Is my Speedometer Correct? (wheel/tire change)

[AlDAngle]

Hello All.

 

I recently switched back to Chevy and purchased a 2019 Silverado LT 4WD DBL. The truck was delivered to me with 18" x 8.5" wheels, and 265/65 R18 tires. I later found out that the truck came from the factory with 22" x 9" wheels, and 275/50 R22 tires. I was told (by dealer service) that the hub had some type of "servo" that would automatically compensate for the wheel/tire change, and the speed displayed on the speedometer would be correct. Can anyone tell me if the information I received was accurate? I believe the speed being displayed is higher than the actual speed, but really don't know for sure. Thanks!

[davester]

How would anyone here know if your truck's speedo works right?  I would suggest driving somewhere with a known, fairly accurate distance, and seeing if the odometer increased by the correct amount.  Or see how the speedo matches driving in traffic on a given street, or follow a friend after asking them to drive at a certain speed?

[AJMBLAZER]

Download a GPS Speedo to your phone. Check it against that. 

[Billet Bowtie]

12 hours ago, asci computer said:

Hello All.

 

I recently switched back to Chevy and purchased a 2019 Silverado LT 4WD DBL. The truck was delivered to me with 18" x 8.5" wheels, and 265/65 R18 tires. I later found out that the truck came from the factory with 22" x 9" wheels, and 275/50 R22 tires. I was told (by dealer service) that the hub had some type of "servo" that would automatically compensate for the wheel/tire change, and the speed displayed on the speedometer would be correct. Can anyone tell me if the information I received was accurate? I believe the speed being displayed is higher than the actual speed, but really don't know for sure. Thanks!

Your new tires are 1.26" taller than your old setup. When your speedo indicates 65 mph your are actually going 67.6 mph. The dealer was incorrect saying that the speedo will correct itself. The only way I know of currently to correct the speedometer is to purchase a device from  hypertech called a inline speedometer calibrator. I have not used one but others on the forum have.

[eppieguy]

^^^ This is correct.

[AlDAngle]

53 minutes ago, Billet Bowtie said:

Your new tires are 1.26" taller than your old setup. When your speedo indicates 65 mph your are actually going 67.6 mph. The dealer was incorrect saying that the speedo will correct itself. The only way I know of currently to correct the speedometer is to purchase a device from  hypertech called a inline speedometer calibrator. I have not used one but others on the forum have.

A smaller tire/wheel was installed. Am I correct in assuming that that the 2.6 mph difference would be in the other direction (when the speedo reads 65, actual rate of speed is 62.4)? Thanks

[Billet Bowtie]

You can plug both of your tire sizes in this calculator and it will tell you the difference between indicated speed and actual speed.

https://www.discounttire.com/learn/tire-size-calculator?&ef_id=Cj0KCQjwuZDtBRDvARIsAPXFx3BQBhaKtiXSX-PTORmFQx_4QzZ1PlSxsutEfKzawI_jFwRneBCOAl4aAgGbEALw_wcB:G:s&gclid=Cj0KCQjwuZDtBRDvARIsAPXFx3BQBhaKtiXSX-PTORmFQx_4QzZ1PlSxsutEfKzawI_jFwRneBCOAl4aAgGbEALw_wcB

[AlDAngle]

46 minutes ago, Billet Bowtie said:

You can plug both of your tire sizes in this calculator and it will tell you the difference between indicated speed and actual speed.

https://www.discounttire.com/learn/tire-size-calculator?&ef_id=Cj0KCQjwuZDtBRDvARIsAPXFx3BQBhaKtiXSX-PTORmFQx_4QzZ1PlSxsutEfKzawI_jFwRneBCOAl4aAgGbEALw_wcB:G:s&gclid=Cj0KCQjwuZDtBRDvARIsAPXFx3BQBhaKtiXSX-PTORmFQx_4QzZ1PlSxsutEfKzawI_jFwRneBCOAl4aAgGbEALw_wcB

Thanks "Billet Bowtie". Using the tire size calculator (https://www.discounttiredirect.com/learn/tire-size-calculator) and inputting the original factory tire as the "Current", then the tire that came with the truck as "New", the results were:

 

Not happy that the dealer gave me a total BS story. Not happy that my odometer will be showing extra miles. I assume that the mpg calculations will also be off.

