Calibrate Speedo AGAIN AFTER I Regear?

So, after I got my Speedo calibrated for my 245/75/16 mud tires, I asked the guy if another calibration was necessary if I decided to regear. He said “yes” . Do you guys think I would have to do it again? Will the new 4.10 gears throw off the tune they did? . I paid $350 bucks.

He told me they did a “Stage 1” tune or calibration. This is what they did:

-They measured the tire size.
-They weighed the car.
-Reprogrammed the wheel speed sensor on the rear diff.
-Reprogrammed the new tire ratio into the transmission.
-They modified the throttle response. Now I don’t have to press the pedal all the way in, especially when fully loaded.

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Liberty KJ 2002 3.7 Limited.
Tow Package.
1.5in Ironman Lift Kit.
245/75/16 Mud Terrains
Speedo and Wheel Ratio Calibrated.
45RFE Transmission.

Your speedo will be out by a bit, I'd check how much against the GPS on your phone and decide from there if it's worth worrying about, it's hard to guess how much it will be out as it's already been modified.

Speedo reads off the differential ring gear, so there is no change with axle ratio.

What does affect the calibration is larger tires. I found that going from stock to 30" tires improved the accuracy.

To be more specific.
The speed sensor reads the rotational speed of the tone ring next to the ring gear, so it is affected by tire size.
The tone ring rotates at the same speed as the axle.
Even if you change the ring gear, the tone ring usually does not change.
What changes when re-gearing is the motor rotation speed.

Does the fact that the speedometer can be corrected mean an ECU tune?

If you put larger tyres, you need to re-calibrate the speedo (readjust revs per mile) with the DRBIII procedure as below:
https://colorado4wheel.com/content/drb_KJ_speedo.html
you do not need to calibrate anything if you regear only, without changing tyres

ikuo78 said:

To be more specific.
The speed sensor reads the rotational speed of the tone ring next to the ring gear, so it is affected by tire size.
The tone ring rotates at the same speed as the axle.
Even if you change the ring gear, the tone ring usually does not change.
What changes when re-gearing is the motor rotation speed.

Does the fact that the speedometer can be corrected mean an ECU tune?

Click to expand...

Good point!

I would really love to hear how they modified the throttle response on a mechanical cable actuated throttle body.....that sh!te is reserved for fly-by-wire applications for people who swear they can feel milliseconds lol.
Tire height changes pinion factor, ratio does not. What ratio will affect is shift points. Correcting pinion factor is in the TCM for RFE vehicles (for any Mopar with a TCM, like NAG1 cars), unless that particular RFE equipped vehicle (such as later rams) has a combined PCM.