37 vs 38’s and 4.88 vs 5.13

[gearhead22]

Stock 3.73s and C rated 37" BFG K02s gasser... No regrets. I get a legit hand calculated 18.1-18.4 mpg week after week, fill up after fill up (until winter gas comes back). My daily commute is 50/50 city/hwy around 40 miles round trip. I've never pulled out in traffic and wished for more and never thought I was underpowered pulling my tractor on my trailer or boat. I am the minority though. I call bs on the guy getting 18 mpg with 5.13s & 37s unless you don't go over 55 mph, for highway speeds your RPMs are too high for that kind of mpg or you are a diesel. Just not possibly mathematically, deeper gearing + faster speeds means more RPM = more gas burned plain and simple.

I’m currently running the same bfg with 4.10’s. No complaints really. But I want a different tire. Really considering the Patagonia mt’s in a 38. But they’re 19lbs heavier per tire than these bfg’s. While I’m content with the bfg’s I’m not sure if I’ll remain content with ~80lbs more tire rolling around underneath the jeep. I really want the 38’s, but I really don’t want to feel the need to regear after lol

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[Panthers65]

I call bs on the guy getting 18 mpg with 5.13s & 37s unless you don't go over 55 mph, for highway speeds your RPMs are too high for that kind of mpg or you are a diesl

ok… I live in Atlanta BTW, you do 55 here and you get ran over…

with a stubby bumper, winch, and flat fenders

 

[Hemy5587]

ok… I live in Atlanta BTW, you do 55 here and you get ran over…

with a stubby bumper, winch, and flat fenders

Show me your RPM at 70 mph, I will show you what your real MPG. That is why I said hand calculated in my post... Not what my dash says...

But figured I would show and tell as well while changing my oil:

Granted my averages creep up to 21-22 mpg when I drive from MN to MO, 1600 miles round trip at 70 +/- mph. However you should be around 2700 rpm in 8th at 70 mph whereas I am around 1900 rpm in 8th at 70 mph. Pick a gear, any gear, any speed and you will be churning more RPM than me, more RPM means more gas burned.

 

[XraytecH]

I've heard on the YouTubes that 5.13 once you've reached highway speeds and need to over take someone, the automatic gear box will not down shift.

 

[Hemy5587]

I’m currently running the same bfg with 4.10’s. No complaints really. But I want a different tire. Really considering the Patagonia mt’s in a 38. But they’re 19lbs heavier per tire than these bfg’s. While I’m content with the bfg’s I’m not sure if I’ll remain content with ~80lbs more tire rolling around underneath the jeep. I really want the 38’s, but I really don’t want to feel the need to regear after lol

I hear ya, I debated 38s before I went with 37s. Weight plays a significant role when picking tires. I had 35 KM3s and then 35 Good Year Ultra-terrains, both heavier ~75 lbs and ~70 lbs vs the c rated K02s ~65 lbs, MPG is the best so far with the year I have had the 37s on. I debated the MT/02s specifically but I have too much snow and ice in MN and figured I need a three peak rated at least. The contact patch on the MT/02s is narrower so that may offset the weight increase. The 8 spd in our trucks makes up for the gearing but others on here will swear up and down going deeper in the gearing is all the difference. I haven't felt the need to do so but it just depends on what your expectations are once you do go the heavier 38s. Your mpg and speed will definitely take a hit, you will just have to decide if you can live with it. Can always try it and regear later .

 

[gearhead22]

I hear ya, I debated 38s before I went with 37s. Weight plays a significant role when picking tires. I had 35 KM3s and then 35 Good Year Ultra-terrains, both heavier ~75 lbs and ~70 lbs vs the c rated K02s ~65 lbs, MPG is the best so far with the year I have had the 37s on. I debated the MT/02s specifically but I have too much snow and ice in MN and figured I need a three peak rated at least. The contact patch on the MT/02s is narrower so that may offset the weight increase. The 8 spd in our trucks makes up for the gearing but others on here will swear up and down going deeper in the gearing is all the difference. I haven't felt the need to do so but it just depends on what your expectations are once you do go the heavier 38s. Your mpg and speed will definitely take a hit, you will just have to decide if you can live with it. Can always try it and regear later .

