Today we collected as much data as we could obtain (and think of) between my truck and gschulte's truck with the hopes of seeing why one truck would get "poor" mpg and another would get "normal" mpg. I get what I consider to be good mileage, he gets what I would consider to be bad mileage. I can get as good of mileage towing 5,000lbs on the freeway as he can get running empty on the freeway.

The big question.........WHY?????? :confused:

Below find 70 mph boost data. Since we had a discrepancy in his speedometer, we standardized the test to RPM of my truck at 70mph which ended up to be 1950rpm. Tire heights were less than 1/4th inch difference so that is a non-factor and the equal rpm means the speeds were very close.

The two spikes in each set are two overpasses on the freeway.

Tell me who's truck is working harder to go 70mph :rolleyes:

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Below find calculated fuel rates same 70mph (1950rpm) comparison.

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WOW!!!:eek:

Your truck is working alot less to do the same. Are they the same year, mods...?

Are these graphs using the EFI Live? IF not what are you using to collect data?

Bill

Uh, Tx what are we looking at? On the first graph, is your truck the blue line and your friends the red line? Also, what s CFR?

[quote=txguppy;898609]Uh, Tx what are we looking at? On the first graph, is your truck the blue line and your friends the red line? /quote]

What's the UOM across the bottom of the graphs? Also, what s CFR?[

In all graphs my truck is the blue, gschulte's truck is the red.

First graph is boost, subtract 15 to get actual boost.

Second graph is Calculated Fuel Rate (CFR) in mm.

UOM is seconds.

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Below find Vane Position differences, 70mph unloaded.

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Both trucks are 4x4 trucks and crew cabs, although his truck is a dually. He has the extra rolling resistance of the dual rear wheels, but it looks to be a wash due to my wider 285/75 16 BFG's versus his 235/85 16 tires.

He normally runs his truck set in what we calculated to be a 50hp setting, thats what he calculates his mpg's off of. I detuned my truck to a 50hp setting to match.

One thing we did find mechanically were his front tires were MUCH more difficult to turn than mine.

Holding both front ends off the ground with a pair of forklifts, using maximum strength to physically spin the tires the best you could get out of spinning Greg's tires was 1 maybe 1 1/2 revolutions before the tire would come to a dead stop. On my truck you would get 3 to 3 1/2 revolutions before the tire came to a stop.

Thats a 2:1 ratio at least and likely more in rolling resistance of the front tires. As speed increases would you expect his truck to need more and more power to overcome that extra resistance?

Crawling under his truck I noticed that both of his front axel tube ends showed signs of leakage where the CV joint flange enters the actual axel tube, whereas on my truck they were bone dry. Perhaps his bearings are dry or ruined causing excessive drag?

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70 MPH @ 1950 RPM?? at 65 i'm right at 2000 RPM 70 I jump to 2150 or so. Why?WHy? Why??

One thing we did find mechanically were his front tires were MUCH more difficult to turn than mine.

<snip>

As speed increases would you expect his truck to need more and more power to overcome that extra resistance?

Couldn't you get a ball-park comparison by coasting side-by-side down a hill?

70 MPH @ 1950 RPM?? at 65 i'm right at 2000 RPM 70 I jump to 2150 or so. Why?WHy? Why??

Probably because TxC is riding on 285s.

Joseph

70 MPH @ 1950 RPM?? at 65 i'm right at 2000 RPM 70 I jump to 2150 or so. Why?WHy? Why??

Tire size?

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Couldn't you get a ball-park comparison by coasting side-by-side down a hill?



Probably because TxC is riding on 285s.

Joseph

Thats a great idea, wish we would have thought of that, although we would have probably used flat ground since there were no hills within 50 miles of any appreciable length to try that on.

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Greg is going to be taking his truck to the dealer for service on those leaking seals, and hopefully will find why the wheels are so difficult to turn.

It might pay 4x4 owners to crawl under their trucks and check for those specific leaks themselves, as well as maybe excessive brake drag. We have had so many discussions of why some trucks get poor mileage, try jacking that thing up and spinning a tire to see if your rolling resistance is in line.

Both of my fronts spun equally as easy, and both of his fronts spun equally as hard, thats why we are thinking he has an issue either in the axel (the leaks says maybe so) or the front brakes are leaving a touch too much pressure on the pads.

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What exactly would we be looking for? Any pics? For the spinning wheel test did you jack just the front end up or the whole truck?

What exactly would we be looking for? Any pics? For the spinning wheel test did you jack just the front end up or the whole truck?

He had two forklifts, so we lifted the entire front ends of both the trucks off the ground using boards on the forks lifting under the front of the skid plate at the crossmember, right where the two back bolts of the splash shield bolts on. That allowed us to go back and forth between the two trucks so we could readily compare the wheel spinning resistance to be sure what we were seeing was right. We checked repeatedly, with each of us trying the spins and the other marking revolutions using the schrader valve as the marker point.

I didn't have my camera with me at the time, but I just went and snapped the couple of pics below to illustrate where his truck was leaking out of the front axels. It was leaking on both sides in the same place, perhaps high heat from drag creating pressure inside his axels and forcing the lube out?

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TX, any chance the front differential has failed to disengage?

TX, any chance the front differential has failed to disengage?

Neither tire had any influence on the other side that we could determine, neither did turning the front driveshaft produce anything out of either front tire.

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I do want to add that on both trucks you can hear the pads dragging on the discs, but whether his are dragging more than mine we were not able to determine in our limited inspection.

But, just be aware that apparently the brakes drag slightly, at least on 2 out of 2 of trucks checked so far :)

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Tx,
All brake pads will drag, the only mechanism to return the pads is the rotor turning through them. When the pressure is released the tension of the pad on the rotor will push the fluid back towards the brake reservoir. As all of you know there is a height differance from the brake caliper to reservoir. This will leave some tension on the pads. If you had no tension on the pads, the brakes would have a "free feeling" when you first apply pedal.

