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Modified JK Tech Tech related bulletin board forum regarding subjects such as suspension, tires & wheels, steering, bumpers, skid plates, drive train, cages, on-board air and other useful modifications that will help improve the performance and protection of your Jeep JK Wrangler (Rubicon, Sahara, Unlimited and X) on the trail.

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Rolling resistance

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Old 02-17-2015, 09:47 PM
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Originally Posted by PET77
Auto or manual tranny? You can declutch your manual to let it roll off the hill. The auto will always drag due to the engine brakeing.
My dad's car has the same w5a580 auto trans, the same or worse power:weight ratio and acceleration times but doesn't slow down the way my JKU does. Which is what got me thinking.
I've never put the jeep to N while moving at 40-60mph but I'm sure things won't change much.
Old 02-17-2015, 09:51 PM
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Originally Posted by Invest2m4
Another reason is that the front axle can't be unlocked, so it adds resistance. Going to manual hubs would add an easy 1-2 mpg. Plus, it would drive better. Not only are the front shafts and gears turning, but so is the front driveshaft and that turns the front of the T case. Talk about a waste of energy.
Sounds like an interesting idea. Also how exactly does it drive better on road or did you mean in 4H/4L?
Old 02-18-2015, 06:54 PM
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Aerodynamics and tires have an effect but it's basically all controlled by the computer on FI vehicles. I had a Buick Park Avenue that barely slowed down at all when the accelerator was released.
Old 02-18-2015, 09:02 PM
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I know exactly what the OP means. I have a 2 door with the 3.6 and sometimes I just wonder if my ebrake is dragging because it "feels" like something is holding it back. Nothing sciencentific in my analysis. ..just strage as the OP stated.

I have an auto w/ 3.73 gears and stock rubi MT tires. Nothing else.

Last edited by demtek9; 02-18-2015 at 09:05 PM.
Old 02-19-2015, 04:44 AM
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Originally Posted by PET77
Auto or manual tranny? You can declutch your manual to let it roll off the hill. The auto will always drag due to the engine brakeing.
Keeping an engine "in gear" down hill will save fuel. When you "declutch" it will be at idle, using fuel to stay running. When in gear it needs no fuel to continue turning.

Edit: forgot to add a link. It is based on semi trucks. However the same rules apply for everything on the road:

https://www.nptc.org/index.php?optio...419&Itemid=527

Last edited by castlerockjeep; 02-19-2015 at 04:53 AM.
Old 02-19-2015, 07:15 PM
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With my jeep, it felt like my rolling resistance was greatly reduced after I got rid of the stock driveshaft and went with a Coast 1310. I think the bearings were going and it was creating some drag.
Old 02-19-2015, 09:33 PM
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Originally Posted by Runewolf1973
With my jeep, it felt like my rolling resistance was greatly reduced after I got rid of the stock driveshaft and went with a Coast 1310. I think the bearings were going and it was creating some drag.
Can't be my issue... mine has under 4000 miles.
Old 02-20-2015, 07:34 AM
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Throw some 35x12.50 MTR's with Kevlar and add the 4.10 gears I have and you will find out about rolling resistance and terrible gas mileage but hey we don't buy and modify these JEEPS for gas mileage or reducing rolling resistance.Throw some heavy bumpers and winches and it gets even better at about 12 mpg...but damn it looks badass and rocks the trails like nothing else out there!
Old 02-20-2015, 07:19 PM
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Originally Posted by JK UNLIMITED
Throw some 35x12.50 MTR's with Kevlar and add the 4.10 gears I have and you will find out about rolling resistance and terrible gas mileage but hey we don't buy and modify these JEEPS for gas mileage or reducing rolling resistance.Throw some heavy bumpers and winches and it gets even better at about 12 mpg...but damn it looks badass and rocks the trails like nothing else out there!
Damn... yours sound like one heck of a build and I wouldn't mind having one like yours at all. The problem is my requirements and situation is very different from yours (as described in the first paragraph of the first post). Also, too often people underestimate the modern Wrangler's capability as a road vehicle... to me it makes perfect sense as a road-only vehicle as well and if i go to discuss why now this thread will go off topic too fast. At any rate, our beloved JK deserves a bit more credit
Old 02-21-2015, 12:03 AM
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Even mine does it running 35s and 4.88s gears. I kind of like it at the same time, I don't have to brake coming to lights as i just coast in most of the time.



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