Tire size adjustment..
 

Got my 87 Custom Perf loaded up and I went into custom options to fix my tire size and though I got it close...didn't get it quite right. I am showing about 2 mph higher then what my GPS says...so I over shot it a little bit. My question is...#1- would you worry about being off that little bit? #2- if I want to adjust it, can I go back into my custom options without going through the whole loading process again?

This will answer your question re: Custom Options.

http://forum.gopowerhungry.com/faqs-....html#post9248

As far as speed being 2 mph off, it's really up to you. There are numerous posts and very good methods for determining the corrected tire size.

Thanks a lot for that link..lots of useful info there. Seems like I am fine with being 2 off on my dash. Gryphon and GPS are "almost" dead on. I'll just leave it. Thanks again. And just fyi to all interested, 2718 is what worked for my 35x12.5x18's

That figure is just a teeny bit larger than what you'd get with a 3% "squish" compensation. Looks like a perfectly reasonable number to me.

- Jack

If you want to get it perfect clear the odometer on the truck and GPS, drive at least 10 miles then use this calculation:
Truck distance / GPS distance x tire size = new tire size
:thumbsup:
Also apparently Ford made the speedometer about 2 mph off.
My GPS, truck and gryphon all say the same thing.