Tire size adjustment

[hunterdan]

This isn't a how to per sé. But every time I've adjusted tire size on my ram, I've employed this method and it's been 100% spot on, every single time.
Download a GPS speedometer app. Set cruise control for 70-75 on a relatively flat/straight road for a few miles. Compare the digital speedometer to what the gps is saying.
I recently switched from 275/60r20 to 285/65r20.
At 70 in the truck I was reading something like 73 on the GPS.
So, a 3 mph difference AT 70 mph. That's not a 3 mph difference at all speeds. That's where people get messed up. It's a percentage. So, to find the percentage off it's
{(New speed - old speed) ÷ old speed }x100
{(73-70)÷70}×100
(3÷70)×100
0.04286x100
4.3%
So when I figured out the new circumference to enter, I took the current size, which I think was 2570 or 2560 or something and since I'm adding 4.3% multiply 2570 by 1.043 which comes out to 2680.51. I rounded up to 2681.
I entered 2681 into Alfaobd, followed the procedures outlined by other posts and went for a drive later on and confirmed my speedometer is dead on to the GPS. This method has worked every time I've tried it. I've never had to go back and readjust it because it was off. The key is knowing the percentage off the speedometer is. And honestly, if your speed limit is higher, you'll probably get a more accurate reading since the faster you go, the greater the difference between the gps and speedometer. Trying to get those numbers at 20 mph will be worthless.

 

[Rayzaa]

Did you have to change the ABS initulization in the Alphaodb? Any ABS code show for the size diff ? Asking because i set mine higher to 2708 and they say i need to set my ABS as well but my start button to run that action is grayed out and wont let me. No code yet for me either but ive only gone like 40-50 miles.

 

[Bigskyroadglide]

I run different size tires on the rear vs front and I haven't had to adjust this for abs until I exceed 125 mph. (Obviously closed course). Rear tires moving at different speed than front.

If you do experience this, it will set a code, throw a light on the dash and generally make cruise control not work.

I have not had it affect the abs to date and it will clear with alfaobd.

I believe you can use alfa to disable this but it's a pain (requires pin) and it's easier to clear the code.

My experience over about 80k miles.

 

[RamDiver]

Did you have to change the ABS initulization in the Alphaodb? Any ABS code show for the size diff ? Asking because i set mine higher to 2708 and they say i need to set my ABS as well but my start button to run that action is grayed out and wont let me. No code yet for me either but ive only gone like 40-50 miles.

I change the wheel circumference twice per year (summer & winter wheels) and have not had to re-initialize the ABS module, but...

One spring day, after tweaking the wheel size, the ABS module went bonkers.

I was driving home after having the stealership swap to my summer wheels as part of the spring warranty inspection/oil change, and I decided to make the adjustments in a parking lot.

I kept the truck running for the AC and tweaked as per usual. After toggling the ignition, the dashboard lit up like a Christmas ornament on steroids with multiple failure notifications.

EPS, EVIC, speedo, ABS, 4WD, etc. I tried to restore settings with a recent AlfaOBD backup file, but that didn't fix the failed systems.

I was in the country in the middle of nowhere, about 5 PM on a Friday, and may have suffered a wee anxiety before calling an SA at the dealership I was at, 25 minutes earlier.

It was interesting driving on the highway with no EPS, EVIC or speedo, but no big deal.
I used an old GPS that I keep in the truck (because the NAV sucks) for a speedo.

The SA dude was awesome. He printed the current BCM settings, reset them to OE default, and wished me a great weekend with a big smile.

The takeaway from this experience: pay more attention to the warnings and notifications on AlfaOBD. Leave the ignition in the off state while tweaking unless advised otherwise by AlfaOBD.

Whenever you tweak the wheel circumference, be prepared to follow the ABS re-initialization process. The ABS module lost its head and was spewing out garbage onto the CAN bus, wiping out several other modules.

I most likely could have reset the ABS module to solve all the grief, next time.
I have reset the wheel circumference with the ignition off several times since, without incident.

.

 

[hunterdan]

Did you have to change the ABS initulization in the Alphaodb? Any ABS code show for the size diff ? Asking because i set mine higher to 2708 and they say i need to set my ABS as well but my start button to run that action is grayed out and wont let me. No code yet for me either but ive only gone like 40-50 miles.

I haven't really had to, but I've gone through the process anyway. It's grayed out because there are procedures that need to be done before that can be done, I believe it tells you in the heading above what needs to be done.

 

[Rayzaa]

I change the wheel circumference twice per year (summer & winter wheels) and have not had to re-initialize the ABS module, but...

One spring day, after tweaking the wheel size, the ABS module went bonkers.

I was driving home after having the stealership swap to my summer wheels as part of the spring warranty inspection/oil change, and I decided to make the adjustments in a parking lot.

I kept the truck running for the AC and tweaked as per usual. After toggling the ignition, the dashboard lit up like a Christmas ornament on steroids with multiple failure notifications.

EPS, EVIC, speedo, ABS, 4WD, etc. I tried to restore settings with a recent AlfaOBD backup file, but that didn't fix the failed systems.

I was in the country in the middle of nowhere, about 5 PM on a Friday, and may have suffered a wee anxiety before calling an SA at the dealership I was at, 25 minutes earlier.

