noob tire size question

[thesilverford]

hey guys i just have my truck in the shop right now getting a lift and 35" tires installed. How do I go about changing the tire size? Do I have to do this for each level?

I realize there is an option " Do you want to make a custom program? (yes)/(no)"

do I have to use this option? Im just afraid of it wiping my custom tunes if
I click yes.

happy thanksgiving.

[Jackpine]

Originally Posted by thesilverford

hey guys i just have my truck in the shop right now getting a lift and 35" tires installed. How do I go about changing the tire size? Do I have to do this for each level?

I realize there is an option " Do you want to make a custom program? (yes)/(no)"

do I have to use this option? Im just afraid of it wiping my custom tunes if
I click yes.

happy thanksgiving.

There's nothing to be afraid of, you won't hurt your custom tunes if you change your Tire Size (TS). However, the process is different depending on what kind of programmer you have. Do you have the older monochrome Gryphon, or is it the newer, color CS or CTS? And, if you tell us your specific tire specs (metric or inch) one of us will probably be able to tell you exactly what value to enter.

- Jack

[thesilverford]

Thanks for the response Jack. I have the older style Gryphon. My tire size is 35x12.50x20.

[Jackpine]

OK, try a TS of 2709mm. That's just 35 x pi x 25.4 x 0.97 (which converts the circumference to millimeters and reduces it by 3% to compensate for "squish" (the flattening that occurs due to weight on the tires). That should be a close starting point.

You will load or simply reload your desired custom tune (you don't have to go back to stock first), and say "yes" to the custom options choice. Scroll to Tire Size, enter that value and hit [Enter]. Then, you MUST scroll to Gear Ratio (GR) and enter the rear axle ratio in your truck if the correct value is not shown. Both the TS and GR values you find in when you open the custom options menu are just "placeholders" and they may or may not be correct. When you've corrected both of these, scroll to "Done" and hit [Enter] to start the programming with these new values.

Check your speedo against a GPS if you have one. You actually want the dash speedo to read about 2 mph fast at 65-70 mph. This will make your odometer read correctly. If you use the speed readout on the Gryphon, it should match the GPS, and it will be slightly slower than the dash.

Make small adjustments to the TS to fine tune from that point.

Once you settle on the correct values and want to change tunes, scroll to "Load Previous Values" and hit [Enter] as the VERY FIRST STEP when you open the Custom Options menu. This will set the TS and GR to what you need. And, with the new tires, you will ALWAYS have to do this whenever you change tunes or your TS will be wrong.

- Jack

[thesilverford]

My screen seems to be frozen with error f1. How do I exit the screen? It doesn't want to power off when I remove my key.

Thanks

[thesilverford]

I just unplugged it and reloaded the tune. I was able to successfully change the tire size. I am not able to check what gear ratio it has programmed but I'm sure it's right as I never switched that in the first place.

Should be good to go

Thanks

[Jackpine]

In the Custom Options menu, you should find a "Gear Ratio" selection. If you click on that, you may or may not see your correct GR. In my truck, it is the installed gears 3.73:1, but others have found different results.

If your speedo is nearly correct now, your GR is probably a valid number, but if it is badly inaccurate, you will likeky need to set it manually. You can find your axle code on the VIN sticker on the driver's door. Here is how you interpret what you see:

19 = 3.55 open
H9 = 3.55 LSD
26 = 3.73 open
B6 = 3.73 LSD
27 = 3.31 open
18 = 3.08 open
25 = 4.10 open
B5 = 4.10 LSD

Again, if you reopen the Custom Options menu, remember to "Load Previous Settings" as the first step.

- Jack