Speedometer question?

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shipmasta

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I just had new wheels and tires installed today (see my thread in the exterior section). The tires I had installed are 315/70R17 (just shy of 35 in). Anyway I was expecting my speedometer to be off, however it is still dead on. My truck has built in GPS and at all speeds my speedometer matches my GPS speed. Keep in mind my speedometer matched my GPS before the new tires.

Am I missing something here?

I was expecting to have to take my truck to the dealer to recalibrate my speedometer, but it appears that will not be necessary.
 

Polaris Pro

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Mine is off around 4mph when it says I am going 60mph. I can tell because I have a portable GPS unit. I have 35s.

I just had new wheels and tires installed today (see my thread in the exterior section). The tires I had installed are 315/70R17 (just shy of 35 in). Anyway I was expecting my speedometer to be off, however it is still dead on. My truck has built in GPS and at all speeds my speedometer matches my GPS speed. Keep in mind my speedometer matched my GPS before the new tires.

Am I missing something here?

I was expecting to have to take my truck to the dealer to recalibrate my speedometer, but it appears that will not be necessary.
 

Stangshcky12

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I'm guessing you had 20's stock?
The stock tire size on the 20" rim comes in around 34" so jumping up to a 35 is only going to throw the speedo off 2% so with the error in the speedo it's hardly noticeable
 

garner

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So yours were around 30" or 31" stock. Weird that your speedometer was still good
 

quietpeen

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i'm not sure the dealer would even do 35 for you. They might say they can only do 33 since that is the other "stock" size
 

Stangshcky12

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Have you checked with the GPS at highway speeds as well?
Being off by a percentage, the faster you go the more it will be off
With the jump that you did you'll only be about 2mph of at 25 but should be 6ish off at 60
 
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shipmasta

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Have you checked with the GPS at highway speeds as well?
Being off by a percentage, the faster you go the more it will be off
With the jump that you did you'll only be about 2mph of at 25 but should be 6ish off at 60

Yes I compared at highway speed. My wife was riding with me and calling out my GPS speeds as I sped up. Speed were dead on till 70 MPH. I did not go faster then that.
 
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shipmasta

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i'm not sure the dealer would even do 35 for you. They might say they can only do 33 since that is the other "stock" size

Talked to the dealer. Told him I was going to run 315/70R17. He talked to the techs, and they said they could do that size no problem. Its possible the techs were wrong. But that is what he told me.
 
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