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Gear ratios and bad advice

billiebob

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While this is cool video with an easy first option to picking a gear ratio, grimm jeepers gear calculator IS the best go to resource before actually buying.
 
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billiebob

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Kootenays, BC, Canada
6-speed manual NSG370
33's - 4.10 more street, 4.56 more trail or mountainous/hilly highway
I drive 24K miles every year, mostly pulling a trailer in the mountains. With 33s and 4.10s. I wish I had 3.73. All too often I will be on a long steady downhill wishing I had one more gear.... or 3.73s That is real world experience, anyone else here put 24K miles on every year, towing a 2000 pound trailer for most of those miles? ... in the mountains?

75251
 
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AndyG

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All the math people use kills me ...and I have seen some real keyboard battles over gearing and octane ......I know it satisfies the mind ...but you can pretty much ask experienced owners like Jerry Bransford , Rob or Chris and end up fine .

Tire sizes vary, they actually become smaller every time you drive the Jeep , and if you get in the ball park you will be fine .

Most folks want to figure it all out ...it's when you first drive the regeared Jeep that you really smile .
 
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Steven

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Ontario
Sorry, a little bit off topic here, but recently found a good deal on a D30/D35 with 4.88 gears. However the rear is disassembled and has a welded diff. If I were to make the buy, and take the ring and pinion off and just use the carrier that is currently on my jeep (also a D35) would that hypothetically work? I checked the teeth on the gear and pinion and everything looks great, and the asking price was below the cost of the gear sets themselves.

To put into perspective, I'm currently running 33's on the stock 2.5L with 4.10 gearing and having to sit in 4th around 3050 rpm at roughly 110km/h (roughly 70mph). I would like to upgrade the rear axle in the future, but for the time being I'm just doing light Overlanding so I have no desire to run anything over 33's, or get lockers for now as it is the D35.

Question being - would it be worth grabbing the axles and putting the two rears together?

Again, sorry for being a little off topic. Just looking for some advice before doing anything I regret.
 
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JMT

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All the math people use kills me ...and I have seen some real keyboard battles over gearing and octane ......I know it satisfies the mind ...but you can pretty much ask experienced owners like Jerry Bransford , Rob or Chris and end up fine .

Tire sizes vary, they actually become smaller every time you drive the Jeep , and if you get in the ball park you will be fine .

Most folks want to figure it all out ...it's when you first drive the regeared Jeep that you really smile .
I should get to drive mine for the first time today. :)
 
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chuck72

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Mar 26, 2018
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i think I've finally found the answer to a question I have been struggling with. I have an 04 tj 5spd. just regeared to 4.56 in preparation to lift and bigger tires. If I am reading and understanding right. 33' tires would be perfect for daily driving and weekend trail riding.
 

AndyG

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i think I've finally found the answer to a question I have been struggling with. I have an 04 tj 5spd. just regeared to 4.56 in preparation to lift and bigger tires. If I am reading and understanding right. 33' tires would be perfect for daily driving and weekend trail riding.
That's my set up..it's great .
 

Yendra Built

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Mar 13, 2019
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Laporte, CO
Soooooo.... I have a 2004 TJ with the 2.4 with 4.56 gears and an automatic and that thing constantly was dumping overdrive. I couldn't drive 75 on the highway without it jumping in and out of OD constantly with the stock little tires.
So one day driving home from the shop the 2.4 dumped its water and seized up.

Now the good news, after researching and looking for something better to replace it with and coming to the conclusion that an LS swap may be the way to go I find on craigslist a 2005 TJ chassis with no body and all the running gear. This thing came with the pedals, the steering column, 4.0 engine, axles (3.07 ratio) and best of all the Mercedes 6 Speed. Now a lot of people may think that 3.07 axles are the way to EPA enlightenment but I'm not buying that, the 4.56 axles are staying. I live at 6200 feet and at that altitude those gears are going to be perfect. This also gives me options for bigger tire sizes later.

My heavy 2000 F250 has a V10, a ZF 5 speed and 4.30 gears and it gets up to 13 MPG because of running a higher manifold vacuum at cruising speed and the fuel rail pressure regulator and ECM, make use of this and therefore it cruises very easily at any speed. And not only that I can pull the 7000 LB boat with ease.
EPA is ideal and probably sea level conditions. In the real world bigger ratios are usually a better way to go and with better drivability.
 