Yeah that’s the thought. I just don’t want to move to the 38 and hate it without a regear. Regearing is expensive lol.

 

[Panthers65]

Show me your RPM at 70 mph, I will show you what your real MPG. That is why I said hand calculated in my post... Not what my dash says...

But figured I would show and tell as well while changing my oil:

Granted my averages creep up to 21-22 mpg when I drive from MN to MO, 1600 miles round trip at 70 +/- mph. However you should be around 2700 rpm in 8th at 70 mph whereas I am around 1900 rpm in 8th at 70 mph. Pick a gear, any gear, any speed and you will be churning more RPM than me, more RPM means more gas burned.

"Prove to me exactly what I want exactly how I want it while standing on 1 foot, rubbing your belly, and saying the pledge of allegience"

I'd rather just....not. You seem to think I care more than I do. I'm getting 18+ on 37's and 5.13's. Stubby bumper and flat fenders. Typically no traffic in the morning but at least 10-15 minutes of sitting in traffic in the afternoon. Believe me or not, don't really care. My jeep is actually fun to drive again with the 5.13's. It doesn't drop gear every time I hit a hill, it pulls my boat substantially better than it did with the 4.10's, and there's plenty of gear left on the highway. Do I drive 90+ on the interstate? No, but I'm not an acne covered 19 year old with daddy's credit card paying for my gas. Buying a Jeep to drive fast is like paying a prostitute to take home to your parents, It might work but we all know it's a stupid decision. 5.13 is a 125% jump from 4.10. Meaning in first gear when I'm trying to get moving, I have 125% (excluding inefficiency) more than I would have had with 4.10's. That's not some backwoods test, that's basic physics and math, and it works.

And it's not hard to calculate RPMs on the interstate. a 10 second google search will pull up our final drive ratio and multiple RPM Calculators

.67:1 overdrive, 5.13 gears, and 35.6" tall BFG's gives you a ROME of 2270.8 at 70mph. 2300 RPM is peak efficiency for our motors. This matches what I see every morning and every afternoon on the interstate. I'm not a tool bag, I don't play on my phone while driving down the interstate.

Again- quite happy with my choice.

 

[Zachanadandy]

"Prove to me exactly what I want exactly how I want it while standing on 1 foot, rubbing your belly, and saying the pledge of allegience"

I'd rather just....not. You seem to think I care more than I do. I'm getting 18+ on 37's and 5.13's. Stubby bumper and flat fenders. Typically no traffic in the morning but at least 10-15 minutes of sitting in traffic in the afternoon. Believe me or not, don't really care. My jeep is actually fun to drive again with the 5.13's. It doesn't drop gear every time I hit a hill, it pulls my boat substantially better than it did with the 4.10's, and there's plenty of gear left on the highway. Do I drive 90+ on the interstate? No, but I'm not an acne covered 19 year old with daddy's credit card paying for my gas. Buying a Jeep to drive fast is like paying a prostitute to take home to your parents, It might work but we all know it's a stupid decision. 5.13 is a 125% jump from 4.10. Meaning in first gear when I'm trying to get moving, I have 125% (excluding inefficiency) more than I would have had with 4.10's. That's not some backwoods test, that's basic physics and math, and it works.

And it's not hard to calculate RPMs on the interstate. a 10 second google search will pull up our final drive ratio and multiple RPM Calculators

.67:1 overdrive, 5.13 gears, and 35.6" tall BFG's gives you a ROME of 2270.8 at 70mph. 2300 RPM is peak efficiency for our motors. This matches what I see every morning and every afternoon on the interstate. I'm not a tool bag, I don't play on my phone while driving down the interstate.

Again- quite happy with my choice.

