Quote:
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?
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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