Most people overlook one of the simplest pieces in the disc brake system, the sliding pins. The entire caliper assembly slides on a set of pins, the same pins you remove when you change pads. These are normally overlooked and will cause excessive brake pad wear, uneven wear, and added friction when they should be free. I replace these whenever I do a brake job if I can, you would be impressed with the differance. By the way, this is one of those things you learn when you start racing stuff hard. In a tough race, I used to use up a set of pads and generally have mushy brakes for several miles, this is one of those little things that make a big differance if it is overlooked. :)

The dually truck will always require more work for the same trip. Two reasons: Weight, he outweighs your truck 645 lbs. stock, that is 10% more weight, more load vs. distance = more work. The second part is aerodynamics, that set of dually wheels are dirtying up the air around the truck way more than you and I can imagine. Dirty air = more drag. The faster we go, the worse it gets. I am amazed at what and where the road grime ends up on the truck when I wash it.

Tx,
All brake pads will drag, the only mechanism to return the pads is the rotor turning through them. When the pressure is released the tension of the pad on the rotor will push the fluid back towards the brake reservoir. As all of you know there is a height differance from the brake caliper to reservoir. This will leave some tension on the pads. If you had no tension on the pads, the brakes would have a "free feeling" when you first apply pedal.

Most people overlook one of the simplest pieces in the disc brake system, the sliding pins. The entire caliper assembly slides on a set of pins, the same pins you remove when you change pads. These are normally overlooked and will cause excessive brake pad wear, uneven wear, and added friction when they should be free. I replace these whenever I do a brake job if I can, you would be impressed with the differance. By the way, this is one of those things you learn when you start racing stuff hard. In a tough race, I used to use up a set of pads and generally have mushy brakes for several miles, this is one of those little things that make a big differance if it is overlooked. :)

The dually truck will always require more work for the same trip. Two reasons: Weight, he outweighs your truck 645 lbs. stock, that is 10% more weight, more load vs. distance = more work. The second part is aerodynamics, that set of dually wheels are dirtying up the air around the truck way more than you and I can imagine. Dirty air = more drag. The faster we go, the worse it gets. I am amazed at what and where the road grime ends up on the truck when I wash it.

I agree, but his 14-15 mpg unloaded against my 18-19 mpg unloaded is a bigger difference than 645lbs and the dually tires. He has 1410mm of tread on the ground, I have 1140, so that difference is 1 tire instead of 2.

The biggest flag is I can get 13-14 mpg towing 5,000 lbs.

Thats way more aero drag than the bubble butt, and the horse trailer adds 4 more tires resistance to me, not to mention the weight.

The things that seem to be adding up are his rolling resistance, his slight weight and aero drag, and the fact that his speedo was off causing him to be going faster than he thought. Also he has his S&B plumbed to the fender holes exclusively which has shown to be restrictive. He has the TxC CAI now so we will see about that.

We took runs with his speedo indicating 70mph and his truck is working even harder than indicating above (no suprise) since he is actually travelling faster than 70mph, eating 100rpm more, more wind resistance, more boost, more tire drag....more everything.

Less mpg.

This also shows that just the correction factor for larger tires for distance to calculate mileage actually leaves a lot of factors on the table making accurate mpg comparisons impossible.

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You are still missing two important factors.

1) That 10% more weight is 70% rotating mass. Now lets look at his 14-15 vs 18-19 ~ 26% mpg right.

If the wheels weigh the same the dually has 30% more rotating mass in wheels. Your 4 wheels arent as heavy as 4 of his.

Another thing people overlook is accessories, longer beds and trucks allow for larger "heavier" accessories.

2) Aerodynamics is not my cup of tea, someone else will have to chime in. The faster you go, the worse it gets.

By the way, 14-15 in a 4x4 dually in 2wd mode is not bad mileage. I have the same truck but 2wd and I got just above that stock empty. With all my mods I am up to 15-16.5 "empty". For the record, getting rid of the cat is the most bang for the buck in mpg that I have noticed.

I meet with a lot of people that tow and have F@rd and D@dge trucks 2500 and 3500 DRW. If we are to believe our "friends" we arent any where off the radar scope. My truck will out tow my buddies F@rd on mpg and power, even though his camper is 4200 lbs lighter.

There are a bunch of factors and they all add up to less mpg.

Some we can't do anything about (drag of a dually).

But the turning resistance of the front wheels, possible intake resistance, and the speedo error CAN be changed, perhaps for the good. Thats the kinda stuff we were looking for.

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I'd take the calipers on all four wheels off and grease the mounting pins and slides. Like D. Lafleur mentioned, disk brakes require the axial runout of the rotors to push the pads back when you let off the brake. On my old '98 gasser the left front caliper was slightly rusty on the mounting slides. The rotor could not push the caliper back and the outer pad was always dragging on the rotor. I could smell the hot brakes when I got out of the truck. A little bit of sandpaper to clean up the mounts, and some grease to keep them from rusting again and everthing was good to go. It is a cheap and easy thing to do in any case.

I dont mean to discount the "leaking seals" or a possible problem with the brake pads or the mounting pins.

You aren't, all of your points were very valid and well taken. The more ideas tossed out the further along we will be.

I don't know for sure that the leaking seals are causing drag inside the axels due to bearings being dry, but I do know they shouldn't be leaking :)

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Tx,
All brake pads will drag, the only mechanism to return the pads is the rotor turning through them. When the pressure is released the tension of the pad on the rotor will push the fluid back towards the brake reservoir. As all of you know there is a height differance from the brake caliper to reservoir. This will leave some tension on the pads. If you had no tension on the pads, the brakes would have a "free feeling" when you first apply pedal.

Most people overlook one of the simplest pieces in the disc brake system, the sliding pins. The entire caliper assembly slides on a set of pins, the same pins you remove when you change pads. These are normally overlooked and will cause excessive brake pad wear, uneven wear, and added friction when they should be free. I replace these whenever I do a brake job if I can, you would be impressed with the differance. By the way, this is one of those things you learn when you start racing stuff hard. In a tough race, I used to use up a set of pads and generally have mushy brakes for several miles, this is one of those little things that make a big differance if it is overlooked. :)

The dually truck will always require more work for the same trip. Two reasons: Weight, he outweighs your truck 645 lbs. stock, that is 10% more weight, more load vs. distance = more work. The second part is aerodynamics, that set of dually wheels are dirtying up the air around the truck way more than you and I can imagine. Dirty air = more drag. The faster we go, the worse it gets. I am amazed at what and where the road grime ends up on the truck when I wash it.



