Jeep Wrangler 4High vs 4Low

[Naveen Raj]

10 minutes ago, Josh S said:

I used 4L on my Rubicon in Sweihan the other day, I got up to about 45/50 kmh, however I am nervous to do this too much as I understand it puts a lot of stress on the car.  Can the transfer case / gear ratio be changed cheaply.

It can be changed, not sure about the cost. @Santoso Marjukihas swapped the transfer case on his rubicon. 

[Santoso Marjuki]

On 2/8/2024 at 9:35 PM, Naveen Raj said:

It can be changed, not sure about the cost. @Santoso Marjukihas swapped the transfer case on his rubicon. 

Well, you can get a good second hand  condition with a great deal ( check several garages in Dubai or Sharjah), if the new one from OEM is a bit costly. 

[Josh S]

9 months and 40 drives into the world of off-roading (and without doubt, the best hobby I’ve ever had) I thought compelled to bring the thread back from the dead with a few additional thoughts and questions!!

I have recently been driving with some experienced convoys in Sweihan. It’s a different kettle of fish compared to the drives in Sharjah and has a lot of switching, higher speed crests and larger climbs. Everyone drives in 4L other than me as my Rubicon doesn’t allow for it  

When it comes to reaching the crest, and either riding it or switching, we tend to be travelling around 40-50km/hr which is right on the red line of 1st. It’s important to keep high RPM here but being so close to red line means there’s little room to blip the throttle if I need to. Meanwhile, if using 2nd gear at the same speed, the RPM is much lower and the torque feels substantially less than I am used to in first, and does not feel like enough, especially if the speed drops a little or the sound is very hot and slippery. As such, neither 1st or 2nd feels right. (Note, I have chosen to drive manual as I find it more enjoyable and engaging than auto).

So my question is, would this be an example where 4L would provide more control leading up to, and on the crest, as the gears are shorter and I’d have much more torque to play with at the same speed, or is this down to wrong technique? I find myself thinking it’s a 4H issue as nobody else in the convoy appears to struggle with the RPM/Torque and they are all in 4L  

 

Edited May 31 by Josh S

[ChrisW]

I have some views @Josh S, but I should caveat the following by saying that I’m not an experienced sand off-roader or Jeep driver! I do however have a technical background and have driven various car setups and terrains over the years.

 

I have a Jeep JK with a six speed manual and 3.8L engine, which is fairly notorious for being uninspiring at the best of times. The powerband really comes in above 3000 RPM - much less and you can easily start to have decaying RPM on an uphill section or soft sand, and sadly 5000 RPM is pretty much where you top out for power and torque; so the useful power window is narrow. 
 

After my first few drives on sand (pre-Carnity) with this car, I was worried that I’d made a bad decision. On technical dunes it was incredibly difficult to drive slow enough in 4H to keep behind folk driving technical dunes, and on faster sections it was a continual swap between first and second car - often with shifts being required mid-manoeuvre! Hard work, not much fun. 
 

I then did the bad thing - I did a drive in 4L. Wow…it was much easier; suddenly now third gear was my default starting gear and I had a lot more control available to me by coming up and down from there. Staying in the useful power band was easy. But…the transfer case really doesn’t want to be driving at high speed…you will kill the planetary gears eventually. 
 

What that did was to set me off wondering why that is - and this is what I found. 
 

- The default Jeep Wrangler Sport has a final drive ratio of 3.21 - so in order you have engine, transfer case, gearbox, final drive (ring and pinion), wheels. What this means is that the car is biased to have less RPM at high speed, whereas on sand (and given the gutless engine), we want more of the RPM at lower speed. Selecting 4L does that. 
 

- The first gear on this particular JK is very long; it covers a really wide speed range. Coupled with a low final drive ratio, it makes  it hard work…you can’t really crawl, and you end up sticking with first gear until quite high speed. 
 

What can be done about this? Good news is that you have options. 
 

You can change the final drive ratio to a variety of different options. This is quite common in the US where the rock-crawling crowd like to run really big tyres, and you need to shift the RPMs around. 
 

