I have several questions regarding gears

[chevymitchell]

Got math? The OP does and 3.73's bring the Jeep pretty close to stock.

I agree with @grimmjeeper that 4.10's are the best choice for the stated needs. I'd go lower for a serious off roader but for back country exploration the 4.10's will be perfect especially with an automatic.

What was the point of starting your post off with "Got Math?". Lol

You must've just looked at an RPM chart.

The RPM charts are just that, an RPM comparison between ratios at a given MPH.

The math includes much more than final drive ratios and engine RPM. The math includes GCVW, altitude correction, air density, fuel type, etc...

Horsepower loss is ~3% per 1000 feet of altitude.

You do not want to do your math based on a straight comparison of RPM. The charts are great, but they do not compensate for anything else.

OP mentioned he's going out-west. You do not want to spend the money to go from a 3.45 to a 3.73 or 4.10 gear on a 34" tire and then head out-west. You need to experience what a stock Rubi does out-west at altitude. 33's and 4.10's are not enough with anything more than the driver in the Jeep. (With the 3.6, anyway)

Stock, Jeep puts 4.10's and 33's on. What makes you think that a 3.73 gear is good for a 34" tire? Jeep puts 4.56's and 315/70's on the 392. I'm curious where your math is. If you've done it right and compensated properly, you would understand that a 3.73/4.10 gear is a waste of money.

You also forgot to include the rest of my post and the context it contained. I've included it here:

4.10 doesn't even compensate for the 34" tire, let alone the power loss at altitude.

"If you're already at 34" tires, I would re-gear to 4.56 to future proof your tire decisions as your wheeling and need for adventure grow with your confidence."

The idea is to cover for the 35 or 315 tire and have already spent the money to do so.

I wouldn't waste the money to go to 4.10's.

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[Kreepin1]

What was the point of starting your post off with "Got Math?". Lol

You must've just looked at an RPM chart.

The RPM charts are just that, an RPM comparison between ratios at a given MPH.

The math includes much more than final drive ratios and engine RPM. The math includes GCVW, altitude correction, air density, fuel type, etc...

Horsepower loss is ~3% per 1000 feet of altitude.

You do not want to do your math based on a straight comparison of RPM. The charts are great, but they do not compensate for anything else.

OP mentioned he's going out-west. You do not want to spend the money to go from a 3.45 to a 3.73 or 4.10 gear on a 34" tire and then head out-west. You need to experience what a stock Rubi does out-west at altitude. 33's and 4.10's are not enough with anything more than the driver in the Jeep. (With the 3.6, anyway)

Stock, Jeep puts 4.10's and 33's on. What makes you think that a 3.73 gear is good for a 34" tire? Jeep puts 4.56's and 315/70's on the 392. I'm curious where your math is. If you've done it right and compensated properly, you would understand that a 3.73/4.10 gear is a waste of money.

You also forgot to include the rest of my post and the context it contained. I've included it here:

4.10 doesn't even compensate for the 34" tire, let alone the power loss at altitude.

"If you're already at 34" tires, I would re-gear to 4.56 to future proof your tire decisions as your wheeling and need for adventure grow with your confidence."

The idea is to cover for the 35 or 315 tire and have already spent the money to do so.

I wouldn't waste the money to go to 4.10's.

Yup. I'm a web wheeler with no real experience that just looked at an RPM chart... NOT!

This is in the Red Mountain Colorado area around 12,000 ft. We are in the JLR; 3.6 with manual transmission, 4.10's and 35's. I assume this is the sort of scenic trail the OP is interested in. I grant you that loss of power at altitude is no joke but we had absolutely no problem running these trails.

Gearing is a tradeoff like so many aspects of our sport. Lower gears are great offroad but you pay a price in fuel economy if they are too low. In my opinion 4.10 is the sweet spot for this use case where most of the miles are on the hi-way, a very few will be at altitude on easy trails, and none will be spent in mud or on rocks. You assume the OP is going to get by the bug and start running harder trails and want bigger tires. I assume the OP knows what they like to do - sight see and run back roads.

 

[word302]

Yup. I'm a web wheeler with no real experience that just looked at an RPM chart... NOT!

