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Discussion Starter #1
with my new 245/75/17 i know my mph are slower on the tach than I real am going. So my question goes out to the tire gurus is..

How to I find out what my real MPH is? I know it's going to be a % and I don't need a nav system.... so whats the formula?

-Seth
 

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56.3mph on tach = 60mph real speed. Awsome.....thanks for the link.
 

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It is really a percentage. So your speedometer is off by 4.7 out of 60 MPH so that is 7.8%. Your odometer is off by that much too, so remember that when calculating your MPG, figuring when you need oil changes, and when doing your expenses for work!!!!
 

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Just a thought, try your jeep with a GPS and then check the speedo. When I went from 245/65s to 245/75R17s my speedo was right at 60MPH. I have checked it with 3 diffrent devices. Just my 2 cents and good luck.
 

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Oh Yhea, if you don't fix it and trade it in or sale it you need to disclose that mileage is incorrect. That will hurt resale!
 

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Your best way to do it is to get a programmer. My diablo has a app that you put your actual tire size in, and it fixes the speedo error. Works great. My speedometer is off, isnt the best excuse with a cop.
 

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Not really SAL, most places there $360 plus. What I did is find them on a website for $274.95 then I call autoanything and they matched and beat it by $1. So I ended up paying $273.95 with free shipping, and then I bought the cable kit for like $40.

For what it offers, $320 is well worth it. Built in code reader, speedo calabrate, just to name a few. The performance upgrade is amazing, plus I averaged a +1.5 mpg increase, and did the math. It will pay for itself in one year.

In my opinion, I regret not getting it sooner. I just pick up one for my GTO and WOW, cant keep it stright. Lines of burnt rubber everwhere.

LuvMyCommander, for the price of that unit, I would just go ahead and get the programmer. Its only like $100.
 
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