Tuning for tire size

[SmokeyJoe101]

When using a tuner to calibrate for tire size changes, does this adjust shift points or is it just calibrating the speedometer?

or does the OEM tune just shift on load RPM regardless of speed.

just trying to see if a tuner is really needed if it just calibrates the speed

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[Reinen]

Well... Yes & no.
The tuner will calibrate the speedo, range, odometer, etc. It will not directly tune shift points. However it is a smart transmission which will use these parameters to adjust shift points over time. You'll start noticing a difference after 100 miles or so.

The JL is a smart electronic vehicle and a lot more parameters are taken into consideration than you'd think. You would be better off if you use a tuner and set the correct tire size.

 

[grimmjeeper]

The computer uses the wheel speed sensors to calculate tailshaft speed in the transmission. It adjusts shift points based on axle ratio and tire size. More based on axle ratio than tire size. But tire size has an impact.

 

[Jeffy56]

Correct axle ratio and tire size is important, especially for the auto transmission. Correcting these made a noticeable difference. For my example: 4.10 gears x 32.62 Tire O.D. as stated in manufacturers spec sheet. Speedo spot on as verified by GPS app.

 

[Soggybottomboy]

What if just going from the factory 33 to 35 inch tire? Would it make that much difference?

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[jadmt]

What if just going from the factory 33 to 35 inch tire? Would it make that much difference?

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yes....I noticed on mine going from stock tires to 35's.

 

[Soggybottomboy]

yes....I noticed on mine going from stock tires to 35's.

Thank you.

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[grimmjeeper]

What if just going from the factory 33 to 35 inch tire? Would it make that much difference?

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Yep. The computer will shift up a little faster or hold shifts a little longer based solely on tire size changes. And that affects how the Jeep feels driving down the road.

 

[Soggybottomboy]

Thanks.

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[Odyssey USA]

I know it’s splitting hairs but I have time to think about these things. I chase that 1%.

If you see the speedo is matching the GPS but if you bump up the tire diameter another tenth or two with the Tazer and it still showed the same on the GPS, would it delay shifts a little more? Would it delay shifting to 8th? Or would it be the other way for both?

After paying for this cam and rear main seal, a gear swap is probably delayed until need year.

 

[2nd 392]

I know it’s splitting hairs but I have time to think about these things. I chase that 1%.

If you see the speedo is matching the GPS but if you bump up the tire diameter another tenth or two with the Tazer and it still showed the same on the GPS, would it delay shifts a little more? Would it delay shifting to 8th? Or would it be the other way for both?

After paying for this cam and rear main seal, a gear swap is probably delayed until need year.

I doubt if the first question would make much difference, However, do recalibrate for gears. I got 35’s and didn’t bother to get a Tazer etc because I can add 4 to 65 in my head, no problem. But about 3 weeks after 4.56’s I got “Service 4 WD” - diagnosed “output shaft speed-wheel speed” Jeep remarkably couldn’t recalibrate even though 35’s, 4.56’s had become a factory option and recommended aftermarket.

Requested in writing and Kept in case of attempted warranty denial due to the Tazer

 

[Odyssey USA]

I doubt if the first question would make much difference, However, do recalibrate for gears. I got 35’s and didn’t bother to get a Tazer etc because I can add 4 to 65 in my head, no problem. But about 3 weeks after 4.56’s I got “Service 4 WD” - diagnosed “output shaft speed-wheel speed” Jeep remarkably couldn’t recalibrate even though 35’s, 4.56’s had become a factory option and recommended aftermarket.

Requested in writing and Kept in case of attempted warranty denial due to the Tazer

Seems odd. I always thought that was an option even though I wasn’t personally interested. And that guy is acting like you need two different programmers?

 

[2nd 392]

Seems odd. I always thought that was an option even though I wasn’t personally interested. And that guy is acting like you need two different programmers?

Mine is a pre XR 21. He knew aftermarket was available, but maybe not the options…. That said……. Jeep couldn’t recalibrate for a factory option ?! I find that remarkable. The dealer tried for 2 days too, starting with flashing the XR code. It cleared the “Service 4WD” but didn’t recal. The warning didn’t return before I got the Tazer either.

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