Tire size/gear ratio affect on speed

I have a 2018 Tacoma with 275/70R17 tires (32.2" diameter) and 4.88 gears. The truck came stock with 265/70R16 tires (30.6" diameter) and 3.90 gears. Driving down the highway speedometer is showing 65MPH, but actual speed is more like 68. Not really a huge deal, but with the changes to tire size and gear ratio it seems to me like the speed reading difference should be the other way around (going slower than speedometer reading)?

 

OOOh...that makes sense. I AM from the "olden days" and sensing speed from transmission was what I had in my head. THANKS

 

try one of these?

https://www.roughcountry.com/speedometer-calibrator-90043.html

 

I have 295/70/17's on mine and it's off by almost 5mph. I tend to have my Android Auto going so I always watch the GPS speed. Your speedometer shows your going slower as your tires are rotating slower than they were before with the bigger size. 659 revs/mile with your 265's compared to 627 with the 275's

 

When changing gears or tire dramatically you should have the dealer do a zero point calibration. Your vsc and abs think you have closer to stock tire diameter. I had to do it in my Land Cruiser but don't know if Tacomas have the same or similar system as the LC.

 

My dealer in Iowa told me it was against the law for them to modify the speed/miles calibration?

 

Dunno. Seems like you're calibrating it not modifying it.