Computer Reset with upgrade from 33" to 35"?

[RamRebelRob]

Upgrading the tires threw off the speedo (which is understandable) - can the dealer fix this?

Also, does the ECU take into account tire size for any of its MPG calculations? Noticed it dipped from 17 down to 13. Didn't expect a 4mpg drop.

 

[djevox]

Yes, it changes mpg calculations and shift points (if too far off). Some dealers will do it and some won’t, so you’ll just have to call your favorite dealer and ask. You have a couple other options though: buy a diy tire size flashtool, use a TazerDT or alfaOBD, or get an independent off-road shop to do it. (I.e. Trick Trucks, 4wd Parts, etc.)

 

[RamRebelRob]

Yes, it changes mpg calculations and shift points (if too far off). Some dealers will do it and some won’t, so you’ll just have to call your favorite dealer and ask. You have a couple other options though: buy a diy tire size flashtool, use a TazerDT or alfaOBD, or get an independent off-road shop to do it. (I.e. Trick Trucks, 4wd Parts, etc.)

Thanks DJ!

 

[RamRebelRob]

Called a couple RAM dealerships and offroading shops in Mesa/Tempe/Scottsdale, no one offers the service, yikes.

 

[djevox]

Called a couple RAM dealerships and offroading shops in Mesa/Tempe/Scottsdale, no one offers the service, yikes.

For around $100 or less, you can use alfaOBD to make the change. Here’s a couple searches to get you started.

Search for changing tire size alfaOBD

Official alfaOBD thread

 

[ram!TH@rd]

For around $100 or less, you can use alfaOBD to make the change. Here’s a couple searches to get you started.

Search for changing tire size alfaOBD

Official alfaOBD thread

That's what I did.. Had a Samsung tablet laying around and came in perfect for AlfaOBD.. Super easy to do.. Invested less than $80 over-all. @RamRebelRob just keep in mind (Dealer or Self) that changing tire size will disable parking proximity sensors. @RamCares The factory knows about this (or has known) but not ETA on a fix yet.

 

[RamRebelRob]

That's what I did.. Had a Samsung tablet laying around and came in perfect for AlfaOBD.. Super easy to do.. Invested less than $80 over-all. @RamRebelRob just keep in mind (Dealer or Self) that changing tire size will disable parking proximity sensors. @RamCares The factory knows about this (or has known) but not ETA on a fix yet.

Thank you, what about collision detection?

I was checking out the RAM compatible interfaces on their website and they all appear to be $200-300. Am I missing something?

 

[SD Rebel]

Yeah, I think I'll go with 34" tires, the speedo difference isn't so bad that I can just live with it.

As for the MPG drop, I had a 1-2 mpg drop on my old F150 by switching to tires just 1/2" larger. Going two full inches should be quite noticeable. Though as mentioned your odometer is likely off, in your favor by the way, but is giving you lower than actual mpg.

I never heard of the parking sensors being affected by changing of tire sizes, that's really interesting.

 

[ram!TH@rd]

Yeah, I think I'll go with 34" tires, the speedo difference isn't so bad that I can just live with it.

As for the MPG drop, I had a 1-2 mpg drop on my old F150 by switching to tires just 1/2" larger. Going two full inches should be quite noticeable. Though as mentioned your odometer is likely off, in your favor by the way, but is giving you lower than actual mpg.

I never heard of the parking sensors being affected by changing of tire sizes, that's really interesting.

Yep, here's another thread where a fellow members have the same issue:

Alfaobd tire size change instructions

All, I've been doing some searching but not having the luck I was hoping... I'm looking for step by step instructions for AlfaObd to change the tire size on a 5th Gen RAM. Specifically I want to make sure I dont miss anything so the 2719mm number doesn't impact park sense or anything else as I...

5thgenrams.com

One thing I didn't share is that, initially, I had the dealer do a wheel alignment and I did ask them to reprogram the speedo while they had the truck. They performed the tire size change successfully, however, the dealer called me back saying the sensors were disabled as soon as they programed the new tires size. They opened a case with RAM where the feedback was:

RAM is aware that changing tire size will disable parking collision sensors and there is no ETA on fix

I haven't swapped out the parking sensor module as one member has (same thread I pasted) but may give it a shot at some point in the future

 

[SD Rebel]

Gotcha, so tire size change by programming is what will disable the parking collision sensors. So if I just go with 34" tires and not mess with the programming, I should be fine.

 

[ram!TH@rd]

Thank you, what about collision detection?

I was checking out the RAM compatible interfaces on their website and they all appear to be $200-300. Am I missing something?

Not following.. Can you share what you searched with regards to compatible interfaces?

 

[RamRebelRob]

Not following.. Can you share what you searched with regards to compatible interfaces?

Probably was following the wrong link, is this what you were referring to?

OBDLink® MX+ - Outstanding Bluetooth-Compatible OBD II Scan Tool

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

 

[ram!TH@rd]

Probably was following the wrong link, is this what you were referring to?

OBDLink® MX+ - Outstanding Bluetooth-Compatible OBD II Scan Tool

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

Yes that one of 3 pieces you need if you want to modify your own setting in the truck's computer
- AlfaOBD software (AlfaOBD)
- Android Tablet (not IOS supported) for AlfaOBD or Windows PC
- Security Gateway Bypass Cable.. You have 2 choice:
- Expensive option (Security Module Bypass | KaodTech)
- Cheaper option which has worked well for majority of us (https://www.amazon.com/gp/product/B08ZL4LRVK/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1)

 

[RamRebelRob]

Yes that one of 3 pieces you need if you want to modify your own setting in the truck's computer
- AlfaOBD software (AlfaOBD)
- Android Tablet (not IOS supported) for AlfaOBD or Windows PC
- Security Gateway Bypass Cable.. You have 2 choice:
- Expensive option (Security Module Bypass | KaodTech)
- Cheaper option which has worked well for majority of us (https://www.amazon.com/gp/product/B08ZL4LRVK/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1)

Hmm, sees to be in line with most of the other after market prices ~$200. Thank you.
$49 - Software
$20 - Cable
$140 - OBD

 

[ram!TH@rd]

Hmm, sees to be in line with most of the other after market prices ~$200. Thank you.
$49 - Software
$20 - Cable
$140 - OBD

For OBD, you could go cheaper.. Others have used this one successfully:

https://www.amazon.com/gp/product/B005NLQAHS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

really depends on what your goal is.. I think (don't quote me) the MX+ can talk to radio module where the cheaper OBD plug cannot

 

[Av1]

I had the parking sensor issue when I was calibrating my speedometer (using Flashcal). What I determined was the parking sensors worked with any rolling diameter input of 33.75" or less. The sensors quit working when an input of 34" and above was entered.

My 35.12" tires (295/65r20) were dead on gps when I entered 34", but I had to use 33.75" so my parking sensors work correctly.

 

[RamRebelRob]

I had the parking sensor issue when I was calibrating my speedometer (using Flashcal). What I determined was the parking sensors worked with any rolling diameter input of 33.75" or less. The sensors quit working when an input of 34" and above was entered.

My 35.12" tires (295/65r20) were dead on gps when I entered 34", but I had to use 33.75" so my parking sensors work correctly.

Do you know if it affects collision detection too?

 

[Av1]

Do you know if it affects collision detection too?

I know the audio and dash indications work now for the collision detection, but I wasn't in a position to verify collision operation when I had 34" input. I have never had it auto brake, even with the stock calibration, so I don't know if that works or not.