I don't drive 90+ on the interstate very often, but the mojave sees those speeds in the desert regularly. You question buying a Jeep to drive fast, but there's literally only 2 vehicles better set up for that in the dirt. The raptor and the trx. I don't think I'd save fuel in either and if I did their $30k-50k higher price would take a whole lot of fuel savings to recoup. Sure I spend a lot on gas, but a Baja bug and it's 2-3 business days to get to 60mph make it boring as hell in the desert, it wouldn't tow a trailer for shit, and there's nowhere for the dogs. I still find it weird when people claim gears make the vehicle more fun to drive because it downshifts less...automatically. Does yours have a cattle prod wired into the transmission that shocks you when it downshifts? Why does shifting upset you or make it less fun to drive? It's an 8 speed auto with 2 overdrives, it's supposed to downshift when load increases and 7th is still overdrive. A sport comes with 3.73s and 32s, which is the equivalent of 4.30 gears and 37s. There's no reason to jump to 5.13s. Of the 6+ gear/ tire combos we've run between our 2 JLURs and my JTM 4.56s and 37s was the best non-stock setup in my opinion. 5.38s and 38s was the worst. It resulted in worse fuel economy than any of the others including 4.10s and 37s, 4.10s and 38s, and 4.56s and 39s. It's too deep for western freeway speeds. If you never go past 70 you can give some of that up, which is likely why you're so happy with your choice. Come west where speed limits start with an 8 and everyone is cruising 85mph and you'll see worse fuel economy than you would with 4.10s and I can guarantee that from personal experience. I don't buy Jeeps to drive fast, but modern freeway speeds are a necessity. The difference just driving to Moab from the house at 85 vs 65 saves me nearly 7 hours round-trip. That's an extra day wheeling in moab, who cares if it costs a bit more fuel than it would at 65mph? And if for a 2nd I believe your story about being the most efficient at higher rpms 7th gear is exactly the same mechanical gearing with 4.10s as you have in 8th. I already have access to that 2300 rpms at 70mph for free. But when it's downhill or there's a tailwind I can cruise at 1900rpm instead. And the transmission does all that...automagically

 

[Panthers65]

...

Getting way out of the gear ratio discussion here but...

Your entire response is centered around interstate/go-fast speeds. I understand that a Jeep is CAPABLE of being a go-fast desert/race vehicle, and with enough money it can be a good go-fast vehicle, but it will never be the best platform to start with. It's a solid axle brick on wheels. Why does Jeep make a Mojave? Because a set of shiny shocks and a slightly better ride sells, and they know that. There's a reason we're seen IFS/IRS explode at King of the Hammers in the last 10-15 years, because even with the rock/technical section IFS is that much better in the desert. These are guys with quarter-half million-dollar cars built specifically for this race, some of the most intelligent, legends of the sport. The Raptor and TRX are both IFS vehicles, and if they put that technology and power-weight ratio in a mid-size pickup it would absolutely smoke the gladiator in the desert, everything else being the same. At the end of the day a hammer will drive a screw into wood, but it's not the right tool for the job. If that's all you have and it has to get done, drive away, but a solid axle brick on wheels will never be the best platform for a go-fast vehicle.

Regear isn't for interstate speeds, it's for torque, getting moving and moving an object with less transmission slippage = less transmission heat = better for the transmission. In first gear, getting a load moving, deeper gears will apply more torque to the tires to get the load moving. 37's and factory gears you can't get a deeper gear to assist with towing, it's just not there. Yes running a deeper gear puts you in the best power band and keeps the transmission from hunting on the interstate, but that a side benefit, not the main reason you regear.

Jeep designed the 3.73 gears to push 32" tires, weighing 50# total. A decent 37" tire/wheel package could be double that. That's double the rolling mass, and double the work the truck has to do to get everything moving. If you go to 4.30's just to get the jeep back, you've still lost power because you didn't account for the additional weight of the tire/wheel package (or all the other heavy crap we hang off our Jeeps). There's a reason Jeep engineers decided it was worth the retooling effort to even offer 4.10's from the factory vs just putting 3.73's in everything. A Sport and Sport Max Tow will have basically the same external dimensions (minimal track-width) and tire size/weight from the factory, yet it's worthwhile to make a special case to go with 4.10's instead of 3.73s specifically for the towing capacity. There's no other reason cheap Jeep would bother with the difference than that. Deeper gears account for additional weight, not just diameter change. Give me a 37" tire package that weights what a 32" Factory combo does, and 4.30's/4.56's all day long

 

[Zachanadandy]

Getting way out of the gear ratio discussion here but...

