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4.88/5.13 Advantages and Disadvantages

Mefford

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So I'm trying to decide on the right gear set for my situation 4.88 or 5.13. Mostly city driving, some highway and probably no extreme offroading (at this time). Pretty much lost 7 and 8 gears and it hunts on the highway with any type of incline with my current setup:

Jeep Gladiator Overland
Automatic Transmission
3.73 Gears
Dana M210 Front Axle
Dana M220 Rear Axle
3.5" Lift
37" Nitto Ridge Grappler Tires w/ Black Rhino Armory Wheels

My question is what are the advantages/disadvantages over the other of these two gear sets?
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jrf

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My vote would be for the 4.88s. They are actually a tad over geared for the 37s but with the added weight I think that's fair. I don't think you have much to gain to go up another step to the 5.13s. Of course...they will both work fine.
 

No IFS

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My vote 5.13. My Rubicon with 32” and 4.10 barley holds 8th gear. It needs 4:56 now factory. 4.88 waste of money. with this 3.6 and eight speed auto it needs all the gear it can get. I highly suggest you go for a ride with someone with 37” tires and 513’s. See how it goes for yourself. it’s a big expense.
 

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Disadvantage? Lower fuel economy on the highway. Less strength. Possibility of opening a can of worms (gear whine, less service life, etc.).

Yeah, if you have it professionally installed then it's on the installer to make it right IF you have issues. But it's still a pain to deal with trying to get it right. I did a lot of gear swaps over the years and finally realized it's not worth it.

And as you go up in ratio, you've got less gear tooth surface area in constant contact, which makes the entire assembly weaker by nature.

I'd rather go down a size in tire than go up a ratio in gear.
 

No IFS

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We’re still waiting on input regarding the strength and pinion head size 4.88 versus 5.13 it has not been firmly established yet the strength difference if any in these next generation axles.
I also question 4.88 versus 5.13 gas mileage results. I would almost wager the 5.13 will get better gas mileage overall.
This is not a conventional application where a higher axle ratio automatically yields more gas mileage.
 

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WhatExit?

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My vote 5.13. My Rubicon with 32” and 4.10 barley holds 8th gear. It needs 4:56 now factory. 4.88 waste of money. with this 3.6 and eight speed auto it needs all the gear it can get. I highly suggest you go for a ride with someone with 37” tires and 513’s. See how it goes for yourself. it’s a big expense.
I'm not seeing any facts here - seems like it's simply one person's opinion. If you have a Rubicon it has 4.10 gears and it came with 33" tires. Just like mine and others' did. If your Gladiator Rubicon "barely holds 8th gear" you're either going uphill (even slightly) or you're accelerating or, something's wrong.

And if you haven't changed gears - if you're not running 4.88's or 4.56's or anything else then you're just talking. Unless you know something that others don't, going with 5.13 gears is not something you should be recommending to anyone.

My Gladiator Rubicon was OK with the stock gears running 37x12.50/R17 tires but I wanted it to run like stock and with the 4.88 gears I put in it it does.

There's an 11 page thread currently running on this forum that will provide a LOT more useful info that IFS has posted here. I suggest you refer to it:
https://www.jeepgladiatorforum.com/forum/threads/gears-for-37-tires.17374/
 

WhatExit?

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So I'm trying to decide on the right gear set for my situation 4.88 or 5.13. Mostly city driving, some highway and probably no extreme offroading (at this time). Pretty much lost 7 and 8 gears and it hunts on the highway with any type of incline with my current setup:

Jeep Gladiator Overland
Automatic Transmission
3.73 Gears
Dana M210 Front Axle
Dana M220 Rear Axle
3.5" Lift
37" Nitto Ridge Grappler Tires w/ Black Rhino Armory Wheels

My question is what are the advantages/disadvantages over the other of these two gear sets?
Please review this thread instead of continuing this one.
https://www.jeepgladiatorforum.com/forum/threads/gears-for-37-tires.17374/
 

MarineHawk

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My Gladiator Rubicon was OK with the stock gears running 37x12.50/R17 tires but I wanted it to run like stock and with the 4.88 gears I put in it it does.
In case I go to 37s, I want to understand better what you’re saying. Do you mean that you are geared lower than stock overall (tires + gears), but because the 37s are heavier, it drives more like stock with the lower gearing?

The reason for my question is that, unless I’m missing something (which is more than possible):

1. Raising the tire size from the stock 32.8” (JTR) tire to 36.8” tire (e.g., Cooper 37s) increases the gearing by 12.2 %.

2. Then regearing from 4.1 gears to 4.56 gears decreases the gearing by 11.2%, which would be within 1% (1.112/1.122) of stock.

3. But regearing from 4.1 to 4.88 decreases the gearing by 19.0%, which, when increasing the tire size to 37s, would decrease the overall gearing by about 6% (1.19/1.122) from the stock overall gearing.

The 37s are heavier, which may be a reason for going to the 4.88 gears. But that gearing is lower than stock, right?
 

WhatExit?

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In case I go to 37s, I want to understand better what you’re saying. Do you mean that you are geared lower than stock overall (tires + gears), but because the 37s are heavier, it drives more like stock with the lower gearing?

The reason for my question is that, unless I’m missing something (which is more than possible):

1. Raising the tire size from the stock 32.8” (JTR) tire to 36.8” tire (e.g., Cooper 37s) increases the gearing by 12.2 %.

2. Then regearing from 4.1 gears to 4.56 gears decreases the gearing by 11.2%, which would be within 1% (1.112/1.122) of stock.

