Gas milage and drivability of 4.10 Rubicon gearing vs 3.45 Sport gearing

[CantThinkOfAHandle]

Don't want to nitpick, but you're mixing terminology and it may be confusing to some. The ZF 8-speed in your BMW is a conventional automatic with a planetary gearset and a fluid-based torque converter (it does not contain a friction-based clutch). The same as the automatic offered in the JL.

DCT's employ constant-mesh gearsets (similar to a manual transmission) and then 2 wet (or dry) friction clutches. There were single-clutch semiautomatic transmissions in the early 2000's (mostly in exotics and high-performance vehicles), but these have since fallen out of favor.

For off-pavement purposes, I find it nice to have a torque converter to soak up driveline shock from jumpy throttle application. That's the one thing I don't like about driving manual Jeeps on faster washboard dirt roads.

Sorry. There were some posts wondering if the JL auto might have a dual clutch, and disappointment to learn it does not. (I hope I got that right.) I posted merely to comment that DCTs seem to be falling out of favor, and also that I liked the ZF in my BMW. I have no idea why I referred to it as having a single clutch. Can I blame a head cold? Thanks for correcting my error.

And thanks also for relating your experiences with manual and auto Jeeps on dirt roads, since I use back roads a lot. In countless hundreds of miles driving dirt roads, I've never navigated them with an auto, and have worried I might miss engine braking with an auto Jeep. I assume that has not been a problem for you? You don't let your foot off the gas in advance of sharp corners and find yourself hurtling into the abyss?

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[Direwolf]

Sorry. There were some posts wondering if the JL auto might have a dual clutch, and disappointment to learn it does not. (I hope I got that right.) I posted merely to comment that DCTs seem to be falling out of favor, and also that I liked the ZF in my BMW. I have no idea why I referred to it as having a single clutch. Can I blame a head cold? Thanks for correcting my error.

And thanks also for relating your experiences with manual and auto Jeeps on dirt roads, since I use back roads a lot. In countless hundreds of miles driving dirt roads, I've never navigated them with an auto, and have worried I might miss engine braking with an auto Jeep. I assume that has not been a problem for you? You don't let your foot off the gas in advance of sharp corners and find yourself hurtling into the abyss?

My personal Jeeps have all been manual, but I've driven a friend's automatic JKU and various automatic JK/JKU's in Hawaii as rentals. The JK's 5-speed auto allowed for the selection of a maximum gear and it would not exceed that gear to provide engine braking. It would still downshift as necessary to prevent lugging the engine. Admittedly, I have no experience in 4-LO or rock crawling with the automatic, but the system worked flawlessly on some pretty steep grades in 2WD or 4-HI.

The JL is the 1st time I'm considering an automatic Jeep. The auto has more ratios this time around and I never was a huge fan of the old 6-speed in the JK. Ultimately, I'll have to testdrive both in my preferred axle ratio and decide if I want to spend the $2k or not.

 

[ResponsibleAdult]

It is hard to say, I would think it would be fairly close, within 1 MPG either way. There are just too many factors that are to be considered. The tire selection itself can make 1-2 mpg difference, as can the gear you are driving in. I know it sounds counter intuitive but lower RPM does not always equal better MPG. When I had one of my lifted TJ's I got better gas mileage on the interstate in 4th than I did in 5th. I assume because even though the engine RPM's were higher the motor was not "working" as hard in 4th.

Another thing to consider is who cares... I remember I was at a dealer several years ago and some guy came up looking at a Hummer H2 and asked about the MPG's, and the salesman just laughed and said if you have to ask you shouldn't even consider it. My point is that a Rubicon is the most capable stock vehicle made on this planet, so you either want that or you do not. It will not ride quite as nice as a sport and will have louder tires, and larger tires which can be more difficult to handle, but at the end of the day you either want the most capable off road vehicle on the market and you are willing to put up with some small quirks or you don't. I would tend to say if you have to ask, go with the sport.

With that said it would be great to take a stock Sahara, Sport and Rubicon out and see what the real world differences truly are though.