This is in the Red Mountain Colorado area around 12,000 ft. We are in the JLR; 3.6 with manual transmission, 4.10's and 35's. I assume this is the sort of scenic trail the OP is interested in. I grant you that loss of power at altitude is no joke but we had absolutely no problem running these trails.

Gearing is a tradeoff like so many aspects of our sport. Lower gears are great offroad but you pay a price in fuel economy if they are too low. In my opinion 4.10 is the sweet spot for this use case where most of the miles are on the hi-way, a very few will be at altitude on easy trails, and none will be spent in mud or on rocks. You assume the OP is going to get by the bug and start running harder trails and want bigger tires. I assume the OP knows what they like to do - sight see and run back roads.

Sorry your lack of experience is showing bright and clear. @chevymitchell has donated more of his time and knowledge to these forums than probably any other member. He knows a thing or 2 about gearing. How much experience do you have with other gear/tire combinations. Those of us who have driven several setups couldn’t disagree with your opinion more. 4.10s and 35s is far from the sweet spot, especially with the manual transmission.

 

[Kreepin1]

Sorry your lack of experience is showing bright and clear. @chevymitchell has donated more of his time and knowledge to these forums than probably any other member. He knows a thing or 2 about gearing. How much experience do you have with other gear/tire combinations. Those of us who have driven several setups couldn’t disagree with your opinion more. 4.10s and 35s is far from the sweet spot, especially with the manual transmission.

LOL, my first off-roader was a Scout with 4.27's and L78 Armstrong Norsemans. That's a 29 inch tire which was a decent sized tire in 1980. Next I wheeled a 2-door Tahoe with 3.73 and 34's. On my CJ I've run 3.54 and 33's; 4.88 with 36's and 40's; currently 5.86 and 43's. My Samurai has 3.73 and 31's but that's a little deceptive since the transfer case net's a 20% reduction in high range and 6.5:1 in low. My TJ had 3.73 and 32's but I never took it off road. Loved that 4.0 engine though. My JK had the 3.6 with 4.10's and 33.5" tires. It too was a daily but I wheeled it once in Moab. As stated above my JL has 4.10 and 35's.

All of the above are with manual transmissions and if the OP had a manual I would have suggested 4.56's. But he doesn't. He has an automatic which will absolutely do everything he wants to do with 4.10's. With 4.56's there will be a gain in perceived power at altitude and a loss of fuel economy in the lowlands. Either way the Jeep will drive great.

 

[word302]

LOL, my first off-roader was a Scout with 4.27's and L78 Armstrong Norsemans. That's a 29 inch tire which was a decent sized tire in 1980. Next I wheeled a 2-door Tahoe with 3.73 and 34's. On my CJ I've run 3.54 and 33's; 4.88 with 36's and 40's; currently 5.86 and 43's. My Samurai has 3.73 and 31's but that's a little deceptive since the transfer case net's a 20% reduction in high range and 6.5:1 in low. My TJ had 3.73 and 32's but I never took it off road. Loved that 4.0 engine though. My JK had the 3.6 with 4.10's and 33.5" tires. It too was a daily but I wheeled it once in Moab. As stated above my JL has 4.10 and 35's.

All of the above are with manual transmissions and if the OP had a manual I would have suggested 4.56's. But he doesn't. He has an automatic which will absolutely do everything he wants to do with 4.10's. With 4.56's there will be a gain in perceived power at altitude and a loss of fuel economy in the lowlands. Either way the Jeep will drive great.

So 0 experience with different tire/gear setups in the JL, just like I thought. You’re not really the guy I’d take advice from.

 

[Kreepin1]

So 0 experience with different tire/gear setups in the JL, just like I thought. You’re not really the guy I’d take advice from.

You are exactly right. Worse, I have almost no experience driving an automatic off road.

So, we are talking gears for a photographer that likes to run down back country two tracks in a 4-door and camp. We are not talking serious trails. Let's assume no passengers, aftermarket bumpers, winch, some recovery gear and 300 lbs of gear. Tires are 35x11.5 all terrains like a Toyo Open Country AT3 on stock wheels. Lift is 2.5". Please @DigitalDiem chime in to correct these assumptions. My guess is driver plus 700 lbs total increase in weight.