3. But regearing from 4.1 to 4.88 decreases the gearing by 19.0%, which, when increasing the tire size to 37s, would decrease the overall gearing by about 6% (1.19/1.122) from the stock overall gearing.

The 37s are heavier, which may be a reason for going to the 4.88 gears. But that gearing is lower than stock, right?

It's all here: https://www.jeepgladiatorforum.com/forum/threads/gears-for-37-tires.17374/
 

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MarineHawk

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Yeah, at one time or another I've read every post in that 11-page thread at least once. I can recall reading there or somewhere else that regearing to lower than stock with 37s helps because of the additional weight of the tire. I can't recall whether you said it or someone else or both.

You inserted substantive views/information in THIS thread. I was asking for a simple answer from you about your views based specifically on the numbers I quoted above, but I'm not going to reread 11 pages to get that, which likely would not be in that other thread anyway. I was valuing your opinion by asking you in response to the substantive information you posted here, hoping to get your views, and I'm sure they're valuable, but not valuable enough for me to reread 11 pages, and they're likely not going to address the numbers I posted above.
 

WhatExit?

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Yeah, at one time or another I've read every post in that 11-page thread at least once. I can recall reading there or somewhere else that regearing to lower than stock with 37s helps because of the additional weight of the tire. I can't recall whether you said it or someone else or both.

You inserted substantive views/information in THIS thread. I was asking for a simple answer from you about your views based specifically on the numbers I quoted above, but I'm not going to reread 11 pages to get that, which likely would not be in that other thread anyway. I was valuing your opinion by asking you in response to the substantive information you posted here, hoping to get your views, and I'm sure they're valuable, but not valuable enough for me to reread 11 pages, and they're likely not going to address the numbers I posted above.
Well, from the other thread, some quotes with thanks to @ShadowsPapa for most of it:

Larger tires, fewer revolutions per mile, slows the engine RPM - fewer engine revolutions for each mile traveled. Good for MPG but you then get out of the sweet spot for power and lug the engine - or the transmission won't upshift.
The gear changes ("re-gearing") we're talking about are used to compensate for larger tires in order to get the JEEP back to factory-like performance(transmission/RPMs) but certainly not MPGs :LOL:

Anyway, if the engine is running too slow you don't keep it breathing at peak efficiency. Air flow rates drop, you don't pack the cylinders as well, combustion pressures are down, a lot of factors.

Every cam grind has a peak power band area, heads flow differently, it gets complex. But bottom line - if you run an engine too slow, you hurt power and mpg. Run it too fast and you waste that power and drop mpg.

The gear changes talked about here are to keep the engine RPM up when the tire size increases as when you go from say a stock 33" tire to a 37" or greater, you slow the engine enough you drop below the power band and hurt power because it's running too slow to produce power.

"Deeper gears" or a higher numerical ratio - which is a lower gear ratio, brings the engine speed back up. So you can run taller tires to get that Jeep off-road stuff back and speed the engine back up with the gear change for the torque you need to crawl that steep grade.
 

MarineHawk

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Well, from the other thread, some quotes with thanks to @ShadowsPapa for most of it:

Larger tires, fewer revolutions per mile, slows the engine RPM - fewer engine revolutions for each mile traveled. Good for MPG but you then get out of the sweet spot for power and lug the engine - or the transmission won't upshift.
The gear changes ("re-gearing") we're talking about are used to compensate for larger tires in order to get the JEEP back to factory-like performance(transmission/RPMs) but certainly not MPGs :LOL:

Anyway, if the engine is running too slow you don't keep it breathing at peak efficiency. Air flow rates drop, you don't pack the cylinders as well, combustion pressures are down, a lot of factors.

Every cam grind has a peak power band area, heads flow differently, it gets complex. But bottom line - if you run an engine too slow, you hurt power and mpg. Run it too fast and you waste that power and drop mpg.

The gear changes talked about here are to keep the engine RPM up when the tire size increases as when you go from say a stock 33" tire to a 37" or greater, you slow the engine enough you drop below the power band and hurt power because it's running too slow to produce power.

"Deeper gears" or a higher numerical ratio - which is a lower gear ratio, brings the engine speed back up. So you can run taller tires to get that Jeep off-road stuff back and speed the engine back up with the gear change for the torque you need to crawl that steep grade.
I have understood all of those generalities for decades. I was asking about specific numbers/situations. Do the 37s with 4.88 gears run like stock to you because it's geared 6% lower, but the tires are about 15% heavier?

What I'm trying to figure out is: Should I run 4.56 gear with 37s, which equates to the stock overall gearing? Or do you still lose 8th gear doing that because the 37s are heavier?
 

WhatExit?

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I have understood all of those generalities for decades. I was asking about specific numbers/situations. Do the 37s with 4.88 gears run like stock to you because it's geared 6% lower, but the tires are about 15% heavier?

What I'm trying to figure out is: Should I run 4.56 gear with 37s, which equates to the stock overall gearing? Or do you still lose 8th gear doing that because the 37s are heavier?
In general it’s not the weight of the tires that’s the issue, it’s the size of the tires.

Tire and wheel weight (unsprung weight) is more of a suspension performance issue
 

MarineHawk

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In general it’s not the weight of the tires that’s the issue, it’s the size of the tires.

Tire and wheel weight (unsprung weight) is more of a suspension performance issue
So, aside from tire weight, you are geared 6% lower than stock. Do you like that better than stock--i.e., 37s with 4.56 gears?
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