Your entire response is centered around interstate/go-fast speeds. I understand that a Jeep is CAPABLE of being a go-fast desert/race vehicle, and with enough money it can be a good go-fast vehicle, but it will never be the best platform to start with. It's a solid axle brick on wheels. Why does Jeep make a Mojave? Because a set of shiny shocks and a slightly better ride sells, and they know that. There's a reason we're seen IFS/IRS explode at King of the Hammers in the last 10-15 years, because even with the rock/technical section IFS is that much better in the desert. These are guys with quarter-half million-dollar cars built specifically for this race, some of the most intelligent, legends of the sport. The Raptor and TRX are both IFS vehicles, and if they put that technology and power-weight ratio in a mid-size pickup it would absolutely smoke the gladiator in the desert, everything else being the same. At the end of the day a hammer will drive a screw into wood, but it's not the right tool for the job. If that's all you have and it has to get done, drive away, but a solid axle brick on wheels will never be the best platform for a go-fast vehicle.

Regear isn't for interstate speeds, it's for torque, getting moving and moving an object with less transmission slippage = less transmission heat = better for the transmission. In first gear, getting a load moving, deeper gears will apply more torque to the tires to get the load moving. 37's and factory gears you can't get a deeper gear to assist with towing, it's just not there. Yes running a deeper gear puts you in the best power band and keeps the transmission from hunting on the interstate, but that a side benefit, not the main reason you regear.

Jeep designed the 3.73 gears to push 32" tires, weighing 50# total. A decent 37" tire/wheel package could be double that. That's double the rolling mass, and double the work the truck has to do to get everything moving. If you go to 4.30's just to get the jeep back, you've still lost power because you didn't account for the additional weight of the tire/wheel package (or all the other heavy crap we hang off our Jeeps). There's a reason Jeep engineers decided it was worth the retooling effort to even offer 4.10's from the factory vs just putting 3.73's in everything. A Sport and Sport Max Tow will have basically the same external dimensions (minimal track-width) and tire size/weight from the factory, yet it's worthwhile to make a special case to go with 4.10's instead of 3.73s specifically for the towing capacity. There's no other reason cheap Jeep would bother with the difference than that. Deeper gears account for additional weight, not just diameter change. Give me a 37" tire package that weights what a 32" Factory combo does, and 4.30's/4.56's all day long

Again, like every other discussion you completely ignore just how deep the 1st gear in the 8 speed is. A tj Rubicon came with the same 4.10s even though the 1st gear was 2.86:1. Under your reasoning it wouldn't even be able to get moving. Stock we already have the gearing of a tj with 6.74 axle gears or a late model JK with 5.13s. And yet you see those rigs all over real rock crawling tails where you need torque doing just fine? Are they magic? Of course not. Do you simply not understand that it's final drive ratio not the axle gears themselves that matters? If you needed 5.13s with this 8 speed to get a 100lb 37 rolling then they would need 8.5 axle gears to do the same. And yet they don't? It's not magic it's math.

 

[Panthers65]

Again, like every other discussion, your ignoring how high the final overdrive is on the 8 speed transmission….

no I’m not, I’m looking at my specific vehicle and application.
Your comparing a 3500lb wrangler with a 6cyl engine and 2000lb tow rating to a 4700 truck with a 6cyl engine and a 7650 tow rating….. if you don’t understand why that’s a ridiculous comparison I can’t help… a Honda accord probably has really high gears, it means absolutely nothing to this conversation. Even base model “performance” cars would routinely come with 2.73 gears, doesn’t mean anything to a gladiator.

Look you either fear your gladiator for speed, or you gear it like a truck that’s designed to work. You’ve obviously got a setup that works for you, but the majority of people on this forum aren’t regularly doing 85+ in their gladiators. For the VAST majority of jeeps of all types of sizes, they are slow, unareodynamic, trail/crawling vehicles or mall crawlers.

 

[Panthers65]

And I’ve sold 100’s of fear sets and installed dozens, had buggies with 130+:1 craw ratios, I understand plenty about gear ratios and how they work.

