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Speed for best economy?
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=26712		 Page 1 of 3
Author:  dgeist [ Mon Nov 19, 2007 4:58 pm ]
Post subject:  Speed for best economy?
So, the police enforcement of traffic law is a little liberal around here and thus, I have some flexibilty in speed of cruising on the interstate. I've been setting the cruise at 65 and getting decent milage ~22 by evic. That's mostly residential and short highway trips. I assumed that since the torque curve maxed at 1800, it would be the best for MPG, but recently I'm thinking closer to 70 might be a bit better. What have you all found as a "sweet spot" for speed to get the best milage with the CRD? Lets assume clear weather, 2wd, and mostly flat roads.

Dan
Author:  dog_party [ Mon Nov 19, 2007 5:22 pm ]
Post subject: 
I get the best mileage between 60 and 65 MPH.
Author:  Threeweight [ Mon Nov 19, 2007 6:16 pm ]
Post subject: 
64 mph on the highway (set cruise and get in the slow lane).
Author:  BiodieselJeep.com [ Mon Nov 19, 2007 6:37 pm ]
Post subject: 
Guys, I think that we beat this one to death.

Answer: get up to 60+ until the OD gear kicks in then slow down to just above 55 (before the OD drops out). This get you into the hella-good mileage range: low rpms, high gear.

Not that I ever drive less than 68 mph on highways here, someone would kill me. And never less than 75 in the TDI...otherwise, what is the point of having a "vine jermahn automobeeel"?
Author:  Pote [ Mon Nov 19, 2007 6:51 pm ]
Post subject: 
not a CRD, but mine kicks into 5th right at 60. 2000 rpms. at 65-70 I'm at 2200 rpms so mileage is not as optimal as at 61 MPH.
Author:  DarbyWalters [ Mon Nov 19, 2007 7:36 pm ]
Post subject: 
Yep...I get to 64 (GPS Speed 62.5) ... get the second overdrive to lock in ... back down to 100km/62.5 (GPS Speed 60) ... set the cruise ... and get 30+ a little with a lift and all ... less than 1800 rpms

If it is hilly, you need to bump up to 65 to keep the torque converter locked up.
Author:  barnez224 [ Mon Nov 19, 2007 7:38 pm ]
Post subject: 
BiodieselJeep.com wrote:
Guys, I think that we beat this one to death.

Answer: get up to 60+ until the OD gear kicks in then slow down to just above 55 (before the OD drops out). This get you into the hella-good mileage range: low rpms, high gear.

Not that I ever drive less than 68 mph on highways here, someone would kill me. And never less than 75 in the TDI...otherwise, what is the point of having a "vine jermahn automobeeel"?


can't put it much better than this.
Author:  MOSFET [ Tue Nov 20, 2007 10:23 am ]
Post subject: 
about 62mph and 1800 rpm.
Author:  Jeger [ Tue Nov 20, 2007 10:39 am ]
Post subject: 
Yep 'bout 62 mph or so....just fast enough to get you a ticket in a 55 zone :roll:
Author:  dgeist [ Tue Nov 20, 2007 12:00 pm ]
Post subject: 
Allrighty. I guess my original thinking was correct on the max torque+best gearing == best economy. Thanks for indulging me, everyone, and Darby, I still think you have some kind of magical incantation going to be getting those numbers :wink:
Author:  Uffe [ Tue Nov 20, 2007 12:01 pm ]
Post subject: 
Funny, my final gear kicks in when I press the cruise control at 96kph. If I manually hold the speed there it won't go in final gear, but if I just press the cruise control it will go to final gear. You can also do the acceleration and backing off trick. I just use the cruise control...
Author:  CATCRD [ Tue Nov 20, 2007 12:32 pm ]
Post subject: 
I can stay in top gear at 56 mph, which shows 34mpg on the EVIC on level road.
Author:  retmil46 [ Tue Nov 20, 2007 1:23 pm ]
Post subject: 
Used to be around 2000 rpm on mine. Now, with different tires, Suncoast, Inmotion, etc, guess I'll have to find out all over again next long trip.
Author:  Jeger [ Tue Nov 20, 2007 1:28 pm ]
Post subject: 
I have also notices that if you are in a large group of traffic I can get around 30MPG even at 70-75MPH, I think wind drag plays a very large part in our mileage...it probably helps when there are 3 semi's in front of you and cars all around cutting the wind. We should all flock together like geese :lol:
Author:  Threeweight [ Tue Nov 20, 2007 1:33 pm ]
Post subject: 
Been discussed before, but wind drag is brutal on these KJ's. As speed increases, drag goes up in geometric progression. Makes you wonder what kind of mileage our CRD engines would get in a less boxy body (like the previous generation Grand Cherokees).
Author:  Uffe [ Tue Nov 20, 2007 2:55 pm ]
Post subject: 
Threeweight wrote:
Been discussed before, but wind drag is brutal on these KJ's. As speed increases, drag goes up in geometric progression. Makes you wonder what kind of mileage our CRD engines would get in a less boxy body (like the previous generation Grand Cherokees).


