Is this guy full of it?
- Thread starter Mrprez
- Start date
The IsARubicon
TJ Enthusiast
Geeze, you guys are tough! Making me think twice before spamming my videos here!
I think it’s because people are easily influenced when presented with an opinion video format. It’s a little more work to pour through forums with knowledge from actual experts than watch a quick vid!
Also as a side note, I think you videos are awesome and you earned another sub tonight!
I thought 3.55s and 33s were pretty good for what I did. Didn't have any complaints. Then I put in a rear axle with 4.56 and good lord, it was like driving a whole new vehicle. I had a ton of get up and go and could maintain speed on inclines. People really don't know what they are missing when they don't regear
I didn't watch it after reading part of the thread but... the notion of building a Jeep for on road is in line with having a penis that isn't for women.
99.9% of the Jeeps here are on-road Jeeps with varying levels of modifications to do weekend off-roading. My neighbor just bought a set of 35" tires to make his Jeep better around town because it was too set up for off-roading and he couldn't use it as much. He trailers it to trails.
Gearing is a system. Rear gears are one of the gear ratios in the compound gear system from engine to rear axle.
Depending on what I want to do, I may be better off replacing transfer case's 2.7:1 gearing with 4.0:1 by replacing the transfer case so I have better 4-lo gearing, than I would be by re-gearing the axles. My six speed manual gives me a 4.46 1st gear compared to the 2.8 range in some of the Automatics.
So gearing is not as simple as gearing the axles. There's enough variation in transmission gearing throughout the years of production that I'd want to calculate my own compound gear ratio and line it up with engine RPM power/torque curves for various on and off road applications rather than rely on random numbers posted on the interwebs.
Gearing is a system. Rear gears are one of the gear ratios in the compound gear system from engine to rear axle.
Depending on what I want to do, I may be better off replacing transfer case's 2.7:1 gearing with 4.0:1 by replacing the transfer case so I have better 4-lo gearing, than I would be by re-gearing the axles. My six speed manual gives me a 4.46 1st gear compared to the 2.8 range in some of the Automatics.
So gearing is not as simple as gearing the axles. There's enough variation in transmission gearing throughout the years of production that I'd want to calculate my own compound gear ratio and line it up with engine RPM power/torque curves for various on and off road applications rather than rely on random numbers posted on the interwebs.
How does the transfer case gearing play a role in highway driving?
The good news is that once you can set your goal on a particular rpm at a given speed and you can wrap your head around the final drive ratio, things become a whole lot less random.
None if each transfer case is 1:1 in high.
But highway and off road and in town are different operating cases with the optimal gearing for each likely being different. So you have to look at what you want from the vehicle and the gearing you have in the transmission, transfer case, and differentials to come up with a good compromise.
Jeep engineers probably did this when they came up with 4.10 gearing in the Rubicons. The optimum gearing when you take on-road, off-road, highway, town, automatic, manual transmissions, and TJ vs Unlimited into account. They likely decided the rear gearing as a compromise on those variables and adjusted its true off road capabilities with the transfer case low range and lockers.
The 6 speed manual has gearing that's likely fine with 3.73 differentials and the automatic could have used something greater; but it's cheaper to standardize between the automatic and manual transmissions. The transfer case and lockers probably make a much larger difference to it's off-roading capabilities then 3.73 to 4.1 differential gearing. The 4.1 gear ratio was picked simply because it was a decent compromise between road and off road, manual and automatic performance for a 4.0L inline 6 engine.
So when looking at upgrades people should look at what their system currently has in it and the main operating scenarios they want to emphasize. Tire size is only one variable and may not be the right one. 4.2L/4.0L/2.4L/2.5L/V8swap/diesel, transmission, transfer case, rear differential, tire size, lift, typical use, parts availability, etc., etc. all play into it.
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Since you've made it both vague and complicated, what should a guy do with 35s, 4.0 and a 5 speed for a do it all TJ? How about a similar build with the 4 speed auto?
OP
I think that would be a great topic. I was thinking about this very thing the past few days. Given a stock TJ in good condition frame-wise and mechanically fit, what would be the path to a good all around vehicle that you could drive to the trailhead, air down, pop the sway bar links and have a day of fun.
I'd build a spreadsheet full of calculations. But that's because I'm an engineer and I do that sort of thing all the time when I'm designing systems. If they are overly complex, I have to use specialized software to take all the variables into account.