So @word302 I've got two questions:

With 4.10 gears will the above Jeep see 8th gear in, say, Kansas doing 70 mph?

With 4.10 gears how often will this Jeep be in 1st gear on, say, Last Dollar Road in Colorado?

 

[Zandcwhite]

Got math? The OP does and 3.73's bring the Jeep pretty close to stock.

I agree with @grimmjeeper that 4.10's are the best choice for the stated needs. I'd go lower for a serious off roader but for back country exploration the 4.10's will be perfect especially with an automatic.

The non-rubicon models have too tall of gears to start with in my opinion, especially considering the double Overdrive transmissions. A stock Rubicon with 4.10's is still taller than it needs to be on 33's. If I were spending the money regearing, I'd opt for the lower side of things for both wheeling and the type of daily driving we do. If you have a long freeway commute, stay on the high side. If it's a few long roadtrips a year, gear low for the daily benefits and spin a few more rpm on the road trips, even if it costs you 1-2 mpg on those occasions. The deep 1st gear and super tall 8th gear allow us to basically run any gearing we choose. Even the factory 4.10's were fine on 37's with the tune on the 2.0t for 2+ years of roadtrips and wheeling. When we decided to regear a few weeks ago, I jumped all the way to the deep end. 5.38's and 38's is probably too deep. Lost 1-1.5 mpg across all types of driving, of course it takes off like a rocket and pulls like a train so that could be happy pedal induced. Still has no problem cruising 80mph on the freeway, but light to light got way more entertaining.

 

[word302]

You are exactly right. Worse, I have almost no experience driving an automatic off road.

So, we are talking gears for a photographer that likes to run down back country two tracks in a 4-door and camp. We are not talking serious trails. Let's assume no passengers, aftermarket bumpers, winch, some recovery gear and 300 lbs of gear. Tires are 35x11.5 all terrains like a Toyo Open Country AT3 on stock wheels. Lift is 2.5". Please @DigitalDiem chime in to correct these assumptions. My guess is driver plus 700 lbs total increase in weight.

So @word302 I've got two questions:

With 4.10 gears will the above Jeep see 8th gear in, say, Kansas doing 70 mph?

With 4.10 gears how often will this Jeep be in 1st gear on, say, Last Dollar Road in Colorado?

No, and your assumptions about MPG going down with lower gears is also wrong. He will see a mild increase in fuel economy jumping to 4.56, even in Kansas. The gearing calculators don’t mean much when your engine bogs below 2000 RPM. I have 37s and 5.13s with the manual and it really is the sweet spot. I’ve driven an auto with 4.56 and 35s and it would be perfect for the ops use.

 

[Kreepin1]

No, and your assumptions about MPG going down with lower gears is also wrong. He will see a mild increase in fuel economy jumping to 4.56, even in Kansas. The gearing calculators don’t mean much when your engine bogs below 2000 RPM. I have 37s and 5.13s with the manual and it really is the sweet spot. I’ve driven an auto with 4.56 and 35s and it would be perfect for the ops use.

I feel like such an idiot. I wasn't thinking about the difference in overdrive ratio between manual and auto. I finally broke out the GrimmJeeper's gearing calculator and 4.10 with Manual is almost exactly the same as 4.56 with auto.

I apologize for mucking up this thread and agree that 4.56 is the best choice.

 

[word302]

I feel like such an idiot. I wasn't thinking about the difference in overdrive ratio between manual and auto. I finally broke out the GrimmJeeper's gearing calculator and 4.10 with Manual is almost exactly the same as 4.56 with auto.

I apologize for mucking up this thread and agree that 4.56 is the best choice.

4.10 with the manual and 35s ain’t great either. In fact the manual needs to be regeared way before the auto does. Like I said, you really need to drive a properly geared JL before you chime in here.

 

[Kreepin1]

4.10 with the manual and 35s ain’t great either. In fact the manual needs to be regeared way before the auto does. Like I said, you really need to drive a properly geared JL before you chime in here.

