[Jackpine]

Originally Posted by th3godf4th3r

Well according to corey i should be getting my custom tunes today

anyway i should have asked this earlier but is there anything i should do before i add the tunes to the gryphon?

the only think i can think of is that i got bigger wheels and tires

well actually went from the stock 20's to 18's but i went to a BFG 285/75/18 tire i believe it is

i know about the tire size calculator in pegasus but i dont know what to do with it?

any help?

other than that anything else?

It's actually pretty easy. You can find the tire size figure right now, using the Pegasus tool by itself. Click on "Calculators", and then the "Gear Ratio Calculator". Then, enter your new tire size in the "Old Tire Size" window as: 285/75-18. When you do this, you'll see your tire circumference in the "Old Circumference" window and it will be: 2711 mm. This is its "rolling circumference with a 5% squish factor. You can change the "squish" in the "Squish %" window on the lower left to see the effect of different squish factors, but I'd start with the 5% result - it will be close.

When you get your tunes, go ahead and load the one you want to use into your PCM, but skip the "Custom Options" step the first time. Let it program the PCM that way. At this point, your tune will be loaded with the stock tire size and gear ratio.

Next, reselect "Power Programming", but this time say "yes" to the "Custom Options" choice. When you see the custom options menu, scroll to "Load Previous Settings" and say yes to it. Always choose this option first! Now scroll to "Gear Ratio" and make sure it is set to what you have - adjust it if necessary! Scroll to "Tire Size" and enter the circumference in millimeters - start with 2711. If you don't want to change anything else (I wouldn't) scroll to "Done" and hit enter. Let the unit reprogram your PCM. It will take longer this time.

On the highway, verify that your speed is correct using GPS, mile markers, police radar, whatever. I'd use the speed readout you can see on the Gryphon to do this. If you are actually going faster than the Gryphon is saying, the PCM thinks your tire circumference is too small - increase it. If you're moving slower than the readout - decrease the circumference. How much?

Well, say the Gryphon says you are showing 70, but the cop's radar has you at 68. That's a 2.9% error. Decrease your circumference by 2.9% or about 79 mm and try that figure.

Don't forget to "Load Previous Settings" and recheck that your gear ratio is correct when you do this.

- Jack