:exactly:

Try 2500 to 2500 and 3500 to 3500 comparo with same general layout detailing tire size, brand, psi ride height etc etc...

One must wonder if TxC's truck has any brake pads left on the front the way he drives! :eek: :D ):h :lol: JJ :)

One must wonder if TxC's truck has any brake pads left on the front the way he drives! :eek: :D ):h :lol: JJ :)

We did take it out and exercise its stop and go ability! :ro)

I think turBeau still can't believe those 2700rpm 4WD launches :D

.

Could there also be a HP and Tq descrepancy on these trucks. Engine to engine should have slighty different HP and Tq numbers. Not sure what tolerances the Auto industry has to live by. I know the marine industry has to use1 a 10% rule. Hp ratings must be within 10%. of the posted numbers. If these problematic trucks were actually performing with 10% less power than other trucks that also might support your working harder for the same speed find.

I dunno just throwing it out there.

I have seen several cars with no issues that had brake pins hanging up. You didnt state the mileage on the truck, what about wheel bearings. If a full size man cant spend a wheel fast enough to overcome the drag for more than one round, something isnt right. I dont think it will solve his "mpg problem".

34k on his 22k on mine.

We thought about wheel bearings, but since it was BOTH front tires equally as difficult to spin......

We put all we could into spinning the wheels, 1 1/2 turn AT BEST from either of his fronts, easy 3 turns to 3 1/2 from either of mine.

.

I am not expecting the clearing up of the rotational resistance to bring his mpg up to what we all consider good, rather an accumulation of things to get him closer in line with "good". I also expect his actual mpg is higher than he has previously calculated due to running fatser than he thought.

One major thing we discovered was how far off his uncorrected speedo was. Since he was using that to calculate his mileage, and we now know he was going faster than indicated, then some of the poor mileage was hiding right there.

We all know the faster you go that mileage goes down.

Below find a graph showing his truck, both colors are RPM of the same truck. The blue is his truck doing 70mph, with the speedo indicating 67mph. The red is his truck doing 70mph as indicated by his speedo.

I expect there is at least 1mpg hiding right there since he was always going faster than he thought, therefore working the truck even harder, to go what he thought was 70mph when in effect he was running 73mph or so.

Even with the correction, as I showed at the start of the thread the truck still works harder at all times to maintain the same speed as mine, so under those terms he will never get as good of mileage.

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Are the standard rearend for a 3500 Dually 410? What gears does he have?

Both 3.73

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Could there also be a HP and Tq descrepancy on these trucks. Engine to engine should have slighty different HP and Tq numbers. Not sure what tolerances the Auto industry has to live by. I know the marine industry has to use1 a 10% rule. Hp ratings must be within 10%. of the posted numbers. If these problematic trucks were actually performing with 10% less power than other trucks that also might support your working harder for the same speed find.

I dunno just throwing it out there.

Cat truck engines leave the factory at EXACTLY their rated power. Each one is dyno'd before it leaves, and if it's not right on, it is adjusted until it is.

I'm not sure about Dmax engines, but it seems that most stock dyno results of the same year truck are within +/- 5 hp. (from what I've seen of dyno numbers posted)

By the way, 14-15 in a 4x4 dually in 2wd mode is not bad mileage. I have the same truck but 2wd and I got just above that stock empty. With all my mods I am up to 15-16.5 "empty". For the record, getting rid of the cat is the most bang for the buck in mpg that I have noticed.

I meet with a lot of people that tow and have F@rd and D@dge trucks 2500 and 3500 DRW. If we are to believe our "friends" we arent any where off the radar scope. My truck will out tow my buddies F@rd on mpg and power, even though his camper is 4200 lbs lighter.

My 2wd 05 CC dually is getting better mpg than yours is..... I am getting 18 unloaded highway. Pulling a 14000 lb high profile 5th wheel I am getting 9 so far on this trip...

In 1971 I worked with an engineer from Delco Moraine Division of GM, I ask him about the disk brakes dragging and he said it was normal when you jack the truck up and roll the wheels by hand but they don't drag while you are driving. To check this out we drove a new truck down the road and stopped with the parking brake, jacked up the front and the wheels rolled freely. This was a new truck so the calipers were sliding freely on the pins.
Wayne

I'm puzzled by the 1/4 difference in tire size , according to the charts it should be closer to an inch between those tires . Also did you happen to do a side by side comparison of the RPM and the speedometer and the odometer . It seems that many have stated that the speedo is more accurate with 265's than with 245's. I'm also suspect of the accuracy of the odometer compared to the speedo. If the odometers are off more than calibrating for tire size it may account for some of the discrepancies we are seeing in MPG .

I'm puzzled by the 1/4 difference in tire size , according to the charts it should be closer to an inch between those tires . Also did you happen to do a side by side comparison of the RPM and the speedometer and the odometer . It seems that many have stated that the speedo is more accurate with 265's than with 245's. I'm also suspect of the accuracy of the odometer compared to the speedo. If the odometers are off more than calibrating for tire size it may account for some of the discrepancies we are seeing in MPG .

These tires were 235/85 16's (his) and 285/75 16's (mine)

We measured using a straight edge across the two dually tires to the ground with a tape measure, and a straight edge across the top of the 285's with a tape measures on the inside and outside to make sure the edge was straight. The difference was less than a quarter inch.

We didn't side by side RPM test, but I used my tuner to correct his speedo like I do for mine and then went back out and checked at 1950rpm he was also turning 70mph according to his speedo. Otherwise he showed 67 uncorrected. We chose engine RPM as our most accurate indicator of everything because the precision of the speedo isn't there or the factory tach, and with my laptop we were able to see actual engine rpm digitally.

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In 1971 I worked with an engineer from Delco Moraine Division of GM, I ask him about the disk brakes dragging and he said it was normal when you jack the truck up and roll the wheels by hand but they don't drag while you are driving. To check this out we drove a new truck down the road and stopped with the parking brake, jacked up the front and the wheels rolled freely. This was a new truck so the calipers were sliding freely on the pins.
Wayne

Good test.