I second that. But why would anyone put such a huge diesel in a smaller car? And how to make it fit? :D

Imagine a little Toyota Aygo or a Citroen C1 with that 2.8 CRD in it. Now that would be a really sweet thing :D (except for the lack of nearly everything on comforts)
Author:  dgeist [ Tue Nov 20, 2007 3:05 pm ]
Post subject: 
Jeger wrote:
I have also notices that if you are in a large group of traffic I can get around 30MPG even at 70-75MPH, I think wind drag plays a very large part in our mileage...it probably helps when there are 3 semi's in front of you and cars all around cutting the wind. We should all flock together like geese :lol:


I loved the MythBusters episode that tackled drafting as a fuel economy technique. The message at the end was "Yes, it really works really consistently as long as you keep stable speed but DON'T DO iT because it's hella dangerous" :)
Author:  geordi [ Tue Nov 20, 2007 3:48 pm ]
Post subject: 
Oh PLEASE on the danger stuff. Certainly don't try to draft on a surface street, but on a long open highway where there aren't any lights to stop you... I draft all the time, and in some vehicles I'm picking up almost a 50% increase in the mileage. (That would be on my supposed-to-be 6mpg RV, which gets a solid 9mpg at 70mpg while sitting 5 carlengths off the back of a semi.)

I've never had a problem drafting, and I'm able to easily maintain a consistent 5 carlengths or so off the back of whatever airplow I'm able to find. I prefer large tourbusses, as they tend to have big airdams under the body, unlike the open underside of a semi trailer. That makes the suction even stronger.

The technique is simple: SLOWLY approach the back end of your airplow until you can feel the side-to-side buffeting from the air turbulence vortexes. This is what you want BEHIND you, as in front of that, is the suction. Keep inching forward, you will feel the turbulence "walk" down the sides of your vehicle. It will eventually stop, that's when you are in the sweet spot, and the turbulence has now extended to behind your vehicle. Now just match your speed using your depth perception between your dashboard and the back of the donor... And set your cruise.

This does NOT work in hilly country, and if you ride a little to the driver's side of the donor, you can still see around him to look for taillights in the distance. Tire fragments are the danger here... You won't get much warning on those. But my philosophy has always been "Better to go straight in, then swerve and sink the Titanic with a badly-executed turn."

I used to draft in my Jetta TDI, and found 70mph and 40mpg easily attainable... But I rarely liked going that slow een zee otto. ;)

Now with my Hybrid Mercury Mariner (fully loaded and with a cargo pod on top no less!) last summer I booked 32mpg at 75 while drafting off trucks, and less than 25 when not drafting. The mileage dropped like a brick.

My KJ I suspect is still breaking in, as I didn't get to the best mileage on the Jetta until it was over 50k miles. When not towing, 215/85/16 tires at 80psi, I get either about 24mpg not drafting, or 27-28mpg while drafting. All numbers are at 70-75mph. My recent full-tank drive while towing at 70-75mph was a glorious 16mpg, and that was loaded down with a combined weight of 8300 lbs, 3200 of which was on the trailer axle.

It's not a magic incantation... It's the front-mounted tow-probe that can hook to the back of a semi. :D *evil grin*
Author:  dgeist [ Tue Nov 20, 2007 5:54 pm ]
Post subject: 
geordi wrote:
Oh PLEASE on the danger stuff.......


Yeah, they say not to make potato guns and not to blow things up with rifle blasts and such too. Life is dangerous. Live a little (but don't draft a motocycle, because that really IS nutty...)
Author:  chrispitude [ Tue Nov 20, 2007 6:52 pm ]
Post subject: 
geordi wrote:
My KJ I suspect is still breaking in, as I didn't get to the best mileage on the Jetta until it was over 50k miles. When not towing, 215/85/16 tires at 80psi, I get either about 24mpg not drafting, or 27-28mpg while drafting.


What tires are you running that they respond well to 80psi?

- Chris
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