Calibrating speedo with larger tires? and settings in DashCommand...

Just put a set of 265/70/R18's on the Taco... now I know the speedo is going to be off, but how to fix it?

I called a local Speedometer Service business, but they said since the Taco isn't controlled by a cable (to which he said they could fix if it were) and the speedo is controlled by the ECM or whatever other computers are, that the only way of fixing it was going to the dealership and having them "reprogram" for the new tire size. My buddy who works for Toyota as a service tech replied "dafuq is he talking about?" when I asked him about said reprogramming. Is this something that my buddy just hasn't run into in all his years working for Toyota (bearing in mind that he dad also works as a Toyota service tech, who also hadn't heard about anything like this), or is the Speedo service guy blowing smoke up my @$$?

Also, anyone have experience in modifying the vehicle advanced settings in DashCommand to make it's speedometer work correctly? I changed the "Tire size specification" but that didn't seem to work. The only other option that I can see is "Speed correction", which seems to only want a number... My initial thought is new tire circumference divided by old tire circumference equal speed correction factor? In my case, from the tire size calculator if I'm correct on this, would be 102.44/95.72=1.0702...

Any thoughts?

 

This is something i was wondering about as well. I'm about to do my first upgrades to the truck and i want the speedo to continue to be accurate. Looking forward to seeing a solution to this.

Also, first post, gonna put a couple of pics up this weekend of my bone stock 2015 Magnetic Grey DCSB TRD Off Road.

 

Have you considered this route: http://www.hypertech-inc.com/products-speedometer-calibrator.aspx