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Old 06-06-2013, 03:33 PM   #1
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5.13 gears to low?

So I am looking at a set of axles, both bolt in 44's with 5.13 gears. I was planning 4.88's but these ate a good deal. Are they to low for some highway use? I have a 97 tj, 4.0 5 spd with 35" tires

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Old 06-06-2013, 03:38 PM   #2
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5.13 isn't too low for 35" tires on the trail but your RPMs would be higher than necessary on the highway. I can calculate the RPMs tonight if you want them.

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Old 06-06-2013, 03:56 PM   #3
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It wouldn't be that bad on the highway. I have 4.88, 33s, and the 5 speed. Wish I could have gone 5.13 for 35s.
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Old 06-06-2013, 04:00 PM   #4
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I appreciate the offer to calculate my rpm, I actually found a good resource for that. Do u know what a good rpm for highway running would be? Or what it would b stock for like 55 mph. None of my wranglers had stock tires so I have no point of refrence.
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Old 06-06-2013, 04:06 PM   #5
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Check this website out. Put your info in and it will calculate you MPH and RPM for gears and you can compare different sets of gears. That way you can decide your highway speed and make sure that you are in the 4.0's power range.

Gear Ratio Calculator
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Old 06-06-2013, 04:07 PM   #6
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I can't tell you what stock RPMs are, but for me personally anything just above 2000 RPM to 3000 RPM I would consider acceptable. I prefer somewhere between 2500 and 3000 though. At 75-80 I'm right around 3k RPM. 65 is usually usually the fastest I go though and sits right at about 2800 RPM.
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Old 06-07-2013, 01:57 PM   #7
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I used the WWW.grimjeeper.com/gears.htm

Basing on 30" tires with my stock 3.55 gears, at 65 I would be at 2584 in fourth and 2042 in fifth. With 35's and 5.13 gears, 65 would be 3201 in fourth and 2529 in fifth. It wld be like losing overdrive. I guess the gears are a tad to low. I then ran it with 3.73 gears as that's the more common ratio, and that's 2715 and 2145 which is about 300 to 400 difference across the range. What do you guys think?
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Old 06-07-2013, 02:18 PM   #8
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And I just ran the numbers with 4.56 gears, just 150 rpm over stock 3.73.
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Old 06-07-2013, 04:18 PM   #9
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You don't really want to base things on stock. Stock isn't exactly the greatest gearing, also increase in tire size is not linear in terms of momentum and un sprung weight. You need the higher RPMs and 2500 would be perfect cruising RPM IMO.

Contrary to popular belief these engines are not afraid of RPM, 3k RPM is nothing. Factory gears high for efficiency. You putting big tires on, throw efficiency out the window. The difference in MPG between 2500 RPM and 2000 RPM is virtually zero. In fact it could even be worse if your lugging the engine.
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Old 06-07-2013, 04:26 PM   #10
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All great points. I don't care about mpg. I just font want to over rev the engine at speed
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Old 06-07-2013, 06:07 PM   #11
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33" tires and 4.10 gears and I'm turning just under 2k at about 58 - 60 (per GPS). It does need a little more umph than with 4.10s tho. Very little in the way of acceleration at speed in 5th gear.
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Old 06-10-2013, 04:36 PM   #12
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I just wonder still if 2500+ rpm is to high in fifth on the highway for the engine.
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Old 06-10-2013, 04:45 PM   #13
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Quote:
Originally Posted by joeylead View Post
I just wonder still if 2500+ rpm is to high in fifth on the highway for the engine.
That is not even close to being too high, I consider those RPMs just right for tires that big. You're not driving a car with tiny tires where the engine doesn't have to work much. My previous TJ with 35" tires and 4.88 gearing/5-speed transmission was pretty close to 2700 at 70 mph and it couldn't have been better. Don't worry about the rpms, they won't be the same as a car & the engine is loafing at that kind of an RPM. Heck after I converted that TJ from its OE 5-speed to a 3-speed automatic, it was right at 3000 rpms at 70 mph. I didn't like the 3000 rpms so I slowed down a little for most road trips but many times I would stay at those rpms if I was a little behind schedule.
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Old 06-10-2013, 05:57 PM   #14
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Jerry pretty much covered it. There are no issue running those RPMs for highway cruising.

There are some large sections of I-70 in the mountains where I can't hold 5th and have to drop it down to 4th. I'll run it at 3500 RPM just to keep up with the big rigs.
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Old 06-10-2013, 07:07 PM   #15
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Thanks guys the reason I was asking was I am looking at a set of axles, tj rubicon 44 with cromoly shafts and some other stuff and a tj 44 with an arb locker and someother goodies both with 5.13 gears for 3500 plus a bit for shipping. Kinda outta my budget, but.if.I just got a. 8.8 from ecgs had my 30 geared and both with lockrites is be pretty close to that anyway. Seemed like a good deal but didn't want to mess up w to low of gears. And I know.it will be kickass on the rocks, I just can't wait to get back out on the trails again.
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Old 06-10-2013, 07:20 PM   #16
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