Speedo calibration
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Posting Guru
Joined: Oct 2009
Posts: 1,340
Likes: 4
From: Bradenton, FL
Speedo calibration
Im looking into getting new rims and tires for my truck. Right now im running 17s with 35s. My new rims will be 20s with 35s. How does the speedo calibration work? By the size of the rim or by the tire?
Token Redneck
Joined: Jun 2007
Posts: 9,331
Likes: 341
From: Breckenridge, TX
Revolutions per mile of the tires is what's programmed into the computer to derive the speedo reading, there are sensors in different places that will account for gearing changes, but not tire size changes. If the outer diameter of the tire doesn't change, then the speedo isn't going to be off.
Here's a quick calculator to show you how far you'll be off:
4Lo.com :: Speedometer Check Calculator
Here's a quick calculator to show you how far you'll be off:
4Lo.com :: Speedometer Check Calculator
Token Redneck
Joined: Jun 2007
Posts: 9,331
Likes: 341
From: Breckenridge, TX
Stock tires vary, off the top of my head 265/70R17, 275/70R18, and 275/65R20 were all available on the the 2005-2007 SDs.
Depending on how you recalibrated the speedo you might already be fine, because differences of less than ~3% of height(~1mph) aren't really noticeable on the not-finely graded gauge on your dashboard.
Depending on how you recalibrated the speedo you might already be fine, because differences of less than ~3% of height(~1mph) aren't really noticeable on the not-finely graded gauge on your dashboard.
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