So bluejay you'll deduct 3% from the edge evo equation also??
I might have to try this when my brain is fully functional

 

Yes, the Edge Evo formula does not include a dedution for the squish factor. I seem to recall that Bill said his forula does include a deduction, though I have not seen his formula.

It amount of reduction needed varies with tires. My Michelins needed a 3% reduction from the Edge formula to be right on and the Falkens I am currently running require a 5% reduction. I used a GPS to check the accuracy in both cases, to get the monitor accurate. The truck speedometer is still off by Ford's 2 mph differential.

 

Your truck's speedo should read atleast 2 and possibly 3 mph faster than the truth.........keep this in mind.

 

since there is, a squish factor, why wouldn't weight be a factor????
because at greater speeds your tires will ballon counter acting the squish!
correct?
I'm not trying to get C0CKY, it just seems that when your factoring for squish there are going to be a hundred other different factors that will counter act the adjustment.

 

yeah something isnt right. I put it on 611 and its way off. It shows be running 70 when im only doing like 55. So im not sure what to set it on. Ive tired just a little bit above stock value and its still off. So i guess ill just leave it how it is, that way i know im 5 mph off.

 

I ran my rev per mile calculation and came up with 634 as your number. This matches the reccomendation from the Tire Rack website too.

Try it and see if it gets you any closer. For those of you who would like to see my math just let me know.

 

Make sure that you have the right gears in the settings. In other words, check the default and if it is not what you have, change it to what you really have. A variance from 55 to 70 is huge for it to be just tires. Changing from 611 to 634 will make only about 3 or 4 mph difference.

 

well from what i can tell i have 3.55 gears, and i have it set on that. I tried setting it on 640 before but it still seems way off. Would the gears make that big of a difference if i have differenct gears in the rear? I dont know, im confused.

 

Have you always owned the truck? Sounds as if someone has put 4.10s in it. Have you done a drive shaft check? Mark a tire with the ground. Mark the drive shaft with the pinion. Turn the tire one full revolution and see how many times the drive shaft turns.

 

BTW, your problem is the opposite direction. My correction for the squish factor just made you farther off. That is why I think it may be the gears.

 

no i just bought it n june. I was told it had 3.55 in it, but its an fx4 and the last i was told all fx4 have 3.73 or 4.10 gears cuz of the off road package. No drive shaft check. So i put a mark on the tire where its on the ground, mark the drive shaft where the pinion is. And then move the truck to see how many times it turns. Got it. Looks like im a need some help. Ill get back with you when i do it later today. Thanks

 

you might want to check the door jamb first just to see. it will tell you the stock gear ratio, so it might not be right, but just read the differential code on the sticker on the driver's door jamb then look it up on here:

Ford differential codes

i would at least try that first, but you probably are gonna have to do a drive shaft check, unless you have another way of confirming the door jamb code.

 

IVE LOOKED AT THE CODE ON THE DOOR, CALLED THE DEALERSHIP AND LOOKED UP BY VIN, AND EVERYTHING SAYS ITHAS 3.55. I EVEN TALKED TO THE PREVIOUS OWNER AND HE SAID HENEVER CHANGED IT. SO I DONT KNOW. IF I LEAVE IT ON STOCK VALUE, AT LEAST I KNOW ITS 5 MPH OFF, BUT IF I CHANGE IT TO ANYTHING, IT THROWS IT FOR A LOOP AND I HAVE NO IDEAD WHAT I AM RUNNING.

 

Green_machine, what brand tires are you using?

 

cooper zeon ltz, 285/60r18