Gears and lockers

[tristan6555]

Then do not undergear it.

Im trying to be sure not to. Im wanting to make sure I find the sweet spot between power and mpg. I know its not huge either way but I figure if I have time to research before I buy then why not look for perfection for what I want. Originally I was going for 4.10 and ive moved to 4.56 lol

 

[John Cooper]

Im trying to be sure not to. Im wanting to make sure I find the sweet spot between power and mpg. I know its not huge either way but I figure if I have time to research before I buy then why not look for perfection for what I want. Originally I was going for 4.10 and ive moved to 4.56 lol

Collectively you have been told 4.88 would be best, by folks who have been doing this for a while, listen to them.

Folks here have a tremendous amount of knowledge and don't mind sharing it listen to them.

 

[lumberjacklloyd]

This is not a collective opinion. 4.56 for 33" tires that have a ~31.5" rolling diameter. Sure, go 4.88 if it is a strict trail Jeep.

Stock Rubicon was ~2500RPM at 70, 4.56 with 33" tires puts you at 2650-2700; 1-200 RPM higher at hwy speed.

 

[97TJNM]

I live in the mountains, about 7k feet above sea level. 97 4.0, AX-15 with 4.88's and 35's. I take my jeep offroading, but also won't hesitate to jump in it and drive 5 hours to get to a trail or hunting spot. I can keep it at 75 on the interstate in the flats, but pulling a hill I have to downshift and im usually going 60-65 by the time I crest the hill. I should have 5.13's. Or even 5.38. I was really pleased with the regear, going from 3.07's on 31's to 4.88's on 35's, but after driving it for a bit, I realised that I left some performance on the table. I really should have gone deeper.

For 33's, 4.56 will be a huge improvement over what you have, and you'll probably be happy with it initially. It will wake it up a lot. But you'll be leaving some performance on the table. 4.88's would be a sweet spot for 33's, and will make you happier. And if you ever go to 35's, it won't be so bad that you'll want to regear immediately.

 

[John Cooper]

This is not a collective opinion. 4.56 for 33" tires that have a ~31.5" rolling diameter. Sure, go 4.88 if it is a strict trail Jeep.

Stock Rubicon was ~2500RPM at 70, 4.56 with 33" tires puts you at 2650-2700; 1-200 RPM higher at hwy speed.

I have a stock 06 Rubi with the automatic and 4.10 gears and 33's. I keep the overdrive turned off. Sure I can run down the interstate at 70mph and be right at 3000 rpm.

Saying all that, I have listened to the folks here that have been there and done this a lot more than I have and when I regear I'm going with 5.38. Why because one day I plan on 35 and that way I won't have to regear twice.

I am not looking for MPG, if I was i would drive a limp wristed prius.........

 

[jjvw]

This is not a collective opinion. 4.56 for 33" tires that have a ~31.5" rolling diameter. Sure, go 4.88 if it is a strict trail Jeep.

Stock Rubicon was ~2500RPM at 70, 4.56 with 33" tires puts you at 2650-2700; 1-200 RPM higher at hwy speed.

The stock Rubicon was a lot of things. But it was not ~2500 at 70.

245/75R16
42rle/29.75/4.10=2237rpm @ 70mph
NV3550/29.75/4.10=2366rpm @ 70mph
NSG370/29.75/4.10=2690rpm @ 70mph

All of these are undergeared from the factory.

Meanwhile, the early TJ with the 32rh was doing this...

225/75R15
32rh/28/3.73=3133rpm @ 70mph

 

[lBasket]

I wonder how much of these conversations partially stem from people that are afraid of RPMs in general and think 3-3.5k is "too high to be safe" for sustained highway cruising

 

[lumberjacklloyd]

The stock Rubicon was a lot of things. But it was not ~2500 at 70.

245/75R16
42rle/29.75/4.10=2237rpm @ 70mph
NV3550/29.75/4.10=2366rpm @ 70mph
NSG370/29.75/4.10=2690rpm @ 70mph

All of these are undergeared from the factory.

Meanwhile, the early TJ with the 32rh was doing this...

225/75R15
32rh/28/3.73=3133rpm @ 70mph

You just reference numbers all around 2500 RPM. 3.73 was optional and for "tow package". Makes sense....

Maybe some of you guys think you're hauling around a bigger load than you actually are.

The forum's own sticky has 4.56's with 5 speed. HERE

 

[jjvw]

3.73 was optional and for "tow package". Makes sense....

Maybe some of you guys think you're hauling around a bigger load than you actually are.

Ok. Tell us what each of the four combinations I posted are intended for. One was for towing. Also explain the reasoning for Jeep to offer the Rubicon with three different transmissions all with the same tire size and axle gearing.

 

[mrblaine]

This is not a collective opinion. 4.56 for 33" tires that have a ~31.5" rolling diameter. Sure, go 4.88 if it is a strict trail Jeep.

Stock Rubicon was ~2500RPM at 70, 4.56 with 33" tires puts you at 2650-2700; 1-200 RPM higher at hwy speed.

You just reference numbers all around 2500 RPM. 3.73 was optional and for "tow package". Makes sense....

