Speedometer Still Off.....

jon200008

jon200008

New member
I bought a 2015 Jk 2 door rubicon with a 2.5 in lift and 35x12.50x20 wheels and tires. I found a Superchips F5 tuner in the console and corrected for wheels and tires. I believe it still has factory gears but my speedometer still is 3mph off. I have changed tried different selections but it is still driving me nuts. Any suggestions...
 
Are you measuring the tire data according to how superchips says to do it? Some programmers do it different ways.

As far as the gears, you can jack up the rear, spin a tire, and count the driveshaft revolutions to make sure you know what gears it has.
 
WJCO said:
Are you measuring the tire data according to how superchips says to do it? Some programmers do it different ways.

As far as the gears, you can jack up the rear, spin a tire, and count the driveshaft revolutions to make sure you know what gears it has.
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I will give it a try....thanks......
 
jon200008 said:
I bought a 2015 Jk 2 door rubicon with a 2.5 in lift and 35x12.50x20 wheels and tires. I found a Superchips F5 tuner in the console and corrected for wheels and tires. I believe it still has factory gears but my speedometer still is 3mph off. I have changed tried different selections but it is still driving me nuts. Any suggestions...
Click to expand...
When I did mine, also with a Superchips tuner, I measured from the shoulder of the tire to the pavement. My "35" was actually just short of 34", that was what I programmed, about every 15-20K miles I remeasure and reprogram.
 
duktrx said:
When I did mine, also with a Superchips tuner, I measured from the shoulder of the tire to the pavement. My "35" was actually just short of 34", that was what I programmed, about every 15-20K miles I remeasure and reprogram.
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Are the "rotations per mile" values that tire makers publish not accurate and useful?
 
duktrx said:
When I did mine, also with a Superchips tuner, I measured from the shoulder of the tire to the pavement. My "35" was actually just short of 34", that was what I programmed, about every 15-20K miles I remeasure and reprogram.
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This^^^

You gotta measure the actual diameter of the tire when loaded. I have an AEV Procal and it has options for every 1/4th of an inch from 30" to 42" and my 35" Trail Grapplers came out to be 34 exactly brand new. Now they're just over 33" and I have since recalibrated. It helps to double check your speedo's accuracy with your phone too. My Google maps mph reading seems to be pretty accurate.
 
As mentioned measure your tire and that will be more accurate than just putting in the size on the s.

you can see how and where to measure in this thread
www.wayalife.com

The Ultimate TRUE TIRE SIZE Database

Before I get this started, it needs to be made clear that when it comes to things like lift kits and tires you can run with them, EVERY manufacturer, shop and person in the industry will always refer to what is written on the sidewall and NOT the true height of the tire. In other words, if a...
www.wayalife.com www.wayalife.com
 
Thanks for all the replies. I found my tires to be 33.75 and gears to be the stick 4.11s. My question now is does the tuner get set to stock gears or the 4.10 since 4.11 is not on there. Also does the stock mean 4.11 or the other size i believe the rubicon came with. I coukd be wrong on that though.
 
jon200008 said:
Thanks for all the replies. I found my tires to be 33.75 and gears to be the stick 4.11s. My question now is does the tuner get set to stock gears or the 4.10 since 4.11 is not on there. Also does the stock mean 4.11 or the other size i believe the rubicon came with. I coukd be wrong on that though.
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4.10 or 4.11 will be the same. Close enough.
 
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