Question about gearing with Rubicon 4.10s, calculation?

[KDR83]

Can someone explain to me what I am doing incorrectly? If a Rubicon has 4.10 gears and comes 33 inch tires. Once you put on 37, that is essentially like having 3.66 gears with 33s which I don't think is terrible. And then I ran the calculation again which shows 3.66 gears on 33s would be like 3.77 gears with 32s. Considering Sports and Saharas have 3.45 gears, why is it so good to regear? Wouldn't the 6 speed manual and the 8 speed auto still be at a higher rpm at any given speed with 37s than a stock Sport or Sahara on stock 32s? Is it simply the weight that kills it when you go that big? Am I doing the math incorrectly?

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[Peanut Butter]

Your calculations aren’t considering for actual tire size. So, there’s some discrepancy in the math. Also, yes weight does add into the consideration.

Third, I have a manual with 37s and stock gears. I plan on upgrading to 4.88 gears. It does surprisingly fine on road. It’s an absolute pig starting uphill and at slow speeds in 4h. 4L is ok, but The trq at low speed is significant between the 37s and 33s.

 

[rustyshakelford]

Your calculations aren’t considering for actual tire size. So, there’s some discrepancy in the math. Also, yes weight does add into the consideration.

Third, I have a manual with 37s and stock gears. I plan on upgrading to 4.88 gears. It does surprisingly fine on road. It’s an absolute pig starting uphill and at slow speeds in 4h. 4L is ok, but The trq at low speed is significant between the 37s and 33s.

We have that combo but with 5.13s. Love it. If we had an auto the 4.88s would be perfect. We’re around 2450 at 70 and average 16-18 mpg

Brett

 

[KDR83]

Ye

Your calculations aren’t considering for actual tire size. So, there’s some discrepancy in the math. Also, yes weight does add into the consideration.

Third, I have a manual with 37s and stock gears. I plan on upgrading to 4.88 gears. It does surprisingly fine on road. It’s an absolute pig starting uphill and at slow speeds in 4h. 4L is ok, but The trq at low speed is significant between the 37s and 33s.

I realize 33s are sometimes 32s but same way 37s are usually closer to 36s. The 0.5 inches one way or another doesn't really move the needle all that much. So in theory or I guess actuality a stock Rubicon with 37s is still geared more aggressively than a Sport or Sahara are and is spinning at a higher rpm going 75 in a 6 speed Rubicon with 37s than a stock Sport with 32s? But with all the weight you want to be in even higher power band a stock non Rubicon. .

I live in Florida barely hills to speak of except bridges so wondering how necessary it will be for me. I am leaning towards a 6 speed Rubicon

 

[Peanut Butter]

We have that combo but with 5.13s. Love it. If we had an auto the 4.88s would be perfect. We’re around 2450 at 70 and average 16-18 mpg

Brett

Thanks. If I’m perfectly honest with myself, I’m still a little on the fence about the 5.13 vs 4.88. Though, I’m leaning heavily towards the 4.88s. Local offroad shop, jeep club guy and dealership all recommended 4.88s. And, I’m about 98% sure I’m not going bigger than 37s.

I spend most of my onroad time at 45mph, not 70. So, I’m not as concerned about highway RPMs. And, for top speed, I’d have no problem using 5th (+1 for 4.88). I used 5th most of the time @ 70 (stock) as 6th netted the same MPG. Figured, might as well have more power.

My biggest concern with 5.13s is 4L being too low. Since we can’t engage the lockers in 4H, how does 4L do when you’re not crawling? Cruising in 5th at 15 mph between obstacles?

 

[rustyshakelford]

Thanks. If I’m perfectly honest with myself, I’m still a little on the fence about the 5.13 vs 4.88. Though, I’m leaning heavily towards the 4.88s. Local offroad shop, jeep club guy and dealership all recommended 4.88s. And, I’m about 98% sure I’m not going bigger than 37s.

