys getting 17-18 with larger than stock tires? I get around 14.5 to 16 or so. My daily commute both ways is 23 miles mostly highway.

 

What were you getting stock?

 

Yeah, you are overthinking. I know the 2nd gen speedo was off, and going up a tire size actually corrected it (like from 265/70/16 to 265/75/16). I don't think there is any auto calibration, although there may be a way to reprogram the ECU to correct if you are so inclined

Your speedo is now about 5% off from the OEM setting. It will show you going 5% slower than you actually are, and you will actually be travelling 5% FARTHER than your odometer states.

 

I only had my truck for 5 days and about 500 miles before I switched to larger tires but I honestly have a heavy foot and can only get about 12-16 mpg on short in city trips. I can only break 18 if im on highway at like 70,mph

 

Same, I have seen 20 mpg if keeping speed around 68 or under on the highway. Go over 70 and mpg starts dropping fast the faster you go. In town just tooling around and sitting through lights I get 15-16.

 

I get 14.5 to 16.5 sometimes ill pull 17 and some but mostly stays between 14 and 16

 

Maybe. Checking against a GPS is the only way to know for sure. Sometimes that small a delta actually corrects a factory error that tends to read high.

No.

See the Hypertech post above. Only you can decide worth based on the error you find with the GPS testing.

No, you are reading slower. So you record less.

Maybe. See GPS comment. However if you are reading slower and recording slower, he is correct. However, your MPG is BETTER than what you are calculating. See 'recording less' above.

Multiply by the % diameter delta from OE to new tires.

Or not thinking through it logically enough.

 

Don’t cruise typically over 72, and don’t have a heavy foot. My avg mpg stays right 18, used to do better until I put the roof rack on. Yes I cruise hwy miles