Speedometer Calibration

[b2000]

Hi All, hoping for some insight on speedometer calibration after installing aftermarket tires. (For a '22 AT4 1500)

I did a slight bump in tire size and make, along with new wheel that made a significant difference in aesthetics and handling without having to lift / level / trim the truck.

Old: (factory set up) 275/65R18 Goodyear Wrangler DuraTrac: diameter of 32.1", a width of 11", and has 648 revolutions per mile. (was on 8.5" wheel)

New: 275/70R18 Mickey Thompson Baja Boss A/T: diameter of 33.4", a width of 10.8", and has 622 revolutions per mile. (is on 9" wheel)

I asked my local GMC dealership if they could calibrate my speedometer to the new tire size and they said no, they won't do that. I called a local speedometer shop, and they said that the software isn't available yet to calibrate a 22 AT4 1500, but that the factory tolerance is +/- 3MPH which I can easily test with a phone app, and if I'm within that range, I may not need to change it.

The MPH reading isn't really my concern (although I would certainly like to avoid a speeding ticket), but I would like my odometer reading to be correct over the lifespan of the vehicle (also a legal requirement) and I'd like my MPG readings to be correct.

Has any one else addressed this issue or have a suggestion how to reset the tire size in truck's software?

Thanks!

 

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[Cocoabean]

Here is a thread of guys talking about the hypertech speedometer calibrator: https://www.at4forum.com/threads/anyone-used-the-hypertech-speedometer-calibrator.241/

I was told by my dealership they can't update the calibration and it would void my warranty if I did it myself, so I used a iPhone speedometer app to determine my speedometer is off by 4.5% for my 35x12.5x17's. Now I just add 5% to my speed and call it a day. Not looking to break land speed records in my 3.0l.

 

[palehorse]

Hi All, hoping for some insight on speedometer calibration after installing aftermarket tires. (For a '22 AT4 1500)

I did a slight bump in tire size and make, along with new wheel that made a significant difference in aesthetics and handling without having to lift / level / trim the truck.

Old: (factory set up) 275/65R18 Goodyear Wrangler DuraTrac: diameter of 32.1", a width of 11", and has 648 revolutions per mile. (was on 8.5" wheel)

New: 275/70R18 Mickey Thompson Baja Boss A/T: diameter of 33.4", a width of 10.8", and has 622 revolutions per mile. (is on 9" wheel)

I asked my local GMC dealership if they could calibrate my speedometer to the new tire size and they said no, they won't do that. I called a local speedometer shop, and they said that the software isn't available yet to calibrate a 22 AT4 1500, but that the factory tolerance is +/- 3MPH which I can easily test with a phone app, and if I'm within that range, I may not need to change it.

The MPH reading isn't really my concern (although I would certainly like to avoid a speeding ticket), but I would like my odometer reading to be correct over the lifespan of the vehicle (also a legal requirement) and I'd like my MPG readings to be correct.

Has any one else addressed this issue or have a suggestion how to reset the tire size in truck's software?

Thanks!

It's easy to calculate using just the revolutions-per-mile. Your new tires are roughly +4.2% different from stock (648 ÷ 622), so you can multiply your mpg or speed readings by 1.042 to obtain your actual values. I know this doesn't solve your main issue with readings and displays, but it should give you a good idea of what the speed differences are at any given speed. Examples:

Displayed Speed: 50 mph
Actual Speed: 50 x 1.042 = 52.1 mph

Displayed mpg: 25 mpg
Actual mpg: 25 x 1.042 = 26.05 mpg

The mpg readings on our trucks aren't very accurate anyways, so the best way to measure those is to simply divide the number of gallons you put in by the distance traveled on each tank (including the 4.2% math I described above for the distance). I use "Trip 2" to track that info for every fresh tank.

 

[RugbyRef]

I bought the Hypertech In-line Speedometer Calibrator for my '22 AT4X and promptly returned it when I found that the connectors are not the same under the dash. Funny thing is - I couldn't find it on their website for my truck, so I called them. The sales rep I spoke with said they hadn't updated the website yet, but that the in-line calibrator they were selling would work, so I bought it. Turns out, it does not work due to different connections. I returned it.

 

[Agent 409]

You cannot tune or use a speedometer calibrator (in line or programmer) for the GM Global B architecture since it is encrypted for reasons of cybersecurity. That means the 2022.5+ model year half ton trucks (there are many other Global B platforms, I don't have this memorized) have no options as of now. I do know that HP tuners finally cracked the ECM as well as some other tuners. That's a complicated process with upgrades/replacements of the ECM. I am going to guess that Rough Country and Hypertech are working on this topic but who knows?? Someone would have to email their sales team/customer service to find out.

