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Im getting ready to have the gearing in my jk changed from 3.21s to 4.56s, and wondered if anybody has 4.56 gears with 35 inch tires. I would like to know about what rpm your vehicle runs at around 45 mph. I know thats slow but thats as fast as I go to work because I'm only 5 miles away and in no hurry. The jk with 285-70-17 tires now runs at 1350 rpms at 45 mph and it chugs along. Thanks
 

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To compare ratio you can DIVIDE your old rpms by the old ratio and MULTIPLY by the new ratio.

If you were at 1350rpm for a given situation using a 3.21 rear-end, you'd be at around 1920rpm with a 4.56 rear-end.

To then estimate the change in tire size you DIVIDE by the new size (35") and MULTIPLY by the old size (approx 32.7" for a 285/70-17). So your new setup would be around 1790 rpm.

Current RPM * (New Rear-End / Old Rear-End) * (Old Tire Size / New Tire Size) = New RPM

To "sanity" check it higher numerical rear-ends should raise RPM, and larger tires should reduce RPM.
 

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315/70R17s 4.56 gears. 2010 6spd manual 45 mph approximately 1700 rpm

You'll be happy
 
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