4.88's 35's and 6spd MPG's?
01-06-2011, 01:28 PM
#21
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Yes
I don't drive like a mad man anymore so 18.6 is what I average from tank to tank. I haven't ever tried to drive only highway or only city for any period of time to separate the two.
01-07-2011, 05:12 PM
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So from what ive seen, a 35 tire might be too small for 4.88's. the rpms seem to be to high for higway, and a 37 might actually be better fit for mpg's.
01-08-2011, 08:40 AM
#24
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Originally Posted by planman
What are too high rpms on an engine that redlines at 5200 rppm and that needs 2500-2700 rpm to get to the beginning of peak torque?
What are too high rpms when a stock 6 speed Rubi with stock, light weight, skinny tires turns over 2500 rpm at 70 mph and 2900 rpm at 80 mph?
What are too high rpms when you add wind drag from a lift and go from a 48 lbs stock tire to a wider, 80+ lbs 35" tire?
The logical answer would be that the extra weight, rotating mass of the tires, wider track of the tires, and wind drag from a lift would require higher rpms than stock due to the need for more horsepower and torque.
The scientific answer would depend on where you live and how you drive, wind, elevation, hills, average speed, weight of your modified JK, weight of your gear and passengers, etc.
Make gearing decisions based on physical science rather than speculation as to the optimal hwy rpm level given your unique circumstances.
Sent from my DROIDX using Tapatalk
What are too high rpms when a stock 6 speed Rubi with stock, light weight, skinny tires turns over 2500 rpm at 70 mph and 2900 rpm at 80 mph?
What are too high rpms when you add wind drag from a lift and go from a 48 lbs stock tire to a wider, 80+ lbs 35" tire?
The logical answer would be that the extra weight, rotating mass of the tires, wider track of the tires, and wind drag from a lift would require higher rpms than stock due to the need for more horsepower and torque.
The scientific answer would depend on where you live and how you drive, wind, elevation, hills, average speed, weight of your modified JK, weight of your gear and passengers, etc.
Make gearing decisions based on physical science rather than speculation as to the optimal hwy rpm level given your unique circumstances.
Sent from my DROIDX using Tapatalk
We have big hills here. I turn 2900 rpm at 65 and 3100 at 70. The big bonus I never have to downshift for a big hill. It flies right up them.
01-08-2011, 08:43 AM
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I agree with you and you obviously make a very good point. By no means am I disagreeing with you and you obviously have far more experience and knowledge with this than I do. I guess what I was thinking of, is if the RPM's are right at 3000 going 70 MPH with a 4" lift, 4.88's and 35's and my stock JK with 3.73's runs right at 2300 RPM's, then I would try and match the right gear to get me back in the ballpark of stock RPM's at 70 MPH. I know you are running 5.13's, but in your opinion would 4.56's be pointless. I live in the Midwest if you will (Ohio) where we have rolling hills and nothing too steep. I do however make frequent trips to Tennessee where the Appalachian mountains are.
What are too high rpms on an engine that redlines at 5200 rppm and that needs 2500-2700 rpm to get to the beginning of peak torque?
What are too high rpms when a stock 6 speed Rubi with stock, light weight, skinny tires turns over 2500 rpm at 70 mph and 2900 rpm at 80 mph?
What are too high rpms when you add wind drag from a lift and go from a 48 lbs stock tire to a wider, 80+ lbs 35" tire?
The logical answer would be that the extra weight, rotating mass of the tires, wider track of the tires, and wind drag from a lift would require higher rpms than stock due to the need for more horsepower and torque.
The scientific answer would depend on where you live and how you drive, wind, elevation, hills, average speed, weight of your modified JK, weight of your gear and passengers, etc.
Make gearing decisions based on physical science rather than speculation as to the optimal hwy rpm level given your unique circumstances.
Sent from my DROIDX using Tapatalk
What are too high rpms when a stock 6 speed Rubi with stock, light weight, skinny tires turns over 2500 rpm at 70 mph and 2900 rpm at 80 mph?
What are too high rpms when you add wind drag from a lift and go from a 48 lbs stock tire to a wider, 80+ lbs 35" tire?