I spend most of my onroad time at 45mph, not 70. So, I’m not as concerned about highway RPMs. And, for top speed, I’d have no problem using 5th (+1 for 4.88). I used 5th most of the time @ 70 (stock) as 6th netted the same MPG. Figured, might as well have more power.

My biggest concern with 5.13s is 4L being too low. Since we can’t engage the lockers in 4H, how does 4L do when you’re not crawling? Cruising in 5th at 15 mph between obstacles?

What we have found so far is there is very little experience with the JL gears especially the new ratios with the manual trans. We wheel ours and it’s pretty heavy with full skids and adding armor as we go. We didn’t find the 5.13s to be a problem at all. Worst case just grab another gear and send it. If you were a highway cruiser and liked to go fast the 4.88s might fit better. I tend to drive around 65 and love the power in 6th.

If you’re considering going bigger than 37s that even more reason to look into the 5.13s more. Wish you were closer and I’d let you try it out.

Brett

 

[Peanut Butter]

Ye


I realize 33s are sometimes 32s but same way 37s are usually closer to 36s. The 0.5 inches one way or another doesn't really move the needle all that much. So in theory or I guess actuality a stock Rubicon with 37s is still geared more aggressively than a Sport or Sahara are and is spinning at a higher rpm going 75 in a 6 speed Rubicon with 37s than a stock Sport with 32s? But with all the weight you want to be in even higher power band a stock non Rubicon. .

I live in Florida barely hills to speak of except bridges so wondering how necessary it will be for me. I am leaning towards a 6 speed Rubicon

With trying to not sound snotty, I’m not going to do the calculations to get the exact numbers. But the difference in circumfrence is different between 32/33 and 36/37. (Which is also not correct because my 37s measure at 35.75” at 30 PSI.) I don’t believe the math would be linear. I don’t believe your statement is giving enough credit for the relatively small numbers. And, I was replying to the 1st part of your comment in asking what’s wrong. As a matter of theory, your math is at best incomplete.

However, practically speaking, I would put 37s and not regear if I was driving onroad in FL. I didn’t use 6th much when it was stock. I never use it now (with 37s). You can always regear later if you don’t like it.

From my experience it’s absolutly fine for driving around town (even driving onroad to the mountains). I am only going to regear for Offroad performance.

 

[Peanut Butter]

What we have found so far is there is very little experience with the JL gears especially the new ratios with the manual trans. We wheel ours and it’s pretty heavy with full skids and adding armor as we go. We didn’t find the 5.13s to be a problem at all. Worst case just grab another gear and send it. If you were a highway cruiser and liked to go fast the 4.88s might fit better. I tend to drive around 65 and love the power in 6th.

If you’re considering going bigger than 37s that even more reason to look into the 5.13s more. Wish you were closer and I’d let you try it out.

Brett

That’s great info. Thank you! I wish I was closer too. I’d absolutely take you up on your offer and have your shop install. Thanks for being involved in the forum and willing to share.

 

[KDR83]

With trying to not sound snotty, I’m not going to do the calculations to get the exact numbers. But the difference in circumfrence is different between 32/33 and 36/37. (Which is also not correct because my 37s measure at 35.75” at 30 PSI.) I don’t believe the math would be linear. I don’t believe your statement is giving enough credit for the relatively small numbers. And, I was replying to the 1st part of your comment in asking what’s wrong. As a matter of theory, your math is at best incomplete.

However, practically speaking, I would put 37s and not regear if I was driving onroad in FL. I didn’t use 6th much when it was stock. I never use it now (with 37s). You can always regear later if you don’t like it.

From my experience it’s absolutly fine for driving around town (even driving onroad to the mountains). I am only going to regear for Offroad performance.

