Speedometer correction for larger tires

[Jax22]

I have a 22 Ram 1500 with the 5.7 e torque 4X4. It is the Laramie Sport model. I put 295/65/20 BFG's on it and want to correct the speedometer. I have had success in the past with correcting the speedometer on my 4th gen and older trucks, but can't get my OBD to connect, I purchased the connector to bypass the security gate for my OBD scanner, but still won't connect. Dealer says they can't fix the speedometer, any suggestions?

 

[kwill]

I have the exact same truck and fixed the speedo with Tazer DT.

 

[Jax22]

Thank you for the info! I will give that a try.

 

[mk2019ORP]

Thank you for the info! I will give that a try.

Fixed mine with JScan. Super easy and straight forward.

 

[dajogejr]

Guys…I need to help a buddy with this…he put slightly larger tires on his truck.
I ** Think ** it’s a 2021 or 2020, I know it is the eTorque Hemi.
To use Jscan or Tazer, do you need the gateway bypass cable/harness assembly, or is this really as simple as plug an approved device in (JScan) and download the app, buy appropriate license, and change tire height?

 

[BlueHemi1500]

I have been able to correct the tire size on my 2020 Laramie using the following equipment:

• AlphaOBD - Software approx $50.00 - runs on Andriod-based platform (I bought the Android version) or Windows (requires different cable)
• A Security By-Pass cable approx $20.00
• https://www.obdlink.com/products/obdlink-mxp/ about $140.00
• https://tiresize.com/comparison/
• Downloaded a GPS speed-tracking app from the Google Play store (free version)
  • also used a second phone using Waze - second reference point as a check on the other system (free version)
• Pen and paper - document changes to help determine what numbers to change when testing
• I tested on a highway on a loop from one exit then a short secondary road and back on the highway
  • Wife drove on all loops
    • I monitored the various computers/phones to see the speeds and make written notes
  • Stopped in a parking lot, made changes in the tire size, and recorded the new values
  • We drove the same loop repeatedly to rule out weather/wind(effects as much as possible) measured and repeated until we were satisfied. dash speed and the 2 devices were in agreement as close as we could measure/account for with the equipment at hand - there is some delay with the GPS phone base readings based on lag time aka the loop to allow speed to stabilize (use cruize control) to keep the speed as constant as possible also measure different speed ranges during this to allow/make the best selection of the most correct tire size
• took the wife out for a good lunch/dinner - her buy-in for her time
• It took me about an hour or so
• I watched several videos and read several posts/forums on making changes
• Make sure to make backups when you make changes to restore if something goes wrong - watch videos

There are other OBD readers that are reportedly functional to the one I bought but I prefer to buy the best-grade tools to cry once (wallet) but have a smile when I use the tool(s) as I consider the equipment as tools and therefore an investment for continued use.

Note - the 2025 trucks as of this time and date are not compatible with the above equipment - but may change in the future as the smarter-than-me folks work on the challenges to figure out how to make things work, time will tell.

BlueHemi1500

 

[theblet]

Jscan was super easy

 

[theblet]

Post in thread 'Ultimate OBD JScan Thread'
Ultimate OBD JScan Thread

 

[1923bob]

Tazer works great very strait forward,

 

[Dewey]

Tazer was as easy as can be. Took seconds to change the tire diameter. Probably 5 minutes total doing the reboot cycles.

 

[RLee276]

You can correct it with tazer or any of these other methods. But be aware that you will have to deal with a permanent trouble code (vin line mismatch ) that you can not clear with any scan tools.
It will not throw a che k engine light, but it will always be there.
If you are ok with the trouble codes then it’s an easy fix.
But I’d rather just know my speedometer is off by 5 mph.

 

[RLee276]

You can correct it with tazer or any of these other methods. But be aware that you will have to deal with a permanent trouble code (vin line mismatch ) that you can not clear with any scan tools.
It will not throw a che k engine light, but it will always be there.
If you are ok with the trouble codes then it’s an easy fix.
But I’d rather just know my speedometer is off by 5 mph.

