Seeking directions / Advice on changing tire size from factory tires...

[BlueHemi1500]

Hello all,

I am getting new tires this Saturday details are below:
Truck 2020 Laramime - Level 1, 4x4, 5.7 non-e-torque, 3.21 rear gears, 5.7 bed - no mods other than a few cosmetics and a few tweaks for Highbeams on and enabled my bedlights with the tailgate down and warning light in the dash.
Current tires/size factory: Bridgestone Dueler H/L size 275/55/R20
New Tires/Size: Bridgestone REVO3 A/T style new size being installed 275/60/R20

Now the questions request for help below:
Revs/Mile I have been looking on several sites for the data - I have found values that range from 612 to 632. I have looked on TireRack/Bridgestone-Firestone/tiresize.com.

• The size makes a difference in setting the calibrations for correcting my speedometer after the tires are installed.
• the different websites also disagree on the diameter of the tires - I think that the proper size is 33.0 inches.
  • Now a Question - Is a 33.0-inch tire one of the preprogrammed tire sizes in the truck computer? If not will I have to reset the ABS brake system with the increased tire size?
  • I have my OBD-alpha - I am not very well versed in making changes other than the above few trivial changes (low risk), changing tire size and adjusting brakes are a much higher risk/safety problem.
  • I also understand that the upsize of the tire change will also affect the transmission shift points.
  • I also understand that the speedometer will now be incorrect from the factory settings - an increased risk of speeding tickets and improper mileage being accumulated. (I base most of my maintenance based on mileage) along with time intervals.

Now the request for directions/ guidance in making the potential changes/calibration steps in AlphaObd - I will print these directions out and follow them out in the truck on Sat/Sun after the tires are installed

• tire size change steps
• update the ABS system
• any other changes required/best practices

I have read numerous posts and I remain somewhat confused/dazed, amazed, and the reasons for this post.

Thanks in advance for reading, your advice, knowledge, and skill.

BlueHemi1500

 

[CHeYeNNe71]

here's a good video

 

[CHeYeNNe71]

Maybe another

 

[CogitoErgoLevo]

Going from your original tires 32" to 33" tires without any recalibration means your speedo will be off and reading lower by only 3.4%.
If you did oil change every 5000 miles you would be off by 170 miles. Not enough to affect maintenance schedule
When at 65mph on speedo your true speed would be 67.2mph, not enough to get a ticket.
I drove for a week before recalibrating mine and did not notice a difference before/after.
I only did it because I already have a tazerDT and I will be using ACC alot this summer on my cross country trip.

You will be fine either way, wether you recalibrate the speedo or not.

 

[HSKR R/T]

Hello all,

I am getting new tires this Saturday details are below:
Truck 2020 Laramime - Level 1, 4x4, 5.7 non-e-torque, 3.21 rear gears, 5.7 bed - no mods other than a few cosmetics and a few tweaks for Highbeams on and enabled my bedlights with the tailgate down and warning light in the dash.
Current tires/size factory: Bridgestone Dueler H/L size 275/55/R20
New Tires/Size: Bridgestone REVO3 A/T style new size being installed 275/60/R20

Now the questions request for help below:
Revs/Mile I have been looking on several sites for the data - I have found values that range from 612 to 632. I have looked on TireRack/Bridgestone-Firestone/tiresize.com.

• The size makes a difference in setting the calibrations for correcting my speedometer after the tires are installed.
• the different websites also disagree on the diameter of the tires - I think that the proper size is 33.0 inches.
  • Now a Question - Is a 33.0-inch tire one of the preprogrammed tire sizes in the truck computer? If not will I have to reset the ABS brake system with the increased tire size?
  • I have my OBD-alpha - I am not very well versed in making changes other than the above few trivial changes (low risk), changing tire size and adjusting brakes are a much higher risk/safety problem.
  • I also understand that the upsize of the tire change will also affect the transmission shift points.
  • I also understand that the speedometer will now be incorrect from the factory settings - an increased risk of speeding tickets and improper mileage being accumulated. (I base most of my maintenance based on mileage) along with time intervals.

Now the request for directions/ guidance in making the potential changes/calibration steps in AlphaObd - I will print these directions out and follow them out in the truck on Sat/Sun after the tires are installed

• tire size change steps
• update the ABS system
• any other changes required/best practices

I have read numerous posts and I remain somewhat confused/dazed, amazed, and the reasons for this post.

Thanks in advance for reading, your advice, knowledge, and skill.

BlueHemi1500

The Rebel uses 33" tires, so set it to the Rebel tire size.

 

[irishwake63]

Speedometer Calibration

Speedometer calibration made easy. Use our speedometer calibration calculator to compare how fast you are traveling and your speedometer reading.

tiresize.com

 

[BlueHemi1500]

The Rebel uses 33" tires, so set it to the Rebel tire size.

What are the factory sizes of the Rebel tires?

I think they are on 18-inch or 17-inch rims.
Please let me know the size of the Rebel stock tires are, and I will see what AlphaOBD lists when I get home from the Firestone dealer which is about 10 or so miles. So I should be ok to drive a bit slow not to meet the local cops . My goal is, to complete the calibration on Saturday before dark, as I do not have any lights in the driveway.
So as far as I understand the truck will provide me a brief list of preloaded tire sizes.
If my truck has the 33 Rebel size in the drop-down menu that means my task in AlphaOBD will be easy and I potentially do not have to reset the ABS system.
That would be great. It is my understanding if one of the predetermined sizes is selected, there is NO ABS reset required is this correct?
I could be done in about 20-30 mins that is great.
Then, go out and road check with the wife to verify with a GPS App while I drive at several speeds to verify, But my luck is that I will have to muck around to get the calibration correct.

