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Unread 05-21-2013, 06:39 PM   #1
Spud100
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1999 TJ Wrangler 
 
Join Date: Apr 2013
Location: Conroe, Tx
Posts: 213
Regearing question

My 99 tj came from the factory with 4.10 gears and 205/75 tires (27 inch diameter). I now have 31s (about 30.5 diameter). Calculating the equation to get me back to stock ratio works out close to 4.56 gears yet everything I read says 4.56 is too low for 31s. What am I missing? Please help.

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Unread 05-29-2013, 11:58 AM   #2
RWKHausSupply
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1990 XJ Cherokee 
 
Join Date: Nov 2009
Location: Yorba Linda
Posts: 319
Well you have a 4cyl if they are 4.10 stock.

If you have added weight and the larger heavier wheels and then tires, the 4.56 should be perfect.
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Unread 05-29-2013, 07:48 PM   #3
jeepdaddy2000
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1971 CJ5 
 
Join Date: Jan 2002
Location: Eagle Point Oregon
Posts: 6,238
Install a tach and see what your spinning at your true target speed. Ie, if your looking to run at 55MPH (actual, your speedo will be slower due to the larger tires), see what the engine is turning. Then decide where the sweet spot in your torque curve is and try to target it.
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Unread 06-29-2013, 08:00 AM   #4
JeeperDon
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1993 YJ Wrangler 
 
Join Date: Jan 2005
Location: Albuquerque, NM
Posts: 6,566
I'd hold off on regearing. My 4cyl ran fine with 31's. You know thats not the end size tire, so wait if you can. I went to 33's and decided that was enough. The math for 33's on a 4 cyl says 4.88, so that's what I did. That was great for 33's. When I later went to 35's, it wasn't really a gear problem, but became a power problem. It was tough for the 4 cyl to spin the larger mass tires to accelerate, even though the tire size was only 6% larger. I then went to a V6 and kept the 4.88s. Life is great now (since the motor in 2004) on and off road.
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'93 YJ, '02 GM 4.3 Vortec V6, SOA, dual ARB's, 8.8+D30(w/WarnHubs), 4.88 gears, 35" BFG KM2's, AX15, 15x7 wheels, NP231+4:1+SYE+2LO, York OBA, Warn M8000, no top or doors Apr-Oct.
Member and Web guy: New Mexico 4 Wheelers My Truck Page on NM4W Site
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