Variance between Gryphon and actual milage

[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

[Savagetwelve]

Thanks Lars! That was short n sweet....

[Jackpine]

Yea, Lars does have a tendency to reduce it all to "essentials" *boring*.

His value is a good starting point, but I think mine is better!

DO use a GPS if you have one. It will give you an accurate readout of your speed. Get the Gryphon to agree with it by changing your TS as needed. Your dash speedo will then read about 2 mph faster, because Ford set it that way.

I suspect LT tires may have less squish, so the circumference value could be larger. The user manual calculation assumes zero squish. If you enter that value, your TS will be too big.

- Jack

[p40whk]

I checked mine with GPS this morning and the Gryphon is much more accurate than the Speedo.

At lunch today I went out to check the custom settings of my TS and GR and they were not set to what they should be. So, I reset them using the custom option. I'm using the 87 canned Tow tune until my performance tunes come in (have a CAI) but I got to thinking (since I don't have the manual handy) Do I need to revert to stock before I make custom changes or change the tune level? I couldn't find this in the Q&A's but thought I read somewhere that you should go back to the stock tune before changing to a Gryphon Tune.

I didn't do that in this case (haven't driven the truck yet) an am wondering if I need to reset it to stock then load the 87 Tow with the custom settings.

[Jackpine]

No, you DO NOT have to return to stock before opening the Custom Options menu. But, you're not really going to be able to "check" things in that menu either unless the first thing you did was "Reload Previous Settings". Even then, your TS will probably be slightly different.

Do look again at the Q & A that I wrote for the Gryphon Custom Options menu. I think it will answer all your questions.

(I probably need to add the part about not having to return to stock though - thanks!)

- Jack