 

[kwill]

I don't have any trouble codes.

 

[theblet]

I don’t have any codes from correcting my speedo. I do know that going with tire size larger than 35’s will cause further issues with sensors. @RLee276 what are you running?

 

[1923bob]

You can correct it with tazer or any of these other methods. But be aware that you will have to deal with a permanent trouble code (vin line mismatch ) that you can not clear with any scan tools.
It will not throw a che k engine light, but it will always be there.
If you are ok with the trouble codes then it’s an easy fix.
But I’d rather just know my speedometer is off by 5 mph.

2022 or newer you deal with the trouble codes my 2021 works great never have had a code.

 

[kwill]

Mine is a 2022. No codes.

 

[RLee276]

I don’t have any codes from correcting my speedo. I do know that going with tire size larger than 35’s will cause further issues with sensors. @RLee276 what are you running?

That may be true. I have 295/65R20 Toyo at3 tires that measure 35 inches.
But like I said it will not throw a che k engine light. But if you scan with a scan tool that shows enhanced dealer codes, you will get a code for vehicle line mismatch. And it can’t be cleared until you change the tire size on what ever programer that you use to change it.

 

[Jimmy07]

That may be true. I have 295/65R20 Toyo at3 tires that measure 35 inches.
But like I said it will not throw a che k engine light. But if you scan with a scan tool that shows enhanced dealer codes, you will get a code for vehicle line mismatch. And it can’t be cleared until you change the tire size on what ever programer that you use to change it.

Let’s get a little more specific here, since I’ve been using alfaobd on CDJR vehicles for about 7 years, and JScan for about 4 years, and have never popped a vehicle line mismatch fault after changing tire sizes (and no, it’s not some “enhanced dealer” code).
What device are you using, what exact tire size are you entering, does your truck have park assist, what is the fault code, and what module is reporting the vehicle line mismatch fault after the tire size change.

 

[RLee276]

Let’s get a little more specific here, since I’ve been using alfaobd on CDJR vehicles for about 7 years, and JScan for about 4 years, and have never popped a vehicle line mismatch fault after changing tire sizes (and no, it’s not some “enhanced dealer” code).
What device are you using, what exact tire size are you entering, does your truck have park assist, what is the fault code, and what module is reporting the vehicle line mismatch fault after the tire size change.

Ive used Alfa obd ,tazer DT, and Diablo sports trinity 2 EX (not all together)
I can’t remember the exact size I entered on Alfa,I’ve since then reverted ecu back to stock tires because the code would bug me and I just allow for the difference in speed in my head now. But I googled the metric size of 295/65R20 and tazer and the trinity 2 allow you to enter the tire circumference in inches which I measured with a tape and entered.
The only way for me to clear the line mismatch code was to reset to a smaller tire.
And yes I have park assist.

And I’m not the only person who has ever had this happen. A simple google search will pull many other people with same issue. The jeep guys also report losing park assist. But that never happened to me. But it was annoying seeing that code every time I scanned my truck. So I learned to deal with the Speedo being off by 5 mph at 55 and above.

 

[RLee276]

Ive used Alfa obd ,tazer DT, and Diablo sports trinity 2 EX (not all together)
I can’t remember the exact size I entered on Alfa,I’ve since then reverted ecu back to stock tires because the code would bug me and I just allow for the difference in speed in my head now. But I googled the metric size of 295/65R20 and tazer and the trinity 2 allow you to enter the tire circumference in inches which I measured with a tape and entered.
The only way for me to clear the line mismatch code was to reset to a smaller tire.
And yes I have park assist.

And I’m not the only person who has ever had this happen. A simple google search will pull many other people with same issue. The jeep guys also report losing park assist. But that never happened to me. But it was annoying seeing that code every time I scanned my truck. So I learned to deal with the Speedo being off by 5 mph at 55 and above.