Got my Gryphon, Got Cpl Q's

[Jackpine]

Originally Posted by 88Racing

Calculations I got with out "squish".

Stock
275/55R20-2546mm

Spare
275/65R18-2559mm

Difference tells me spare has 1/2" more tire in circumfrance. The post I did earlier this thread about being about equal is not true. The spare should only be ran as a spare(temporary) unless you change all 4 wheels to that size or get a 20" spare.

Lars

Interesting, Lars. TG150 (Tony) and I have had several back and forth's by PM this morning. For everyone's information, he loaded Level 2 without doing anything with "Custom Options" and his Gryphon speed exactly matches the speed shown on his GPS (and, of course, the truck's dashboard speedo reads 1-2 mph faster). I suggested he leave well enough alone and not mess with the tire size.

Lars, I don't think he ever said what his stock tires were, but the new tires are different than yours. So, it's quite possible they have the same rolling circumference.

I'd be quite cautious in any case if the stock spare were put on either of your trucks. I'd sure keep the speed below 55 (like when using a space saver spare) and try to get the road tire back on as soon as possible.

- Jack

[88Racing]

Jack

Tg150 said that he had a set of stock oem wheels and tires 20".
From what info and comparrison I did this morning that's why I posted the calculations.
I have the exact set wheels and size tires as he is running.
After doing the calcs w/o squish I found it interesting that there was that 1/2" difference between the 18" and 20" wheels/tires. I do think with the squish factor that it may actually be the same circumfrence. The 18" having a taller sidewall and the 20" having a shorter one.

Lars

[Jackpine]

Originally Posted by 88Racing

Jack

Tg150 said that he had a set of stock oem wheels and tires 20".
From what info and comparrison I did this morning that's why I posted the calculations.
I have the exact set wheels and size tires as he is running.
After doing the calcs w/o squish I found it interesting that there was that 1/2" difference between the 18" and 20" wheels/tires. I do think with the squish factor that it may actually be the same circumfrence. The 18" having a taller sidewall and the 20" having a shorter one.

Lars

You could be absolutely right about the "squish" effect. I may have misunderstood something in his first post.

- Jack

[tg150]

Hello all..

I appologize for never mentioning the size of my previous 18" wheels and tires vs my 20" wheels..

the 18's were P275/65/R18
the 20"s are P275/55/R20

After i installed the Gryphon on level 2 i took my truck for a drive like Jack suggested "Before" going into my "Custom Options" and changing the TS and GR, which turned out to be a great idea. My trucks speedo was approx 1-2 miles faster than the gryphon so i figured i must have been right on from what i read. But i wanted more proof so i went home and got my Garmin gps and sure enough the MPH on the gps and the gryphon matched exactly. So come to find out there really is no difference between the oem 18" wheels and oem 20" wheels.

Overall i love my gryphon..i did notice and improvment in perfomance, quicker shifting and responce.. I cant wait to get my 87 performance tune.

I'd like to thank everyone that replied and helped me figure this out and hope this post helps others that might be wondering the same thing. TY..

Jack.. a special thank you to you for accepting my PM's and walking me through it step by step all day long. Your a great guy and i really appreciate it. TY..

Corey.. Ty for being so polite when i called and answering all my emails quickly.. I enjoyed all the goodies that came along with my Gryphon and it sure made my day

Thank you everyone..
-Tony

[Jackpine]

Thank you Tony, you're quite welcome, and, thanks for posting your tire sizes, so I could find out something for sure (not that I doubted you Lars)!

Here's what I get for the two tires using Bill's super easy calculator in Pegasus:

No Squish - Stock: 2559mm, 20's: 2545mm (a 14mm difference - about 0.55 inches, just as Lars said)!

5% Squish - Stock: 2503mm, 20's: 2498mm (a 5mm difference - only 0.02 inches)

7% Squish - Stock: 2480mm, 20's: 2479mm (only 1mm difference - virtually identical - only 0.004 inches for those of us who are metrically challenged)!

As I've said in other posts, the 7% rubber squish seems right for me with my 275/65R18's inflated to the recommended 40 psi. That's why I recommend it as a starting point.

Tony did not set his tire size when he loaded his tune - he bypassed the Custom Options!, so, the tire size was a "stock value" taken from the PCM's VID area. Clearly, Ford allows for "squish" too. And, interestingly, when squish is factored in, the two very different tires cover virtually the same distance in each revolution!

Again, thanks Tony, for confirming your tire sizes so I could explain what happened (to myself at least). This is a pretty neat bit of data to add to the database!

- Jack

[88Racing]

Thanks Jack for posting the info.
The aftenoon break was to short for me to put my pencil to the numbers and post them.
Someday I will get a laptop with an air card to do better posts instead of the blackberry.

Lars