I'm posting here because it seems the guys with deisels get the best response from the techs. I have a 2006 lariat 4 x4 with the 6.0 . I had to change the 18"
rims to 17" rims to get a good set of snow tires. The speedo is now off at least 10% even though I tried to get a tall enough tire to minimize the the change I thought. I called the dealer to see if they can change the software to compensate for the "standard 265/70/r17" tire size. I talked to three techs
each thought you might be able to do it but had never been asked to do it.
They also said you are limited to the number of times you can do it. If I was to change from 18" to 17" each winter I run out of attempts in maybe three years?
My question if I had them try how bad can it screw up the basic engine program. I ask because after a software update last year it took a couple trips back to the dealer to get the truck to run acceptable. At the rate I'm going
I'll run my extended warranty out 10,000 ahead of time.
Second question, is there a good tuner that allows me to program the tires size change myself. I do a fair amount of towing and am a little worried about running any "hot" programs. But If I have to go through having the dealer do this twice a year the tuner might pay for itself in removed headaches.

Any help from techs would be greatly appreciated. I really don't want the truck to run worse just to get the speedometer corrected.

Jeff Rzepka

 

Any change in the tire diameter is going to throw off calculations made by the computer. This is going to affect your speedometer, odometer, ABS, and will have some limited effect on transmission shifting (if it is an automatic).

What you will need to do is get the "Tire Revolutions per Mile" (TRPM) for the new tires from either the tire manufacturer's web site or the tire shop that installed the tires. Take this figure into a Ford dealership & have them program this into your computer. For example, a BFG Rugged Trail T/A in a similar size has a TRPM value of 658.

I have NEVER heard of any vehicle computer having a limited number of flashes. This sounds very much like misinformation/rumor.

And, yes, some tuners allow you to set the TRPM value.

 

well you should be able to get a tire close but if you cant, ids has preset tire sizes and a calculator in it for this issue. no limit on the amount of changing the tire size, and they might ask you to pay for it. basically it reprograms everything, but mainly it should not affect anything at all.

 

I took the truck in today got the oil and filter changed and asked them to program the pcm for the snow tire size now on the truck. LT265/70/r17

Their answer was "Unable to do for that size tire". Because my door post said
it started with Lt275/70/r18.

If they could have done it they wanted $40. Is it rocket science or do I need
to start searching for another Ford Garage.

Can the Sct tuner/ programer reprogram the tire size?

Is the sct safe or can be made safe for towing 10,000#-14,000# ?

This is a 2006 6.0psd

Thankyou for the help

JEff

 

Yes it can reprogram the tire size. If you don't want the added power, it can simply change your tire size. It's tow program is very safe also. Call Eric at Innovative Diesel. I bought mine from him too. His customer service is awesome! He'll let you know exactly what you need and how to do it.

 

Find another dealership. On both my Ranger & Dakota, I've had no problems getting the dealer to program the truck for a new/different size of tires. I will say that the $40 charge would've been nice. They've hit me for a full hour of labor (shop minimum) on every reprogram that I've requested.

The tire you are moving to is basically a 31x10.50 equivalent. And, while there are are some limitations in what they can program in, this would fall well within the acceptable range.

I know that the computer will not accept a TRPM value any lower than 600. I think the stock 265/75R20's clock in at 608. So that equates out to the computer not being able to accept anything larger than a roughly 34" tall tire.

I'm pretty sure they put a low-end limit on there as well, but I have absolutely no idea what that might be.