Sitting here in the land of freezing rain and snow, I tend to think more rubber on the road is always a good thing. I’m what ways are the larger tires more difficult to handle?

 

[DanW]

Man, I love this forum. It has been a Godsend for not only all the info, but for the LOONNNGGGG wait for our JL's. The topics go all over the place, and they are fascinating. This is a great way to kill time while waiting for our Jeeps! I learn so much from all of you!

On the tire width, my JKUR has tall, narrow tires. The narrow tires have demonstrated great traction in all kinds of terrain, and shockingly, even do quite well in sand dunes! They don't look as cool as wider tires, but they've been through some incredibly tough terrain, from mud to sand to the rocks of Moab, and they've performed exceptionally well everywhere, while not killing my mileage on the highway. Rolling resistance is important, but at highway speeds, aero resistance is a much bigger deal. My JKU's tires, btw, are 255/80/17 BF Goodrich KM2's. I've been completely impressed with them, and would put another set on right now, if I wasn't going to have 5 brand new KO2's off my JLUR, when I go to the 35's.

 

[liquids]

Sorry for getting people on the wrong track with the dual clutch assumption. (Although it did turn into an interesting discussion!) I just assumed that with the claimed mpg improvement it must have been a DCT.

Regarding borrowing money at 3% to invest at 6%: You can make a decent argument that loans the size of a car are a stable bet, but do you do that with a loan the size of your home? One could argue that the housing crisis, which triggered the great repression (recession/depression with no one wanting to believe it was actually happening), was caused by too many people borrowing on the assumption that their investments were sound and growing in value.

 

[wanderer]

For off-pavement purposes, I find it nice to have a torque converter to soak up driveline shock from jumpy throttle application. That's the one thing I don't like about driving manual Jeeps on faster washboard dirt roads.[/QUOTE]

please explain this more about the manual. I am going in that direction but I haven't driven a manual for a while.

 

[wanderer]

The JL is the 1st time I'm considering an automatic Jeep. The auto has more ratios this time around and I never was a huge fan of the old 6-speed in the JK. Ultimately, I'll have to testdrive both in my preferred axle ratio and decide if I want to spend the $2k or not.[/QUOTE]

Me the exact opposite I am going 6 sp manual. Kind of wondering about mileage, but cosnsidering I am in the 12 range on a 2008 jeep 4-dr rubicon with the 4 spd auto and 315-70-17 tires. Thinking about going to a similar size tire right off the bat or maybe swapping to the 34-10.50. So what do you guys think of that idea?

 

[The_Phew]

Regarding borrowing money at 3% to invest at 6%: You can make a decent argument that loans the size of a car are a stable bet, but do you do that with a loan the size of your home? One could argue that the housing crisis, which triggered the great repression (recession/depression with no one wanting to believe it was actually happening), was caused by too many people borrowing on the assumption that their investments were sound and growing in value.

I was talking about investing in the S&P 500, a diversified basket of the strongest companies in the world. Borrowing to 'invest' in a single family home is and was a very risky proposition.

 

[Martindfletcher]

Not entirely sure this is the case. In the cycling world, pros (and avid racers like me) have gone from 21mm tyres to 23mm and even 25mm tyres in recent years as they have proven to have much less rolling resistance. And it's a big deal on a bike when you are pushing the pedals yourself for a 100 miles
Again, don't claim to be car tyre engineer but thought I'd toss that in. I'm still likely getting the Rubicon....

Yes true, but it's due to high tire pressure on skinny tires on real roads with imperfections . On the velodrome it's not true. I doubt at 30-35 psi the wider tires are better on a car.

Edit reversed better or worse.

 

[liquids]

I was talking about investing in the S&P 500, a diversified basket of the strongest companies in the world. Borrowing to 'invest' in a single family home is and was a very risky proposition.

