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Just put larger tires on. Any need to reset the TCM or just adjust tire size?

dcmdon

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Hi all,

I just went from 33s to 35s. It there any need to reset the TCM to set it back to defaults so it "learns" the new tires? Or just go with it?

If I should reset it, what is the best way??

I have adjusted tire size with a Tazer.

Thanks,

Don
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pcrawfordpt

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You should update the computer. Can be done by paying dealership, or by purchasing a Tazer. Tazer has more functionality, but needs to be unmarried when taking to dealership in case they make any computer upgrades. If not, the dealership computer upgrades would be lost when marry/unmarry Tazer. Therefore you would need to reset tire size every time you unmark/remarry for dealership visits. Not a big deal, but maybe more than some want to deal with. The dealership computer upgrade would be permanent. Not upgrading when going from 33's to 35's would not be the end of the world, but shift points, speedometer etc will be off.
 

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Jscan and AlfaOBD can be used to make the changes for tires and other settings. They donā€™t suffer from the marry/unmarry issues that the Tazer does, and cost a lot less.
 

Mr._Bill

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Hi all,

I just went from 33s to 35s. It there any need to reset the TCM to set it back to defaults so it "learns" the new tires? Or just go with it?

If I should reset it, what is the best way??

I have adjusted tire size with a Tazer.

Thanks,

Don
I don't think putting the transmission back in learn mode is needed. Maybe if there's a big change, like stock to 38's or 40's, but changing the tire size is all that is supposed to be necessary. Putting it back in learn mode is done to reset and try to fix it if it is having trouble finding its way in the lower gears. Learn mode is necessary when the transmission fluid is changed.
 
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dcmdon

dcmdon

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Jscan and AlfaOBD can be used to make the changes for tires and other settings. They donā€™t suffer from the marry/unmarry issues that the Tazer does, and cost a lot less.
I consider the Tazer to be worth it just for the live functions.

If I wanted to use Jscan to set tire size and some other "non-live" functions, can I do it while the tazer is still plugged in??

Do I still need a security gateway bypass cable?
 

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Mr._Bill

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I consider the Tazer to be worth it just for the live functions.

If I wanted to use Jscan to set tire size and some other "non-live" functions, can I do it while the tazer is still plugged in??

Do I still need a security gateway bypass cable?
One suggestion I read is to make the changes with Jscan before marrying the Tazer. That way it sees them as part of the 'factory' setup that it restores when unmarried. I think you would still need the bypass cable and OBD module to make the changes with Jscan.
 

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Do I still need a security gateway bypass cable?
The Tazer will act as the security gateway bypass. Plug your bluetooth straight into the OBD port.
 
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dcmdon

dcmdon

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The Tazer will act as the security gateway bypass. Plug your bluetooth straight into the OBD port.
Thanks. That's the info I was looking for.
 

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I have not bothered to use my tazer in the year I have had 35s. My 35s have made my Speedo closer to accurate now than it was stock, though itā€™s still off.
 

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dcmdon

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I have not bothered to use my tazer in the year I have had 35s. My 35s have made my Speedo closer to accurate now than it was stock, though itā€™s still off.
That's interesting. My speedo was spot on. From 20 mph to 85 mph from day 1. It has always matched up perfectly to GPS speed on my Garmin.

I wish more people knew. It would make their lives much easier.
I kind of suspected that was the case. I'm trying to adjust my speedo using J-Scan for the least amount of money since I've already got the Tazer. I may be overthinking it. I bought the extension cables. I may just reset it every time I go to the dealer.

If there was someone local who already had the dongle and software and all I had to do was pay for a VIN license from Jscan, then it would be a no-brainer.
 

yoda13

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Thatā€™s cool. I GPS checked mine as well. I donā€™t really care, just an observation:). Is yours a ā€˜22?
 
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dcmdon

dcmdon

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Thatā€™s cool. I GPS checked mine as well. I donā€™t really care, just an observation:). Is yours a ā€˜22?
Yes. Its actually freakish how accurate it was. I was thinking that it had to be GPS corrected, but who knows.

My Garmin reads to the tenth mph and updates 6x per second, and its crazy close.
 

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33 to 35s on '20 Rubicon, speedometer's off by 2.5
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