 

If anyone knows a solution other than the Hypertech device, please chime in. I have seen elsewhere that there may be some sort of change that can be made via the PCM?

[garagerog]

Your dealer is trying to bend you over without benefit of lube. It seems pretty obvious that they removed and swapped the factory installed wheels that were delivered with your truck to make a sale on a less equipped truck. Take your window sticker or whatever paperwork you have to document your claim of the truck originally equipped with the 22 x 9's, get in their face big time and demand whatever satisfaction suits you.

 

[MaverickZ71]

It will require a PCM programming change.  You can either pay a GM dealer to do it, or you can buy a Hypertech or Diablo or other aftermarket tuning device that has the capability to adjust between tire diameters.  A few hundred $ either way.  The dealer you purchased from should have had the intregrity to reprogram the truck for the new tires before you bought it, so the speedometer/odometer would have been correct.  All they did was do a swap for somebody else who wanted bigger wheels and it left you in the lurch.  

[newdude]

16 hours ago, asci computer said:

Hello All.

 

I recently switched back to Chevy and purchased a 2019 Silverado LT 4WD DBL. The truck was delivered to me with 18" x 8.5" wheels, and 265/65 R18 tires. I later found out that the truck came from the factory with 22" x 9" wheels, and 275/50 R22 tires. I was told (by dealer service) that the hub had some type of "servo" that would automatically compensate for the wheel/tire change, and the speed displayed on the speedometer would be correct. Can anyone tell me if the information I received was accurate? I believe the speed being displayed is higher than the actual speed, but really don't know for sure. Thanks!

 

The more important part is WTF happened to the wheels that were SUPPOSED to be on the truck?  I hope they knocked the $3000 or so off the MSRP for the missing wheels. 

[AlDAngle]

2 hours ago, MaverickZ71 said:

The dealer you purchased from should have had the intregrity to reprogram the truck for the new tires before you bought it, so the speedometer/odometer would have been correct.  All they did was do a swap for somebody else who wanted bigger wheels and it left you in the lurch.  

Agree.

 

My question at this point is whether or not the dealer has the ability to reprogram the PCM for the tires that are on the truck? I do not want to go with an aftermarket solution that may cause other issues down the road. 

[AlDAngle]

15 hours ago, asci computer said:

My question at this point is whether or not the dealer has the ability to reprogram the PCM for the tires that are on the truck? I do not want to go with an aftermarket solution that may cause other issues down the road. 

Anyone?

 

I will be contacting the dealer today about the speedo issue. Since they gave me a BS story last time around, it would be great if I knew what can (or can't) be done before I speak with them. Thanks

[AJMBLAZER]

There ought to be a few different programs/settings In the computer since the different tire sizes are noticeably different. 
 

 

That said...check your actual speed vs the speedo. I’ve seen more than a few vehicles over the years where the factory speedo was off with the stock tires. I once heard years ago that GM considered a 5% speedo variance ok. Not sure on that though. 

[newdude]

2 hours ago, asci computer said:

Anyone?

 

I will be contacting the dealer today about the speedo issue. Since they gave me a BS story last time around, it would be great if I knew what can (or can't) be done before I speak with them. Thanks

 

If you want to keep the 18"s then yes the dealer can go back to a calibration for those wheels/tires.  If you want the 22"s that were supposed to be there, leave it alone. 

 

They will have to program the ECM, the BCM, the Electronic Power Steering Module and the front camera module if it has one.  They will have to call GM Techline and get a programming authorized on it.