It was interesting driving on the highway with no EPS, EVIC or speedo, but no big deal.
I used an old GPS that I keep in the truck (because the NAV sucks) for a speedo.

The SA dude was awesome. He printed the current BCM settings, reset them to OE default, and wished me a great weekend with a big smile.

The takeaway from this experience: pay more attention to the warnings and notifications on AlfaOBD. Leave the ignition in the off state while tweaking unless advised otherwise by AlfaOBD.

Whenever you tweak the wheel circumference, be prepared to follow the ABS re-initialization process. The ABS module lost its head and was spewing out garbage onto the CAN bus, wiping out several other modules.

I most likely could have reset the ABS module to solve all the grief, next time.
I have reset the wheel circumference with the ignition off several times since, without incident.

 

[Rayzaa]

I dont know why this is replying elsewhere than your post and dont see a delete option but,.....

Interesting since every video says to put it in RUN to use the ODB. My speedo has been 3-4 mph off since changing the circumference so i went in the changed it to a smaller circumerence and now it is good. but i changed the circumference and forgot to put it to run and it worked. I was surprised.

Got to say though before i ever used the AlphaODB2 my truck could sit not being used for days and would always start. Now after a couple days or so i have to jump it and while driving the battery values are fine per eTorque specs.
Not sure if the ODB caused a parasitic draw from somwhere or my battery is just weak. Its only 2.5 years old. idk, this eTorque system is weird. Id rather they didnt have the eTorque in them.

Dealer didnt charge you to fix it? SA is service agent?

 

[joesstripclub]

Good advice on the percentage increase. I tried to calculate the circumference and I went from say 3mph under to 3mph over. split the difference and I was right on.

 

[hunterdan]

I dont know why this is replying elsewhere than your post and dont see a delete option but,.....

Interesting since every video says to put it in RUN to use the ODB. My speedo has been 3-4 mph off since changing the circumference so i went in the changed it to a smaller circumerence and now it is good. but i changed the circumference and forgot to put it to run and it worked. I was surprised.

Got to say though before i ever used the AlphaODB2 my truck could sit not being used for days and would always start. Now after a couple days or so i have to jump it and while driving the battery values are fine per eTorque specs.
Not sure if the ODB caused a parasitic draw from somwhere or my battery is just weak. Its only 2.5 years old. idk, this eTorque system is weird. Id rather they didnt have the eTorque in them.

Dealer didnt charge you to fix it? SA is service agent?

Are you leaving the obd adapter plugged in all the time or removing it when done? (I'm not referring to the security bypass).

 

[Rayzaa]

Are you leaving the obd adapter plugged in all the time or removing it when done? (I'm not referring to the security bypass).

Remove it, and put it back in the drawer.

 

[04fxdwgi]

Unless you changed something else, the AlphaOBD (software), when the OBD dongle is removed, has no effect on anything if you only changed the tire sizes. Looking at something totally unrelated, like an iffy battery perhaps. Batteries can be on the edge, even if the "specs" say they are OK. Have you tested it with an actual toaster style load tester? .

 

[RamDiver]

I dont know why this is replying elsewhere than your post and dont see a delete option but,.....

We do not have the ability to delete posts, but we can edit our posts for a period of time.
This gives us the ability to add forgotten comments or correct a typo etc.

In the lower left corner of our posts, you can click on the edit button to make any changes. Sometimes, editing a post that includes a quote window adds challenges to edit outside of the quote portion, especially when using an Android device.

I can teach you how to fix that condition when you're using a PC, by using the BB code settings, if you're interested.

Dealer didnt charge you to fix it? SA is service agent?

No charge, just a smile.

SA = Service Advisor or Agent.

.

 

[Rayzaa]

We do not have the ability to delete posts, but we can edit our posts for a period of time.
This gives us the ability to add forgotten comments or correct a typo etc.

In the lower left corner of our posts, you can click on the edit button to make any changes. Sometimes, editing a post that includes a quote window adds challenges to edit outside of the quote portion, especially when using an Android device.

I can teach you how to fix that condition when you're using a PC, by using the BB code settings, if you're interested.




No charge, just a smile.

SA = Service Advisor or Agent.

.

I know how to edit, but there should always be a delete option imo. Like if I decide not to reply to your post after hitting quote, I should be able to delete this but once you hit quote your are obligated....personally I just don't like that but,....whatever.
All forums are different but most let you delete, but not all

 

[RamDiver]

I know how to edit, but there should always be a delete option imo. Like if I decide not to reply to your post after hitting quote, I should be able to delete this but once you hit quote your are obligated....personally I just don't like that but,....whatever.
All forums are different but most let you delete, but not all

To say deleting a post is almost semantics.

While we can't go to an older post and hit a delete button, because of the setup configuration here, we can delete the entire content and replace it with something else in any one of our authored posts, provided the edit period hasn't expired.

Modifying or deleting a quote window at any time is simple in the BB mode.

Select the 3-dot stack on the upper right side, click on [], the entire quote window will become text characters with BB codes leading and following.

Delete any of the text between the control characters to modify or all of it to delete.
Easy peezey.

.