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374gatorgirl

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Exactly, couldn't have said it better myself. Unfortunately, that wasn't mentioned to the thousands of viewers of that fan base so who knows how many were led incorrectly.

I'm very glad I picked my gear ratios off of some very informed guys I followed on the forums. Most of my info came from Jerry and Blaine and then anybody they had given advice to who ended up liking it (which was pretty much everybody). Glad I didn't get my advice from videos of doing math. It just isn't the same.

Please know what you're talking about before making a video to the entire world about something. While the intentions of this video are good, and Bleepin' Jeep usually has good information for its viewers, I don't think I've ever groaned more over a Jeep topic than I did watching this video.

This video is full of misinformation. The worst part about it is the multitude of comments from people who had no idea what gear to run and are now thanking him for "helping" them pick out what they should run. Those will be some sorely disappointed folks when they realize how bad his advice was.

He starts by teaching one how they "should" calculate their new gear ratio. He bases his calculations off of stock gears (3.07 in several cases) and uses 29" tires as the basis for his calculations. This is problematic for several reasons.

1) 3.07 was a horrible gear ratio, even for stock tires. On 29" tires with the AX15, you end up right at 2200 RPM at around 70 in 5th gear which lugs the engine. Not good.

He ends up doing the math for 33's which results in him giving 3.55 as a recommendation for 33" tires. I don't know if any of you have tried that ratio, but it sucks.

So, he's already basing his recommendation off of a pretty poor example. If you want to do the math equation, start with Rubicon gearing. The 5-speed manual Rubicon TJs were really the only Jeeps properly geared from the factory in my opinion. The automatic should have had 4.56 for 31" tires, not 4.10 like its manual counterpart.

2) He adds nothing to compensate for larger, heavier tires, extra weight on the Jeep, lift height pushing it into the wind stream, etc. The lift height is almost negligible but the other items I mentioned make a huge difference.

3) His 2.5 example is flawed for several reasons.

First, he starts with using his YJ as an example. He uses 29" tires and 4.10 gears to describe why his 4.88 on 33" tires has the RPM "through the roof".

The flaws begin with the tire size. The largest tire size on a 2.5 YJ was 205/75R15 (27.1"), not 29". There was an option for 215/75R15 (27.7") which my 4.0 YJ had but I believe that was for the 4.0 only. So, he's already nearly 2" off on his calculation method. That makes a huge difference in what he's going to recommend.

Next, he does his math using 29" tires and 4.10. He ends up getting a number of 4.95 for 35" tires. Rather than going to the lower option of 5.13, he chooses to drop back to 4.88. Bad decision, that means if his Jeep came stock with 4.10 and 29" tires, he would now have even less gearing with 35's than he did stock on those 29" tires that don't exist on the YJ model.

He follows this up by saying he regeared to 4.88 expecting to run 35's but ended up with 33's instead because of a deal he got or something. He proceeds by saying his RPM is way too high and that he hits 3000 RPM at 55 mph. False, that setup doesn't reach 3000 until about 69-70 mph.

He also says his poor gas mileage comes from running 3000 RPM, also false, the 2.5 did more than that stock and it sure didn't ever hurt gas mileage. That's the nature of the beast on a 2.5.

4) Real world vs. math. Numbers are good but gear ratios on paper are nowhere close to realistic when you actually drive the Jeep with all the variables the world throws at it.

You can't tell me that 3.55 gear ratio he recommended for his 33's will end up driving well or even close to it.


To end this long rant, don't listen to the people telling you to use your stock gear ratio to determine a new gear ratio for a larger tire. It may add up on paper but it doesn't translate properly in the real world.

The only good combination from the factory was the 5-speed Rubicon and then some of the 32RH combinations.

One other combo that was okay when stock was the 5-speed 3.55 package that came with about 27.7-28" tires. However, you can't follow this for larger ties because it'll end up at 4.10 for 33's, 4.56 for 35's, etc., which aren't ideal setups.

There should have never even been 3.07 offered at all in my opinion.

I sure hope that YouTube guy has played around with his ratios and tires a few more times since the production of this video and has figured out that his advice was very misleading not ideal in the slightest.

