« Reply #27 on: October 02, 2008, 07:14:45 PM »
Stock differential gearing is 4.something. It's plenty adequate when turning the stock 26" pizza cutters. But, throw on some meaty 31x10.50 mudders and you will certainly feel a power loss because of the larger rotating mass of the 31's. To offset this, you can lower the ratio of the differential gearing on the front and rear differentials. This is fairly easy to do on these trucks because both the Vitara and Tracker and the older Sidekicks all use removable third members which have all the gears installed in them already, so you don't need to take it to a shop and have things swapped from third member to third member.
What I plan to do on my Vitara once I put 31's on it is take the lower (but numerically higher) 5.13 diff gears out of my Sidekick and install them in the Vitara. It should eliminate any power loss from running the 31's and will keep the vehicle feeling spritely as ever. That's the plan anyway, I'll get back to you how it works out when I get to it.

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97 Sidekick 4door 5 speed, 1.5 spacer lift, 2" body lift, CJ rims, locked rear, 31's, 4:1 low <SOLD>
01 Vitara 2.0L 5 speed, 2.5" Calmini lift, 2" body lift, Sidekick rims, locked rear, 31's, 4:1 low, 5.13 diffs <SOLD>
03 XL7 2.7 5 speed, 4.5" AE lift with OME springs, 2" AE body lift, 5.13 diffs, 3:1 low, 235/80R17 BFG AT's on Ultra 17x8 with 1" spacers, skid plates, Balmer Fab front bumper