AlfaOBD and Tire Pressure, and MPH!?

[alorentz]

I hope someone has experience with AlfaODB, or other application to adjust tire size, and knows what they are doing...because I'm guessing!!

I have 2022 RAM 1500 Crew Cab, 5.7L, 2300 miles. Stock were Alenza Dueler 31in tires. I switched out for Wildpeak AT3W 275/60/20, which are 33.1 in. I noticed my AVG MPG was pretty low, at around 10.9 MPG, and the MPH was not correct as compared to GPS app. Gas mileage is terrible, and speedo is wrong. I read that I need to change the config so the new tire size is accurate, which affects MPG and speedo, on other stats. The dealer doesn't do this, so I purchased an SGW bypass, and downloaded the AlfaODB app on an Android. Hooked it all up, and am able to change configurations in the vehicle. Stock tire circumference of the 31in was 2462mm. The new 33.1in tire is 2642mm (approx). I adjusted the Tire Program Size in the app, and set the config to 2642, and then tested MPH on the highway with the GPS app. It appears the truck was running about 3 MPH higher than the GPS app, meaning speedo showing faster than actual. So, I dropped the tire circumference in AlfaODB to 2585, and then the truck ran about 1 MPH under GPS. So, I changed circumference to 2595. Now the truck MPH and GPS MPH are running the same, so at 2595 truck speedo is accurate.

Here's the question, am I supposed to put in the exact circumference of the tires, which is 2642, which makes the truck speedo/MPH faster by about 2-3 MPH than the vehicle is actually going. OR, am I supposed to adjust tire circumference in the config until the speeds match in the truck and GPS, which is about 2595...which is smaller than the actual 33.1 in tire? I'm lost.

 

[Dookie]

Match GPS, you are good. You can choose from the drop-down list as well and chose a prefilled size that is roughly close to the same as your current tire, wheel/rim size doesn't make any difference. As long as the overall diameter is the same or very close, just choose that and check against GPS.

 

[alorentz]

Match GPS, you are good. You can choose from the drop-down list as well and chose a prefilled size that is roughly close to the same as your current tire, wheel/rim size doesn't make any difference. As long as the overall diameter is the same or very close, just choose that and check against GPS.

At this point actual is 2642. But to get the speedo accurate, I had to scale down to 2595 (originally 2462). The reason I'm adjusting is to get the MPG more accurate, which seemed really low at 10.8 MPG.

The prefilled sizes for 275/60/20 are roughly 2600+ too. Those all put the speedo 2-3 mph over GPS.

 

[Dookie]

Rated/advertised actual and mounted and proper inflation on the truck under weight actual are usually two different things. Matching GPS is the best and most accurate way.

 

[alorentz]

Thanks for the information. Another question, I had read you may need to adjust ABS after tire size is changed (was previous years RAM, 2018 perhaps). In my 2022, I didn't get any faults or lights after changing the tire size in AlfaOBD ... so it seems like everything is fine. Do you happen to know if adjusting ABS is necessary in the 2022, despite not faults or warnings?

 

[squid013]

I hope someone has experience with AlfaODB, or other application to adjust tire size, and knows what they are doing...because I'm guessing!!

I have 2022 RAM 1500 Crew Cab, 5.7L, 2300 miles. Stock were Alenza Dueler 31in tires. I switched out for Wildpeak AT3W 275/60/20, which are 33.1 in. I noticed my AVG MPG was pretty low, at around 10.9 MPG, and the MPH was not correct as compared to GPS app. Gas mileage is terrible, and speedo is wrong. I read that I need to change the config so the new tire size is accurate, which affects MPG and speedo, on other stats. The dealer doesn't do this, so I purchased an SGW bypass, and downloaded the AlfaODB app on an Android. Hooked it all up, and am able to change configurations in the vehicle. Stock tire circumference of the 31in was 2462mm. The new 33.1in tire is 2642mm (approx). I adjusted the Tire Program Size in the app, and set the config to 2642, and then tested MPH on the highway with the GPS app. It appears the truck was running about 3 MPH higher than the GPS app, meaning speedo showing faster than actual. So, I dropped the tire circumference in AlfaODB to 2585, and then the truck ran about 1 MPH under GPS. So, I changed circumference to 2595. Now the truck MPH and GPS MPH are running the same, so at 2595 truck speedo is accurate.

Here's the question, am I supposed to put in the exact circumference of the tires, which is 2642, which makes the truck speedo/MPH faster by about 2-3 MPH than the vehicle is actually going. OR, am I supposed to adjust tire circumference in the config until the speeds match in the truck and GPS, which is about 2595...which is smaller than the actual 33.1 in tire? I'm lost.

Tinker till its right. At what speed are you off by 1 mph. If its at 70, you are 1.5% off. At 1.5% i wouldn't bother any more, that is the difference in a tire having a few psi different or having the tread wear down. Fenerally tires are all under the advertised size and because of the weight of the truck being on them, they lose a smidge of height and by proxy circumference.

Sent from my SM-G996U using Tapatalk

 

[squid013]

Thanks for the information. Another question, I had read you may need to adjust ABS after tire size is changed (was previous years RAM, 2018 perhaps). In my 2022, I didn't get any faults or lights after changing the tire size in AlfaOBD ... so it seems like everything is fine. Do you happen to know if adjusting ABS is necessary in the 2022, despite not faults or warnings?

You only have to do the abs learning and reset if you got error lights. My power wagon, because of the tech packages required it.

Sent from my SM-G996U using Tapatalk

 

[alorentz]

Tinker till its right. At what speed are you off by 1 mph. If its at 70, you are 1.5% off. At 1.5% i wouldn't bother any more, that is the difference in a tire having a few psi different or having the tread wear down. Fenerally tires are all under the advertised size and because of the weight of the truck being on them, they lose a smidge of height and by proxy circumference.

Sent from my SM-G996U using Tapatalk

Yes, tested at 70-71. GPS is slightly under, by like .5 MPH ... sometimes it jumps to match speedo, but stays 1 MPH lower at current tire size settings. Not sure if I need to adjust it down as few mm to match exactly, but probably OK now.

 

[MannyN]

Yes, tested at 70-71. GPS is slightly under, by like .5 MPH ... sometimes it jumps to match speedo, but stays 1 MPH lower at current tire size settings. Not sure if I need to adjust it down as few mm to match exactly, but probably OK now.

And then, when you lose a little tire pressure, you have to adjusted it again to match the GPS Speed. After that, you air up the tire to the correct PSI reading........and you guessed it, you have to do it all over again. You will never be done. Leave well enough alone.

 

[HSKR R/T]

Thanks for the information. Another question, I had read you may need to adjust ABS after tire size is changed (was previous years RAM, 2018 perhaps). In my 2022, I didn't get any faults or lights after changing the tire size in AlfaOBD ... so it seems like everything is fine. Do you happen to know if adjusting ABS is necessary in the 2022, despite not faults or warnings?

Thnically when you adjust tire size with the AlfaOBD, it is changing it in the ABS menu. I have a Snap-On scan tool, and when I adjusted the tires size in my Dakota with it, you had to go into the ABS menu to alter the revolutions per mile number. I'm sure alfaOBD does that automatically based in the circumference you enter through the app