Re-gearing: 4.56 or 4.88

[Kon]

So I did my research in Grimmjeeper. I should mention that I input 30'' as tire height since I run 31'' KO2s and plan to replace them with same tires in the coming months and here are the results;

	4.11 (current)	4.56	4.88	5.13
O/D: 70mph (4th High)	~2200RPMs	~2500RPMs	~2600RPMs	~2800RPMs
Direct: 50mph (3rd High)	~2300RPMs	~2600RPMs	~2700RPMs	~2900RPMs
Crawl Ratio (1st Low)	~32x	~35x	~38x	~40x

Not sure if I'm thinking it right, but what I tried to figure out with each item is to check how highway, city and off road performance respectively will change. So I'm thinking that:

5.13 is out of the question for my driving conditions as, even though I don't drive on the highway so often, when I do I don't want to be as a high as 2800+ RPMs, considering that a kickdown on the throttle will send the RPMs close to the rev limit. Also it will kill my mpg in city driving which is the primary driving condition for the Jeep.

Between 4.56 and 4.88, I understand that the difference is small and at the end of the day it may has to do with personal preference. Since there is a possibility of going with 32'' tires in the future but definitely not with 30'' I'm leaning towards 4.88.

The ways I see the pros and cons of 4.88s;
+ Will give me a significant lower crawl ratio (19% lower compared to my current one), which is something that I feel I need in order to have better control when going downhill off-road
+ Better acceleration in city driving or less need for throttle input to keep engine within its efficient powerband as the auto will now change gears at approx. same RPMs as before but now at lower speed than before (correct me if my thinking is wrong here)
- Fuel economy in city driving
- A bit less convenient highway driving. worst case I switch my cruising speed to 65mph and have the same RPMs I would have at 70mph with 4.56 gears and problem solved.

Thoughts everyone?

 

[machoheadgames]

So I did my research in Grimmjeeper. I should mention that I input 30'' as tire height since I run 31'' KO2s and plan to replace them with same tires in the coming months and here are the results;

	4.11 (current)	4.56	4.88	5.13
O/D: 70mph (4th High)	~2200RPMs	~2500RPMs	~2600RPMs	~2800RPMs
Direct: 50mph (3rd High)	~2300RPMs	~2600RPMs	~2700RPMs	~2900RPMs
Crawl Ratio (1st Low)	~32x	~35x	~38x	~40x

Not sure if I'm thinking it right, but what I tried to figure out with each item is to check how highway, city and off road performance respectively will change. So I'm thinking that:

5.13 is out of the question for my driving conditions as, even though I don't drive on the highway so often, when I do I don't want to be as a high as 2800+ RPMs, considering that a kickdown on the throttle will send the RPMs close to the rev limit. Also it will kill my mpg in city driving which is the primary driving condition for the Jeep.

Between 4.56 and 4.88, I understand that the difference is small and at the end of the day it may has to do with personal preference. Since there is a possibility of going with 32'' tires in the future but definitely not with 30'' I'm leaning towards 4.88.

The ways I see the pros and cons of 4.88s;
+ Will give me a significant lower crawl ratio (19% lower compared to my current one), which is something that I feel I need in order to have better control when going downhill off-road
+ Better acceleration in city driving or less need for throttle input to keep engine within its efficient powerband as the auto will now change gears at approx. same RPMs as before but now at lower speed than before (correct me if my thinking is wrong here)
- Fuel economy in city driving
- A bit less convenient highway driving. worst case I switch my cruising speed to 65mph and have the same RPMs I would have at 70mph with 4.56 gears and problem solved.

Thoughts everyone?

You’re overthinking it.

1) 2800 at 70 is awesome and no, it doesn’t necessarily kill fuel mileage. It likely would help your city mpg if you can keep your foot out of it, which is hard with the newfound power but that’s on you. The lower gears around town make it easier on the rig to speed up, and easier saves fuel.

Members here frequently regear to where they run 2800 at 70 and 3000 at 75 for their 5 speed manual. Have not found one single person who doesn’t like it. The 3 speed auto already revs at 3250 at 70 from the factory so you’re still better off than them.

2) 5.13 puts a downshift at 70 to hit 4000 rpm in 3rd. That’s nowhere close to redline. You already lose 2nd gear at highway speed with a regear so you honestly need 3rd to be as good as it can get. The kickdown thing when you go to 3rd is going to apply no matter what because there isn’t that much difference from ratio to ratio.

