Speedometer to Allison

[mopar440cu]

I don’t know if this is the correct place to put this question so moderator please don’t get mad. Lol

I have a 2012 Silverado 3500 he LML with a Allison auto and the speedometer is registering 3 miles over on the dash. Is there a way to fix this? Maybe cable or by a electronically adjustment of some sort with a hand held electrical OBD ?

I am using the Garmin Zumba out of my VMax motorcycle on the dash for the wife for now, but really got to fix it. Any help would be appreciated.

 

[Chevy1925]

you will either need to put the factory size tires back on or get a tune that changes that in the programming. this would require something like EFI Live or the like to change the ECM tire size parameter so the speedo reads correct.

 

[Mike L.]

MDI might do it.

 

[mopar440cu]

you will either need to put the factory size tires back on or get a tune that changes that in the programming. this would require something like EFI Live or the like to change the ECM tire size parameter so the speedo reads correct.

The tires are the same height just thinner than stock, according to the sticker on the inner door.

 

[duramax on fire]

The tires are the same height just thinner than stock, according to the sticker on the inner door.

When there thinner that means shorter also in metric. 265/75/16. 265mm width tread. 75 percent of 265 is the hieght of side wall. So dropping to a 245/75/16 it will be shorter.

My Matco modus says it can adjust for tire height. Maybe find someone with one. Which part of Florida are you in?