Whether one invests their money in the S&P500 or in gold or in any other (hopefully) appreciating asset, people argue for borrowing money to buy a car instead of paying "cash" because they make a higher return on their investments than the rate they'll pay on a car loan. Similarly, people also argue for borrowing money to buy a house with borrowed money for the same reason.
When I paid off my house, I had a financier suggesting that I remortgage it so I could invest the borrowed funds and increase my returns. I was just attempting to suggest that there is potential fault in the basic argument borrowing (any amount) at a low rate expecting returns at a higher rate. More defensible (to me) is investing saved, not borrowed, funds.

 

[Direwolf]

For off-pavement purposes, I find it nice to have a torque converter to soak up driveline shock from jumpy throttle application. That's the one thing I don't like about driving manual Jeeps on faster washboard dirt roads.

please explain this more about the manual. I am going in that direction but I haven't driven a manual for a while.

When you're driving a solid axle vehicle with a fairly rough ride on a rutted dirt road at moderate speeds, it can get pretty bouncy in the cabin. If these bounces are bad enough, then your right foot ends up bouncing a bit on the accelerator pedal. Modern vehicles with electronic throttle can program out some of these quick throttle on/off transitions, but not all, and the vehicle ends surging in addition to bouncing (can also get into a weird feedback/occilation situation if the ruts are at a constant interval).

Anyway, the fluid-based torque converter in an automatic transmission can soak up some of these quick throttle transitions, whereas the engaged clutch in a manual transmission has no such ability. It is more of a second order effect, but definitely noticeable to anyone who as driven both auto and manual transmissions on the same rutted road.

 

[The_Phew]

Whether one invests their money in the S&P500 or in gold or in any other (hopefully) appreciating asset, people argue for borrowing money to buy a car instead of paying "cash" because they make a higher return on their investments than the rate they'll pay on a car loan. Similarly, people also argue for borrowing money to buy a house with borrowed money for the same reason.
When I paid off my house, I had a financier suggesting that I remortgage it so I could invest the borrowed funds and increase my returns. I was just attempting to suggest that there is potential fault in the basic argument borrowing (any amount) at a low rate expecting returns at a higher rate. More defensible (to me) is investing saved, not borrowed, funds.

Unbeknownst to most people, even if they are investing their own 'saved' funds, they are ultimately investing using 'borrowed' funds. Virtually every major corporation maintains debt; i.e. they borrow cheap and invest that $. Apple, who has the largest cash hoard of any corporation at nearly $300 billion, maintains about $100 billion in debt. Even Apple can't borrow money at 1.99% (my current auto loan rate), and would jump at the opportunity. So if I can borrow at that rate to free up cash flow to invest, I'd be crazy not to. At 4%, it would be a tougher sell.

 

[wanderer]

what do you think gas mileage will be with a 6 sp rubicon soft top 4dr?

 

[liquids]

Apple, who has the largest cash hoard of any corporation at nearly $300 billion, maintains about $100 billion in debt. Even Apple can't borrow money at 1.99% (my current auto loan rate), and would jump at the opportunity.

Apple only started borrowing money because the majority of its $300B ($200B at the time) was overseas and they would have have to pay 35% tax to repatriate it and invest it. It was less expensive to issue bonds.
I stand by my position: don't borrow money to invest if the collateral of that borrowed money is your home. It it's your car? meh, do whatever you you want.

 

[DaveNH]

On the tire width, my JKUR has tall, narrow tires. The narrow tires have demonstrated great traction in all kinds of terrain, and shockingly, even do quite well in sand dunes! They don't look as cool as wider tires, but they've been through some incredibly tough terrain, from mud to sand to the rocks of Moab, and they've performed exceptionally well everywhere, while not killing my mileage on the highway.

...

My JKU's tires, btw, are 255/80/17 BF Goodrich KM2's. I've been completely impressed with them, and would put another set on right now, if I wasn't going to have 5 brand new KO2's off my JLUR, when I go to the 35's.

I could swear I've seen someone on this forum (perhaps you?) post this link before:

http://www.expeditionswest.com/research/white_papers/tire_selection_rev1.html

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