Nonsense. I've had 35's on my Jeep practically from day one and it drove great on the street and trails like the OP describes. The only time I have to downshift is to climb hills or pass - which is how it should be. No question the manual would benefit from lower gears on tougher trails. Last fall I had the Jeep tuned (mostly to get rid of rev hang) and switched to E85. Can't wait to get out on the trails and try it out!

 

[word302]

Nonsense. I've had 35's on my Jeep practically from day one and it drove great on the street and trails like the OP describes. The only time I have to downshift is to climb hills or pass - which is how it should be. No question the manual would benefit from lower gears on tougher trails. Last fall I had the Jeep tuned (mostly to get rid of rev hang) and switched to E85. Can't wait to get out on the trails and try it out!

See that’s just it, you don’t know what you don’t know. You have 0 experience with anything other than 4.10s and 35s. You would be amazed at what 4.88s would do for you.

 

[Kreepin1]

See that’s just it, you don’t know what you don’t know. You have 0 experience with anything other than 4.10s and 35s. You would be amazed at what 4.88s would do for you.

More nonsense. I totally get what a crawl ratio around 100:1 is like and what it would do for my JLR.

But you lost all credibility with me when you first claimed the OP's Jeep wouldn't see 8th on 4.10's and 35's and then claimed it would be even worse with a manual. I shifted into 6th at 60 mph before the tune and had no trouble holding speed unless there was a hill or serious headwind. This matters because lower RPM's do translate to better fuel economy. Do you seriously think FCA engineers put 3.45's in these Jeeps just for the heck of it? Is it just possible it's to get a little better fleet fuel economy?

I am done arguing with you.

 

[word302]

More nonsense. I totally get what a crawl ratio around 100:1 is like and what it would do for my JLR.

But you lost all credibility with me when you first claimed the OP's Jeep wouldn't see 8th on 4.10's and 35's and then claimed it would be even worse with a manual. I shifted into 6th at 60 mph before the tune and had no trouble holding speed unless there was a hill or serious headwind. This matters because lower RPM's do translate to better fuel economy. Do you seriously think FCA engineers put 3.45's in these Jeeps just for the heck of it? Is it just possible it's to get a little better fleet fuel economy?

I am done arguing with you.

First of all I never said anything about the op and 8th gear. 2nd of all I’m not even talking about off road performance. Have you driven a JL with 3.45 gears? It’s fine if you don’t like what I have to say but for you to be throwing advice around based on your single setup experience is laughable. You do realize vehicle manufacturers do all their mpg proving at 60mph and below on flat ground? Talk about losing credibility. You can call it nonsense all you want but some of us actually have real world experience driving different combinations. Enjoy your little bubble.

 

[c20040215]

More nonsense. I totally get what a crawl ratio around 100:1 is like and what it would do for my JLR.

But you lost all credibility with me when you first claimed the OP's Jeep wouldn't see 8th on 4.10's and 35's and then claimed it would be even worse with a manual. I shifted into 6th at 60 mph before the tune and had no trouble holding speed unless there was a hill or serious headwind. This matters because lower RPM's do translate to better fuel economy. Do you seriously think FCA engineers put 3.45's in these Jeeps just for the heck of it? Is it just possible it's to get a little better fleet fuel economy?

I am done arguing with you.

My personal experience is that 34" (285/75R17) with 4.1 gear and 6 speed is "fine". Holds 6th gear at highway speed as long as its relatively flat. I can see where you coming from, a mildly mod two door with a set of smaller & lighter 35s (I assume that's the case). It probably works "fine". I would suggest you drive a jeep similar to yours but with 4.56, you might change your mind. Off-Road wise, the crawl ratios between 4.1 and 4.56 is not that significant, especially a Rubicon.

Gearing is one of those things that invites different opinions. Engine type, weight, terrain, diving style, and tire choice all play a part. Given only one or two factors alone, no one can tell you what the magic set up is, but it gets you a ball park range.

I agree with most people here that 4.56 with 34" on 8 AT auto would give you the best flexibility. Not too aggressive where you trade lot MPG for power, and still wouldnt be under gear going with 35" if op choose to in the future.

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