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  #13  
Old 11-13-2012, 04:53 PM
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Re: 3.45 Axle Ratio

Options would be good.
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Old 11-14-2012, 10:09 AM
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Re: 3.45 Axle Ratio

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Originally Posted by ColdCase View Post
Rear end ratio is only a part of the story. I had 3:73s in my Dakota and RAM and they were brutal on the highway. At highway speeds the engine felt like it was going to fly apart and mpg went into the toilet. I oversize the tires 10% on the RAM to make it reasonable which also improved gas mileage about 20% under every driving condition (many owners added overdrives). I just lived with it on the Dakota.

In the RAM's case, the manual transmission gearing had a lot to do with it. We never used 1st gear, always starting out in 2nd unless pulling heavy. So when you talk about ideal axle ratios, you cannot ignore transmission gearing.
That was probably back in the day of 4 speeds? My '12 Ram has 6 speed auto, and 3:92s. At 80 mph, it's running ~2250 rpm -- which is about perfect. 3:45 in the WK@ Hemis is probably a happy medium. 3:06 in the Pentastars is not. It would be my only complaint about my Jeep. Having to shift down at every little hill wastes gas. Lower gears would prevent this, and may not affect overall gas mileage at all.
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Old 11-14-2012, 02:50 PM
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Re: 3.45 Axle Ratio

The RAM was a six speed manual, the Dakota probably a four speed. But these new 6 speed autos are just adding overdrive gears. If you don't like the annoying down shift to 5, just run in 5 instead of D. I run my WK2 routinely in 5 to reduce the amount of annoying shifting. Doesn't affect gas mileage. The only time I use D is cruising out on the highway. A much more satisfying experience. For the V6, try running in 4th instead of D, which is the direct 1:1 ratio.

You can think of putting the transmission in 5 (if you have a 6 speed) as the same as changing the axle ratio.

Changing the axle ratio for the street makes sense if the ratio you want is not provided either on the low or high end of the gear box.

For example, I'm not sure what the top trans gear ratio of your RAM is, but if its the same as the WK2 V8, its top gear is 0.67 when combined with your 3.82 ideal rear end ratio, that is 2.56 overall, the V6 automatic top gear ratio is 0.83 and when combined with your 3.06 axle.. guess what... thats 2.54 overall, near identical to your ideal final drive.. you are already there
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