Performance impact of 35s with Rubicon 4.10 gears

R00STER

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You want 6th to be efficient, not powerful. Who cares if you have to occasionally downshift climbing mountains or passing, isn’t that part of the fun of rowing your own gears.
I agree to a point, and thats why Jeep did this (for cafe standards), but the downshifting isn't occasional. More shifting = more wear, and less shifting = more lugging of the engine. Its not ideal setup from the factory. This is a 4 spd with 2 overdrives.

@AVGeek99 - since you want real life performance check out the following videos I took. Here are the variables for this run:

  • Vehicle : 2021 JLUR 3.6 6sp (stock wuth no rocksliders)
  • Rearend : 4.10
  • Tires : Stock wheels with KO2s (33s)
  • Gas Level : ~1.5 gallons
  • Cargo : none
  • Passengers : 1 x 230 lbs (I'm working on it :blush:)
  • Head wind : none
  • Tail wind : none
  • Starting Conditions : In gear at 70 mph
  • Testing conditions : instant full throttle held till end of video (watch GPM gauge for transition ~5 secs into each video)
  • Grade (for hill testing) : 2% per Offroad page

The following videos were conducted on flat pavement, in 5th and 6th (respectively):

5th gear - Flat
6th gear - Flat

The following videos were conducted on a 2% grade, in 5th and 6th (respectively):

5th gear - 2% incline
6th gear - 2% incline

Sorry for the camera shake, I braced off the steering wheel and i was driving on shitty Illinois roads......the state that diverts tax payer money away from roads and into slush funds for their democratic supporters....there is a reason 4 of our past 6 recent govenors spent time in jail (and the current one probably should).

Hope this helps with your decision.
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AVGeek99

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Thank you all for your replies. And @ROOSTER thanks for the videos. @omnitonic , after I posted my thread I noticed yours and a few others in the "Similar Threads" below.

This is the type of anecdotal info I was looking for. Will it hold speed at 70-85 on the interstate, most of the time. I would never expect it to going up western mountain passes. But what is it like in non mountain areas. It sounds like 6th may be useable if it's not too windy. No worse and maybe a little better than my JKU Sahara when it had stock 3.21s.

Disappointing that the 6spd in the JL is geared so much higher than the JK. Of course for EPA fuel efficiency ratings, but why not offer 4:56s or 4:88s as an option. Most are going to stick with stock anyway. I would have gone for the XR package if it was available with a 6spd.

Oh well, I'm sure I'll be happy. If it's that bad I'll just change the order of upgrade path and do new gears before lift or bumpers/winch.
 
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supermike

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8 speed ? not much difference, but since you had a 6 speed manual, YES, VERY.

With stock 33 you can start from 2nd gear without adding gas. 35 1st gear, or you have to ridding That clutch. On 241, I-15, I-5 Cajon pass, Tejon pass, I was able to accelerating slowly in 4th gear uphill going 75+ mph. After 35 in ko2, I’m bleeding off speed full throttle in 4th. Before 35 in tire I had never used 5th gear, always skip it, but after, the 5th will be your new 6th.

Is it drivable and liveable? Yes, but forgot anything about accelerating. SLOW AF.
 
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AVGeek99

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The problem is he's asking for anecdotal evidence. With vague questions like "hills" or "wind".

How steep are these hills? How windy is this wind? How many people are in the car? Is it loaded up with gear?

What is fast? What is slow?

Blah blah blah...

We already know it's going to be slower. He does too. These questions are too vague to be helpful.

Shoots 🤙🤙
I apologize for not being more specific in my question. 6th gear is purely intended to be overdrive. I would never expect it to accelerate quickly in 6th regardless of tire size. I would also expect 6th to be pretty useless on hills that most would consider steep.

I guess I could have explicitly asked "will it hold speed (70-85mph) with light headwinds (10-15mph or less) on normal interstate (non "steep grade") hills.

I do like the gear ratio tools and dyno charts, but I'm not enough of a gear head to know when it will have enough power to hold speed at certain RPM levels. According to the Gear Ratio calc tools 35" tires with 4.10 gears at 2500rpm will result in a speed of 86mph. Ok, but does it have enough power to hold 2500rpm with 35" tires?

My wheels and tires will be XD137 FMJs 20x9 ET0 with Cooper Discoverer STT Pros 35x12.5 R20.

The only thing I have to compare too right now is my JK and my memory of what it was like when it had the stock 3.21s. It would barely do 80mph. Granted 3.21s is a LOT higher than 4.10s, the JK 6spd is geared lower than the JL, but not that much lower. Knowing this I expect the JLUR with 35s won't be as bad as my JKU Sahara on stock 3.21s, but is 6th gear on a JLUR useable as a pure overdrive in the real world, or will it not hold speed in most cases?
 
