Speedometer off by 20mph

I recently had the 4.88 gears installed on my 2016 auto Tacoma. Love the performance enhancement, but my mpg and mph seem to be way off. I'm particularly concerned with the speedometer being off 20mph when traveling on the hwy.

I know that a cell phone app isn't the best way to gauge how accurate my speedometer is, but when my WAZE app states that I am going 80mph, my speedometer shows 60mph. The difference gets less and less as I go slower. The mpg is now hovering around 10mpg, whereas before the re-gear it was closer to 14mpg. I was told that the re-gear would improve mpg, which I have yet to see.

About to go back to the shop to have the guys who installed the gears recalibrate the speedo again, but this time by not simply entering the gears and tire size (285/75/16). I had read that there was a way to recalibrate by connecting the laptop to the truck cpu while also driving with the driving app (WAZE) open on my phone to hone in on the accuracy? Can someone please detail this procedure and testify on its effectiveness?

 

Going to numerically higher gesrs means the shaft will make more revolutions for each tire revolution. In other words to go the same speed the engine rpm must be higher. That means more fuel. Which means lower gas mileage.

Who ever told you otherwise is an idiot. If it’s the same guy who did the work, find another shop.

 

No way it’s off by 20mph. That’s a over 30%. Something in your calculations is wrong. Are you all stock?

 

I believe that you just change actual tire height, as speedo is calculated from the wheel speed sensors on these trucks, not the transmission output speed.

Changing both might be throwing off your numbers.

 

Yeah I believe this is correct, I used one of the inline speed calibrators and just changed the the tire size when going to 33s, changing the gear ratio in the calibrator will really mess up your speedo readings

 

When traveling at 80mph on Waze, my speedo reads 60mph. The difference decreases as I go slower. There are no calculations done. I'm simply reporting what I see.

 

Are you in km/h? 40 mph is 60 km/h.

 

Good point!

 

Nope. I'm reading m/h.

 

This is a good point, and one I will need to ask about when I visit with them this afternoon to recalibrate the speedo. I too am running 33's. I am not sure if they input the gear ratio when recalibrating, but I am doubtful that they did.

 

Either way the gears don’t affect speed as it’s picked up in the ABS sensor. The difference between stock tires and a 285 is about 7%.

If you are using hypertech or similar you just put in the tire size.

That said the last thing going I would ever trust is Waze as it’s not a true GPS

 

What would you trust then?

 

https://www.tacomaworld.com/threads/speedo-calibration-on-3rd-gen-tacoma.547766/

 

Well you can do basic math, use true GPS or find a speed sensor that police set up.

 

Or a buddy going a set speed that doesn't have a modified setup.

 

i prefer to jump on the highway, put the gas pedal to the floor and wait for the cops to give me a printout of my speed

 

I use "GPS Test" (for android). Also, observe the traffic around you. Assuming you travel the same roads everyday, you probably have a decent idea how fast everyone else drives on that road.

At the bottom of every TW page is this link which will tell you how much your speedo is off between stock and your current tires
https://www.tacomaworld.com/tirecalc

 

Mine was clearly off by 20mph when I entered the gear ratios. Just have them leave that part blank. I personally use Google maps to check my speed, and my spedo is still slow by 2-3 mph, so I'll need to fine tune the tire diameter in the Rough Country app. I'd do a test drive afterwards if I were you, just in case your still off by 2-3 mph like mine..

GL!

 

Yeah, but then you have to question how much off their radar gun is. If they're using a freakin' laser beam, that's a different story. But that's a good method too.

 

also need to make sure in the calibration if using hyper tech that the original tire size is correct. Also my suggestion is leave the USB plugged in and rout it below the steering wheel this way you can change it whenever you need. I have mine setup lien that’s Dms can plug in anytime. It’s easy to adjust if you can access it. If not then you need to pull the dash apart each time.