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I think turBeau still can't believe those 2700rpm 4WD launches :D

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Without sleeves. With a stock tranny. Chris must have got one of the ones that was built on a Tuesday. It was interesting, to say the least :ro) .

My 2wd 05 CC dually is getting better mpg than yours is..... I am getting 18 unloaded highway. Pulling a 14000 lb high profile 5th wheel I am getting 9 so far on this trip...

I would probably wet my pants if I got 18 mpg. I suspect that I may get 17 in a 55-60 mph run, but who knows. I never have that much time on my hands. I have extra parts on my truck also, my "empty weight" includes a 20K fifth wheel hitch, a tool box with ~200 lbs of god knows what sometimes, plus the stuff behind the seat, 50 dvds, power converter, game cube, etc. I also have mud flaps front and rear, I am sure that doesnt help my areo profile.

When towing in the 60-65 mph range I get ~11.3 hand calculated. My fifth wheel is 39'8" long and 13'2" high and weighs in at 15,700 loaded no groceries and ice. I spend more time in this config than in the "empty" config, so I will trade your 18 for my 11. :)

The roads you travel make a big difference too. Flat highway will always be better than any hilly area. Darin often tows to hilly areas, so there goes some of his mpg.

I think Darin will want to keep his 11mpg towing versus your 9!

:)

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The roads you travel make a big difference too. Flat highway will always be better than any hilly area. Darin often tows to hilly areas, so there goes some of his mpg.

I think Darin will want to keep his 11mpg towing versus your 9!

:)

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If you take into account the conditions of our roads vs your roads I proably have 20% more travel over the same distance. That is why our cars rattle more. :(

I will also add that asphalt does not produce the mileage concrete roads do. Especially those slighty rough asphalt roads.

I frequently travel a stretch of asphalt where it seems my DIC never goes above 20mpg. Its extremely flat stretch of road from Katy to Brookshire just a bunch of rice pastures.

We did take it out and exercise its stop and go ability! :ro)

I think turBeau still can't believe those 2700rpm 4WD launches :D

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I can believe it after riding with you. Just wait though. If they don't tear it down and fix right, you and I will be seeing a lot of those launches.

Interesting post. For the turning resistance you might consider a torque wrench on the axle hub to measure the initial inertia. This could give you a hard number to check against to see if changes make a difference and to what extent.

Wow what a lot of intrest. Tx just wanted to let you know, that I have scheduled to take my truck to the dealer on the 31st. Will post if the dealer finds anything. Again thanks for all the help. Tomc good idea on the torque reading. I will try to get a reading on the front hubs before I take it in.

Wow what a lot of intrest. Tx just wanted to let you know, that I have scheduled to take my truck to the dealer on the 31st. Will post if the dealer finds anything. Again thanks for all the help. Tomc good idea on the torque reading. I will try to get a reading on the front hubs before I take it in.

Do you need the directions for the TxC CAI ? PM me where to mail it if so.

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Do you have access to a hand-held GPS? A GPS will give you a good way to duplicate vehicle speed independent from tire size.

If there is a difference in tire size, running at the same engine RPM will not give you the same vehicle speed.

Vehicle speed plays a big part in fuel economy. I recently checked my truck on a 160 miles round trip using my GPS to determine the speed. (My truck speedometer reads approximately 1 mph HIGH at 70 mph. GPS 70 vs Speedo 71)

My calculated fuel economy dropped almost 4 mpg between 70 mph vs 80 mph as indicated on the GPS.

See here:
http://dieselplace.com/forum/showthread.php?p=874723#post874723

Also, you can get a good ballpark figure on the differeces in tire sizes by using this website to calculate it.
http://www.discounttiredirect.com/direct/brochure/info/tmpInfoTireMathNS.jsp

Hope this helps.
Ray

Do you have access to a hand-held GPS? A GPS will give you a good way to duplicate vehicle speed independent from tire size.

If there is a difference in tire size, running at the same engine RPM will not give you the same vehicle speed.

Vehicle speed plays a big part in fuel economy. I recently checked my truck on a 160 miles round trip using my GPS to determine the speed. (My truck speedometer reads approximately 1 mph HIGH at 70 mph. GPS 70 vs Speedo 71)

My calculated fuel economy dropped almost 4 mpg between 70 mph vs 80 mph as indicated on the GPS.

See here:
http://dieselplace.com/forum/showthread.php?p=874723#post874723

Also, you can get a good ballpark figure on the differeces in tire sizes by using this website to calculate it.
http://www.discounttiredirect.com/direct/brochure/info/tmpInfoTireMathNS.jsp

Hope this helps.
Ray

Since we measured the tires to be less than 1/4th of an inch different then RPM is our best speed indicator.

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Since we measured the tires to be less than 1/4th of an inch different then RPM is our best speed indicator.
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My calculations show 2.4 mph difference in speed at the same RPM for those two tire sizes around 70 mph.

My calculations show 2.4 mph difference in speed at the same RPM for those two tire sizes around 70 mph.

And thats what we observed on the speedos as well. He showed 52.5mph when I showed 55mph and he showed about 67-68mph when I showed 70mph. My speedo is corrected to gear ratio and measured tire height. His is not.

RayMich, have you ever actually measured two different brand tires of the same size? Don't place so much faith in your tire charts, tires of the same size by different manufacturers vary greatly in actual diameter. "The results of this calculator are based on the mathematical equations of the sizes entered, not the actual tire specs provided by the tire manufacturers. Please refer to the guides supplied by manufacturers for exact specifications."


By the way, your GPS resolution is 10 feet, over a short distance it can be off 20 feet point to point. Over a long distance that is insignificant, but in a mile it is noticeable.

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Another thing, his tires were relatively new compared to mine, and had almost all of the original tread depth. Mine have a helluva lot of tread height gone since new. They lugs were fairly deep when new, now they aren't. So of course, tire heights change over time.

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Quick question guys,

I have 265/75/16s on my truck and I have used the Predator to correct the speedo. Does this also correct my odometer as well? I' am concerned that my odometer is off. I think it is slow by 1 tenth of a mile for every mile traveled. When I hand calculate do I need to factor in my tire size adjustment even though I have a predator?

