having problems calibrating the speedo correctly

[bigmoose153]

Per my GPS, the speedo is 5MPH off using the tire settings off of my tires. So I tried various differen sizes but the speedo is still off. sometimes as little as 2MPH and as much as 5MPH depending using various wheel/tire sizes. No matter what I end up putting in, the vehicle is always faster than what the Speedo says.

I have an 2005 LLY DMax crew cab running Kumho 285/75R16's.

I've already tried the spreadsheet on this website for the tire size calculator and still doesn't work

Help!

[mikel]

I would suggest contacting Kumho to see what they list as the actual installed height for the tire, and use that info to set the speedo.

Thanks

[bigmoose153]

Yep, already did that and it still didn't work....

[mikel]

Well if its only off by a little bit, try dialing it in using the aspect ratio parameter.
if you are currently entering 285/75/16, try 285/73/16 or 285/77/16.
This will allow you to make finite adjustments to the overall height setting.

Thanks

[mvn]

I have a 2007 Classic and use the 7186 Predator. Speedo calibration was off when using 285/75/16 as the tire size for the BFG AT T/A's I have. Using a GPS for calibration, I found my speed reading on the speedo was 6% too high. I simply keyed in 285/69/16 as the tire size on the programmer and it is perfect!

Awesome product!

Mark

[rev.dennis]

Actual Advertised Tiresize: 285/75/16

Could you tell me if I need to adjust because my truck is going faster then what the speedometer is saying then I go up or down with the middle number?

76+ = speedometer moves up to meet actual speed
74- = speedometer moves down to meet actual speed