The logical answer would be that the extra weight, rotating mass of the tires, wider track of the tires, and wind drag from a lift would require higher rpms than stock due to the need for more horsepower and torque.
The scientific answer would depend on where you live and how you drive, wind, elevation, hills, average speed, weight of your modified JK, weight of your gear and passengers, etc.
Make gearing decisions based on physical science rather than speculation as to the optimal hwy rpm level given your unique circumstances.
Sent from my DROIDX using Tapatalk
01-08-2011, 03:27 PM
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Never see it listed in the Pros and Cons of owning a manual vs. an automatic, but I suppose one could say that a minor Pro of the 6speed is the ability to "test" future gearing by not shifting into ones tallest gear(s), at least for the upper end comparisons at highway speeds. Never hear about anyone with an automatic doing this - anyone know if that's practical.
01-09-2011, 04:05 AM
#27
Originally Posted by planman
With rolling hills in Ohio and 4.56 gears, you would find yourself downshifting more frequently than with 4.88 gears.
If I lived in a place like Texas (flat and closer to sea level) and did a fair amount of highway driving, I'd run 4.56s with a 6 speed and 35s.
Living in Montana at 3500+ feet above sea level, with the Rocky Mountains all around me up to 10,000+ feet above sea level, I'd run no less than 4.88s with 35s. Since I don't spend much time over 65 mph, I geared 5.13s and ran 35s on it for quite a while.
Frequently downshifting to 5th gear will eat more gas than running high enough rpms in 6th gears so that you don't have to downshift. It really depends where you live, how fast you drive, what will be your max tire size, etc.
I was born in Northern Indiana in Elkhart County. In that neck of the woods, I'd want higher rpms because of the rolling hills and modest speed limits.
You definitely do not want to re-gear to approximate stock rpms when running larger, heavier tires with more wind drag from a lift, and a heavier overall rig due to armor, etc. You want higher rpms to produce more HP.
Elkhart County is where I'm from and currently live just northwest from there in Mi., I plan on sticking w/ 33's and want to regear, my rig does some highway travel & will be taking more trips in the future. In your opinion, shall I install 488 or 456, I do have the 488's already to install but looks like I may need to go 456 since my job is going to force me to Chicago once/twice per week. What's your advice?
01-09-2011, 04:37 AM
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I ordered my 4.88 gears and 35 KM2's at the same time and wish I had ordered 37's. When I travel the highway I travel at speeds of 65 to 75 usually. I like taking the jeep on vacations and trips and that is when the gas milage matters. All other times I could care less. I would love to know what people are getting with 37's.
I have not re-geared yet, but run 35s on a 2DR manual with 4.10s. Just to get a feel for how the 4.88s might feel at highway speeds, I drove around for a couple of weeks without ever shifting into 6th gear. From what I understand here on the forum, running 5th gear with 4.10s is almost equivalent to running 6th gear with 4.88s. If that's true, I can look forward to a 3-4 mpg drop in my fuel economy (spare me the jejune Prius comments - this thread is also about gas mileage) . . . unless I go with the 37s I'm planning to install shortly, at the time I re-gear.
Never see it listed in the Pros and Cons of owning a manual vs. an automatic, but I suppose one could say that a minor Pro of the 6speed is the ability to "test" future gearing by not shifting into ones tallest gear(s), at least for the upper end comparisons at highway speeds. Never hear about anyone with an automatic doing this - anyone know if that's practical.
Never see it listed in the Pros and Cons of owning a manual vs. an automatic, but I suppose one could say that a minor Pro of the 6speed is the ability to "test" future gearing by not shifting into ones tallest gear(s), at least for the upper end comparisons at highway speeds. Never hear about anyone with an automatic doing this - anyone know if that's practical.
01-09-2011, 05:56 AM
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Gear Ratio Calculator
I have been using this calculator to play around with the gear ratios, however I don't know how accurate it is compared to our engines. It is posted on a Ford Ranger website.
http://www.therangerstation.com/tech...tioChange.html
http://www.therangerstation.com/tech...tioChange.html