Using a GPS for speed is not an accurate rate. Any deviations in the road and/or angle to satelites used for the triangulation will affect this number. If you think your speedo is close use one lane of an interstate against 10ea. mile markers, this is one of the easiest and most reliable test. Do not use the exit as a marker those are rounded. Keep the truck in the right lane at the right side line. Your odometer will tell you the error.

By the way that 10 ft. error is sales literature numbers for a handheld GPS. :eek:

Using a GPS for speed is not an accurate rate. Any deviations in the road and/or angle to satelites used for the triangulation will affect this number. If you think your speedo is close use one lane of an interstate against 10ea. mile markers, this is one of the easiest and most reliable test. Do not use the exit as a marker those are rounded. Keep the truck in the right lane at the right side line. Your odometer will tell you the error.

By the way that 10 ft. error is sales literature numbers for a handheld GPS. :eek:

Thats true it measures straight point to point, so curves kill GPS distance/time calculations. Non-military GPS actually has shown to be way off it is true, they do "claim" 10ft (3meter) resolution though.

I have never verified the odometer, so I am unsure about that.

Mile markers against my stopwatch has always been my favorite speedo checking method. :)

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tomc, after work today I jacked up the front end of my truck and used an inch/pound torque wrench to measure the rolling resistence of the front tires. I made one revolution turning the tire real slow. Pushing on the wrench
just enough to make the tire turn. The passenger side took 90 inch/lbs, and the drivers side took 100 inch pounds. Can any body else with 4wd do this same test?

Thats true it measures straight point to point, so curves kill GPS distance/time calculations. Non-military GPS actually has shown to be way off it is true, they do "claim" 10ft (3meter) resolution though.

I have never verified the odometer, so I am unsure about that.

Mile markers against my stopwatch has always been my favorite speedo checking method. :)

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The 3m quality is only if your receiving the WAAS correction. If not, it's more like 10m. Just trying to clarify things.

I made a trip to Phoenix last year in my dually with the outside tires off to see if it made much difference in the milage. It was worth about 2 mpg. Looks weird but does get better mpg. I have found that tread pattern has a lot to do with milage. A good highway rib tire can yield as much 2 mpg over a blocky M/S pattern all else being equal.

The 3m quality is only if your receiving the WAAS correction. If not, it's more like 10m. Just trying to clarify things.

:exactly:

The point is, your GPS is worthless for measuring distance and speed on the road. It is incapable of measuring the ACTUAL distance traveled unless you travel level in a straight line, therefore its calculation of your speed is also not accurate.

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I made a trip to Phoenix last year in my dually with the outside tires off to see if it made much difference in the milage. It was worth about 2 mpg. Looks weird but does get better mpg. I have found that tread pattern has a lot to do with milage. A good highway rib tire can yield as much 2 mpg over a blocky M/S pattern all else being equal.

I know a guy that ran his truck like this all the time. He also claimed a gain in mpg. It sure does look funny. I wont even put my tailgate down. -:t Tires and road surface also make a differance.

I posted this previously

Technical paper from Cummins :

"Secrets of Better Fuel Economy - The Physics of MPG"

It's for big trucks, but some good general info...

http://www.everytime.cummins.com/every/pdf/MPG_Secrets_Whitepaper.pdf

Things which surprised me were...

- Differences in road surface can account for 30% difference in MPG. Polished concrete is best, chip-seal asphalt is worst.
- wind resistance doubles going from 55 mph to 70 mph.
- Worn tires give better MPG.
- Biggest variable is driver = 30% difference between a "good mpg driver" and a "bad mpg driver".

Page 28 gives a good summary...

jeff

tomc, after work today I jacked up the front end of my truck and used an inch/pound torque wrench to measure the rolling resistence of the front tires. I made one revolution turning the tire real slow. Pushing on the wrench
just enough to make the tire turn. The passenger side took 90 inch/lbs, and the drivers side took 100 inch pounds. Can any body else with 4wd do this same test?

That torque measurement isn't correct for two reasons. One, the torque wrench isn't turning at the center, it has a few inches of leverage at the bolt center. So the actual number is higher. Also, that isn't measuring the rolling resistance of the tire, just part of the drivetrain.

:exactly:

The point is, your GPS is worthless for measuring distance and speed on the road. It is incapable of measuring the ACTUAL distance traveled unless you travel level in a straight line, therefore its calculation of your speed is also not accurate.

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I don't know what kind of GPS you have but my Lowrance measures distance and speed with great accuracy. It samples all the time and computes both speed and distance on the fly. The only time it uses straight line to compute distance is when you use it for navigation to a waypoint or to the cursor. Even then it doesn't take into consideration the curvature of the earth and uses the chord distance.

damn that other truck is working 2 times as hard and that front axle problem is not good look in the wheel openings there should be grease if the cv shaft was leaking and that could be the problem because that is a lot of drag to overcome

i did not see the pics before my post above i thought that it was leaking from the boots not from closer to the diff my bad

I don't know what kind of GPS you have but my Lowrance measures distance and speed with great accuracy. It samples all the time and computes both speed and distance on the fly. The only time it uses straight line to compute distance is when you use it for navigation to a waypoint or to the cursor. Even then it doesn't take into consideration the curvature of the earth and uses the chord distance.

Go test that for us, find an empty parking lot and turn your wheel as tight as you can and run ten circles and see how far your GPS says you went.

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That torque measurement isn't correct for two reasons. One, the torque wrench isn't turning at the center, it has a few inches of leverage at the bolt center. So the actual number is higher. Also, that isn't measuring the rolling resistance of the tire, just part of the drivetrain.
__________________
Marcdeluca, I realize this is not an accurate reading comming off the lug nut. But I thought this would be an easy test to duplicate for comparisons. Thanks for the input.

i think i get the best mileage going to and from the keys you really can't go ove 55 - 60mph traffic and there is no stopping and starting (lights) so it HC at around 19mpg city sucks 15mpganything over 70 mileage goes down hill.

That torque measurement isn't correct for two reasons. One, the torque wrench isn't turning at the center, it has a few inches of leverage at the bolt center. So the actual number is higher. Also, that isn't measuring the rolling resistance of the tire, just part of the drivetrain.
As a comparison for bearing and brake drag it is as long as the bolt pattern is the same and the angle of the torque wrench is as pictured from the center.

