Any advice?
 

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

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

ok so i think i got this right

for old tire size i typed in

275/65-20 (i believe thats the stock size, havent looked)

that came out to

old diameter 33.37" ( 847 mm )

old circumference 104.83" ( 2662 mm )

old R/mile 604

for the new tire size

285/75-18

which came out to

new diameter 33.98" ( 863 mm )

new circumference 106.75" ( 2711 mm )

new R/mile 594

with a 5% squish on 3.73 gear ratio the effective ratio is 3.66 with a new ratio of 3.79


so i should put 2711mm for the custom options, should i change the gear ratio? or leave it at 3.73??


how will i know i am going faster than 60mph? i have mph as an option on the gryphon but i will not be able to have a police radar me or anything

You're "overthinking" this a bit (I do it all the time, so you're not alone).

Don't worry about entering your stock tire size at all. You just want to know the circumference of the tires on your truck. Enter 285/75-18 in the "Old Tire Size" window and leave the "New Tire Size" blank. This gives you 2711 mm as the circumference with 5% squish.

What you did by entering your REAL old tire and then the new tire sizes and the gear ratio was to find out what your new, "effective" gear ratio is (which is 3.66). So, you don't have quite the "pulling power" with the new, larger tires as you had with the old ones, but you may get better mileage at cruise, since your RPMs should be lower.

If you wanted to keep an effective gear ratio of 3.73 with the new tires, you'd actually have to change your gearing to 3.79, and, if you could do this, you'd effectively be back to stock.

So. use the 3.73 gear figure if that's what's in the truck and a starting circumference of 2711.

As far as verifying your speed, if you can't borrow a GPS that shows speed, you can do things the hard way, which is what I did at first. The next time you drive a long stretch of highway with mile markers (interstates are best) note your odometer reading as you pass a mile marker. Then, after a long drive (I used an actual distance of 100 miles, according to mile markers) note what your odometer reads again. If it says 100.0 miles after 100 actual miles, you are dead on for speed AND distance. If it shows, say 101 miles, it's because the tire size you entered is too large and you are driving 1% slow. Decrease the circumference by 1% or 27 mm.

You can do this over shorter distances, but it won't be as accurate.

By the way, you'll see some people recommending measuring the distance your tire rolls on your driveway in one revolution and using that figure. It's just a starting value too and doesn't take into account the "expansion" of a tire as it rotates at high speed. (Think of a dragster's tires during a burnout).

- Jack

Most local police will help you with this sort of thing if you just pull over and talk to them.

You could have someone pace you in a vehicle that you think is accurate. You can also time yourself between mile makers, if you're doing 60mph, it should take you exactly one minute between markers, then use Jack's formulas to calculate which way to tweak the computer. Neither is nearly as accurate as Jack's method, but they should get you close till you can take the road trip to really test it.

Especially if you want to verify that you're doing 70 in a School Zone! :smiley_roll1:

Cajun is quite right on the 60 sec to do 1 mile at 60 mph. If you get that so it looks right, you'll probably be within +/- 1 mph of the real speed.

And, in case you've missed other posts on this - The truck's speedo will ALWAYS read 2 mph high if you "dial in" the Gryphon displayed speed to be dead accurate. At this speed though, the odometer will be accurate. You can think of this discrepancy as Ford's attempt to keep you from getting a ticket, since you think you are going 2 mph faster than you really are. :rofl:

- Jack

ok thanks guys.


yeah i would use GPS but i got the stupid one that came with the truck and hate it.

i wasnt wanting to get one with a gps because i was going to put an aftermarket one in but the only white one they had, which had the features i wanted had GPS


ill figure it out, im sure 2711mm will be close enough. im never really worried about a speeding ticket here

I often use the previously described 60/60 method (60 MPH for 60 seconds) to see just how close I am with tire size. It work really well for those who don't have a GPS. For more accuracy, set the cruise at 60 and do 5 miles vs. 300 seconds. This will get you REALLY close.

And as Jack said, the speedo is nearly always 2 MPH faster than the actual vehicle speed so even if you're 1-2 MPH off, you should still be safe.

Take care.

thanks Bill

whats the break in period btw, if any??

i can tell the difference in power immiediatly, but one of the main reasons i got it was to try and get better mpg.


especially in Seattle there are alot of hills and stop and go's.


i was averaging 12.5 or so without the gryphon, what do you expect with it?


btw im pretty light on the throttle never really any jack rabbit starts

oh and another thing, i dont have a load previous settings option after i click on "custom options"

however when i went to tire size, it went to a screen saying something about that it couldnt be done or something, ill try it again tomorrow and write it down if it happens again

but then it froze.


ill give it another shot tomorrow