Going from 16" to 17" speedo calibration

cquam · #1 (**permalink**) 07-16-2008, 02:36 PM

I have spent several hours searching and reading all the posts I could find on this subject. I learned a bunch but still have a question.

Since both the 16" and 17" were factory options is there a setting on the ecm or speedo to compensate for the size difference. I compaired the registerd spped vrs my gps and at 70 there was a 5mph difference.

Any help would be appreciated.

jdeaton · #2 (**permalink**) 07-16-2008, 02:44 PM

The wheel size doesnt matter for calibration... its the tire size. I believe the stock 16" tires are 265-75-16 and the 17" are 265-70-17... the tire diameter is the same for both tires. To change the speedometer calibration you need a truspeed (i think thats what its called)

Jetes03tundra · #3 (**permalink**) 07-16-2008, 03:11 PM

stock 16" is 265/70/16 and yes truspeed is what you need but the install looks like a pain in the *** from what i saw

cquam · #4 (**permalink**) 07-16-2008, 03:14 PM

thanks for the promt replys.!

Seems difficult to believe that if I purchased a new truck and a 17" rim was an option from Toyota that they or I would have to install an aftermarked calibration device for my seedo to be correct.

FLTundra06 · #5 (**permalink**) 07-16-2008, 03:49 PM

The sidewall on the tire that came with the 17" rims is shorter than the sidewall of the tires that came with the 16" rims so the outside diameter is the same for both, meaning that the speedo calibration is the same for both. If you have the stock size tire that was on the 17" rims your speedometer should be close. I had stock 16" rims and now have 20" rims and my speddo is 1 mph off per my gps.

skinny2 · #6 (**permalink**) 07-16-2008, 05:03 PM

That swap shouldn't make a difference, as they theoretically should be the same overall diameter. Did you check the speedo before the swap? There can be a slight difference in diameter between brands/styles of tires. Not usually much....1/4"-1/2" at most...so maybe a 2mph difference worst-case scenario.

USAFTUNDRA · #7 (**permalink**) 07-16-2008, 05:29 PM

use this it should help
Tire size calculator

cquam · #8 (**permalink**) 07-16-2008, 06:39 PM

thanks for the link. My manual calculation gave me a 7% difference. I was .1% off.
The stock tires were 245/70-16 and I went to 265/70-17 My speedo is off by about 5mph. I have called a dealer and they are "looking into it" If and when I hear back I'll post the reply.

I also plan on grounding the pink wire. If someone is doing the same and can post a pic it would help many whom have asked in other posts.

Thanks again