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Old 05-11-2010, 07:21 AM   #1
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front/rear gearing question

lets say i put 4.10s in the rear....whats the reason for putting 4.09s in the front...just doesn't make sens to me

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Old 05-11-2010, 08:09 AM   #2
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You can run different ratios front and rear, but they must be within like 2%. 4.10 vs. 4.11 or 3.55 vs. 3.54 for example. They gotta be close. They generally aren't spot on. If you run 2 different ratios it's simply too much stress on the transfer case while in 4wd. This is why you see shit break using 4wd on pavement. You usually can run on dry pavement, but it's alot of uneeded wear and tear and eventually will result in premature transfer case and/or ring and pinion failure. You can run different ratios in the axles, just don't use 4x4.

The idea behind slightly off ratios is to for example install 4.09 in the front axle and 4.10 rear so that the front end pulls slightly more while in 4x4 for a little extra stability.

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Old 05-11-2010, 11:19 AM   #3
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i understand the part of if i were to change to rears ratio, id obviously need to change the front as well, to me that common sense

and the front pulling more is making a little sense to me to now

but wouldnt it be perfectly fine if i ran 4.10 in the front and 4.10 in the rear?
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Old 05-11-2010, 01:12 PM   #4
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That's due to the location of the pinion relative to the ring. Fronts generally have a different bevel than rear gears. that in return means you get a different number of teeth. That's what actually makes the ratio higher or lower. The design just doesn't allow it.

Like with everything, you get limits when designing things. Gears are no different.
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Old 05-11-2010, 01:22 PM   #5
Knows a couple things...

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It really makes no difference on or off-road if you run 4.10/4.10 or if you ran 4.10/4.11. In 2wd, it doesn't matter at all because the front axle is free-wheeling anyway. And in 4x4, the front and rear tires already rotate at different rpms whenever you make a left or right turn, or even drive around a curve because whenever you do either, your tires rotate faster than the rear tires do... there is more difference then than the little .01 difference in 4.10 vs. 4.11 ratio that makes them rotate at very slightly different rpms.

Plus off-road, the slight difference in f/r ratios is a 100% non-issue as the tires slip around on the low traction surfaces or, again, as you even turn left or right which exaggerates the f/r tire rpm differences.

The reason for the slightly different f/r ratios like 3.54/3.55, 3.73/3.74, 4.10/4.11 etc. is due to the different sizes of the ring gears in the front and rear axles. It costs the R&P too much $$$ to make them exactly alike when the ring gear diameters are different. Only the Rubicon with its matching f/r Dana 44 axles have exactly the same f/r axle ratios.
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Old 05-11-2010, 06:22 PM   #6
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Quote:
Originally Posted by GroundHawg View Post
The idea behind slightly off ratios is to for example install 4.09 in the front axle and 4.10 rear so that the front end pulls slightly more while in 4x4 for a little extra stability.
No, that has nothing to do with it. Urban myth, of sorts. You'll get more effective difference by having a slightly worn set of tires at one end and a fresher set at the other.

In reality, the difference is a simple result of finding a tooth count/tooth size that works with two different ring-pinion sizes. If you had the same axle front and rear, you wouldn't see the ratio differences.
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Old 05-11-2010, 09:23 PM   #7
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I said that.

Don't tell me, tell the other guy. I don't care lol
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Old 05-11-2010, 09:47 PM   #8
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ok i get it now, thanks all
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Old 05-12-2010, 09:33 AM   #9
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I ran 5.89 front D44, and 5.86 rear D60 for a long time, never could tell any difference than when I ran 5.89 in F/R D44s. Now have 5.86 in F/R with the D60s.

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