As a comparison for bearing and brake drag it is as long as the bolt pattern is the same and the angle of the torque wrench is as pictured from the center.

:exactly:

Thats what I was thinking too, it still would be an apples to apples comparison if it were done in the same manner.

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Go test that for us, find an empty parking lot and turn your wheel as tight as you can and run ten circles and see how far your GPS says you went.

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The satellites the GPS lock on to are far enough away that minor changes in direction and altitude are irrelevant. They are accurate enough to survey and guide missiles and planes.

Every time I have checked my GPS speed reading against a marked mile on a straight level road with a stop watch it has been dead on. This was not a typical mile marker on the public roads. This was a calibrated mile at the proving ground. I have also used a fifth-wheel speedometer and it was close enough for what I needed - within 0.1 mph, which is a lot closer than can be observed with the truck speedometer. (Fifth-wheel speedo uses a tire that looks like a bicycle tire and is attached to the vehicle bumper)

I have to add that there are times when atmospheric conditions are such that a GPS reading will be all over the map. But with my unit I can generally tell because the readings become erratic.

The satellites the GPS lock on to are far enough away that minor changes in direction and altitude are irrelevant. They are accurate enough to survey and guide missiles and planes.
]
Rick those gps units are different from ours. Even with the WAAS on, we dont get those units. I run the survey units three or four times a year and they are quite a bit different from my Magellen that I bought at the sporting goods store.

I wont say you cannot get accurate readings on your GPS, but over a distance the GPS unit will disregard deviations in travel. This is based on the units memory, settings, and the size and time spent deviated from the straight line. The survey and aircraft units do this also, they are designed to get you to a destination and back, they were not designed to have you touch the same reflector at mile marker 19 unless you make it a waypoint when you do it, otherwise that deviation will be lossed on a 200 mile trip.

I would think that unless the drag issues were really bad that these two trucks should get similar mileage. If it were me, I'd probably want the dealer to do an injector contribution test and pull one out to see how it patterns. It's alot of work, but to me there are only a few things that would cause consistant ineffiency without any obvious codes or damage. I wonder if- at the same speed and run distance- the pyrometers would read similarly. Since the engine is a chemical conversion device, the lower mileage truck would theoretically generate more heat. (due to the ineffiecent process). That heat would represent wasted fuel, and therefore combustion problems. Oh well, what do I know- My truck is in the shop so much I need a picture to remind me what it looks like. :mad:

nice

Last post here on the GPS issues unless we move it to the off topic area. I tried the test that TxChristopher suggested. It is sort of an incomplete test as the variables weren't all defined and a tough one for the GPS as it is keeping the entire test somewhere near the reported limits of GPS/WAAS. But here goes. I taped my unit on the front of the hood on the passenger side (longest radius) and made a left hand loop. Drove around a bit till the odometer just clicked to a new tenth. Drove till the odo had clicked to 3 tenths more. The GPS registered .36 miles. Not going to do this again with the GPS on the drivers side of the hood (shorter radius), I am still dizzy :) from the loops. I suspect if I did it would be a bit less than the 3 tenths of a mile. I don't know how the odometer calculates the distance, drive shaft rotation, wheel sensor or what. I could go measure the diameters of the two circles my tracks made and calculate the actual distances but that seems to be a bit much work also. Suffice it to say I have found my iFinder Pro to be very close on regular trips, within 1 or so miles of the odometer on a 200 mile trip. And when used on my boat on our lakes around Denver to be within 10 to 15 feet of the lake elevation. That close on elevation is good enough accuracy for me for the price paid for that unit.

Last post here on the GPS issues unless we move it to the off topic area. I tried the test that TxChristopher suggested. It is sort of an incomplete test as the variables weren't all defined and a tough one for the GPS as it is keeping the entire test somewhere near the reported limits of GPS/WAAS. But here goes. I taped my unit on the front of the hood on the passenger side (longest radius) and made a left hand loop. Drove around a bit till the odometer just clicked to a new tenth. Drove till the odo had clicked to 3 tenths more. The GPS registered .36 miles. Not going to do this again with the GPS on the drivers side of the hood (shorter radius), I am still dizzy :) from the loops. I suspect if I did it would be a bit less than the 3 tenths of a mile. I don't know how the odometer calculates the distance, drive shaft rotation, wheel sensor or what. I could go measure the diameters of the two circles my tracks made and calculate the actual distances but that seems to be a bit much work also. Suffice it to say I have found my iFinder Pro to be very close on regular trips, within 1 or so miles of the odometer on a 200 mile trip. And when used on my boat on our lakes around Denver to be within 10 to 15 feet of the lake elevation. That close on elevation is good enough accuracy for me for the price paid for that unit.

I love the DP. :ro)

Never seen a group of people who walk the talk as on here, as in willing to spend their own time and effort to try things and get things done, even when its for someone that they don't even know. It is very refreshing change from the world in general where people talk all sorts a sh!t and never follow through with even 10% of it.

:grd:

I hope everyone realizes what a resource this BB is.

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I suspect that the error you will find is directly related to the centerline of the vehicle versus the position of the GPS receiver. The differential of the vehicle will slow the inside tire down and speed the outside tire up to make up for the turn. Your drivetrain upstream of the rear end doesnt know it was making a turn.

Back on topic. The dually will not do as well in mpg as the exact same engine and tranny in the 2500 HD short bed. To much differance in the trucks.

gschulte
Have you had your truck to the dealer yet? Any differnece in the front wheels being hard to turn over?
When I suggested the torque wrench I had intended for you to use the center hub nut. But what you did will work for a before/after compare on your truck. Another way to check initial effort to turn a wheel is with a force gauge (digital fish scale) and wrap heavy string around the tire a few wraps and measure the force it takes to get the wheel to turn. Tire diameter will effect readings so a truck to truck compare would need to compensate for that. I will check my truck latter today or tomorrow.

I have a dually we could test it against.... It's only 2 wheel drive though.. But it's a lot closer to the problem truck that Tx's is...