4.10 is the lowest ratio that would allow a 2nd gear downshift at speed and barely, as that is nearly 5100 rpm at 70. You already have 4.10 so that goes out the window. 4.56, 4.88, 5.13 all put 2nd gear above redline. So to get the most possible passing power, you need 5.13 which will maximize the one downshift gear you are limited to, which is 3rd, and as I said, 3rd is not even close to redline @ 4000.

3) 4.56 would be a waste no matter what coming from 4.10 and it will not fix 4th gear sluggishness you already experience. 2460 rpm at 70 would not be good.

4) if you go to 32’s possibly, that makes every point I said based on 31’s even more valid.

FWIW - I use a 30” dimension for 31’s too.

 

[Irun]

Use the numbers to guide you.

With a 31" tire (using a real number of 30.7") and 4.88 gears.

Gear
Road RPMs at given speed in miles per hour
1	1517	5309	10618
2	839	2935	5870
3	534	1869	3739
4	369	1290	2580
5	-	-	-
6	-	-	-
7	-	-	-
8	-	-	-
9	-	-	-
10	-	-	-
R	1180	4131	8262

With a 32" tire (using a real number of 31.7") and 4.88 gears.

Gear
Road RPMs at given speed in miles per hour
1	1469	5141	10283
2	812	2842	5685
3	517	1810	3621
4	357	1249	2498
5	-	-	-
6	-	-	-
7	-	-	-
8	-	-	-
9	-	-	-
10	-	-	-
R	1143	4001	8002

With a 31" tire (using a real number of 30.7") and 5.13 gears.

Gear
Road RPMs at given speed in miles per hour
1	1595	5581	11162
2	881	3085	6170
3	561	1965	3930
4	387	1356	2712
5	-	-	-
6	-	-	-
7	-	-	-
8	-	-	-
9	-	-	-
10	-	-	-
R	1241	4343	8686

With a 32" tire (using a real number of 31.7") and 5.13 gears.

Gear
Road RPMs at given speed in miles per hour
1	1544	5405	10810
2	854	2988	5976
3	544	1903	3806
4	375	1313	2626
5	-	-	-
6	-	-	-
7	-	-	-
8	-	-	-
9	-	-	-
10	-	-	-
R	1202	4206	8412

As you can see, there is less than 200 RPMs difference, so go with 5.13 gears. You will not regret the decision. FWIW, I've talked to numerous shops that told me 5.13 was way to much gear for a small tire. They all shared one thing in common, i.e. a complete lack of practical knowledge about the pathetic .69 overdrive in the 42RLE!

 

[Kon]

Thanks guys! Indeed now that I think about it, 4.56 is small change but on the other hand I'm not brave enough to go to 5.13 (I could be wrong but just don't feel I need it), so I guess 4.88 is the way to go.

Any suggestion on brands?

I have heard that revolution gears are popular with many people here, however due to my situation of shipping to Greece my options are not as broad as if I were in the States. My common go-to place is quadratec since we have a good collaboration with their international shipping procedures.

The options I see there are essentially G2 and Yukon with these two brands being the most popular (if not the only ones) I have ever seen in Greece.

I'm thinking of going with this one;

https://www.quadratec.com/p/yukon-g...tall-kits-jeep-wrangler-dana-30-front-dana-44

I seems to have everything included and is also currently at a discount.

 

[tjryder]

I have regeared XJ 4.0 Auto on 31's to 4.88

Super happy, no regret, would do it again.

 

[Kon]

And one last thing. I'm confused on which speedo gear should I purchase for 4.88 and 31" tires since the various tables I see on the internet suggest different ones (from 41 teeth to 44).

Also, when choosing speedo gear should I think the nominal tire size (i.e. 31'') or the real one (30")?

Thanks!

 

[Kon]

I have regeared XJ 4.0 Auto on 31's

Super happy, no regret, would do it again.

With 4.88 gears? Does it have the 42RLE auto or the 3-speed auto?

 

[tjryder]

AW4

 

[Kon]

AW4

Thanks for the info. Our cases are different though.

 

[machoheadgames]

Thanks for the info. Our cases are different though.

His RPM in 4th would be same as yours with 5.13 in 4th. His 0.75 OD vs your 0.69 OD.

 

[machoheadgames]

And one last thing. I'm confused on which speedo gear should I purchase for 4.88 and 31" tires since the various tables I see on the internet suggest different ones (from 41 teeth to 44).

Also, when choosing speedo gear should I think the nominal tire size (i.e. 31'') or the real one (30")?

