Speedo and Odometer Correction?

Just changed from 265/65r17 to 265/70r17 and now both speedo and odo are off by 3.3%. Measured with gps speedometer and confirmed it is off now.

I have read that people who have gone to this tire size said their speedometer was actually correct, but thats not the case with me apparently.
Is there any way to calibrate the speedo, and maybe the odometer?

 

I wouldn't worry about that small of a difference....at 100mph you'd only be off by 3.3mph. That difference will also decrease as the tires wear.

 

You are well within the acceptable range of error allowed by engineering standards. The aim is for the speedometer to read higher rather than lower than actual speed for obvious liability reasons.

Society of Automotive Engineers, J1226, which is pretty lax. To begin with, manufacturers are afforded the latitude to aim for within plus-or-minus two percent of absolute accuracy or to introduce bias to read high on a sliding scale of from minus-one to plus-three percent at low speeds to zero to plus-four percent above 55 mph. And those percentages are not of actual speed but rather a percentage of the total speed range indicated on the dial. So the four-percent allowable range on an 85-mph speedometer is 3.4 mph, and the acceptable range on a 150-mph speedometer is 6.0 mph.

But there is more to it than just that as the tires wear and manufacturing differences between tire manufacturers etc...

 

As your tires wear down it will change. Your 265/70/17's will be the same diameter with 40,000 miles on them as 265/65/17's when they are new. That is why it is impossible for manufacturers to get it 100% accurate. There is a range of acceptable tire sizes and even if it is accurate when it leaves the factory it will change as the tires wear.

 

Hey guys. I went from the stock 245/75/16’s to 265/75/16’s last night. The tire size chart says I’ll be off roughly 4mph at 60mph. Should I go get it recalibrated? And if I do, do you know how much it will set me back?

 

Yes you have to buy a device that allows you to reprogram your speedometer and install it.

I run your tire size and my speedometer is off. Supposively the speedometers are a little off from the factory but I’m not sure the exact percentage.

 

Will Toyota do it or will I have to do it myself?

 

Toyota will more than likely not do it snd if they did they would probably charge you out the butt for it.

4Wheel Parts does it.

 

Yeah, I kinda figured. There’s a few 4x4 places around here, I’ll see if they can do it. I just looked on Amazon for a calibration unit. Yeah, 100 to 300 bucks for a one time thing is crazy.

Thanks for the quick response!

 

Its not really a one time thing if you change tire sizes again lol.

It allows you to adjust at any time.

I did not install one. I just multiply my trip distance by 1.033 to get my real distance traveled when I do my MPG calculations.
Then I’m just mindfull of the speedo being off 1-2 mpgs around 65-70mph.

But if you are running anything larger than a size up its probably worth the adjustment

 

I thought going from 245 to 265 was one size up. I know they make 255 but not common on trucks. Am I wrong?

Oh and what about my odometer? Doesn’t it throw that off as well?

 

You have to look at the whole tire size not just tread width.

Circumference change in the tire is what changes your odometer.

Wider tires will be taller but you can also get taller tires that aren’t wider.

Also does any Tacoma come stock with 245s? Thats a tiny little tire.

 

Yeah, my 2018 comes with firestone destinations at 245/75/16’s. I just went to 265/75/16. A little taller but an inch wider.

 

You need a Hypertech calibrator if you want to adjust your speedo/odo. http://www.hypertech-inc.com

 

@Gator352, confirm that your speedometer has s actually off before you bother recalibrating. Not sure where the 3rd gens stand but with the 2nd gen my speedo was off less than 2mph at 70 when I checked it against GPS after installing 265/75/16s.

 

I think I’ll do that first. My truck doesn’t have GPS but I have a Tom-Tom I’ll use to check. Great idea, thanks!

 

Why don’t vehicles that have gps in them recalibrate the spedo/odo automatically? My phone knows exactly how fast I am going, not sure why the gps enabled head unit can’t do the same and talk to the cluster.

 

Stock tires here. At 70 MPH I’m off about 2 MPH. I know this because I have like 3 GPS and they are all the same. I have a Driveluxe 51 on my dash the whole time and pretty much just watch my speed from that. I look at it like my truck odometer is recording less miles than I’m actually driving. The truck isn’t “wearing” out as fast.

 

I was curious about that. Bigger tires equals less revolutions to roll the same distance equals less odometer miles?