Not having the ability to recalibrate my speedometer after tire OD upsizing likely will keep me from lifting my truck for now.

As a further note, I know many don't do this but having my speedometer accurate and transmission shift points correct matters to me on my vehicles.

 

[Teegunn]

It's easy to calculate using just the revolutions-per-mile. Your new tires are roughly +4.2% different from stock (648 ÷ 622), so you can multiply your mpg or speed readings by 1.042 to obtain your actual values. I know this doesn't solve your main issue with readings and displays, but it should give you a good idea of what the speed differences are at any given speed. Examples:

Displayed Speed: 50 mph
Actual Speed: 50 x 1.042 = 52.1 mph

Displayed mpg: 25 mpg
Actual mpg: 25 x 1.042 = 26.05 mpg

The mpg readings on our trucks aren't very accurate anyways, so the best way to measure those is to simply divide the number of gallons you put in by the distance traveled on each tank (including the 4.2% math I described above for the distance). I use "Trip 2" to track that info for every fresh tank.

I do the exact same thing as you described. Find the revolutions per mile difference between the new and old tires. Use that math to figure speed and MPG.

Obviously over wear and use, tires get slightly smaller as tread wears off. Revolutions per mile as listed by manufacturers is not always 100% of actual, either. So I also use a couple very accurate GPS apps on my phone to determine the actual speed I am travelling on the apps, vs what the trucks speedometer reads. Using both methods, one can get a pretty accurate percentage of the difference between stock and aftermarket tires.

I also use trip 2 for my tank to tank figures. I simply take the mileage that the trip 2 shows that I travelled, and take that times 1.04 (my tires are a tad over 34" tall). And I write on each receipt after I fill the tank the actual MPG that the truck got.

As far as speed - I figure that if the speedo says 80, I am actually a bit over 83 mph. And this adds up with what my accurate GPS apps on my phone show also.

As far as the odometer - well, if GM won't let us recalibrate the speedometer, then what choice does one have. I figure I have around 1000 miles more on my truck now than the ODO actually shows.

 

[Wes]

Hi All, hoping for some insight on speedometer calibration after installing aftermarket tires. (For a '22 AT4 1500)

I did a slight bump in tire size and make, along with new wheel that made a significant difference in aesthetics and handling without having to lift / level / trim the truck.

Old: (factory set up) 275/65R18 Goodyear Wrangler DuraTrac: diameter of 32.1", a width of 11", and has 648 revolutions per mile. (was on 8.5" wheel)

New: 275/70R18 Mickey Thompson Baja Boss A/T: diameter of 33.4", a width of 10.8", and has 622 revolutions per mile. (is on 9" wheel)

I asked my local GMC dealership if they could calibrate my speedometer to the new tire size and they said no, they won't do that. I called a local speedometer shop, and they said that the software isn't available yet to calibrate a 22 AT4 1500, but that the factory tolerance is +/- 3MPH which I can easily test with a phone app, and if I'm within that range, I may not need to change it.

The MPH reading isn't really my concern (although I would certainly like to avoid a speeding ticket), but I would like my odometer reading to be correct over the lifespan of the vehicle (also a legal requirement) and I'd like my MPG readings to be correct.

Has any one else addressed this issue or have a suggestion how to reset the tire size in truck's software?

Thanks!

How is ride quality? Any rub with no level?

 

[Agent 409]

Someone finally makes a MY 2022+ speedometer recalibration option for the refresh trucks. Interested to find out if anyone has bought this on the forums here

Speedometer Calibrator | Chevy/GMC 1500 2WD/4WD (22-25)

Speedometer Calibrator | Chevy/GMC 1500 2WD/4WD (22-25)

www.roughcountry.com

 

[gemarsh]

Good God, no wonder it took so long to come out with this re-calibrator, after reading the install guide.

 

[pinebaron]

Good God, no wonder it took so long to come out with this re-calibrator, after reading the install guide.

That's funny

 

[Viking Truck]

tiresize.com says your new tires are 3.4% larger in diameter and at a reading of 80 mph you will be going 82.7.

I agree with wanting it right but I think I could live with that difference.

Tire Size Comparison

Tire size comparison the easy way. Use our tire size comparison calculator to compare diameter, width, sidewall, circumference and revolutions per mile.

tiresize.com

 

[pinebaron]

tiresize.com says your new tires are 3.4% larger in diameter and at a reading of 80 mph you will be going 82.7.

plus fewer miles on the odometer