Superchips Flashcal

[Bigb312]

I bought a Superchips Flashcal to calibrate my speedometer after putting new tires, 275/65/20, on my 2015.  I've used the Flashcal as directed but according to the GPS app I downloaded on my phone I cannot get it to calibrate closer than 1-2 mph.  Is that the best I should expect or should it calibrate dead on??  Superchips customer support has been no help so I was hoping to get some information/help here.

Thank you

[michigan2500hd]

Not uncommon for stock speedos to be off 2-3 mph. I could handle it being off1-2 mph.

Mines off about 5-6 % in favor of not getting a ticket. Makes some drivers mad and then I remember it's not really 70 that I'm going lol. 

[dcarl]

Make sure you are measuring your tire size on the ground installed with a straight edge from the top of the tire to the ground. You will find that measurement is less than the advertised tire diameter. Enter your new number and you should be much closer.

Mine is about as dead on as can be...

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[Bigb312]

Thanks for the information, I wasn't sure if I had a defective unit or what.