BlueHemi1500

 

[HSKR R/T]

What are the factory sizes of the Rebel tires?

I think they are on 18-inch or 17-inch rims.
Please let me know the size of the Rebel stock tires are, and I will see what AlphaOBD lists when I get home from the Firestone dealer which is about 10 or so miles. So I should be ok to drive a bit slow not to meet the local cops . My goal is, to complete the calibration on Saturday before dark, as I do not have any lights in the driveway.
So as far as I understand the truck will provide me a brief list of preloaded tire sizes.
If my truck has the 33 Rebel size in the drop-down menu that means my task in AlphaOBD will be easy and I potentially do not have to reset the ABS system.
That would be great. It is my understanding if one of the predetermined sizes is selected, there is NO ABS reset required is this correct?
I could be done in about 20-30 mins that is great.
Then, go out and road check with the wife to verify with a GPS App while I drive at several speeds to verify, But my luck is that I will have to muck around to get the calibration correct.

BlueHemi1500

275/70/18

 

[JF19Longhorn]

I believe you're over thinking this.. alot of people have done this exact upgrade without doing anything else.

I upgraded to that exact size, but in a LT Mickey Thompson Baja Boss and I have 3.92's.

Things I noticed changed:
- speedo reads 70mph when I'm actually doing around 71.5 mph.. with the factory tires it was reading 70mph when I was actually going 68-69mph.. so no big deal there.
- shifting literally has had zero change other than it'll down shift to 7th in places it use to stay in 8th. Probably a combination of the slightly larger diameter, but more than likely due to the massive weight difference.
- fuel mileage dropped.. how much it's hard to say because this truck will get 16mpg one tank and 14mpg the next.. same drive, same driver, same station.. but the overall avg I'd guess dropped 1-1.5 mpg.
- Towing is more stable (LT tire) with slightly worse acceleration (diameter & weight).

 

[CHeYeNNe71]

- fuel mileage dropped.. how much it's hard to say because this truck will get 16mpg one tank and 14mpg the next.. same drive, same driver, same station.. but the overall avg I'd guess dropped 1-1.5 mpg.

If you didn't fix speedometer, then your MPG are not true. Fix the speedo and it will fix MPG.

 

[JF19Longhorn]

If you didn't fix speedometer, then your MPG are not true. Fix the speedo and it will fix MPG.

You can use Math to figure out your mpg without fixing your speedometer and be pretty darn close.

 

[CHeYeNNe71]

You can use Math to figure out your mpg without fixing your speedometer and be pretty darn close.

How are you going to do that if your mileage is off? Plus it was a general statement, that still holds true.

 

[JF19Longhorn]

How are you going to do that if your mileage is off? Plus it was a general statement, that still holds true.

I know roughly how much it is off @ 35mph & 70mph. The dash tells you how far you traveled and how long it took so you can get your avg mph for that tank. Use that information to get the distance you're 'off', add it to the miles traveled for the tank. Then it's your normal mpg calculation. It's not 100% accurate, but it's pretty close.

 

[CHeYeNNe71]

I know roughly how much it is off @ 35mph & 70mph. The dash tells you how far you traveled and how long it took so you can get your avg mph for that tank. Use that information to get the distance you're 'off', add it to the miles traveled for the tank. Then it's your normal mpg calculation. It's not 100% accurate, but it's pretty close.

too much calculation, just fix the speedo and be done

 

[JF19Longhorn]

too much calculation, just fix the speedo and be done

I agree, but at the time I was worried I'd f something up with my warranty.. now I'm so used to it, I just do it.

 

[HSKR R/T]

I know roughly how much it is off @ 35mph & 70mph. The dash tells you how far you traveled and how long it took so you can get your avg mph for that tank. Use that information to get the distance you're 'off', add it to the miles traveled for the tank. Then it's your normal mpg calculation. It's not 100% accurate, but it's pretty close.

If you know how much it's offz the just adjust the miles driven by that percentage. No need to get mph mixed in with calculations

 

[JF19Longhorn]

If you know how much it's offz the just adjust the miles driven by that percentage. No need to get mph mixed in with calculations

Faster you go the more it is off.. that's why you need the time and distance.

OP: Sorry this apparently derailed your thread.

 

[HSKR R/T]

Faster you go the more it is off.. that's why you need the time and distance.

OP: Sorry this apparently derailed your thread.

That's not how it works for the odometer. The odometer will always be a percentage off. It doesn't vary by speed.

 

[CogitoErgoLevo]

It will be consistently off by 3.4%.
Whatever speed you see on speedo add 3.4%. At 100 mph on speedo, you are actually going 103.4mph...
Whatever distance you see on odometer add 3.4%--> 100 miles reported is actually 103.4 miles driven.
Same with mpg reported or calculated, 20mpg is really 20.68 mpg.
The difference is not much when going from 32" to 33" tires

 

[JF19Longhorn]

Guess I was over thinking it. Not surprised haha