Ford Techs read this!!! recalibration of speedometer

[thebigmo]

2004-E350 V10 Quigley conversion.
I need help my ford dealer tells me that they cannot reprogram my computer to recalibrate my speedometer. I changed from the stock 245-75/16 tires to a more better tire 265-75/16 because I weigh around 10k lbs most of the time and when I tow even more. When they try to recalibtate they tell me the computer says that the new tires are out of parameters??? Is this true?? I had them even try to calibrate to the standard 235-85/16 that my older van runs on and they cant do that either. I have had other people tell me that the dealer is wrong. Well are they?? If you have an answer or suggestion tell me and I will tell them!! Or will I have to put in a new aftermarket chip??

[Gaucho Cali]

That doesn't sound right Bigmo. I run 315/70-17 tires on my Quigley and the local dealership was able to reprogram the PCM so the speedo is now accurate within 1 mph. It cost me $100. I was told the computer in the van has fewer options than the pickups/excursions, but they should be able to get it to read properly.

Using a tire size calculator from the web, the stock tire is 30.5" tall and does 662 revolutions per mile. The new tire size is 31.6" tall with 637 revs/mile and will read 3.9%too slow (60 mph on the speedo will really be 62.3 mph).

I was able to get the necessary reprograming info for my tire size from a van conversion place because my tires weren't on the option list in the PCM. It was a fairly convoluted process and involved inputing a different rear axle ratio to make it work. I can't believe the computer can't accept input for a 265 tire. I don't have the needed info for that tire size.

There are several aftermarket boxes you can wire up to manually correct the speedo that cost between $200-$300. I didn't want to hack up the factory wiring, but with the boxes you can make as many changes as you want for no cost.

[thebigmo]

Thanks Gaucho my tire calc. reads the same also I am going to take this info to the dealer tomorrow and see what they say. But if it is as usual they will say it cant be done. haha