SlyFX4Guy

iTrader: (-1)

I have 35" tires with a tuner/speedo recalibrated and my GPS is showing I'm still 2mph at highway speeds.

Question: How do I compensate/correct? Tell the computer it has slightly larger or smaller tires? By how much to compensate for the 2mph diffference(60-80m? I can adjust .4" incriments.

Thanks!

Coyote Five O

2mph at what speed exactly ?

to increase speedo speed tell it your tires are bigger
to decrease speedo speed tell it your tires are smaller
.4 of 35 = 1.1%

Livoniabob

It's late and my mind thinks it's the other way around,,,, I will think again in the morning..

Heck I'm not even sure but I think he is saying the speedometer is reading 2 mph slower than the gps? But at what speed highway can be anywhere from 55 to 90+mph..

SlyFX4Guy

iTrader: (-1)

The GPS is saying 2mph slower than the Speedo at hwy speed 60-80mph

E. Manuel

Use a rotations per mile calculator like this one: https://tiresize.com/calculator/

Then enter how many revs/mile it is under that option for your tuner and download it to your truck.

Livoniabob

Go up one tire size.. Actual speed = GPS speed = 70mph speedo shows 72 so you need to slow down the number of wheel turns per mile.. So bigger tire..

Coyote Five O

That will make things worse
His speedo is faster than gps
If he goes bigger it will read even faster, like another poster said its all about revolutions per mile.

The new tire size is over 8% larger diameter than stock
The tune calibration was close but slightly over estimated the tire size

If speedo reads 72 when actual (gps) is 70 he is 2.8% out (too big)
The truck thinks his tires are 2.8% bigger than they are.

Since he can only adjust in .4" increments ( which is roughly 1.1% of his 35" tires he needs to downsize by either .8" (2.2%) or 1.2" ( 3.3%)
One of those to will get his where he needs to be
His tires may not be exactly 35" in diameter so just have to play around till he gets it as close as possible.