285's, speedo question.

Just installed 285/70-17's and my speedometer does not seem to be off too bad. I've only taken it to 50mph with Google maps running on my phone for true speed. Speedo seems pretty accurate until about 52mph and then it seems to only be about 2mph off. Does this sound right? I realize the faster I go the more it will be off but wondering if I should worry about recalibration or not. Thoughts?

 

https://www.tacomaworld.com/tirecalc

 

This is awesome! Thanks brother

 

No problem

 

33’s are only 6-7% larger in diameter. Your numbers seem about right.

 

https://www.roughcountry.com/speedometer-calibrator-90043.html?find=2021-toyota-tacoma-4wd-756520

Here is the next best thing you can do after lifting your truck and getting 285's. Easy to install and makes your
Tacoma drive so much better. MPH's get spot on and shifting and MPG's are way better.

 

+1 for the hypertech/rough country speedo calibrator. As long as you have a computer running windows, set up is cake and install is super easy.
Set your original tire size metric (p265/65/17) and use actual measurement (average of all four. Ground to top of tread) for your new tire size (my 33s came out to 30.75”) for the most accurate starting point.
Leave the usb cable connected and dangling behind the dash so you can adjust it later if you need to

 

That's close enough to not worry about. Tires get smaller as they wear out anyway. By the time you have 40,000 miles on they will be the same diameter as a tire one size smaller and your speedometer will again be accurate. Even if you recalibrated it wouldn't be accurate for long.

Even with factory tires speedometers have never been accurate to within more than 2-3 mph. It's just that before GPS we didn't know.

 

Getting a recalibration module is completely up to you. I only went up to 265/70R17's but decided to get the Rough Country speedo cal module. I just prefer knowing my speedo is correct.

Also the Hypertech and Rough Country modules are the same thing... you came even use the software on each one, but the RC is much better priced. If you do decide to go that route.

 

can you explain how this product works and if it indeed does a good job at its intended effect?

 

This got me thinking about mileage.. if I’ve had 255/85/16’s on the truck most of its life, does that mean I actually have quite a few more miles than my odometer shows?

 

In my experience your tires are the ones the speedo is calibrated to, not the smaller stock tires. Smaller stock tires read 2-4 mph fast at highway speed.

which is why 33’s are not off by much…nearly the same amount as the stock tires are off by, but in the other direction.

 

It intercepts the speedometer signal and converts it by a factor based on you tire size setting that you program. This new signal is then supplied to the speedometer, ECM etc to allow for the correct information based on the new tire size.

 

Yes.

 

is it an easy install? I use a windows pc but don't have a windows laptop.

 

You can use a PC. I set up the module using my PC then installed the module behind the dash. It plugs in between the harness and instrument cluster. There is enough wire that you can move the module behind the heat tubing and then you can reach up under the dash and remove the module for reprogramming without removing the instrument cluster again.

I have been told you can even reprogram it still installed in the vehicle, but it didn't work when I tried to do it. I may give it another try though. That would be convenient.