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Old 05-10-2010, 08:27 PM   #1
Join Date: Apr 2010
Posts: 12
Cool Speedometer error

My TJ has 16" tires and I recently installed a Garmin GPS unit. The readings between the Speedometer and GPS are as follows (speedometer reading will be first then GPS reading) 30MPH ~ 35MPH, 40MPH ~ 49MPH, 50MPH ~ 60MPH, 60MPH ~ 71MPH. I am assuming is is due to tire size. Am I right????

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Old 05-10-2010, 08:42 PM   #2
frankenbury's Avatar
Join Date: Mar 2010
Location: Emporia, KS
Posts: 138
Most likely. I assume you probably have 32" tires or so and 16" wheels. Bigger tires than stock will make your speedo show slower than you are actually going. If you go to the following link, plug in your vehicle on the top and select your tire size below it will show the speedo differences for the different tire sizes.

Tire Size Calculator - tire & wheel plus sizing

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Old 05-10-2010, 08:42 PM   #3
TJWhosYourMama's Avatar
Join Date: Feb 2010
Location: Denver, CO
Posts: 46
16" would be your wheel size. It's looking like you increased your tire size by a good amount if your speedo is off by that much. You can get a new speedo-gear to correct the discrepancy.
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Old 05-10-2010, 08:49 PM   #4
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Location: arvada, co
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check partsmike.com you give them your tire size and gearing and they will hook you up with a speedo gear for $30. I went through them and they were the cheapest and most accurate speedo gears I could find.
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Old 05-10-2010, 08:58 PM   #5
Join Date: Apr 2010
Posts: 12

Got it.............thanks
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