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Old 04-07-2008, 01:06 PM   #15
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I have been a proponent of slowing down for a long time. A couple of years ago drove our 01 Impala (not a small car) with a 3.4 litre, from MN to Milwaukee and back. I kept the speed down to 55-60. I got just over 35mpg both ways. I also try to never exceed 60 when I am using the 04 Silverado. It has the 5.3 and 3.73 rearend. When I am not towing I can get right around 20 mpg. It also helps to not have jackrabbit starts and stops.

Go ahead, save some gas.
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Old 04-07-2008, 02:16 PM   #16
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Quote:
Originally Posted by finalcutjoe
3-revenues from speeding citations would increase exponentially
Yes, that too...
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Old 04-07-2008, 02:35 PM   #17
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The data has changed

The speed vs MPG chart has changed over the years (see attached). I wasn't able to find this figure on the EPA site, but it is supposedly EPA data. Notice that MPG loss at speeds above 55 mph has improved since the 70s. I added the arrow at 60 MPH. I wish these figures were available for pickups iin adddition to the combined data for all vehicles.

My current TV (91 F250 7.3L PSD) is fairly new to me, however, it was my impression on the one long trip I have taken it on that it was using less fuel at 60 than 55. I can't prove that as this impression came from watching the gauge, but I wonder if the extra 5mph off set some of the hill climbing issues? Also, this observation was based on a small (under 200 mile) segment of the trip, so other factors such as wind might have been in play. In any case, at 60 mph I was able to get just over 15 mpg towing.

Another question I have is this: what is the best driving approach for fuel economy on the two lane (ie slower speed) mountain roads with lots of climbs and descents? Much of my summer will hopefully be spent towing on these roads so the better the mileage the better.
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Old 04-07-2008, 02:42 PM   #18
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Way back when, 50 was considered optimum for cars, and 60 was considered optimum for large trucks, as they were supposed to be geared to operate more efficiently at 60. President Nixon ordered the 55 mph national speed limit as a compromise between the two. Of course, he also said he wasn't a crook...
I do know that current EPA MPG highway test speed is 48 mph.
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Old 04-07-2008, 03:41 PM   #19
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Originally Posted by Gen Disarray
The speed vs MPG chart has changed over the years (see attached). I wasn't able to find this figure on the EPA site, but it is supposedly EPA data. Notice that MPG loss at speeds above 55 mph has improved since the 70s. I added the arrow at 60 MPH. I wish these figures were available for pickups iin adddition to the combined data for all vehicles.

My current TV (91 F250 7.3L PSD) is fairly new to me, however, it was my impression on the one long trip I have taken it on that it was using less fuel at 60 than 55. I can't prove that as this impression came from watching the gauge, but I wonder if the extra 5mph off set some of the hill climbing issues? Also, this observation was based on a small (under 200 mile) segment of the trip, so other factors such as wind might have been in play. In any case, at 60 mph I was able to get just over 15 mpg towing.

Another question I have is this: what is the best driving approach for fuel economy on the two lane (ie slower speed) mountain roads with lots of climbs and descents? Much of my summer will hopefully be spent towing on these roads so the better the mileage the better.
GD, your mpg is most likely due to diesel engines reaching peak efficiency at 1800 RPM. I have found same (not towing mpg); better mpg at ~73 mph (22mpg) than at 65 (~18mpg)...at some point, of course, increased friction forces at greater speed would catch up to you and you would notice a decrease, but I do not drive faster than 73 mph so I never reached the point of diminishing returns...

BTW-enjoy your adventure!

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Old 04-07-2008, 03:42 PM   #20
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Another freebie to save gas is to set the tire pressure on the tow vehicle at the highest pressure printed on the side of the tire. It lowers rolling resistence thus improving gas mileage.

Unfortunately this practice may have a deleterious effect on handling. There is, generally, a front-to-rear pressure differential depending on the vehicle make and model. This is not always the manufacturers way of ensuring a smooth ride, that has generally been superceded by, first, the need for overall fleet economy, and, two, by closer inspection of safe handling by engineers and the lawyers looking over their shoulders since the Explorer/Firestone debacle of a few years ago.

For example, my Dodge truck has guidelines for tire pressure when loaded and unloaded. In both cases the front pressure is to remain at one point, only the rear is increased.

If, after towing (and having been at the rear limit) I go to drive around town -- the handling, while on the freeway -- is markedly inferior to the unloaded tire pressure dynamics. It is obvious to the passenger (the truck sways).

When, in this truck, the pressure is set at the lower, recommended limit, the soft tires and propensity toward sway tend to work together. The steering input and reaction of the truck to same is moderated by having a "softer" tire.

