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4.88 manual?

atmotocrosser

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I just got back from two weeks in Colorado and Utah in the 2-door manual on 4.88s and 37" K02s. I did Red Cone, Black Bear Pass, Imogene Pass, Fins and Things, Hell's Revenge, Poison Spider, Top of the World, Elephant Hill, and a couple others I'm probably forgetting.

For people wondering about manual + 4.88 + 37s:

-Highway driving with this setup does indeed suck at high elevation and/or on steep grades. 5th and 6th gears are distant memories in these situations. 4th actually worked very well for passing and maintaining speed in a lot of cases, but I frequently needed third to maintain progress up hills. You're going to be working a lot. If I lived in an area like this, and was dead set on 37s with a manual, there's no doubt I would want 10-20% deeper gearing for quality of life purposes.

-Slow, technical rock crawling is still very, very good on 37s, thanks to how short 1st gear is. It's absolutely not a chore to start out in the middle of a tough obstacle with the Jeep sitting at a precarious angle. You can easily two-foot drive at idle with the clutch and brake to crawl and then subsequently hold yourself on obstacles.

-That said, for the toughest/steepest slow obstacles, there were still plenty of situations were I wanted a little slower crawl speed and a little more wheel torque in 1st gear. This was easily done by leaving the clutch partially/half engaged while you climb a ledge or negotiate an obstacle at idle. While I found this easy to do, and it wasn't abusive to the clutch, it's definitely a case where 10-20% deeper gears would make things a little easier.

-On 37s I found myself kind of 'between gears' in certain situations. First would be simply too slow, while second didn't give quite enough wheel torque at low RPMs, mandating you keep the RPMs and speed a little higher than you'd ideally like. There were a lot of situations where I found myself thinking that shorter gearing would allow 2nd gear to be more useful in more slow/technical situations.

Overall, this setup on the 37s is "perfectly usable", and I'm very happy with it, but it's "not ideal". IMO 5.13 or 5.38 would allow
-First to crawl a tad slower for the absolute toughest obstacles
-Second to be much more useful in more low-speed situations
-Much better manners at high altitudes

Hope this helps anyone considering 37s.
Thank you for the write up.
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I just got back from two weeks in Colorado and Utah in the 2-door manual on 4.88s and 37" K02s. I did Red Cone, Black Bear Pass, Imogene Pass, Fins and Things, Hell's Revenge, Poison Spider, Top of the World, Elephant Hill, and a couple others I'm probably forgetting.

For people wondering about manual + 4.88 + 37s:

-Highway driving with this setup does indeed suck at high elevation and/or on steep grades. 5th and 6th gears are distant memories in these situations. 4th actually worked very well for passing and maintaining speed in a lot of cases, but I frequently needed third to maintain progress up hills. You're going to be working a lot. If I lived in an area like this, and was dead set on 37s with a manual, there's no doubt I would want 10-20% deeper gearing for quality of life purposes.

-Slow, technical rock crawling is still very, very good on 37s, thanks to how short 1st gear is. It's absolutely not a chore to start out in the middle of a tough obstacle with the Jeep sitting at a precarious angle. You can easily two-foot drive at idle with the clutch and brake to crawl and then subsequently hold yourself on obstacles.

-That said, for the toughest/steepest slow obstacles, there were still plenty of situations were I wanted a little slower crawl speed and a little more wheel torque in 1st gear. This was easily done by leaving the clutch partially/half engaged while you climb a ledge or negotiate an obstacle at idle. While I found this easy to do, and it wasn't abusive to the clutch, it's definitely a case where 10-20% deeper gears would make things a little easier.

-On 37s I found myself kind of 'between gears' in certain situations. First would be simply too slow, while second didn't give quite enough wheel torque at low RPMs, mandating you keep the RPMs and speed a little higher than you'd ideally like. There were a lot of situations where I found myself thinking that shorter gearing would allow 2nd gear to be more useful in more slow/technical situations.

Overall, this setup on the 37s is "perfectly usable", and I'm very happy with it, but it's "not ideal". IMO 5.13 or 5.38 would allow
-First to crawl a tad slower for the absolute toughest obstacles
-Second to be much more useful in more low-speed situations
-Much better manners at high altitudes

Hope this helps anyone considering 37s.
Damn good review - and about a week late for me :CWL: I guess it's kind of a good news/bad news


I was worried 4.88 were going to be a little too much and scream on the highway. Good to hear that's not necessarily the case. However, I wanted to do as much as possible to preserve the stock crawl abilities of the manual Rubicon. Looks like I'll be a little off in that category, but it'll be doable.

Thanks again!
 

Go_Galt

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Damn good review - and about a week late for me :CWL: I guess it's kind of a good news/bad news


I was worried 4.88 were going to be a little too much and scream on the highway. Good to hear that's not necessarily the case. However, I wanted to do as much as possible to preserve the stock crawl abilities of the manual Rubicon. Looks like I'll be a little off in that category, but it'll be doable.

Thanks again!
No prob! I want to reiterate that this setup is really, really good for crawling on 37s, and I'm using the word 'ideal' in it's true sense- it's not 100% *ideal* with 37s, but this it's still ridiculously good, and I suspect will completely satisfy most people's expectations for slow, technical crawling.

I took the hardest lines in Moab that my wheelbase and clearance would allow, and had no trouble on the trails I mentioned (Keeping in mind I had a Jedi for a spotter that kept me on good lines).

I suspect 5.13 or 5.38 is going to be in my future, but after this experience I'm not in any rush to do so.

For high elevation/hilly/mountain people though- I rule that 37s suck fairly badly with 4.88 in these. This is mostly a function of how weezy the 3.6 Pentastar gets at altitude, and would be remedied if us manual guys had a forced induction option (which I fear probably won't happen).
 

