In doing my research and trying to decide on what gear ration to get, I stumbled across an interesting question (at least in my mind). There is a wide range in tire size placed on these trucks, anything from 32" dia to 34" dia. Does the tune of the truck get adjusted based on the tires to make up for the gear ration change?

Example 275/65/18 = 32" Diameter with 3:73 rear end it ='s a 3:73 final gear ration.
Same truck with 275/65/20 = 34" Diameter with 3:73 rear end ='s 3:52 final gear ratio.

Am I doing something wrong here? I really don't want to end up with a final gear ration that is too tall.

If I am over thinking this just tell me I am an idiot.

 

Your overthinking this.

Feel better?

You are talking about a 5-6% difference give or take. Likely they do a speedometer correction or shot for the middle number but I would be shocked if they re-tune.

 

If your buying the 6.2 gas motor then the only gear you should be thinking of getting is the 4.30 with electric locker

 

Blanket statement of summary judgement that does not answer OP's question while immediately making all us chumps that did you follow your golden rule feel like...nevermind...

Instead, in the same number of characters you used to make yourself look like a troll, why is the 3.73, 6.2L combo that I sought out for months the wrong one for my needs?

 

If the payload and towing is a priority, buy according to the towing guide. You'll find the higher the tow rating, the smaller the tire. If towing is not a priority , go for your personnel preferences as in looks, ride and handling.

 

not sure about the tune but i think some of the trucks have the ability to be re programed for different tire size, mostly to correct the speedometer but possibly other things at the same time? like shift points??

 

I don't believe ford adjust the speedo for different gears. I have owned one 06 F250 with 410s and a 2012 with 430s. Both speedos read "fast' with stock tires. Checked by gps both trucks were going slower than the speedos read. Adding 35 tires to both these trucks made the speedo run very close to correct [1-2mph off]

 

engine is tuned for EPA and Ford standards.. not tire size or gear ratio...


that is why the engine is controlled by its own computer.. self adjusting for engine needs.


timing, fuel needs, engine load, throttle opening/ air temperature/ cooling system temperature/and the list continues.

 

These trucks are so much more powerful, "optimized" is a relative term. When you're dealing with a three speed transmission and 3500rpm operating range with a huge variation in fuel consumption in that range, gear ratio is a huge concern. With five or more speeds, lockup torque converter, and broader operating range, gear ratio isn't quite as important until you are pushing the tow rating.
I would lean towards keeping the RPMs down, unless you will be pushing the tow limits.

 

i am pretty sure my tech said he re programed my 06 truck to accommodate for the taller tires relative to the speedo

 

He changed the revs per mile number so the speedometer reads correctly. He didn't change anything in the engine tuning parameters.

The 6.0/5R110W can have unusual shift issues if you have drastically different tire sizes compared to what it's programmed for, but that's not related to engine tuning.

 

I just went from 245/75r17s to 35x12.5r20 and the really need to check speed with a GPS. Here is a chart I found. I am not sure how accurate it is.

Speed Difference
245x75r17 35x12.5r20
20 mph 22.2
30 mph 33.3
40 mph 44.4
50 mph 55.6
60 mph 66.7
70 mph 77.8
80 mph 88.9
90 mph 100