Tire size change - can’t get at programming cables.

[Reddout99]

Funny how the OP posted a simple question about getting those cables out and it quickly diverted from that to how to get the proper tire diameter/circumference

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[Hootbro]

Funny how the OP posted a simple question about getting those cables out and it quickly diverted from that to how to get the proper tire diameter/circumference

True if the OP just left it as the only comment, but he kind of opened the gate going into dimensions of what he was trying calculate for.

 

[jav_eee]

I squeezed the tab with one hand and pulled it out by the wires with the other. Not for the faint of heart!

 

[MattKay]

Quick question somewhat on topic: does changing the tire size in the computer change shift points in the automatic? Or does it just recalibrate the speedometer to be correct and that’s it?

 

[Hemi09]

Cables are a pain to get to. This is a simple device that works

 

[Wolf Island Diver]

You measure the static loaded diameter (on the ground w/ the proper air pressure) with a level at the top of the tire and a tape measure. Running 37” mud tires, my speedometer is dead on with 2 different GPS devices. If for some inexplicable reason you encounter a programming device that wants circumference, you’d calculate that from the diameter measurement. If you measure the circumference of the unloaded tire, your measurements will be wrong.

On a related topic, you DO NOT get tire pressure from the sidewall, EVER. For stock tires use the door placard. For oversized, aftermarket tires, you chalk test them on a flat surface and check the contact patch itself. Put chalk on the tire, roll over the ground and check the pattern left on the ground or chalk the ground and check the pattern on the tread. This is super easy to do.

 

[Mojave2021]

True if the OP just left it as the only comment, but he kind of opened the gate going into dimensions of what he was trying calculate for.

Yeah it was entertaining seeing all of you fixated on the easy part?. No big deal
though as you all helped me figure this out.

 

[KevinC]

Just a couple of cuts on my fingers. Managed to get them back in (easier for me than pulling them out) but agree that I need to get some extension cables if I plan to do any future adjustments. I don’t have any plans for now though.

Since you paid for the JScan app, you might as well get your money worth. It can do a lot more than change your tire size.

Important things I have done
1. Adjust the TPMS down to 28PSI. I run 32-33 PSI in my 37x12.50x17 BFG KO2. If my PSI get below 28 I'm still good to drive but getting the warning lets me know something is amiss.
2. Turned of the seat belt warning. Hooking up a trailer or launching my boat at the boat ramp, seat belt not used. Annoying alarm gone.


KevinC

 

[Hemi09]

Quick question somewhat on topic: does changing the tire size in the computer change shift points in the automatic? Or does it just recalibrate the speedometer to be correct and that’s it?

The ECRI device I used definitely changed the shift points. Shifts much better now.

 

[ShadowsPapa]

The ECRI device I used definitely changed the shift points. Shifts much better now.

The device didn't - it simply told the BCM of the new tire size and the systems compensated.

 

[Hemi09]

The device didn't - it simply told the BCM of the new tire size and the systems compensated.

You're absolutely correct , poorly stated on my part .

 

[AstroZombie]

Did the OP figure it out or is he still fiddling under his dash?

Kids: Mom why did Daddy leave us?
Mom: he didn't kids. He's still trying to figure disconnect the wires under his dashboard so he doesn't have to subtract 2 from speedometer display..

 

[Gizmo]

For me searching all the threads I could find on this topic here and any other 4x4 forum. I found it easy enough to find one with a post that had the numbers I needed for my exact tires and started with those numbers. First try worked for me . Like the OP found , getting the wires unplugged which once again the search tool gave me plenty of ideas and to install the security cable so I never had this issue again . Search tool is your friend here and Wrangler forms

 

[Camaroboi13]

Kids: Mom why did Daddy leave us?
Mom: he didn't kids. He's still trying to figure disconnect the wires under his dashboard so he doesn't have to subtract 2 from speedometer display..

I would normally laugh at this, but in my case my tires are 14.05% larger now than they were from the factory. The math is a little different for some, especially when it comes to figuring out mileage. When my dash says 19mpg average, it’s closer to 21.7mpg. At 65mph I’m doing somewhere around 74?‍
One of these days I’ll find someone with small enough arms to get those cables out… I’ve had JScan for over a year now and haven’t been able to use it ?

 

[Hemi09]

I would normally laugh at this, but in my case my tires are 14.05% larger now than they were from the factory. The math is a little different for some, especially when it comes to figuring out mileage. When my dash says 19mpg average, it’s closer to 21.7mpg. At 65mph I’m doing somewhere around 74?‍
One of these days I’ll find someone with small enough arms to get those cables out… I’ve had JScan for over a year now and haven’t been able to use it ?

Ha ha, I couldn't get to them. So my son in law who has smaller hands and arms came by and got to them without a problem

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