I Have A 2004 F350 4x4 6.0 I Have Change My Tire Size From 265/75/r16
To 305/70/r16 The 265 Are 31.7 In And The 305 Are 33.0 In Tall The
Transmission Is Not Shifting Like It Did Before Can I Have It Program
To Shift Like It Used To I Have Lost Fuel Mileage I Do Not Know If It
Has Any Thing To Do With The Size Of The Tires Or The Transmission
Shifting Thanks For Any Help

 

When you talk about not shifting the way it was, do you mean under all types of driving conditions? I'm guessing, and I stress "guess" that under heavy acceleration the taller tire would cause the tranny to wait until a higher rpm to shift to the engine having to work a little harder.

I hope someone who really knows can answer. I'm waiting on a set of 305/65/18 to replace my stock 275/70/18 due to the fact that the only available tire in NM in my size is the Continental that came on the truck and I would not take these if they were given to me so there's absolutely no way I'll pay for them. Due to Goodyears strike I cant get the Wrangler so I was left to improvise. Even at that I've had a very difficult time trying to get the ones I've ordered. I can't believe something as mundane as buying tires would be so difficult. Its stupid.

 

Changing the tire size on a MY04 will not effect the transmission shifting in anyway. The vehicle does not use wheel speed sensors for transmission shift points.

I just changed mine from stock 275/65R18's (32.1" tall) to 35X12.5R18. Nothing has changed in the performance of the transmission, braking/ABS, etc.

Now when it comes to fuel economy and bigger tires , you will lose some in the city, but should be better on the highway. I do approximately 60% highway and 40% city and have actually gained about 1.2 mpg overall.

 

Not entirely true.

The SD reads its vehicle speed from the rear ring gear, so tire size does affect it, because you have changed the N/V value of the vehicle. The N/V ratio in the computer is however self adaptive, and will correct its shifting over time down to a 27 inch tire, up to a 34.6 inch tire.

The speedometer is not self adaptive, and will need to be recalibrated by the dealer for true accuracy.

 

Thanks for the input, as im always interested in more information.

I was just going buy another article I read on the subject, as well as the person who is going to adjust the RPM's for proper speedometer calibration. I am very confident with his knowledge on Ford electroinics, as it is his occupation. He works with Ford and International engineers, among others. Working on both production and prototype vehicles.

The shift scheduling on a '04 is determined by the...

OSS - Output Shaft Sensor
TSS/ISS - Turbine Shaft Speed/Intermediate Shaft Speed

These sensors combined control how the transmission shifts. I guess you would call it adaptive, yet mine performed the same when I took it in with stock tires as it did when I took it home. No adaptive time needed, it just shifted as it should.

 

Moved to proper forum, enjoy.

 

What gears do you have on your truck? when you go with larger diameter tires, you do change the final gear ratio which is why you feel the difference. Also the fuel economy loss.

 

Assuming the 04's are like the older ones, changing my speedo was simply a matter of plugging into the OBDII and entering a new tire size. Unfortunately for me, there's a limited selection available to select from. We went with the closest diameter and then timed it. Only a couple seconds off at 60mph. Good enough.

 

"The speedometer is not self adaptive, and will need to be recalibrated by the dealer for true accuracy." Yea, let me know when you find a dealer in Sounthern California that will do it!

 

From what I understand, you would be correct. I do not know about aftermarket programmers, as early on there was alot of talk about not being able to change tire size with one. If this is still true I do not know. As for the Ford computer there is the abiltiy to select from predetermined tire sizes, or there is a override that will manually allow you input the tires RPM (Revolutions Per Mile). There is supposed to be a limit on this also, only allowing you to go as low as 600 or 601 RPM's. This makes sense based on what PSD 60L Fx4 said about the computer being able to adapt to a 34.6" tire, as a tire around that size should spin about 600 RPM's.

 

The local dealer told me that if I changed tire size, they can correct the speedo for about $80. They said they would recalibrate the computer to compensate for the error.

 

Question? If my 05 came stock with 17'' wheels and the newer ones come with 20'' wheels and both have the same overall gear ratio of 3.73 are the newer ones actually geared lower to begin with to get this final ratio? I would assume the tires are not the same height unless they were of a lower profile?

 

No there is no compensation. 3.73 gear is the same if you have 17"s or 20"s. Only the final ratio changes. So effectively trucks with 20"s have a different final drive ratio then ones with 17"s, from the factory. The 20"s are 34.1" tall, and I believe the 17"s are around 31.5" tall. Less lowend with 20"s.

 

All SRW PowerStrokes come with 3.73 no if's n's or but's!
DRW PowerStrokes have a few options.
All gas SRW or DRW have options.
And yes the 20in wheels have a taller tire which in turn throw the 3.73 ratio out!
Stock gas now comes with 4.10 along with the 17in rims.
Now what burns my arss is a 20in rim on a gasser with 4.10 gears!
Seeing how the 20in rim comes with a 34in tire they should come stock with 4.30 gears
I guess the same goes for a PowerStroke taller tire needs a taller gear.
Taller tire will effect trans shifts, as in lugging the engine = more fuel, kinda like towing a lite load.
Anyone who decides to run taller tires needs to understand the effects!
Taller tire needs a taller gear # towing heavy also needs a taller gear #

 

By changing from a 31.7 inch tire to a 33 inch tire, you changed your effective differential ratio from 3.73 to 3.58. You would have to install something close to a 3.88 ratio to keep it like it was stock. Not a huge change but one that will be noticed.

It will change the way the trasmisssion feels and shifts. You might try the disconnecting the battery to clear the programming and then the "Torqushift Shift Relearning Strategy" from this web site:

http://home.austin.rr.com/sbv1/Proce...ngStrategy.htm