I have a dually we could test it against.... It's only 2 wheel drive though.. But it's a lot closer to the problem truck that Tx's is...

Well, we need to hook up and get numbers on yours as well. The more info the better.

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Its a shame that as a part of the test the ecm from one truck wasn't switched with the other to see if the figures changed with module or stayed with truck, that is of course if you can switch ecm's between trucks as I sure don't know that as fact.
Merle

Well, we need to hook up and get numbers on yours as well. The more info the better.

. I am free Sunday... :D

I am free Sunday... :D

Do you charge on the other days? ):h

I need to get back up north anyway and get with Melvin and try to finish up the TxC CAI Mega, when Sunday?

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Do you charge on the other days? ):h



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Theres one in every crowd.. Keep your day job :)

I get off duty at 7 am... IF I don't catch a late run.. I am working at the Lake Houston Station so I could come to you if you promise to start reading better joke books....

Right now, I am free on Sunday as well. Well, at least up until late afternoon, as all the latest and greatest TV commercials come on that afternoon; someone even said there may be a football game in between the commercials.

PM me and we can schedule something.

So if swatkins is able, and you are willing, we could meet at your place in the morning?

What time?

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Melvin is north side near 249, grant road-louetta-north eldrige-spring cypress area.

9am work?

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Works well for me!

I have been informed by my better half that her Dad's B-day is Sunday, so we need to get done within 3 hours so I can get back and be present for that stuff, which should be easily achieved. The ride with you swat shouldn't take long then I can work some more on getting the Mega CAI done with Melvin's truck.

.

Will be fine with me.... Should be there by 8:15 IF I dont catch a late run...

Thats even better. I can meet up with you and we will get numbers on your truck, then after that we can pester Melvin :)

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Tomc, The dealer is working on my truck today 2/28/06. I will let you know if they find anything.

I checked the front wheels on my truck today. Bone stock with 21K miles on the clock. Transfer case was in 2 wd
Using the torque wrench on the lug nut I got 22FtLBS on the drivers side and 26 ftlbs on the passenger side. The wheels felt like they turned over easily.
I also check with a string hooked to a digital scale and wrapped around the studs. I pulled each side 4 times rotating 1/4 turn before each pull to see the effect of any warpage on the rotor.
My pulls were 11,13,14,&17 lbs on the drivers side and 13.3,12.5.16.4 & 18.7 on the passenger side. I pulled in both forward and reverse directions with now real difference in the numbers.

14663

I found away to improve the mpg on my truck by 2mpg. It was quite simple actually. I had a friend who needed a truck to pick up a 4 wheeler, so I lent him mine. His dad did the driving to and from Tennessee from LA. They got 19.06mpg (hand calc.) with my dually. To say the least I was impressed, I normally get ~17 mpg.

The way to do it, SLOW DOWN, it appears that Pat's father like to look at the scenery, he tells me he drove 60 most of the way unless he wasnt on the interstate, then he drove 50 or mph.

It is just that simple.

I found away to improve the mpg on my truck by 2mpg. It was quite simple actually. I had a friend who needed a truck to pick up a 4 wheeler, so I lent him mine. His dad did the driving to and from Tennessee from LA. They got 19.06mpg (hand calc.) with my dually. To say the least I was impressed, I normally get ~17 mpg.

The way to do it, SLOW DOWN, it appears that Pat's father like to look at the scenery, he tells me he drove 60 most of the way unless he wasnt on the interstate, then he drove 50 or mph.

It is just that simple.

:exactly:

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Its a shame that as a part of the test the ecm from one truck wasn't switched with the other to see if the figures changed with module or stayed with truck, that is of course if you can switch ecm's between trucks as I sure don't know that as fact.
Merle Can't swap ECMs; they will be "theft-locked" the moment they can't match the VIN in the BCM, unless you are willing to go through the whole One-Hour procedure with a Tech-II to get them to re-learn the VIN every time you swap.

Can't swap ECMs; they will be "theft-locked" the moment they can't match the VIN in the BCM, unless you are willing to go through the whole One-Hour procedure with a Tech-II to get them to re-learn the VIN every time you swap.

Thanks! Didn't know about that. :cool2:

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Hey Tx are we still on for tommorow?

Hey Tx are we still on for tommorow?

As far as I know yes.

.

Where do we meet up ?

Now you wanna get all technical on me......

.

My work truck [ GMC ] is getting 9 MPG highway or city which I believe is poor MPG. My D/C is 16 highway towing 27.5' 5ver and 20 empty at 70 MPH. Is this normal for the DMAX? The bosses truck is a 01 250 ford diesel with 8' service bed and getting 17 MPG hi or city. He blames my driving for the poor MPG, the estimated weight is 4000# with no mods

Today we took some numbers on swatkins truck, a 2 wheel drive 05 crewcab dually that gets what we consider good mileage.

Below find boost data 70mph for my truck (C in blue) and swatkins (S in red)

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Below find 70mph boost data all three trucks, TxC in blue, swatkins red, and gschulte in yellow.

Again, gschulte truck works hard for a living to do what others do.

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Below find a graph showing RPM at 70mph.

Even though swatkins has smaller tires and therefore has to turn over faster to go the same speed as my truck and gschulte's truck, he still gets good mileage.

TxC blue, gschulte yellow, swatkins red

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Hopefully we can pin down what it is that causes gschulte's truck to get poor mileage, the data consistently shows his truck is working harder to go the same speed.

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Were you by any chance able to check tire rolling resistance in Swatkin's truck?

How about Gshulte's truck, did he have the dealer look at the front end to see why so much more rolling resistance than yours?

Thanks.

Were you by any chance able to check tire rolling resistance in Swatkin's truck?

How about Gshulte's truck, did he have the dealer look at the front end to see why so much more rolling resistance than yours?

Thanks.

Dangit, we didn't. Maybe we can get swatkins to jack his up in front and spin his tires for a comparison. We were on a limited timeframe due to my other commitments (the womans daddy's b-day) and the commercial fest coming with that game in between the commercials.

Gschulte truck is either at the dealer or scheduled for it, so we are still waiting for an answer back from him on that.

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I will check mine out in a couple of days....

