Variance between Gryphon and actual milage

[88Racing]

Running the canned tunes mine was off by about 1.5+--2.0+ mpg. With the customs more like 0.5+--0.75+ mpg.

Lars

[p40whk]

Thanks for the quick replies, I'll add the circumferences tonight.

I wasn't sure what was more accurate since my speed on the Gryphon reads about 3 mph slower than what my dash needle shows. I would imagine the Gryphon is what's accurate since I regularly go by police with my truck in cruise control set 9 over and have never been pulled over. When my Gryphon shows me going 79 my dash gauge says I'm doing 82. Since the readings are coming from the computer and not converting the speed to an anolog gauge I am assuming that the Gryphon is more accurate. I hope I'm right! Otherwise I may get pulled over real soon!

[88Racing]

Your needle on the dash will always read 1+--2+ higher than what a gps or gryphon will read out. That's with a correct value for the tires in the gryphon. Some weird thing Ford did?

Lars

[Savagetwelve]

I have a quick question:

on the Gear Ratio Calculator in Pegasus what does Squish reffer to?
I am running 285/55R20's so how much Squish is that?

Does anyone what stock Gear Ratio was on the 04F150 STX? How would I find that info?

[p40whk]

I just assumed squish was the weight of the truck pushing down and flattening out (squishing) the tire. But, you know what happens when you assume.

You should be able to find the gear ratio on the dataplate inside the door frame. I think

[Jackpine]

Originally Posted by Savagetwelve

I have a quick question:

on the Gear Ratio Calculator in Pegasus what does Squish reffer to?
I am running 285/55R20's so how much Squish is that?

Does anyone what stock Gear Ratio was on the 04F150 STX? How would I find that info?

In the gear ratio calculator, "squish" refers to the "flattening" of the rubber tire under the weight of the vehicle. The metal wheel does not deform, but, the rubber part does. So, if the "squish" value is 5%, the distance between the rim and the ground is reduced by 5%. That's a constant value as the tire rolls, so the distance between the axle and the ground (the rolling wheel radius) is reduced by that much tire deformation all the time. Ford uses this 5% rubber deformation value when they calculate the number of revolutions your axle makes per mile on stock tires (according to Bill). I've found, for my tires, that a 7% squish value in the calculator makes the Gryphon speedo dead accurate. Other people have found it works for them too.

But, here's where it gets tricky. You can "pretend" that the entire wheel-tire combination compresses under the weight of the vehicle to simplify calculations. So if the zero-squish radius to the edge of the tire is 32", then using a 7% reduction in the rubber part is about the same as a 3% reduction in the 32" value. And, if the zero-squish tire circumference is 2559mm (my tires) then subtracting 3% (about 77mm) gives 2482mm - almost exactly what the calculator gives at 7% rubber squish (it says 2480mm).

What I'm getting to in all this, is, if you know the "unloaded" circumference of your inflated tire, you can subtract about 3% for squish and you'll be very close.

Going back to your question though, if I were you, I'd change the "squish" value in the calculator to 7% and use the resulting 2511mm value for the Tire Size in the Custom Options Menu. (I tend to be long-winded, don't I?)

For the stock Gear Ratio, look at the sticker on the driver's side door. Near the bottom, you'll see the word "Axle" and below that, you'll see a "code". Mine is "B6", but yours could be two numbers. I did a quick internet search and found this for F150s and F250s:

Axle Codes (LS=Limited Slip / Traction Lok):

F-150:
19 – 3.55 Non-LS
18 – 3.08 Non-LS
H9 – 3.55 LS
B6 – 3.73 LS

F-250:
27 – 3.31 Non-LS
26 – 3.73 Non-LS

Hope all this makes sense!

- Jack

[Savagetwelve]

Jack it some worlds it does make sense! Thanks for that lond detailed explaination!
I guess you just have to play with that squish # untill you get it right!
What are you comparing the Gryphon to? The speedo?

I am running LT tires would that mean they are less squishy? Therefore less of a % (eg. 1-2) making Squishy 8-9%
The calculation in the user manual does not account for the squishy?
( I just like uing the word squishy! )

W/O the squishy I calculate manually 285/55R20: 2581mm

I guess this will have to be my starting point!

[88Racing]

Start out at 2500 and use a gps.

Lars