Speedometer recalibration after wheel and tire change/gas mileage question

[JGC1]

Hey everybody I got a few questions about my 19Ram big horn 4x4 with the Hemi. It came from the factory with the 18 inch wheels. I recently changed them out for the factory chrome Ram 20 inch wheels and added 33x12.50 Toyo ope country AT III tires and added a level kit. My question is does anyone have any experience with using the inline recalibration device from rough country? Also while I am aware that adding larger tires will lower gas mileage however it appears my Ram went from averaging 17 mpg or so daily driving to now about 11 mpg. I thought this was a little excessive. Is this the. Norm or is it actually getting a “little” better and is figuring it incorrectly due to not having recalibrated the truck for the 20 inch wheels and larger tires? Any feed back would be appreciated

 

[Farmer Fran]

I would not trust the DIC. DO a manual MPG check. No clue about the speedo recal.

 

[retired]

If you don’t calibrate for the larger tires your miles will show less than what you are actually going, so mpg will show less. How much taller are they in actual height not advertised height?

 

[CanRebel]

I changed mine from 18 to 20. I was around 23-24 on screen, went down to 19-21 range.
I do mostly highway driving, and a lot off-roading.

I did make the adjustment for new rims and tires with alfaobd, that was mostly for speed difference.

 

[Daw14]

What is the actual outside diameter of your old and new tires . Wheel size does not effect height,just the empty space in the middle of the tire .

 

[JGC1]

I changed mine from 18 to 20. I was around 23-24 on screen, went down to 19-21 range.
I do mostly highway driving, and a lot off-roading.

I did make the adjustment for new rims and tires with alfaobd, that was mostly for speed difference.

What year model is yours.. from what I am being told the new body style 19s and newer cannot be recalibrated using OBDII connector and must use and inline connector behind the instrument cluster

 

[CanRebel]

What year model is yours.. from what I am being told the new body style 19s and newer cannot be recalibrated using OBDII connector and must use and inline connector behind the instrument cluster

2021 Rebel. Used obdlink+ , Security Gateway Bypass Module from Z Automotive
and AlfaOBD. You can get Bypass cable, which is cheaper, but pain to connect those cables. So for $15 more I got module which is easier.

 

[JGC1]

Do you have a link for this stuff everything I search just brings me back to the rough country in-line

 

[CanRebel]

Do you have a link for this stuff everything I search just brings me back to the rough country in-line

Security Gateway Bypass Module

Description All 2018+ FCA(Stellantis) vehicles are built with a Security Gateway Module (SGW) that prevents access to the vehicle from the OBD2 port by anything other than the dealer diagnostic tools. Simply locate and unplug the SGW module, plug the SGW Bypass block in its place. The OBD2 port...

www.zautomotive.com

OBDLink MX+

The OBDLink® MX+ is the top-of-the-line OBD II scan tool to use with forscan and comes with bluetooth. Get one here today and gain access to your vehicle!

www.obdlink.com

I purchased it directly from each company. Likely could get them cheaper, or other brands.

For Alfaobd, I purchased the windows version and put it on surface pro.
You can get android version from play store.