I did some maths using the transmission data sheets, and what I found is that the golden 2/3/4th gears in 4L could be approximately replicated as 1/2/3 in 4H if I swapped the rack and pinion from 3.21 to 4.56. You can also go to 4.88 and 5.21 if you want your 4H first gear to be a crawling gear - the caution just being that you’ll be cruising on the highway at high RPMs (…as is often the case with engineering issues, you can only optimise for one thing at a time!). 
 

Circa five thousand dirham later I now have a Jeep I enjoy driving on sand, and the lingering thought that I perhaps bought the wrong car in the first place…but we learn. This car isn’t my daily driver, so optimising it for the low end worked for me - and I just enjoy drifting along at 100-120kph on the main road. 

Edited June 1 by ChrisW

[ChrisW]

For those sufficiently curious - these were the quick total drive ratio sums… 

[Zed]

2 hours ago, Josh S said:

9 months and 40 drives into the world of off-roading (and without doubt, the best hobby I’ve ever had) I thought compelled to bring the thread back from the dead with a few additional thoughts and questions!!

I have recently been driving with some experienced convoys in Sweihan. It’s a different kettle of fish compared to the drives in Sharjah and has a lot of switching, higher speed crests and larger climbs. Everyone drives in 4L other than me as my Rubicon doesn’t allow for it  

When it comes to reaching the crest, and either riding it or switching, we tend to be travelling around 40-50km/hr which is right on the red line of 1st. It’s important to keep high RPM here but being so close to red line means there’s little room to blip the throttle if I need to. Meanwhile, if using 2nd gear at the same speed, the RPM is much lower and the torque feels substantially less than I am used to in first, and does not feel like enough, especially if the speed drops a little or the sound is very hot and slippery. As such, neither 1st or 2nd feels right. (Note, I have chosen to drive manual as I find it more enjoyable and engaging than auto).

So my question is, would this be an example where 4L would provide more control leading up to, and on the crest, as the gears are shorter and I’d have much more torque to play with at the same speed, or is this down to wrong technique? I find myself thinking it’s a 4H issue as nobody else in the convoy appears to struggle with the RPM/Torque and they are all in 4L  

 

@Josh S i think this has been answered before, I hope you're reading this and not skipping it  

1. If any of your experienced friend or marshal in J.N. has Rubicon, they will have already swapped their transfer case from 4:1 ratio to the JL 2.7 ratio so they can drive Rubicon in 4Lo. Refer to table at end of post below. The higher the number, the higher the torque BUT less speed.  The lesser the number the lower the torque but more speed. As mentioned in previous post, Santoso has changed his Rubicon transfer case, and though you see him as 50 drives only, he's a Senior (1 level below Marshal) in UAEO***.   Complete Table of Calculated Drive Ratios between Rubicon 4:1 and JL 2.7 is at the end of this post, cos I have other solutions too and didn't want you to skip the maths  

2. Another option: Grind your camshaft so it will change your torque & speed profile at higher rpm. This would increase your rev limit so driving 5000rpm feels like factory 3500rpm.

3. Another option: talk to a tuner and see if they can program the computer differently. Am not familiar with the Pentastar engine, but let's say if any of the ratio is hardcoded somewhere, you can change the constant of 4 multiplier to 2.7 multiplier electronically without mechanically changing stuff.

4. Stay incumbent in status quo: clubs like J.N. would put you last before sweeper so as not to slow down the experienced drivers in front  

TABLE of JL 2.7:1 Transfer Case vs Rubicon 4:1 Transfer Case

Now because 4Lo is a gear reduction system, basically driving in 4Lo reduces your max speed, and the reduction is done via the 4Lo ratio, Rubicon Max Speed of 50km/h in 4Lo is due to Max Speed in 4Hi divide by 4:

And here's a complete table of calculated drive ratios.

