Gryphon won't correct tire size
 

I had custom tunes by PHP, but my computer was reflashed 2° new motor being installed. I have an 05 F-150 with a 06 motor. I updated my gryphon to the canned tunes offered through Pegasus. I install in truck and every is a go except for the tire correction. I have 285/70/17 and inputed 2610 and hit enter. i check back before programming and it saved my tire input mm. When i go to program my speedometer is 7mph fast according to GPS. When I go back to reprogram truck I load previous settings and everything loads except for the tire size and it reverts back to 2356mm or whatever. I tried it atleast 4 times without success. I updated to the newest firmware and calibrations prior to tuning everything.

Anybody have a clue why its not doing my tire size correctly?

It MAY be because you are "checking" the Tire Size (TS) BEFORE loading the tune, or, you may be looking at the TS BEFORE you "Load Previous Settings". but first, the TS value you are entering is too large, which is what is making your speedo read so fast. (If it were actually programming in the 2356 figure, your speedo would read SLOWER than you were actually doing). The 2610 figure is correct for an unloaded tire - no "squish". You have to reduce that value to account for the "flattening" of the tire on the pavement which reduces its effective radius. I've found a 3% reduction works well, which in your case would be a value of 2532mm. However, if your speedo is 7 mph fast at highway speeds, you probably need to reduce that value even more, maybe to about 2453mm (which is a 6% squish).

Now, to get the Gryphon to "show" you that the TS is correct: As soon as you OPEN the Custom Options Menu - scroll to and select "Load Previous Settings" and hit <Enter>. THEN, scroll to TS and hit <Enter> to see the value, then hit <Enter> again to accept it. (Don't push the <Menu> key in any of this and DO NOT go to the TS entry before you "Load Previous Settings"!

Don't be surprised if the TS is just a bit different after reloading the previous settings. If you had entered 2532, I predict you will see 2534 after reloading it due to rounding errors (it's not a big deal).

Let us know how this works out for you, OK?

- Jack

Yes, make sure your tire size and gear ratio is correct after you load previous settings.

I also found that the easiest way to get the tire size close to actual is with a simple conversion using the odometer (higher accuracy than the speedometer). What I do is drive about 10 miles after clearing the odometer on the truck and GPS.

*Make sure the GPS has been able to get an accurate location otherwise it will say you are travelling when in reality you can be sitting still. That can be a real problem because the distance you never traveled is recorded on the GPS odometer.

Truck distance(truck odometer)
Actual distance(GPS odometer)

...multiply the tire size by whatever this value is.

Here is an example of how it should look.
Truck odo: 11.0
GPS odo: 10.54
Programmed TS: 2410

Math: 11/10.4=1.058 (so it means your current TS is about 6% too small, a real difference when the value is in mm)
2410 x 1.058=2550 after rounding

It may take a few tries if you are using short distances but you will get close eventually. The further you drive the more accuracy you will get, but the short 6-10 mile trips will work well enough to get within a decent % error.

And just to add, the tire size calculator in pegasus is very helpful in getting a close size in the beginning. Jack is probably right with the 3% squish on stock rims but wider rims+stock tires (like mine) are around 4.5%

Colby, that's a clever use of the odometer to correct things.

For anyone that doesn't understand why, it's because the odometer doesn't depend on speed. You can drive that distance at varying speeds and it won't matter. The same error that's present in the odometer is also present in the speedometer, so by correcting the TS by that amount, you correct both odometer and the speedometer.

- Jack

Thanks guys...i swear i did the same procedure earlier but it did work. I adjusted the tire size wo the 6% squish (great explanation btw) and i'm about 3mph off. I haven't had time to fine tune it but thats acceptable by me.

Thanks for the help guys!

noticed that mine is off as well

my gps says the distance between my office & apartment is 24.9 miles

odometer says 28

my speedo is also reading slower than the gps as well

So then to correct it all you have to do is multiply your current tire size by 1.1245 (28/24.9)
Also, write down the new tire size on a piece of paper. That way, if you have to adjust the tire size more you can multiply the odometer/gps fraction by the number you wrote down.

Its also a good policy to write every change you make with the gryphon down onto a piece of paper and save that paper for future reference. I keep my paper in the pod behind the gryphon after I fold it so that it wont be able to slide out of any cracks...I resort to the good old fashion paper ball fold. :hehe:

OK, Ive tried the formula using the odometer and my speedo is still off by the same amount. GPS reads 67, CTS Unit reads 70, and Truck speedo reads 73. Stumped. If it helps, I have Nitto 325/60/18 so I used 2660. Truck odometer was 10.7, GPS was 10.3. I got 1.0388 x 2660=2763 2763-3% for squish=2680. THats what I used.

Unloaded circumference is 2662mm. Allowing a 3% squish factor = 2662 x .97 = 2582mm

Double check:

10.3/10.7 = .96

2582/2680 = .96

Also make sure that you are properly saving the custom settings.

http://forum.gopowerhungry.com/faqs-...ions-menu.html

Looks to me like you've INCREASED your TS for "squish", which would make your CTS read "too fast", A 3% squish on your tires reduces the circumference to 2581. That may be too small, looking at your numbers, but the correct TS should be somewhere between 2660 and 2581.

Edit: You're too fast for me Shotgun! And you were absolutely right.

- Jack