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Thread: Regear with 38s

  1. #31
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    Quote Originally Posted by Brian View Post
    Your temps would be spiking because of the load on the engine not because of the RPM

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    Increasing due to increasing load I'll give you. But in my experience a spike comes at certain shift points.

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  3. #32
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    Quote Originally Posted by chitown35 View Post
    Increasing due to increasing load I'll give you. But in my experience a spike comes at certain shift points.
    What year Jeep are we talking about because these newer engines with the programs in fuel injection can run at 5000 RPMs all day long without overheating

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  4. #33
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    Quote Originally Posted by Brian View Post
    What year Jeep are we talking about because these newer engines with the programs in fuel injection can run at 5000 RPMs all day long without overheating

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    2012+ JKs. Lots of people seeing 230+ easily.

  5. #34
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    Quote Originally Posted by chitown35 View Post
    2012+ JKs. Lots of people seeing 230+ easily.
    I can imagine there are tons of people overheating because not many actually re gear like they should to keep the load the same on the engine. Let's face it in this thread we have a guy who is geared properly and is going to gear himself all the way back to close to a stock Rubicon for going up in tires almost 5 inches. Purely incorrect

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  6. #35
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    Quote Originally Posted by Brian View Post
    I can imagine there are tons of people overheating because not many actually read year like they should to keep the load the same on the engine. Let's face it in this thread we have a guy who is geared properly and is going to gear himself all the way back to close to a stock Rubicon for going up in tires almost 5 in purely incorrect

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    Fair point in general. But if you run the numbers, 4.56 for 37s is pretty close in gearing, through all the gears, to a stock auto with 32s and 3.73 gears. Actually a little lower, almost like with 4.10s. And remember the 4.10s aren't even considered necessary on a Rubicon, they're optional for the auto. (Makes me think Chrysler doesn't think they match up well with the 5 speed).

    Look at the numbers below, which make me think a lot of people are actually OVERgearing compared to stock...

    This is 4.56 with 37s vs 3.73 with 32s.


    Then 5.13 with 37s vs 3.73 with 32.

  7. #36
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    Here's vs 4.10s, not much difference.

  8. #37
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    Quote Originally Posted by chitown35 View Post
    Fair point in general. But if you run the numbers, 4.56 for 37s is pretty close in gearing, through all the gears, to a stock auto with 32s and 3.73 gears. Actually a little lower, almost like with 4.10s. And remember the 4.10s aren't even considered necessary on a Rubicon, they're optional for the auto. (Makes me think Chrysler doesn't think they match up well with the 5 speed).

    Look at the numbers below, which make me think a lot of people are actually OVERgearing compared to stock...

    This is 4.56 with 37s vs 3.73 with 32s.


    Then 5.13 with 37s vs 3.73 with 32.
    You're comparing stock numbers with smaller tires in comparing RPM and I'll think about the load with tires that way two to three times the amount as to what stock ones do along with rims that way two to three times the amount so you're rotational mass increases exponentially. That my friend is why you need higher gears than stock along with better brakes

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  9. #38
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    Y’all, before you blow a gasket over this gearing thing there are a few facts you need to know.

    Kid will be living in south Alabama (flat).

    Home will be 5 hours north (still flat)

    Off road use will be limited for a quite a few years as he will be focusing on college, being a collegiate athlete and med school.

    BFG KO2 37s are more like large 35s.

    He’ll be fine on the 4.56 gears until he is employed and can make this jeep a dedicated trail rig.

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  11. #39
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    Quote Originally Posted by Brian View Post
    You're comparing stock numbers with smaller tires in comparing RPM and I'll think about the load with tires that way two to three times the amount as to what stock ones do along with rims that way two to three times the amount so you're rotational mass increases exponentially. That my friend is why you need higher gears than stock along with better brakes

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    I follow you on acceleration/brakes to a degree, but how much of an effect does that rotational mass have on maintaining a constant speed? Esp with all the other weight added to the jeep.

  12. #40
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    Quote Originally Posted by chitown35 View Post
    I follow you on acceleration/brakes to a degree, but how much of an effect does that rotational mass have on maintaining a constant speed? Esp with all the other weight added to the jeep.
    This is pretty basic I mean how easy is it to keep a bicycle wheel turning at 35 miles an hour by hand or how easy is it to keep a 200lb 37 inch tire turning by hand there's obviously going to be a lot more load on a much heavier and wider Tire. We're not even getting into the fact that they stick out farther from the vehicle.

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