Speedo correction after wheel/tire swap

[Walkerman]

I have a 2020 GMC Sierra 3500HD that came stock with 18" wheels and 275/70/18 tires. I want to go to the Denali wheel/tire that is 275/65/20. Question is can the dealer reflash the ecm to reflect that change? the 275/65/20 is 1" larger in diameter. I would think that it's possible because the powertrain is the same.

[Z45]

The dealer can't/won't do it unless you bought accessory GM wheels and tires from them.  That's the only way they can get a calibration for different sizes as they can ONLY do it for GM approved tire/wheel combination.  Doing it for customer supplied wheels/tires  has liability concerns.  

Edited March 8, 2024 by elcamino

[newdude]

On 3/7/2024 at 9:13 AM, Walkerman said:

I have a 2020 GMC Sierra 3500HD that came stock with 18" wheels and 275/70/18 tires. I want to go to the Denali wheel/tire that is 275/65/20. Question is can the dealer reflash the ecm to reflect that change? the 275/65/20 is 1" larger in diameter. I would think that it's possible because the powertrain is the same.

 

 

It all comes down to if that wheel/tire combo could have been ordered for your truck as a standard wheel/tire option.  

 

So if you have an SLE that was ordered with 18"s, but when ordering it could have been ordered with 20"s, then yes GM would be able to issue a new calibration.

 

If you have a base truck (Sierra Pro), those could only be had from the factory with 17" or 18" wheels/tires from the factory, so GM would NOT offer it.

 

Here's the PI explaining recalibrations - MC-10227674-9999.pdf (nhtsa.gov)

 

The only other approved way to calibrate is a GM accessory wheel/tire package.  

[elkhunt]

Rough country make's a speedometer recalibration tool 

I have one that I have used on my 2020 &2022 2500HD

when going from 20" summer tires to 18"winter tires

Edited March 9, 2024 by elkhunt

[Diver6]

I would save your money, your originals are 33.2 diameter and the new ones are 34.1 diameter which means at 70mph your only out 1.9mph. You won't get pulled over for that difference in speed. It's out even less at slower speeds, not worth it in my books. Tire Size Comparison

[davidm767]

The Banks iDash has the ability to calibrate the speedometer (as a percentage difference from stock tires). This is just one of many benefits to owning the gauge. (EDIT: Correction, only the iDash will show corrected speeds)

Edited May 17, 2024 by davidm767

[64BAwagon]

The Scangage2 and Scangage3 also have the ability to make adjustments to the speedo. 

I had the SG2 on my 2005 Duramax with 285's instead of the puny 245's   I could adjust the speedo but I dont think the odometer was ever completely accurate. 

[Elite130]

Before you go down the road of researching speedo calibration, put the tires on and see how far off you actually are. I put 295/65/20s on my '22 which are 1" taller than the OEM stock tires and my speedo is a dead nuts match to my GPS and roadside radar. IMO, its not a big enough difference or deal to calibrate a speedo. If anything the speedo will show slower than actual speed. 

[Epsilon Plus]

I am using a Pulsar LT with great results. After a little experimenting with stock size vs current I've got the speedo dialed into GPS speed on the nose with 37s. Added benefit of running 50psi all around with no TPMS warnings as I've dropped the threshold to 45. The reduced throttle delay also gives a great response and helps mitigate the 2-1 downshift clunk as well. 

 

Very happy with the unit

[aro]

Is there any calibration tool for the 2024 models? Rough Country and Pulsar LT don't do it.

[davidm767]

On 7/3/2024 at 3:58 PM, aro said:

Is there any calibration tool for the 2024 models? Rough Country and Pulsar LT don't do it.

Same problem here. I believe until enough companies learn to crack into the new ECU architecture it may be awhile. Until then I've memorized my speed correction between 50-80mph and Banks iDash provides a corrected speed. However they have not provided a way to reprogram the ECU to adjust for size.

Edited July 7, 2024 by davidm767

[Dirtbiker]

I have the opposite problem on my 2024 2500 AT4. I like 18 inch rims instead of 20’s so that the truck rides better with more sidewall. They told me they could not order the 18’s at the time and I had to get the 20’s option. I made a deal that when the truck came I would get 18 inch wheels and tires swapped. In the past the outside of the tire never changed with factory wheels only the rim size  and sidewall did. 
So I got the truck and new rims and factory sized 18 inch tires. I have come to realize the 20 inch rims had 34 inch tires and the 18 inch factory tire size are only 33 inch. My speedometer is out 5%. So I have to do 105kph to actually be going 100kph. Not the worst thing but here is the catch - I am going to lose my warranty early. About 5000 km early. And that sucks.

Two dealerships said even though it is factory size they can not adjust the speedometer. So I am searching for solutions. Yes I could just buy tires that are 34 inch OD but tires are expensive and with. 1mm offset the 33’s just barely do not rub anything. I hate rubbing. 34s will rub. 

[chris21]

On 3/7/2024 at 9:13 AM, Walkerman said:

I have a 2020 GMC Sierra 3500HD that came stock with 18" wheels and 275/70/18 tires. I want to go to the Denali wheel/tire that is 275/65/20. Question is can the dealer reflash the ecm to reflect that change? the 275/65/20 is 1" larger in diameter. I would think that it's possible because the powertrain is the same.

That tire change will most likely make the current calibration of your speedometer and odometer accurate.