Tire size change alfaOBD

[Justin33]

I just did 2 tire size changes yesterday morning, one on a 2017 and the other on my 2019 classic. I wrote down and printed instructions just to be sure I followed them to a t. My truck was off about 2.8%, 2 mph at 70. I added 2.8% to the oem setting and programmed it. Had zero faults pop up. When I went to do the initialization, it wouldn't give me that option, on either truck. Cleared rolls information. Cleared the faults on all modules, even tho it didn't have any. Settings took on both trucks, speedometers are both accurate. My tire size was 275/65/20, the other guy was 35/12.50 (set circumference at 2714).
Is it possible that if you change the settings, you may not need to do all the abs stuff? Fwiw, the truck seems to perform better, feels stronger off the line and the shudder I had on take off seems to be gone.

What size are you using in mm as I can’t get the truck better than 2mph off. I have 275 65 duratracs but can’t find the sweet spot. Right now when truck is going 70 I’m getting 68 on phone gps.

 

[hunterdan]

What size are you using in mm as I can’t get the truck better than 2mph off. I have 275 65 duratracs but can’t find the sweet spot. Right now when truck is going 70 I’m getting 68 on phone gps.

I'm not sure. I'll have to check and let you know.

 

[Justin33]

I'm not sure. I'll have to check and let you know.

Yes let me know as when I’m going 70 Via gps on phone the truck is showing showing 68

 

[paul10053]

Quick write to help with this. However I bear no responsibility for any changes that you might not like. Only ones you do.

Start off with key in run.
Open app
Select dodge/ram button, Ram 1500 or 2500 From drop down, Body Computer, then body computer MY2013-2017
Connect then click on the icon at the bottom with the hood open
From the drop menu select "Program tire size"

Right above start on this page is a text box that allows you to input the tire circumference in mm or you can use the drop menu to select a preprogrammed size. (Best way to get your mm number is to measure mounted height and then do your conversion, always round up or down to a whole number. This might take a couple adjustments from that to get perfect at 60.)
View attachment 145954

Press start and it should take a couple seconds to complete.
Once done back out to main page.

Cycle the key, at this point you can get all kinds of lights on the dash, so then you need to do the abs module.

Now select dodge/ram button, Ram 1500 or 2500 From drop down, ABS, then ABS Ate/Continental
View attachment 145953


Connect then click on the icon at the bottom with the hood open
From the drop down select ABS iniatiliazation
View attachment 145952

Read the instructions

View attachment 145951

Go back to the drop down and select static ECU initialization
Press start and wait to complete
Click on the check engine icon and clear faults
Then cycle key
Click back on the car icon
Select clearing Rolls Information from drop down, then start
After complete clear faults in the Body control module and the engine.
Cycle key
Once complete start your ram and take it for a spin, and check speed vs a gps. If your still off you can redo the process and adjust as needed.

This was performed on a 2018 Ram 2500 with version 2.1.4.0 on a android with OBDlink MX and a bypass cable

If anybody has noticed any differences on their vehicles or has any input to edit this let me know.

Thanks so much for the instructions. My 1st try at adjusting for tire diameter change resulted in loss of speedo function and the various dash lights. After reading your post and a lot of related posts I was able to go back and finish the change by doing the ABS initialization and removing the trouble codes and warnings (I did not have to recal the accel). Thanks again - I now have confidence to attempt the TPMS limit adjustments on my 2013 RAM.

 

[djlr55]

For 295/65R20 @ 70PSI. Speedometer currently showing ~1mph fast at 60, input 2760mm into alfaobd.

 

[78Staff]

I tried 2774mm. I got all the blinking lights and errors. When I was trying to do the abs reset it kept failing on the clearing rolls. My digital speedo just had dashes and the errors wouldn't clear. I shut it off and went back an hour later to try the abs reset again and everything was back to normal. I'm gonna try it again this weekend when I have more time.


Sent from my Pixel 2 XL using Tapatalk

Older thread, but this is simlar to the issue I'm having with my 2016, after trying to reset mine down from 35's back to 33's. I've used Alfa quite a bit over the years, and have rarely had issues, but this one is stumping me. I set the tire size in mm fine, but then I get CEL for Check Integrated Trailer Brake, dashes for MPH, Speedo doesn't move, can't engage 4wd, and tbh steering is kinda stiff. Not manual steering stiff, but stiffer than normal.

Doing the ABS reset, the ECS Init pasess, but when I try to do the Clearing Rolls, I get error "Failed - Service not supported in Active Diagnostic Session".

