Real MPH? - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 14 (permalink) Old 09-28-2010, 07:09 PM Thread Starter
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Question Real MPH?

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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post #2 of 14 (permalink) Old 09-28-2010, 07:25 PM
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http://www.performanceprobe.com/index2.php?redirect=http://www.performanceprobe.com/misc/index.php?do=calc&page=tire



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post #3 of 14 (permalink) Old 09-28-2010, 07:38 PM Thread Starter
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56.3mph on tach = 60mph real speed. Awsome.....thanks for the link.
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post #4 of 14 (permalink) Old 09-28-2010, 08:17 PM
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Quote:
Originally Posted by ER NURSE View Post
56.3mph on tach = 60mph real speed. Awsome.....thanks for the link.
I'm sure you probably know this but if you figure out the percentage of error than you can accurately calculate your fuel economy as well. I know mine is 2MPG off of what the gauge says.


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post #5 of 14 (permalink) Old 09-28-2010, 08:37 PM
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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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post #6 of 14 (permalink) Old 09-28-2010, 08:44 PM
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a gps with speedo....
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post #7 of 14 (permalink) Old 09-28-2010, 08:46 PM
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a gps with speedo....
Thats cheating LOL


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post #8 of 14 (permalink) Old 09-28-2010, 09:01 PM
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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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post #9 of 14 (permalink) Old 09-28-2010, 09:08 PM
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You could permanently fix it.


http://www.hypertech.com/products-results.aspx
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post #10 of 14 (permalink) Old 09-28-2010, 09:20 PM
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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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