Things like this where the people giving out info seem very knowledgeable end up convincing people who don't know an better that they can listen to the person who speaks in confidence, even if they aren't right. Since this guy had some confidence in the things he said, I wouldn't be surprised at all if he lead quite a few people down the wrong road of picking the proper gear ratio if they chose to regear their axles.

Bottom line, listen to people who have real world experience with all the different ratios and tire sizes, not the guy on YouTube using math to figure out what he'll run. There are quite a few very experienced guys out there who can steer you to the exact ratio you want off of the top of their head. Those are the guys you want to listen to.

Rant over.

Just to provide something useful out of this post, here are what I and many other forum members have determined to be the best ratios for Wranglers older than 2007 that have the 4.0L, 2.5L, or 2.4L engines.

4.0L engine

5-speed manual (AX15/NV3550)

31's - 4.10 (this is how the Rubicon came)
33's - 4.56
35's - 4.88
37's - 5.13 or 5.38 (personally I'd choose 5.38 which adds about 100 RPM to help for the larger 37" tires)

3-speed auto (32RH) used 1987-2002, deemed the TF999 in older 1987-1991 YJ Wranglers

31's - 3.73
33's - 4.10
35's - 4.56
37's - 4.88

4-speed auto (42RLE) used 2003-2006, actually used longer in the JK but I'm not including JK Wranglers.

31's - 4.56, even though the factory Rubicon used 4.10 unfortunately
33's - 4.88
35's - 5.38 (Rubicon's have to change carriers to support this deep of a gear ratio)
37's - forget about it unless you get axles that support 5.89.

6-speed manual NSG370
31's 3.73 more street, 4.10 more trail or mountainous/hilly highway
33's - 4.10 more street, 4.56 more trail or mountainous/hilly highway
35's - 4.56 more street, 4.88 more trail or mountainous/ hilly highway

2.5L & 2.4L engine

5-speed AX5/NV1500

31's - 4.56/4.88 (either is good, 4.88 really helps keep speed on the highway)
33's - 4.88
35's - 5.38 if you have the axle for it, otherwise 5.13

3-speed auto 30RH

31's - 4.10
33's - 4.56
35's - 4.88

4-speed auto 42RLE

31's - 4.88
33's - 5.13 or 5.38 if you can run them.
35's+ - wouldn't even consider it.
Looking for some help. I have a 2002 TJ, 4.0 that I purchased from and individual. They did not do the modifications so no clue what was done and what wasn’t. I’m just trying to fix things as I can. It has 33” tires but the speedometer gear was not changed out so it’s about 5 MPH off on the highway. I found the tag on the rear axle but it’s not clear. I can see 07 where the gear ratio should be so I am assuming it’s 3.07. On most of the charts, 3.07 gear ratio doesn’t coincide with 33” tires to give me an answer as to which speedometer gear to get. What should I do? Thanks in advance.
 

JMT

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Forgot to add this is an automatic transmission
I can’t imagine how much of a dog 3.07 gears and 33’s are. They may not make a speedo for that combination because it shouldn’t be run. Not that it’s not safe, but that it’s so dog gone horrible it’s unthinkable. That thing should be regeared to 5.13. Then get a new speedo. Or drop to stock tire size.

How much lift is on it? 12” stock up front, including the coil spring isolator, 8” in rear. Anything above that is the amount of true lift you have.
 

374gatorgirl

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Messages
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Location
South Carolina, USA
I can’t imagine how much of a dog 3.07 gears and 33’s are. They may not make a speedo for that combination because it shouldn’t be run. Not that it’s not safe, but that it’s so dog gone horrible it’s unthinkable. That thing should be regeared to 5.13. Then get a new speedo. Or drop to stock tire size.

How much lift is on it? 12” stock up front, including the coil spring isolator, 8” in rear. Anything above that is the amount of true lift you have.
Yes I went into this without the knowledge I should have had had. The tires were already on and fairly new. It’s a daily driver so has mileage is less than ideal. I’m not sure of what inch lift. Total girl here but trying to learn. I am ashamed to say I don’t do off road but I love my Jeep! How can I measure the lift properly? Here is a pic to give an idea.
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