Maybe some of you guys think you're hauling around a bigger load than you actually are.

The forum's own sticky has 4.56's with 5 speed. HERE

Or, maybe he was showing your MPH and giving the relative RPM around your chosen speed?

 

[lumberjacklloyd]

Or, maybe he was showing your MPH and giving the relative RPM around your chosen speed?

He absolutely did, which, happen to be numbers +/- ~200 from the 2500 RPM number I referenced.

Followed by "But it was not ~2500 at 70."

I fundamentally have no problem with 3k+ on the highway and am not chasing MPG, but the theory of this forum to get hwy cruise at peak torque (3000-3250) is a philosophy I have not seen followed anywhere else.

 

[lumberjacklloyd]

Ok. Tell us what each of the four combinations I posted are intended for. One was for towing. Also explain the reasoning for Jeep to offer the Rubicon with three different transmissions all with the same tire size and axle gearing.

Sounds like the other 3 are uses similar to most of us; general gearing for road/highway and offroad.

 

[mrblaine]

He absolutely did, which, happen to be numbers +/- ~200 from the 2500 RPM number I referenced.

Followed by "But it was not ~2500 at 70."

I fundamentally have no problem with 3k+ on the highway and am not chasing MPG, but the theory of this forum to get hwy cruise at peak torque (3000-3250) is a philosophy I have not seen followed anywhere else.

Maybe I'm daft, which of those are 2500 at 70?

 

[JMT]

but the theory of this forum to get hwy cruise at peak torque (3000-3250) is a philosophy I have not seen followed anywhere else.

Maybe you should get out more.

So you prefer to have inadequate power and continue to downshift to get the rpms you need to get up a wee little hill?

 

[John Cooper]

but the theory of this forum to get hwy cruise at peak torque (3000-3250) is a philosophy I have not seen followed anywhere else.

Could be because folks here understand what is going on.

 

[BlueC]

the theory of this forum to get hwy cruise at peak torque (3000-3250) is a philosophy I have not seen followed anywhere else.

Not to throw things out into the weeds further, but every Dodge with a Cummins that I've ever driven ran 70 just under the 1,500 RPM range. Ironically that's also where most were rated for peak torque. Seem like the Ford diesels did similar. I don't believe in coincidence.

 

[Apparition]

Not to throw things out into the weeds further, but every Dodge with a Cummins that I've ever driven ran 70 just under the 1,500 RPM range. Ironically that's also where most were rated for peak torque. Seem like the Ford diesels did similar. I don't believe in coincidence.

I asked AI

11

The ideal RPM for cruising at 70 mph varies by vehicle but typically falls between 2,000 and 4,000 RPM, with many modern passenger cars sitting in the 2,500–3,500 RPM range in their highest gear. Factors like the vehicle's engine, gearing, and driving conditions (like hills) will influence the exact RPM. The key is to be in the highest gear that allows the engine to operate smoothly without "lugging" or straining.

Factors that influence the ideal RPM

• Vehicle type: Motorcycles will have a much higher ideal RPM than cars.
  
  
• Engine and transmission:
  • A car with a 6-speed manual or modern automatic will likely be around 2,500 RPM.
    
    
  • Older cars or those with fewer gears might be higher, potentially 3,000–4,000 RPM or more, as noted in this Reddit thread.
    
    
  • Diesel engines generally have a lower optimal cruising RPM than gasoline engines.
    
• Driving conditions: Going uphill will require a higher RPM to maintain speed than driving on a flat road.
  

How to find your ideal RPM

• Check your tachometer: Look at the RPM gauge while at 70 mph in your highest gear.
  
  
• Listen to the engine: The engine should sound smooth and not strained. A good cruising RPM is one where you don't need to frequently downshift when encountering a slight incline.
  
  
• Test different gears: On a manual transmission, try shifting into the highest gear and see how the car handles 70 mph. If it feels sluggish or you have to push the accelerator hard, try a lower gear. If you are in a very low gear and the engine is racing loudly, try shifting up.

 

[Rickyd]

I wonder how much of these conversations partially stem from people that are afraid of RPMs in general and think 3-3.5k is "too high to be safe" for sustained highway cruising

Mixed with the myth that low rpm/high load in a heavy pig like the tj is going to get you good mpg's and it's a recipe for these threads to always wind up like this

 

[GoldenGorilla]

I am not looking for MPG, if I was i would drive a limp wristed prius.........

A 2025 Prius does 0-60 in 7.2 seconds. An 06 Wrangler with an auto did 11-12 seconds stock when the magazines tested them. You might want to have some basic facts about the mighty TJ. The Wrangler has long had a reputation for attracting a certain demographic of owners. Kinda like Subaru. Just sayin.

 

[John Cooper]

A 2025 Prius does 0-60 in 7.2 seconds. An 06 Wrangler with an auto did 11-12 seconds stock when the magazines tested them. You might want to have some basic facts about the mighty TJ. The Wrangler has long had a reputation for attracting a certain demographic of owners. Kinda like Subaru. Just sayin.

I don't care if a prius could beat a top fuel dragster, I won't drive one, just like I won't drive a Subaru......