My tires are new, but the oem item. The shocks are also new, the alignment dead on. I also have several CAT Scale tickets which show my truck, solo, loaded or unloaded for purposes of planning. I recommend this tip highly.

Safety trumps fuel economy. Therefore, should one be willing to experiment it would need to be with no dimunition of safe handling or braking. In example, a harsher ride can be more wearing, offsetting any potential gains.

I fully agree with the premise that overall low cost of ownership for a given number of miles over a given period of time is through close attention to details and careful experimentation.

I would say the same for modifying the suspension: one may lower the nose for better wind penetration, but then the vehicle balance is, again, deleteriously affected.

And the same is true for engine modifications. There are kits to change the mechanical ignition timing for some engines. This may work well in situations where the engine is under no load, and increase mpg incrementally. But the engine "may" overheat under load, or begin to wear at a faster rate. Etc.
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Old 04-07-2008, 04:10 PM   #21
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My truck tire pressure is a recommended 30 psi, all tires, all loads, but have a maximum pressure on the tire of 35 psi. They are the big 20 inchers. I run 35 psi all the time, and cannot find any adverse handling or ride as a result.
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Old 04-07-2008, 04:49 PM   #22
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Quote:
Originally Posted by BillTex
GD, your mpg is most likely due to diesel engines reaching peak efficiency at 1800 RPM. .....
Bill
I was wondering if it wasn't something like that. What are the chances you can direct me to where that data is? At one point I thought for sure there would be a figure out there somewhere showing my engine and optimal performance using the transmission I have. So far no dice. Given all the gear heads out there I am pretty surprised I cant find that data.
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Old 04-07-2008, 06:28 PM   #23
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Red, I think all that is true with "performance" driving, but in my "ease it down the road" style I just don't see that much difference in comfort or control. Plus, on some of the better highways, I can tell no difference at all!

And....it may have something to do with the vehicle brand. My Tundra just doesn't go into self destruct mode or loss of control when the ride gets a bit bumpy. Part of the credit goes to Toyota, the other part goes to Bilstein.
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Old 04-08-2008, 07:36 AM   #24
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Originally Posted by Gen Disarray
I was wondering if it wasn't something like that. What are the chances you can direct me to where that data is? At one point I thought for sure there would be a figure out there somewhere showing my engine and optimal performance using the transmission I have. So far no dice. Given all the gear heads out there I am pretty surprised I cant find that data.
GD, I'll PM you some data, charts, links...


As for Toyota handling bumpy roads, have you seen this? Not sure if this guy is running bilsteins, deygo tires or what; YouTube - Ford F150 vs Chevy vs Toyota - Bed Bounce
I am not a Ford guy, but that is scary!

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Old 04-08-2008, 11:31 AM   #25
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Quote:
Originally Posted by BillTex
GD, your mpg is most likely due to diesel engines reaching peak efficiency at 1800 RPM.

Bill
Bill, thanks for the links. So is my best bet to aim for the 1,800 RPM range and let the speed fall where it may?
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Old 04-08-2008, 12:36 PM   #26
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Bill, thanks for the links. So is my best bet to aim for the 1,800 RPM range and let the speed fall where it may?
Hey Rodney, if you read that link to the other mpg thread, you will see the experiment I tried last time I was out (our truck is not a daily driver) and I found the 1800 RPM peak efficiency to be true. Several other running CTD's have found the same. So I guess the answer is yes. This is what long haul truckers do (of course they have more gears to select from) and I know diesel Moho drivers follow this method also, as well as boats (I run Tuna boats offshore and fuel use becomes critical...you don't just "pull in and top off"!).

Report back what yopu find!

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Old 04-08-2008, 03:04 PM   #27
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I an avid road cyclist. When riding in groups we all take turns to fight the wind. Drafting tight behind the other guy helps like having the tires running at 125 psi. On recent trips out west when only on the open roads and usually behind a tandem fed ex or the like I would get comfortable but not in any way tail gate the beast. I like it best in heavy head winds and man the savings were just huge. The lie o meter would show instant savings of over 5 mpg. I know some will say bad boy, but It broke up the long drive across the desert. Once I was in a battle to see who could last longest before a pee stop. That guy had to have a bottle or something cause I lost.
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Old 04-08-2008, 10:46 PM   #28
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Quote:
Originally Posted by Gen Disarray
Bill, thanks for the links. So is my best bet to aim for the 1,800 RPM range and let the speed fall where it may?
I just saw in my travel notes that while towing 4th gear 1,800 RPM was 45 MPH and in 5th gear 1,900 RPM was 65 MPH. I suspect that 60 MPH would put pretty close to the 1,800 RPM sweet spot (if thats where the sweet spot is).

Is maximum torgue what I am looking for?
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