Gear ratio for 35" tires -
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post #1 of 10 Old 02-08-2012, 09:06 AM Thread Starter
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Gear ratio for 35" tires

Does anyone have any info on what is a good gear ratio to use with 35" tires. Running M20 rear/ dana30 front diffs with chromoly axles on a CJ5. Stock gears are 3:56.
Also is it worth putting the funds into these diffs or should I just upgrade to d44's

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post #2 of 10 Old 02-08-2012, 09:32 AM
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1979 CJ7 
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Is this a DD, or trial only rig? What shape is the motor that I mean is it stock or does it have any mods? What is your major complaint now? Too sluggish off the line?
Personally the 20 rear should be good to go w/alloy 1 piece shafts. Yeah 44's would be nice, but under 250 hp, and not beating on it in a rock climb should be fine. My 304 lived through He!! when stock, and upgrades were considered exotic back in the '80s.
Truthfullness alert. When I needed an new frame I lucked out on an '86, that has a 44 rear. I put 4.10s in it to got w/a 400hp 360. It's not finished, so nothing to report.
Good luck.

I've also learned that sometimes... when people don't agree with you .... its best to hold them down and kidney punch them till they agree with you
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post #3 of 10 Old 02-08-2012, 09:45 AM
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Gear ratio calculator found here:

Plug your variables into it to find out what gear ratio would work best.
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post #4 of 10 Old 02-08-2012, 09:48 AM
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Have a look at some Gear Ratio Charts, they are based in a reasonable RPM at 65mph.
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post #5 of 10 Old 02-08-2012, 04:43 PM Thread Starter
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Thanks for all your help with the charts.
Running stock 4.2 with a 300 t-case. The 3.56 gears are a bit sluggish and rpm is really low in 4th as most of the time I drive in third.

With the info loaded into the charts, 4.11's are looking pretty good.

thanks again.
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post #6 of 10 Old 02-08-2012, 06:21 PM
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I run 4.88s but it is not a dd but great trail response "as stated above go with the one paice rear axles,you wont regret it" happy wheeling
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post #7 of 10 Old 02-08-2012, 08:42 PM
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I have 33's on one piece axles.the 3.31 gear is it .Still running my 20/30 /300.So it is all in what you are really looking to do with it.
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post #8 of 10 Old 02-09-2012, 02:37 AM
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I run 33's with 4.56 gears, biggest the 30 will handle are 4.88 witch surprisingly shares the same pinion as 4.56. If you plan on attempting any sort of decent off roading you should stay with atleast 4.56-4.88, if street only you might be ok with 4.11 but to me that's a waste if your going to dig into the diff's

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post #9 of 10 Old 02-09-2012, 03:18 AM
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The 33s are plenty big enough for standard axles, though some owners go to 35s without problems.

The change to Dana 44s or better would be a good one but why bother if they are not broken?

4.11s may hack it but a greter ratio such as 4.56 would be better.

You didn't say which gearbox you had but a T176 would work OK with 4.11, a T5 would be a PITA in 5th gear as it is an overdrive and you would be too far down the rev range with 4.11 gears.
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post #10 of 10 Old 02-09-2012, 06:01 AM
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I'm running with 4.10's and 35's. I have a 304 and a t-177 (little bit deeper 1st then the 176) off road, it's manageable but a little more gear would be nice. that being said, 65 on the highway is not a problem and I'd have no concerns doing this every day. it's a very fine line dealing with 35's and no overdrive.

I was looking at 4.27's when I swapped out the 2.73's but could not find them at a decent price for my dana 30, and 4.56's were a not going to cut it for me on the highway. My Jeep does not see a trailer to get to the trail.

To keep everything in a "happy place" RPM wise, it's going to be either 4:1 t-case gears/ swap in a 5 speed and new 4.88's/ or find a t-18 with a DEEP first.
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