Not snotty at all, I guess what I am saying is that even if you are comparing to the tire being actually closer to 32 inches on a factory Rubicon and the 37 inch tire is a real 37. The calculation would still put the theoretical gear ratio as more aggressive than a stock Sport or Sahara on stock 32s. Even if it lowers it a bit, it won't go down from my calculation of 3.77 to 3.45 or below. You would still be at a higher RPM. But yes I get that it is not just gearing, you have to factor in probably like 20+lbs of unsprung weight at each corner and crappier aero due to the lift from tires plus presumed lift to fit the tires under the car. I guess I just need to do it and see how I like it. Since I am leaning towards a 6 speed, even if I regear my all in would be probably right at the price of an auto or just below and feel it would be better to have a properly geared 6 speed than a too low of a geared auto.

 

[rustyshakelford]

Not snotty at all, I guess what I am saying is that even if you are comparing to the tire being actually closer to 32 inches on a factory Rubicon and the 37 inch tire is a real 37. The calculation would still put the theoretical gear ratio as more aggressive than a stock Sport or Sahara on stock 32s. Even if it lowers it a bit, it won't go down from my calculation of 3.77 to 3.45 or below. You would still be at a higher RPM. But yes I get that it is not just gearing, you have to factor in probably like 20+lbs of unsprung weight at each corner and crappier aero due to the lift from tires plus presumed lift to fit the tires under the car. I guess I just need to do it and see how I like it. Since I am leaning towards a 6 speed, even if I regear my all in would be probably right at the price of an auto or just below and feel it would be better to have a properly geared 6 speed than a too low of a geared auto.

37s, 4.10s and a 6 speed is a terrible combination for daily driving and driving off road. You’ll just about lose 6th gear unless you’re going down hill or very level road. The off the line acceleration is reduced. I ordered my wife a JL with an auto and we might leave the gears alone. Depends on how it drives with the 37s and what she wants to do. Theoretical is just that, a fancy guess. When we ran the numbers for ours I think it put my rpms at 70 around 2300. We’re every bit of 2450. Doesn’t seem like much but it’s a decent spread.

We love our 6 speed but if I ordered it again, it would be an auto too. It is just so easy off road and for daily driving. The 8 speed nailed it

Brett

 

[ChattVol]

37s, 4.10s and a 6 speed is a terrible combination for daily driving and driving off road. You’ll just about lose 6th gear unless you’re going down hill or very level road. The off the line acceleration is reduced. I ordered my wife a JL with an auto and we might leave the gears alone. Depends on how it drives with the 37s and what she wants to do. Theoretical is just that, a fancy guess. When we ran the numbers for ours I think it put my rpms at 70 around 2300. We’re every bit of 2450. Doesn’t seem like much but it’s a decent spread.

We love our 6 speed but if I ordered it again, it would be an auto too. It is just so easy off road and for daily driving. The 8 speed nailed it

Brett

Agreed 100% about preferring an automatic offroad. I went offroading with my 6 speed twice last wknd and rode in backseat of Litebrite's jeep with an automatic all afternoon on Saturday doing tough trails. It was amazing to see how much easier the automatic was to control offroad not having to fool with the clutch in tight spots....night and day difference. I've always been a purist and felt a proper jeep required a manual, but not anymore. The automatic is a gamechanger.

 

[LLRubylady]

put 35 ridge grapplers on my rubicon and it’s a slow pig.

Have new rims ready to go back to stock. Hubby said I could regear if I want.
I just don’t know if I want to spend the coin.
And then of course if I have issues down the road my warranty is out the door.
If you don’t wheel is it worth spending to regear just to keep the look of 2 inches more tire?

 

[ChattVol]

put 35 ridge grapplers on my rubicon and it’s a slow pig.

Have new rims ready to go back to stock. Hubby said I could regear if I want.
I just don’t know if I want to spend the coin.
And then of course if I have issues down the road my warranty is out the door.
If you don’t wheel is it worth spending to regear just to keep the look of 2 inches more tire?

have you sold your nittos?

 

[LLRubylady]

have you sold your nittos?

Not yet. I’m supposed to have my tires changed tomorrow.

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