Need for Speedo recalibration w/ tire change?

[JRL1164]

So I got 18" wheels I wanna put 275/70R18 on the truck. I wanna know if I need to have the speedometer re-calibrated via something like hypertech or something similar. I know the speedometer will be off but will the shift points of the transmission of anything like that will be off because of the tires. I don't want to throw everything off, i don't mind hand calculating my mileage.

[sprayed99]

Yes it will effect several things by not recalculating the diameter on the tires. Shift points being one of them.

[Norcal Flyfisherman]

I changed to 275/70R18 a few weeks ago and didn't recalibrate anything. I don't remember the website, but I looked at one that compared tire sizes. It indicated about 1 mph difference with the larger tires. It was on the Internet so it has to be true.

[AZRenegade]

I went from stock 17" to 18" on my '15 Sierra and it actually made my speedo more accurate as compared to my GPS. This was also the case when I upsized the wheels on my '14 Sierra and my '93 Sierra. I wouldn't worry about it. It seems like auto manufacturers purposely calibrate the speedo's off by a small amount.

 

To be honest, the only speedo I've ever had that was accurate right out of the box was my Harley. Go figure.

[TJay74]

There will always be some speedo error, manufactures have to account for tire wear and come up with a calibration that is close all of the time. I would see what the tire size difference is, if it is less than .5" from stock you should be fine. Any more than that and I would look into getting the speedo re-calibrated.

[JRL1164]

Thanks guys, I think what I'm gonna do after I get the tires on I'll check the speedometer against GPS and determine if its off enough to warrant the re-calibration. Today on the way home from work I checked it against GPS and I'm roughly 1 mph slower than the truck says. So it may not need to be done after the larger tires.