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For high elevation/hilly/mountain people though- I rule that 37s suck fairly badly with 4.88 in these. This is mostly a function of how weezy the 3.6 Pentastar gets at altitude, and would be remedied if us manual guys had a forced induction option (which I fear probably won't happen).
https://magnusonsuperchargers.com/products/01-19-36-003-bl

The thought has crossed my mind.

Still, on gearing: I run in the mountains with 4.88's and 34/35's and it's been just fine. I expect to not be running in 6th going up the mountains. Even 5th is too tall at times. But 4th brings all the power you need to pass up to the Eisenhower Tunnel.

On 37's: Agree fully that I would really rather have deeper gears and chromoly axle shafts.

Don't plan to go that big, but then I didn't plan to modify this Jeep at all either. 😂 🤷‍♂️
 
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Update for my 2 dr 4.88's with the 6 speed in a Rubi.

The ONLY thing I am not a huge fan of is the grab point of the clutch being higher than I am used to.
Big deal?

Nope.

Just something to be mindful of. If you are expecting a high performance clutch in general, this ain't it.

The 4.88's (vs my last JK with 3.73's and 33 inch tires) give me reason to be in 5th at times around town. 6th is still useless until about 60mph IMHO.

I can see how a lot of people would say to go 35's or 37's to get the "sweet spot"

With that said, the stock rubi 33's are a hoot, not WILDLY impractical and quite honestly very fun if you are just messing around in town.

Off road, no experience yet, but for the mall crawlers, two thumbs up.
 

Go_Galt

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With that said, the stock rubi 33's are a hoot, not WILDLY impractical and quite honestly very fun if you are just messing around in town.
I really do miss how quick mine was on the 33s.

Couldn't believe how fast second gear would rip you to ~40 mph. And third on a freeway on-ramp would pull so well you could quickly lose sight of the fact that you're going way faster than a wrangler should be negotiating a curve. It really was fun.
 
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I really do miss how quick mine was on the 33s.

Couldn't believe how fast second gear would rip you to ~40 mph. And third on a freeway on-ramp would pull so well you could quickly lose sight of the fact that you're going way faster than a wrangler should be negotiating a curve. It really was fun.
2nd and 3rd are my favorite gears.
 

atmotocrosser

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I really do miss how quick mine was on the 33s.

Couldn't believe how fast second gear would rip you to ~40 mph. And third on a freeway on-ramp would pull so well you could quickly lose sight of the fact that you're going way faster than a wrangler should be negotiating a curve. It really was fun.
What size are you on now?
 

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Go_Galt

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What size are you on now?
37x12.5 K02s which are a 'small' 37.

On-road performance at sea level is 'good/adequate'. First and second are still quite zippy, and first is now a more useable gear for accelerating. Third pulls very well for highway merging.

But it definitely does not haul ass in 2nd and 3rd anymore like it did with the 33s.
 

atmotocrosser

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I was planning to go straight to 37s but I would love to keep the zippy feel. I wonder if a lightweight 35” would be a better choice.
 

Go_Galt

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I was planning to go straight to 37s but I would love to keep the zippy feel. I wonder if a lightweight 35” would be a better choice.
I had the luxury of trying a set of 37x12.5 KM3s on mine before committing, so I knew what I was getting into and what kind of effects they would have on performance. I wanted the clearance and grip of a 37 for off road, and ruled it was an acceptable trade off after driving them.

If that quick on-road performance is going to be a significant factor for you, I would probably NOT go to 37s.
 

atmotocrosser

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I had the luxury of trying a set of 37x12.5 KM3s on mine before committing, so I knew what I was getting into and what kind of effects they would have on performance. I wanted the clearance and grip of a 37 for off road, and ruled it was an acceptable trade off after driving them.

If that quick on-road performance is going to be a significant factor for you, I would probably NOT go to 37s.
I was looking at the KM3s in the same size. What made you pick those over other all terrains or mud terrains?
 

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I was looking at the KM3s in the same size. What made you pick those over other all terrains or mud terrains?
I ultimately went with 37x12.5 K02s (the KM3s I was just trying, on a friend's set of wheels/tires) for sole reason that KO2s were lighter- just trying to save every bit of rotational mass that I could.

If I were to go back and do it again, I would probably get the KM3s or maybe Cooper STT-Pros.

Reasons:
-After doing all of the trails I did in CO and UT, the KO2s did very well. Overall I'm very happy with how they performed. But my friends running the same size KM3s, aired down to the same pressure, just seemed to grab certain ledges a little bit more easily than I did. This is totally anecdotal, but I attributed this to the bigger tread blocks and bigger voids on the KM3s.

-My KO2s are totally chunked out now. I acknowledge that two straight weeks of trails, rock crawling, and hundreds of miles of high speed dirt/gravel travel, all aired down, mostly in very hot weather, are the worst possible conditions for tire wear. But the chunking out of the tread blocks on mine are what I'd call 'excessive' for this amount of use, on tires with only 3,600 miles on them. My friends KM3s didn't look this bad.

-They're not good in mud. I took Hole-in-the-Rock road in Escalante, UT out to the Reflection Canyon trailhead after several days of heavy rain. This road is known to impassable for most vehicles in these conditions, due to the deep mud that will form in all the washes along the way. I made it out there and back just fine, but got to experience how badly K02s will pack up with mud and become a racing slick. It really wasn't a big deal- they were mostly easily cleared with some judicious throttle application, and like I said, I traversed the road just fine (needing to use a little momentum in places). Not a big deal, but if there are other options that perform better in mud, why not?
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