Bigger Tires Vs. MPG/Speedo Reading

This seems like it's been beat to a pulp, but I have a question. I recently swapped out my factory Firestone 245/75r16's for some Copper AT3 4S 265/75r16's. Everything I read said that getting bigger tires (granted these are only about an inch bigger than factory) would throw off my calculations. However, on stock tires, I noticed that my speedometer consistently read about 2 to 4 mph lower than gps on my obsessing, and the little speed sign warnings on the side of the road. Now, with the larger ties, the speedometer airstrips to be dead on with gps readings and speed sign warnings.
My question is, now that the speedometer appears to match the actual speed the truck is traveling, does that mean that the odometer and the MPG rating in the center console are actually accurate, or is they're some calculation that needs to be done?
The only thought process that makes me think it's now reading correct is that the TRD models come with larger tires than the SR5 (which I have) and if all of the computers are the same across models, perhaps it was incorrect with the smaller factory wheels.
Any inputs?

 

They are now inaccurate.

Speedometers are allowed a variance, odo is not.

 

Most cars read a bit low as a conservative cushion for speed limits, tire wear, and such.

My Taco was generally about 1mph low before the new tires, same diameter as yours (265/70R17). Now, my speed reads 1mph high, about a 2% difference. Just because of consistency, I add 2% to my MPGs in my head, but my fuelly.com numbers are going to be off going forward.

The way to check your Odometer is to look for the ODO check signs on the highway. They are usually done in groups for about four or five miles. I still need to do that.

Otherwise, you could use an GPS logging app to see how the distances compare. But like I said, there will be some drift as the tires wear.

 

Does your windshield GPS not have an odometer/trip feature on it that you could compare to your dash odo? I think every GPS i’ve had in the last 15 years (a lot of them) have had ‘Trip/Odo’ options.......Or maybe DL a GPS app on your phone and compare.......Just a thought....

 

I found the same thing when I went to 32s. My GPS on my phone and my ham radio are both reporting similar speeds to the speedometer after the tire swap, but the speedo was slower before the tire swap. Only a few mphs though.

 

While the width of the tires varies (245 vs 265), all trim levels have tires of the same diameter (~30.5”-30.6”).

 

I've found where you really lose MPG is in tire weight and tread pattern.

 

This. Weight and rolling resistance is huge.

When you hear a loud tire like a MT its because of the huge lugs that are often feathered to death. Noise = friction.

 

You’re not wrong, but that is not at all relevant to this thread.

 

This thread isn't about complaining about a loss of mpg's or anything like that. Just curious if any of the readings (like mpg or the odometer) are actually "correct" now that bigger tires made the speedometer reading more accurate. I suppose the next best option is actually driving it and comparing the distance traveled on the gauge to a map app or something similar

 

Probably not a concern because the difference is so little. If its 2% off then at 10,000 miles that is only 200 miles which is nothing to a tacoma.