[Joshg]

I just put new tires on my truck and they are bigger so I Need to change it in the programmer, I know how to change it and all that I just don't know what size my tires are in MM? I've read that there's a chart in the owners manual but I bought my gryphon used so I don't have the manual. So if someone could please help me out and give me the correct numbers to put in would be much appreciated, I asked for help on f150forum but got a bunch of smart remarks. My old tire size was 275/65/18 and my new size is 285/70/18. Thanks and plz no smart comments.

[JackandJanet]

We only give "dumb" answers here. Your Tire Size has an unloaded circumference of 2689 mm. I'd try reducing that by 3% to account for "squish" (weight on the tire) which gives 2608 mm.

If the speed on your Gryphon reads slower than actual, increase the value. If the Gryphon reads fast, decrease the number. Remember your dashboard speedo will always read 2-3 mph faster than the Gryphon in the 70 mph range. Compare the Gryphon speed to some known accurate value like from a GPS.

- Jack

[Joshg]

Thanks. So if the speedo is right then my odometer will be right correct?? Sorry I'm puzzled with this stuff. So I want my gryphon reading true to a gps and truck speedo reading 2-3 mph fast and everything will be back right and accurate??

[88Racing]

Originally Posted by Joshg

Thanks. So if the speedo is right then my odometer will be right correct?? Sorry I'm puzzled with this stuff. So I want my gryphon reading true to a gps and truck speedo reading 2-3 mph fast and everything will be back right and accurate??

Yep......

[JackandJanet]

I want to clarify: If the Gryphon speed is correct, then your dash odometer will also be correct.

The reason for the dash speedo error is that there are issues translating a digital signal from the PCM (a true value) into a mechanical display on the gauge. The odometer has no mechanical parts, so it is not effected. The Gryphon speed is likewise simply a display of what the PCM is sending, with no "translation error".

- Jack

[Joshg]

Ok so I put 2608mm in and this is the results: gryphon speedo and gps read the same and truck speedo reads 1-2 mph faster. My car gps doesn't have a odometer or trip thing in it so I had to get a odometer app for my iPhone, so compared to the iPhone trip/odometer my trucks odometer is right and reads the same. But I'm not sure how accurate the iPhones gps odometer is? But I did compare my iPhone gps speed to my real car gps speed and they are the same so 2 gps's are dead on with my gryphon speedo and truck speedo is 1-2 mph faster than all 3 of those. So if I havnt lost anyone lol does it sound like everything is right??

Also these are toyo mt tires, they are a E10 10 ply tire, these tires are VERY stiff hard and heavy so I'm sure that will take account for less "squish"

[ticopowell]

That sounds right, 1-2 off is on the low side so you are lucky
Glad you got it working right!

[Longshot270]

If your app is that accurate then I say write down your tire size and stick the paper in the glove box.

Also, GPS location is based on mathematical calculations so any unit that can receive a signal will be able to locate your position within a decent area.

[JackandJanet]

You're good to go, Josh.

- Jack

[Joshg]

Thank you all for all yor help it is very much appreciated! Also I have noticed over like a 10 mile distance my truck odometer ends up getting like 1/10 faster than the gps. Is than anything to worry about or can that just be that they are 2 diff devices reading 2 diff ways and they aren't synced together so they aren't gonna be dead accurate with each other??