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AVGeek99

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Depends on weight of tire and if you’re using stock wheels or heavy aftermarket ones , but you lose performance no matter what. If it’s a 35” KO2 (AT) it’ll be (significantly) less noticeable than say a 35” Nitto (hybrid or MT).
My wheels and tires will be XD137 FMJs 20x9 ET0 with Cooper Discoverer STT Pros 35x12.5 R20.
 
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AVGeek99

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Technically you wont notice ANY difference. You wont have anything to compare it to since you will be driving it from the dealer with 35s already on. Just sayin😁
Well I'll have my JK to compare too. I don't expect it to keep up with my JK on 4.56s, but really just wondering if 6th gear will be useable or will I more or less be relegated to a 5spd until I regear? Based on the responses, it sounds like MMMV, pun intended.
 
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AVGeek99

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I have a thread I am too lazy to look up, where I thrashed this question to death in the context of my own build. I basically concluded that if I already had 4.10 gears, I would probably do nothing.

Since having that discussion, I threw the 35s on my Jeep, and it still has the stock 3.45 gears for the time being. I am most definitely looking forward to the day I drive away on my new 4.56 gears, but it's not THAT bad on the 3.45s. It's not good, but it's not THAT bad.

I definitely still feel like if I already had 4.10 gears, I would just skip the complication and expense of regearing. I could almost certainly live with 4.10 gears. I could just about live with 3.45 gears if I really had to, but luckily I don't.

Your experience sounds a lot like my JKU Sahara when I was running 35s with the stock 3.21s. It was acceptable for daily driving, but it was slow. Mine was bad enough that I wondered if I'd be able to get around on the hills of Duluth, MN. If you've never been, hills as steep as San Francisco streets, but not as big.
 
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AVGeek99

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AVGeek99

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You want 6th to be efficient, not powerful. Who cares if you have to occasionally downshift climbing mountains or passing, isn’t that part of the fun of rowing your own gears.
Yes 6th gear is supposed to be for efficiency. However if the vehicle doesn't have enough power to hold speed very well, then you are giving it more throttle just to hold speed and using more gas.

I discovered this with my JK before regearing. On the interstate I would get better mileage @75mph in 5th gear than in 6th. In fifth, the engine was turning enough RPMs to easily hold 75. In 6th I had to more or less keep it floored just to hold 75, and if there was any incline it wouldn't even hold 75. It was a difference of 4-5mpg.
 

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I had 39’s on the 4.10 gears for a bit. I even wheeled it. I will say it is totally doable. It did become a 4 speed for my particular usage (no interstate). But here’s the long answer:
If you have plans to do a locker or axle upgrade later, you will be fine to wait and do it all at once. No point regearing now, then paying for upgraded axles that come with the “correct” gears later. Also, not worth doing labor on an axle twice. If you had to save to do a locker and gearing at once, 4.10’s would be fine until you could do it all at once.
That being said, if you’re sticking with the D44’s and not doing future upgrades like trussing or anything, and budget isn’t a constraint then a regear seems smart. I would recommend you drive it a while on 35’s though. It might surprise you. I jumped to 5.13’s and don’t understand how people run this gearing on 37’s. My 39’s hit 6th gear around 55 mph. I usually wait until 60 to put it in 6th though.
 

BuyHold

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I have 35in Nitto Trail Grapplers on my 6sp 2door Rubicon. These tires are heavy AF.

My experience is that 4.10s are completely acceptable on road and off-road. Around town is fine though starts are a little more sluggish than with the 33s (obviously). I use 6th on flats ~70mph but as you already suspect, I am not passing people on freeway in 6th with a setup like this. The biggest drawback of this setup is actually reverse. Reverse gear is very tall and I find myself feathering clutch much more, especially backing up hills and/or immediately after starting car, engine is cold, and idle RPMs are still high.

If you gave me a factory option to get shorter gearing then I would with out question option my vehicle with it (total hypothetical here since this isn't an option... unless we are talking about Rubicon XR). 4.10s on 35s is not performance focused gearing but as I said, completely acceptable and I still completely love my manual.
 

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The point @BuyHold made about reverse is something I forgot about and is very on-point. Reverse is amazing for me now that I’m in 5.13’s, almost normal even.
Reverse on 4.88’s is still too tall.

I love my Jeep with the new gears and highly recommend it for 35’s. I’m spinning higher on the highway and still downshift to pass, but it’s so much more “right” now. Was well worth it for me. /.02
 

BuyHold

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Reverse on 4.88’s is still too tall.

I love my Jeep with the new gears and highly recommend it for 35’s. I’m spinning higher on the highway and still downshift to pass, but it’s so much more “right” now. Was well worth it for me. /.02
With 35s, sounds like 4.88s on manuals is the sweet spot for people who highway and trail their Jeeps. Correct me if I am wrong but you seem to be very pleased with your 4.88s/35tires/MT, Yeah?

I would also go as far to say that 4.56s is gearing Jeep should have in the standard MT Rubicon and 4.10s in all the lower trim MTs.
 
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