Even though I went through everything twice, I recall sometimes you just have to let it sit... so I waited a bit, went back out, and while I still have a CEL, it seems the other stuff is back to normal, ie the speedo is moving again, the 4wd works again, and the steering is back to normal as well.

Not sure what the CEL is, I am letting it sit a bit more, and also charging my tablet.

Hopefully can get it sorted, but was curious if anyone else had ran across the errow when Clearing Rolls? Will also have to test the tire size, I am down from BFG 35's to Toyo 285/60R20's... essentially 33.5, but I dropped a half inch and went with 2633mm. Still have to see how close I am, I guess with GPS app on phone is best way...

 

[78Staff]

Quick followup - Stil showing a CEL, but otherwise things appear to be sorted out. I tested with GPS and it's .5-1 mph over at 60, which I am fine with.

CEL is annoying, I checked Body Computer, ABS, both the ABS/Tewes module and the Int Trailer Braking part, none are showing any faults. I checked a few more, but haven't found any faults yet. Got tired of chasing it, will let it sit overnight and check again tomorrow.

Does Alfa have a "check all faults" regardless of module option, or is it only able to pull from connected modules? I guess I could just connect to every one and try to find what is causing the CEL to light up...

 

[78Staff]

CEL seems to have cleared.. never did find it, but it's gone. If it pops again I'll just stop by the parts store and let them scan it I guess.

 

[RamDiver]

CEL seems to have cleared.. never did find it, but it's gone. If it pops again I'll just stop by the parts store and let them scan it I guess.

I've experienced the CEL that clears instantly and other times it hangs around for a day or 2.

I have no explanation for why you received the fault or CEL after your tweaks but I've noticed the older truck BCMs seem to be a slight bit more finicky than recent models.

All bets are off if you're using an android device.

I use AlfaOBD for windoze because I don't trust anything google-related and won't connect one to my truck.

I used a stand-alone old-style TomTom GPS to verify my wheel size adjustments. The Wheel size setting gets switched 2 times per year with the summer/winter wheels change-over.

Thanks for reporting your experience, I'm confident that others will benefit.

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[GeauxinUp]

Wanted to give my experience with this, as it seems I was a lucky one (for once in my life). For some reason I was pretty nervous about tackling this, even though I've torn apart engines, transmissions, and pretty much do all of my own maintenance/upgrades. Anyways, I've run oversized tires on this truck since it was brand new and never really cared about the speedo being off, but got a ticket last week for speeding and it pissed me off.

Truck is a 2015 Laramie 4x4

Here's what I did:

1. Laid a level across the top of all 4 tires centered above the hub and took the average of 33.15 (tires are toyo r/t 275/65/20).
2. 33.15 x 3.1416 x 25.4 = 2645mm
3. After following step one to enter the tire size in the BCM (I used 2015MY), cycle pushbutton off, open door, close door, pushbutton to on/run, I had no codes or flashing lights on the dash.
4. I figured I'd go ahead and attempt the rest of the procedure, so I selected ABS, but I didn't have the "ABS Ate/Continental" others were choosing, so I selected the one that seemed to fit best for my truck which is in the pic below.
5. After connecting, I did get a couple of lights flashing on the dash, but after selecting "ABS iniatiliazation" the start button stayed grayed out.
6. I decided to back out and disconnect everything and the lights on the dash went out.
7. Cranked truck, took it for a drive, and it's dead nuts accurate with 2 different gps's @ 40, 60, 70, and 80mph.
8. Stopped at store to buy a lottery ticket.

 

[oe542bob]

GeauxinUp, nice when things work out. I remember a truck or 2 ago when I did the same with ALFAOBD. I first used the advertised diameter, but the speedo was still off a little. So it bugged me enough that I used the level method like you did and it was perfect then. I actually only did one tire, but it’s a good idea to do all 4 like you did.
Sometime things just go right and it makes you smile!

 

[GeauxinUp]

GeauxinUp, nice when things work out. I remember a truck or 2 ago when I did the same with ALFAOBD. I first used the advertised diameter, but the speedo was still off a little. So it bugged me enough that I used the level method like you did and it was perfect then. I actually only did one tire, but it’s a good idea to do all 4 like you did.
Sometime things just go right and it makes you smile!

Measuring all 4 was probably a little overkill, but it all worked out.

 

[RamDiver]

Measuring all 4 was probably a little overkill, but it all worked out.

I was much lazier and used a calculator, GPS and a bit of fudging.

Plus, I have too many starving insects in my area from April through to sometime in October.

I started with one of the AlfaOBD wheel size offerings that was close to my tire size, then verified the error using a GPS and calculated how much correction was required.

IIRC, the process required about 2 or 3 tweaks to get the speedo nailed to the GPS value.

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