Thanks!

Is your Speedo calibrated perfectly right now? Instead of buying a gear based on a chart, do the math to figure out how much the needed speedo gear teeth will need to change based on percentage of gearing and you should be able to figure it out. Need to know what tooth count you currently have to do that.

 

[tjryder]

And one last thing. I'm confused on which speedo gear should I purchase for 4.88 and 31" tires since the various tables I see on the internet suggest different ones (from 41 teeth to 44).

Also, when choosing speedo gear should I think the nominal tire size (i.e. 31'') or the real one (30")?

Thanks!

Speedo gear is "out of range" for 4.88 and 31's. I took the 4.56 gear for 31's and it is 10% off (too low).
Side note:
My Jeep is mainly used city and offroad. I do regulary trips of 60 miles and more to get into the mountins. 2.300rpm at 65mph.
Also - I installed NiftyShifter for the gearbox from NickInTheTime and it is just great.

Onroad I use TQ lock all the time and shifts now like modern DSG. Off road - I go in low range, manuallsy selected second and TQ locked - instant crawl control.

For the TJ - I have bought 4.11 gear set, but it is a ma ual, with much lower 1-st gear. So crawl speed will be the same.

 

[Kon]

Is your Speedo calibrated perfectly right now? Instead of buying a gear based on a chart, do the math to figure out how much the needed speedo gear teeth will need to change based on percentage of gearing and you should be able to figure it out. Need to know what tooth count you currently have to do that.

Yes, it's perfectly calibrated as is and I do have the one with 38 teeth. So you mean that, since going from 4.11 to 4.88 is a % increase of about 19% this should correspond to an equal % increase in teeth? Therefore, 45 teeth? Well no chart suggested that!

 

[tjryder]

I installed 42 gear for 31/4.88 combo.
No bigger gear that I found at that time.

 

[machoheadgames]

Yes, it's perfectly calibrated as is and I do have the one with 38 teeth. So you mean that, since going from 4.11 to 4.88 is a % increase of about 19% this should correspond to an equal % increase in teeth? Therefore, 45 teeth? Well no chart suggested that!

Yes; the way I do it is divide new ratio by old, which is 1.19 in this case, then multiple your existing teeth by that. So yes, 45.

You can get a 44 and it’ll be off by 2-3 mph. You could also get a Speedo healer and just calibrate the rig with your existing gear. Bit more expensive but adjustable to 100% correct and you can change later for your 32’s too.

 

[Kon]

Yes; the way I do it is divide new ratio by old, which is 1.19 in this case, then multiple your existing teeth by that. So yes, 45.

You can get a 44 and it’ll be off by 2-3 mph. You could also get a Speedo healer and just calibrate the rig with your existing gear. Bit more expensive but adjustable to 100% correct and you can change later for your 32’s too.

Thanks, got it! No idea what a speedo healer is. Any links to check it out?

 

[machoheadgames]

Thanks, got it! No idea what a speedo healer is. Any links to check it out?

Speedo healer is a programmer that plugs inline with your speed sensor wiring and interrupts the signal and sends a modified multiplied signal to the gauge and pcm. People have to use them to calibrate rubicons which don’t have a speedo gear. They also have to use them on super short SYEs which deletes the gear from the NP231.

In your case you have the 38 tooth gear so it would just need to be corrected based on the gear you have. So it would be programmed to a 1.19 correction factor. Let me see if I can find the link, searching for TJ speedohealer should find it easily.

 

[machoheadgames]

Speedo healer

 

[Kon]

Speedo healer

Thanks! Just to make clear that it's the nominal tire size on which the speedo gears should be selected?

 

[machoheadgames]

Thanks! Just to make clear that it's the nominal tire size on which the speedo gears should be selected?

Typically but I don’t like that because all the charts conflict with each other so it’s hard to pick. We definitely determined that a 45 is what you need and those are nonexistent from what I’ve seen. Me following the chart years ago based on “31” ended up with my Speedo reading high by 3 mph at 70. I bought a 32 tooth and should have gotten a 33 tooth for my smallerish 31’s. But some charts recommended 33, some 32, so I didn’t know what to pick.

FWIW I ran 31’s on 4.10 with a 38 also and it was correct.

If I were you I’d probably budget for the speedohealer. Otherwise you’re going to buy a gear that isn’t perfect now, and later your gear for 32’s might not work either, though if you do buy a 44 tooth it probably would work because 43 tooth is usually what is wanted for 4.88 and 33’s.