I drive a 6 speed manual because it allows me to play with the overall gear ratio from engine to ground on the fly. I can go the same speed at 3000 RPM or 2000 RPM by controlling the shift point myself. Over time, I instinctively get a feel for what I believe is the best performance vs efficiency shifting and I can adjust based on what I want to accomplish. With a manual transmission in these older vehicles you don't have that flexibility. However, many new automatics allow the driver to override the computer shift points and electronically "manually" shift the vehicle. I liked that option on my last vehicle and used it all the time in winter driving or when towing.
If I built a spreadsheet it would probably start with speed then tire radius from axle to ground (compressed tire), rear differential to drive shaft, transfer case gearing, transmission gearing, engine RPM. Then I would take the power, torque, efficiency design curve for my specific year 4.0L engine and estimate the numbers at the given RPM. I'd have to take into account my manual transmission can overlap speeds at different RPM levels unlike the automatic which is computer controlled for specific engine RPMs (likely shifting to maintain engine RPMs at closer to peak efficiency).
Then I'd play with the rear gearing making sure not get on the wrong side of the curves throughout my operating ranges. If you're at a certain RPM were the curve flattens out, you'll get a lower HP and/or Torque response by adding gas to increase engine RPM. Anything over 4000 rpm on the 4L is probably a waste and getting you close to the back side of the peaks on the engine HP/Torque curves.
The numbers can be worked both directions so they probably should be. This assumes no wind forces, weight changes, etc. I'm sure the engineers took all that into account also.
If I was building a rig that never saw the interstate it would simplify the calculations considerably and could make me choose completely different gearing as top speed becomes less of a concern. The calculations can be re-done to change transmissions and transfer cases and determine which alternative may be the best option. If I ran across a used transmission that fit the profile better, that may be a cheaper option than axle work. Transfer cases, likewise, if it keeps everything the same except the gearing in 4lo.
With my current setup I'm running around 2,500 rpm in 6th gear at 70-75 mph which puts me at a good spot on the torque/power curve. It's likely why I feel I have enough left to pass people. If I rev the engine past 4500 rpm I'm falling off the curve and would accelerate faster by letting off the gas a little.
I drive a 6 speed manual because it allows me to play with the overall gear ratio from engine to ground on the fly. I can go the same speed at 3000 RPM or 2000 RPM by controlling the shift point myself. Over time, I instinctively get a feel for what I believe is the best performance vs efficiency shifting and I can adjust based on what I want to accomplish. With a manual transmission in these older vehicles you don't have that flexibility. However, many new automatics allow the driver to override the computer shift points and electronically "manually" shift the vehicle. I liked that option on my last vehicle and used it all the time in winter driving or when towing.
If I built a spreadsheet it would probably start with speed then tire radius from axle to ground (compressed tire), rear differential to drive shaft, transfer case gearing, transmission gearing, engine RPM. Then I would take the power, torque, efficiency design curve for my specific year 4.0L engine and estimate the numbers at the given RPM. I'd have to take into account my manual transmission can overlap speeds at different RPM levels unlike the automatic which is computer controlled for specific engine RPMs (likely shifting to maintain engine RPMs at closer to peak efficiency).
Then I'd play with the rear gearing making sure not get on the wrong side of the curves throughout my operating ranges. If you're at a certain RPM were the curve flattens out, you'll get a lower HP and/or Torque response by adding gas to increase engine RPM. Anything over 4000 rpm on the 4L is probably a waste and getting you close to the back side of the peaks on the engine HP/Torque curves.
The numbers can be worked both directions so they probably should be. This assumes no wind forces, weight changes, etc. I'm sure the engineers took all that into account also.
If I was building a rig that never saw the interstate it would simplify the calculations considerably and could make me choose completely different gearing as top speed becomes less of a concern. The calculations can be re-done to change transmissions and transfer cases and determine which alternative may be the best option. If I ran across a used transmission that fit the profile better, that may be a cheaper option than axle work. Transfer cases, likewise, if it keeps everything the same except the gearing in 4lo.
With my current setup I'm running around 2,500 rpm in 6th gear at 70-75 mph which puts me at a good spot on the torque/power curve. It's likely why I feel I have enough left to pass people. If I rev the engine past 4500 rpm I'm falling off the curve and would accelerate faster by letting off the gas a little.
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One thing about driving a stick is you can get a feel where you are on the Torque/HP curve and use it to your advantage at various speeds or operating scenarios. I've been driving this one since September and I'm still learning it.
And I can warm up my engine faster in the winter running it at a higher RPM at first.
And I can warm up my engine faster in the winter running it at a higher RPM at first.
Wildjeeper
New Member