Mine could be easily changed by backing off the bearing nut if it's too tight,,, Not sure what you do for a 4 wheel drive...

Tx....

IF I were to put bigger tires on the truck what would happen?

I would think that I would get even better MPG because of the decrease in RPM's... I always thought Chevy put the smaller tires on to keep the power curve where it needed to be.... With the numbers we took today it seems that I could still put te bigger tires on and still have plenty of reserve.... Am I on the right track?

Guys,

It has always been my theory that when you go oversize tires/rims, you will sacrifice city mileage. My reasoning is simply this, the tires are bigger and heavier and have greater mass, hence it takes more to get them rolling Vs a smaller tire. I also believe that you would get somwhat greater (reletively speaking) while cruising, because you don't need the power required to get you rolling (acceleration), and you have the RPM benefit. What do you guys think?

Bill

this is true. when you go bigger, you lose mileage in the city. don't forget to compensate for your mileage as for the difference in the circumference of the tire. But with 285s on 16s you should be around 2000 RPMs at 67-70. If you keep your truck below 2000 RPMs, people have been getting great fuel mileage.

I think what is important is the comparison with trucks with equal size tires. I have 285 x 16's on my and get much worse than others with the same tires. There are just some trucks that get much worse milage than others and it is great a few are trying to figure out why. Most dealers are clueless about the problem or otherwise there would be a fix.

What these guys are saying sounds good. I am very confident you would get better cruising down the freeway, but they may be right about the city mpg's. I know the power difference is very noticeable with the 285's versus stock, so around town your truck might be working excessively from every stop.

Driving habits have a lot to do with that too, as slow as you cruise around you might get away with it.

The only real way to be sure would be to run a real mpg test on 1 truck, doing the same 200 mile city loop and the same 200 mile highway loop and measuring mpg with only the tire change. Then we would KNOW.

I might be willing to eat the test in the name of DP research if I had someone local willing to swap wheels for a day.

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I think what is important is the comparison with trucks with equal size tires. I have 285 x 16's on my and get much worse than others with the same tires. There are just some trucks that get much worse milage than others and it is great a few are trying to figure out why. Most dealers are clueless about the problem or otherwise there would be a fix.

:exactly:

We have shown with hard data there are real differences truck to truck, thats why I suggested the test above on 1 truck with just a tire change. As it turns out I may be putting stock tires on mine soon and not need any external help.....

No promise that this particular test will occur anytime soon......but it would be nice for us to know one way or the other to be able to make a tire selection based on mpg's as well as looks.

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Hey Chris, figured I would check up on this thread, since I obvisiously missed something ;) .

Anyway, I have my stock rims and tires sitting at the house. If you promise not to treat them the way you treat your tires, you could borrow them :) . I might have to do a before and after tread depth check :muahaha: .

I will also add that I have kept detailed records on mileage from day one, and have not seen any difference in mileage between the stock 245's and 285's. LB7, but I don't think that will make any difference.

HoustonDMAx heres the links I promised you...

http://www.watkinscamper.blogspot.com/

And http://www.watkinstruck.blogspot.com/

And here is what I replaced the Starwood with and I am pulling now...

http://happyheartdesigns.com/trailer.jpg

3000 mile round trip to San Diego from Houston. 8.9 MPG usually about 70 mph and fighting winds.

tomc, finally got my truck back from the dealer last friday. last night I jacked the front of the truck up to check the front tires. To me they seemed turn hard. I used your method, the string and a fish scale, wrapping the string around the lug nut studs. For oal average, I got readings of 35 to 40 lbs
of pull needed to make the front hubs rotate. Thats 3 to 4 times greater than your truck. Next I took the calipers off and ran the test again. IT only took 11 to 12 lbs to make each side rotate. Put the front calipers back on. Regreased the bolts, started the truck, pushed the brake pedal several times,
and again it took 35 to 40 lbs to make the hubs rotate. Now what? What else could be keeping pressure on the front calipers. If I can find figure it out,
I will try to start a new thread in the driveline section.

Hey Chris, figured I would check up on this thread, since I obvisiously missed something ;) .

Anyway, I have my stock rims and tires sitting at the house. If you promise not to treat them the way you treat your tires, you could borrow them :) . I might have to do a before and after tread depth check :muahaha: .

I will also add that I have kept detailed records on mileage from day one, and have not seen any difference in mileage between the stock 245's and 285's. LB7, but I don't think that will make any difference.

Ok, we have a stock tire source! That was fast. :lol:


The driving would all have to be "normal" as in reasonable and steady, which I can do for good research, obviously not the way I normally scoot around :muahaha: and stock tires wouldn't stand a chance of keeping traction on my truck the way it is. For the test I would bring it to completely stock (eewwwww!) and make the tires the ONLY change. My truck can be returned to completely stock very easily.

Unfortunately it will more than likely be more than a month before such a test could be tried since I have other projects in progress, so even though it will likely happen it won't be right away.

After I am done with this overheating thing we can look at the mpg test further.

Oh and the layout of the Mega CAI looks to be determined, now its design time and proof for it. All the TxC CAI's will likely go to this style so that 1 model can cover the truck whether ya got a Mega or not. :ro)

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tomc, finally got my truck back from the dealer last friday. last night I jacked the front of the truck up to check the front tires. To me they seemed turn hard. I used your method, the string and a fish scale, wrapping the string around the lug nut studs. For oal average, I got readings of 35 to 40 lbs
of pull needed to make the front hubs rotate. Thats 3 to 4 times greater than your truck. Next I took the calipers off and ran the test again. IT only took 11 to 12 lbs to make each side rotate. Put the front calipers back on. Regreased the bolts, started the truck, pushed the brake pedal several times,
and again it took 35 to 40 lbs to make the hubs rotate. Now what? What else could be keeping pressure on the front calipers. If I can find figure it out,
I will try to start a new thread in the driveline section.

If you do start a thread there, leave a link here so we can also see what you find, as it surely impacts this thread.

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" The driving would all have to be "normal" as in reasonable and steady, which I can do for good research"

In your dreams!

Christopher, I tried before, but was unable to figure links and quotes out. Also I was unable to open your attachment on your e-mail. Could You mail the instructions to me.