Recalibration after regearing

[Honor2afault]

Ok, here's the newb question of the day.
After regearing front and rear axles for tire size and proper restoral of "power", is there still a need to recalibrate the cpu with a Diablo, AEV or other equivalent. And, if so, why? Isn't that kinda the purpose of the regearing to begin with? (If I have missed a previous post on this subject, I do apologize, in advance.)

 

[WJCO]

Ok, here's the newb question of the day.
After regearing front and rear axles for tire size and proper restoral of "power", is there still a need to recalibrate the cpu with a Diablo, AEV or other equivalent. And, if so, why? Isn't that kinda the purpose of the regearing to begin with? (If I have missed a previous post on this subject, I do apologize, in advance.)

Yes. To the best of my knowledge, all vehicles computers will be affected by your final drive gear ratio as your tires will be spinning at different speeds with new gears. Older vehicles would require a little plastic gear to be changed in the transmission or transfer case to adjust the speedo accordingly, but new vehicles are all computer controlled which means you will have to buy something electronic to compensate for that. This not only makes your speedo accurate, but also helps your transmission shift accurately.

 

[frenchjk]

Yes because when you changed the gear set the rev's/mile of the engine-gearbox-transfer vs wheels has changed too, hence the reprograming of the speedo and odometer. It has nothing to do with the power band that you have in instance restored by re-gearing.

 

[Honor2afault]

Thank you, for older jeeps that makes sense. However, newer jeeps (jk) are computer controlled so why the need to regear in the first place for larger tire sizes, why can't you simply tell the cpu that it has bigger tires to change shifting parameters and restore the lost power that adding said tires removed? I feel as if there's an aspect to this that I'm not seeing.

 

[WJCO]

Thank you, for older jeeps that makes sense. However, newer jeeps (jk) are computer controlled so why the need to regear in the first place for larger tire sizes, why can't you simply tell the cpu that it has bigger tires to change shifting parameters and restore the lost power that adding said tires removed? I feel as if there's an aspect to this that I'm not seeing.

Doesn't work that way. Larger tires rob your engine and complete powertrain from power. So regardless of what the computer sees, larger tires create a mechanical disadvantage to the vehicle's powertrain. Example, run across a football field with a small child on your shoulders. Then do the same thing with a huge fat person on your shoulders. Doesn't matter what your brain is thinking, your body will definitely feel the weight of the heavier person. Changing the gears allows to the tires to spin at different speeds causing less work on the engine (like changing speeds on a bike).

 

[notnalc68]

That's what you are doing, when you recalibrate, but underneath it all, the JK is still an automobile and the basic mechanics are the same, thus the need for gears. Gears are what determine the final drive ratio, and crawl ratio.

 

[Honor2afault]

Well, that does make much more sense. Thank you Frenchjk, and WJCO for the information. And, WJCO, that's an exceptional analogy, truly superb.

 

[frenchjk]

Well, that does make much more sense. Thank you Frenchjk, and WJCO for the information. And, WJCO, that's an exceptional analogy, truly superb. 

take a mullti speed bike out (shift to big ring small gear combo: that is what you get when you change for larger tires with the OEM ratio...feel it? the change to small ring big gear....that is your regrearing (schematically) feel the difference.

the CPU is your brain telling your muscles to put more power to pull that big gear faster but its physically impossible. Switch the gearing and your muscles can follow your brains will....that is the effect of regearing better power to ratio to road performance.

 

[notnalc68]

^^^ Well said.