 

[Zachanadandy]

Again, like every other discussion, your ignoring how high the final overdrive is on the 8 speed transmission….

no I’m not, I’m looking at my specific vehicle and application.
Your comparing a 3500lb wrangler with a 6cyl engine and 2000lb tow rating to a 4700 truck with a 6cyl engine and a 7650 tow rating….. if you don’t understand why that’s a ridiculous comparison I can’t help… a Honda accord probably has really high gears, it means absolutely nothing to this conversation. Even base model “performance” cars would routinely come with 2.73 gears, doesn’t mean anything to a gladiator.

Look you either fear your gladiator for speed, or you gear it like a truck that’s designed to work. You’ve obviously got a setup that works for you, but the majority of people on this forum aren’t regularly doing 85+ in their gladiators. For the VAST majority of jeeps of all types of sizes, they are slow, unareodynamic, trail/crawling vehicles or mall crawlers.

Well the 3.6L powered ram with the 8spd has the same tow rating as a max tow, weighs more, and has 3.21 gears. More magic I guess? The JT is a unicorn that needs crazy low gears to move even though nothing else does? But of course that's only if you put 37s on it. Show me the built wrangler on 37s that only weighs 3500lbs. Likely closer to 5k in my experience. But this is Jeep number 15 in 3 decades. Sure the tall overdrive let's you get away with running deeper than necessary gears, but it doesn't cover going too deep. 5.38s and 38s was the worst combination for fuel economy and didn't gain any performance period. I'll take 4.10s and 37s over that any day.

 

[Orange01z28]

My first one had 5.13s but this one has 4.88s. Both trucks on 37s

I actually feel like the better highway gear is the 5.13s as opposed to the 4.88s, as it will allow you to use 8th more. I’m getting worse MPGs with this new one with the 4.88s than my old one with the 5.13s

THAT BEING SAID
1. This newer one has heavy MTs (Nitto Trail Grapplers) while the old one had Milestar XTs. I’m pretty sure each Milestar is 15lbs lighter than the Nittos. That alone makes a huge difference
2. A lot of people say a numerically lower (higher gear) is stronger due to pinion engagement. On the street this doesn’t matter but off road it does

All in all, I’d say the 5.13 is better for a DD which is counterintuitive

 

[Panthers65]

Well the 3.6L powered ram with the 8spd has the same tow rating as a max tow, weighs more, and has 3.21 gears. More magic I guess? The JT is a unicorn that needs crazy low gears to move even though nothing else does? But of course that's only if you put 37s on it. Show me the built wrangler on 37s that only weighs 3500lbs. Likely closer to 5k in my experience. But this is Jeep number 15 in 3 decades. Sure the tall overdrive let's you get away with running deeper than necessary gears, but it doesn't cover going too deep. 5.38s and 38s was the worst combination for fuel economy and didn't gain any performance period. I'll take 4.10s and 37s over that any day.

the ram has a higher tow rating because of the weight, wheelbase, width, COG, and a host of other factors. If you think the only thing that factors into tow rating is HP and gearing, cameros mustangs and corvettes out there should be kicking our butts.

you were comparing factory rubicons to factory gladiators, and now that it doesn’t match your stance you have to throw “built” in there.
And the longest industry standard was to overgear the TJS even deeper than the JTs TJs were right in the time when I was in the industry and 456 on 33s for DD/488s for performance was the norm.

Keep your 37s and 4.10, you clearly drive more high-speed than the vast majority of Jeep drivers. the majority of Jeep owners and people on this form, they’ll appreciate the performance of a deeper gear set. If the Jeep engineers wanted the max tow gladiator to be at the final ratio of 4.10: and 37s, they wouldn’t have equipped it with 32s with those same 4.10s.

for a towing/trail riding/working truck:
4.10 and 32s
4.56 and 35s
4.88-5.13s for 37/38s
5.38s/axle swaps for 40s+

if you tow often/spend all your time driving around tow , go a little deeper. If you spend most all your time on the interstate and rarely tow anything more than a lawn mower trailer, gear a little higher.

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