Gear Ratio Change 2016 F350 4x4

ETS · September 5, 2016

Hello All, Long time no see!

Just purchased one of the last Reg. Cab Duallies in 4 states. Not too crazy about the new Aluminum Bodies. Want to change from 3:73 to 4:30 gears for mountain towing. Differential modifications are pretty straight forward.

My question is;

How do I make speedo read correctly afterwards? The old days it was a simple switch of speedo gears in trans. 1 Tooth was 7mph. Asked Shop Forman at local dealer and all I got was a dumb look. He had never done that before. Is there a Reflash Involved?

Please excuse me if question is in wrong Forum. Thought it fit best here.

Thanks In Advance. Mike

ETS · September 5, 2016

After searching other topics; I find this may not be possible. Found a long thread on wheel/tire size. Maybe taller gears and larger tire? Kind of defeats the purpose! :chinrub2:

YukonTyler · September 5, 2016

Programmable parameters generally has options for tire sizes and axle ratios. However, as the years have gone on the ability to customize those settings has lessened. What you want to do may not be possible on a 2016.

forddieseldoctor · September 5, 2016

The speedo is gonna be correct after the gear swap because it uses wheel speed sensors instead of using the oss on the transmission. The bigger question is gonna be if the truck cares that the calculated gear ratio is different that what it's got programmed.

YukonTyler · September 5, 2016

The speedo is gonna be correct after the gear swap because it uses wheel speed sensors instead of using the oss on the transmission. The bigger question is gonna be if the truck cares that the calculated gear ratio is different that what it's got programmed.

Agreed - this is what I was inferring. In my experience I've seen phantom wrench lights (no codes) and ABS coding issues.

ETS · September 5, 2016

I have seen countless phantom ABS Warnings on Modified Tundras Especially braking and turning down hill. Something I had not considered. Everything is on a network now. Maybe I had better leave this one alone.

Someone else also suggested there may be shift point issues.

Beginning to miss my 06.

mchan68 · September 5, 2016

I have a 2016 F-250 optioned with LT275/65R20 tires and a 3.55 gear from the factory. The last winter that passed, I switched to my LT275/70R18 snow tires on steel rims without issue, using programmable parameters in IDS. I do recall axle ratios being selectable, but never tried selecting it obviously.