Shift points, transmission lug, and bigger wheels.

[c3k]

Folks,

Most of you have probably forgotten more than I'll ever know about this stuff. So...my questions.
I've got an ecoDiesel with the 3.21 rear. Driving it on stock wheels and tires (275/55 on 20" rims), it seems to downshift at 1,000 rpm when there is no load. (Coasting, etc.)

If I go with 285/65, that will increase my diameter by 8.5%. After adjusting the computer for the larger diameter, what will this do to my shift points?

I'd think the torque would be plenty with a taller tire, I'm just not sure what that would mean for drive-ability. Any thoughts?

Thanks.

 

[Raydar]

I don't own a diesel, but since nobody has bothered, yet, I'll venture a guess.
Your engine is probably keyed to throttle opening, and load.
Taller tires will present more of a load, for a given throttle opening. Your trans will likely appear to downshift "more easily" (sooner?) than it does now.
Your truck may not feel as responsive as it does now, but it will still likely be operating at the optimal RPM/gear for whatever you are doing (speedometer error notwithstanding.)

If anyone disagrees, that's fine. Just one person's opinion.

 

[Tgryphon]

i have an ecodiesel with 3.92 rear end. went to a 6 inch lift with 35x12.5r20 from stock. recalibrated via TazerDT for the new diameter. spot on verified GPS against speedo etc. driveability is fine. the change isnt preceivable. Th ecodiesel is very torquey, shouldnt make a difference for you at all.

 

[c3k]

Thanks guys.

I'll jump on the tires I want and not worry about it. If anything, the GDE tune (if it comes out soon???) will add even more torque and adjust the shifts appropriately.

(I get confused by modern computer transmission controls: too much black magic going on in there...but damn, do they work. )

 

[jmt8706]

Thanks guys.

I'll jump on the tires I want and not worry about it. If anything, the GDE tune (if it comes out soon???) will add even more torque and adjust the shifts appropriately.

(I get confused by modern computer transmission controls: too much black magic going on in there...but damn, do they work. )

GDE is a great choice. I like how they squeeze out extra HP, and torque, and fuel economy while keeping all the safety parameters active.

 

[theduster22]

i have an ecodiesel with 3.92 rear end. went to a 6 inch lift with 35x12.5r20 from stock. recalibrated via TazerDT for the new diameter. spot on verified GPS against speedo etc. driveability is fine. the change isnt preceivable. Th ecodiesel is very torquey, shouldnt make a difference for you at all.

I'm in the same boat right now, ordered a TazerDT and just waiting for it to show up. What GPS / App do you recommend for verifying speed + calibrating?

 

[Tgryphon]

I'm in the same boat right now, ordered a TazerDT and just waiting for it to show up. What GPS / App do you recommend for verifying speed + calibrating?

Waze