• Yellow means when Rubicon is driving 4Hi 1st Gear, it's equivalent to JL 4Lo 3rd Gear >> this is why JL peeps drive in 4Lo cos they have more "variations" before they hit cruising speed at 4Lo 8th Gear. 
• Rubicon ideal sand gear is 4Lo 6th gear, but due to gear reduction max speed is limited to 50km/h. Only way to drive faster in 4Lo is to change transfer case to JL version.

 

Cheers,

Z.

 

[Naveen Raj]

26 minutes ago, Zed said:

@Josh S i think this has been answered before, I hope you're reading this and not skipping it  

1. If any of your experienced friend or marshal in J.N. has Rubicon, they will have already swapped their transfer case from 4:1 ratio to the JL 2.7 ratio so they can drive Rubicon in 4Lo. Refer to table at end of post below. The higher the number, the higher the torque BUT less speed.  The lesser the number the lower the torque but more speed. As mentioned in previous post, Santoso has changed his Rubicon transfer case, and though you see him as 50 drives only, he's a Senior (1 level below Marshal) in UAEO***.   Complete Table of Calculated Drive Ratios between Rubicon 4:1 and JL 2.7 is at the end of this post, cos I have other solutions too and didn't want you to skip the maths  

2. Another option: Grind your camshaft so it will change your torque & speed profile at higher rpm. This would increase your rev limit so driving 5000rpm feels like factory 3500rpm.

3. Another option: talk to a tuner and see if they can program the computer differently. Am not familiar with the Pentastar engine, but let's say if any of the ratio is hardcoded somewhere, you can change the constant of 4 multiplier to 2.7 multiplier electronically without mechanically changing stuff.

4. Stay incumbent in status quo: clubs like J.N. would put you last before sweeper so as not to slow down the experienced drivers in front  

TABLE of JL 2.7:1 Transfer Case vs Rubicon 4:1 Transfer Case

Now because 4Lo is a gear reduction system, basically driving in 4Lo reduces your max speed, and the reduction is done via the 4Lo ratio, Rubicon Max Speed of 50km/h in 4Lo is due to Max Speed in 4Hi divide by 4:

And here's a complete table of calculated drive ratios.

• Yellow means when Rubicon is driving 4Hi 1st Gear, it's equivalent to JL 4Lo 3rd Gear >> this is why JL peeps drive in 4Lo cos they have more "variations" before they hit cruising speed at 4Lo 8th Gear. 
• Rubicon ideal sand gear is 4Lo 6th gear, but due to gear reduction max speed is limited to 50km/h. Only way to drive faster in 4Lo is to change transfer case to JL version.

 

Cheers,

Z.

 

Detailed explanation Bro.. Long story short sell the rubicon and buy sport or Sahara, problem solved 😁

[Josh S]

So after all this about no 4L, it may actually be that in my instance, with the rubicon gearing and style of driving, that 4L is much better than 4H…

[ChrisW]

I’m not sure that’s the case:

- The Rubicon transfer case is 4:1…you’ll be spinning the engine and transmission really fast when running at average speeds

 

- The Rub’s transfer case is also meant for rock crawling…running it continuously at higher RPMs and power will likely cause it to prematurely fail. 
 

That’s not to say that when conditions call for it (certain climbs, recoveries etc), then it makes sense - but full time general sand driving will probably trash the transfer case or other parts prematurely. 

[Josh S]

3 minutes ago, ChrisW said:

I’m not sure that’s the case:

- The Rubicon transfer case is 4:1…you’ll be spinning the engine and transmission really fast when running at average speeds

 

- The Rub’s transfer case is also meant for rock crawling…running it continuously at higher RPMs and power will likely cause it to prematurely fail. 
 

That’s not to say that when conditions call for it (certain climbs, recoveries etc), then it makes sense - but full time general sand driving will probably trash the transfer case or other parts prematurely. 

Yes, I am aware the Rubicon is not suitable for four low which I mentioned earlier, so perhaps I should be changing my car or changing my transfer case as I am struggling to see this is a technique issue since it is related to RPM and torque. This of course contradicts all that has been previously said on this thread about for low being unnecessary, even at an expert level.