Speedometer Question

[chief1600]

Howdy.  I have a 2018 Silverado Z71 CC w/5.3.  I just had new BF Goodrich All Terrain KO2s installed in the stock tire size and a Rough Country level lift installed.  Now it seems my speedometer is off a little bit.  If I have the cruise set at 55, my GPS tells me I'm traveling at 53.5 or 54.  Seems like I'm getting passed more often on the interstate.  My question is, if the stock tire size has been maintained, why would my speedometer be any different.  No other modifications have been made.  Opinions are appreciated.  Thanks!

[tyler.frost92]

No matter if two different tires are sold as the same exact size they wont always measure out the same. I dont think there would be enough difference to notice more people passing you though. 

[Jglew82]

Did you verify the actual tire size on your new tires? Not common, but still possible they may have pulled the incorrect size. 

[1SLOW1500]

Tires sizes vary. Some brands are well known to claim a size but measure up different. But in your case look for the tire diameter and compare to stock.

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[Jacoby]

1mph really!!!

[16LT4]

Most factory Speedo’s are off by more than 1 mph, I’ve seen some off by up to 5 at 75. Don’t worry about 1)the difference and 2) being passed. It’s not a race. 

[Mileguru]

4 hours ago, Jacoby said:

1mph really!!!

I love how you and I get bothered by the same little things!

You just call them out more often than I do and then I get to have a good laugh at your hilarious posts.

[chief1600]

My apologies if I've offended anyone by asking a question within a forum which is meant to promote the opportunity for knowledge transfer.

[TXGREEK]

My apologies if I've offended anyone by asking a question within a forum which is meant to promote the opportunity for knowledge transfer.

You’ll get some insecure individuals from time to time that’ll have something negative to say cause it makes them feel better, the world is full of them but depending on the site your on most are helpful, some are full of trash more so than others that will contradict literally anything out of the norm for them, they lack communication skills and most of the time only have what they consider as their only friends, on forums. 1slow1500 most likely had the best answer to your question, Tire size make a big difference especially certain brands run larger than others. Good luck


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[KARNUT]

Don’t worry about getting passed. I just traveled from Texas to South Carolina with my cruise set at 75 MPH. I was the slow guy.


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[14 gmcl83]

So I just got hp tuners and started to learn how to tune with some help Of friends and 1slow1500 and what I noticed my tire size on my truck was way wrong from the factory tune  it was only 30.87 inches its all fixed now since I have the bfg k02 in a 275/60/20 size. I just thought that was very odd.