Town MPG in a CTD

[slowmover]

Yes, the OEM's will be sold. I expect to re-coup most of the discounted price on the new ones (yay!). As to FE: the OEM ones -- when down -- present a solid, smooth piece. The CIPAs have those two arms -- even when retracted -- and a bigger, flatter head. I'm guessing .5/mpg at 65-mph and under (minimum).

[skyking]

I think not while towing. Maybe as a bare truck, but the trailer hit will make that measurement unlikely.
I shot you a PM on other matters, BTW.

[slowmover]

Looking at the mirrors now mounted my initial thoughts on how to mount a 6" convex will have to be changed. The arms describe a V-shape from above, thus putting an arm-mount convex "behind" the mirror head (plane). Am considering mounting to the A-pillar, slightly above the mirror arms, and then rearwards. Getting nasty from an aero point of view, unfortunately. Wont' be solving this right away.

[slowmover]

Made [2] round trips north to just west of Ft. Worth to buy a new-to-me 35' 1990 SILVER STREAK Sterling travel trailer [TT] to replace the '76 32' I have at present. Had to work around both Xmas & New Years (bank & state offices) thus two trips. I was a little surprised at not being able to get some service done prior to turning south, but, as a test of "worst" there is nowhere to go but up so far as mechanical baseline is concerned, for:

1] TT axle alignment (rear off by 1/2-degree plus worn parts).
2] Brake controller failed, so tow vehicle [TV] had to do all the work.
3] No weight distribution hitch [WDH] attached, so all tongue weight [TW] was on TV rear axle [RA].
[4] Truck is in need of some work.

In short, how not to do it. And holiday traffic on IH-35. A long slow drive carefully near (but not next to) the outer white line. 40-years experience is nice to have (and the years as a pro driver), but it was still a long, long day of keeping the TT tail from swinging inadvertantly.

Freezing temps in northern Texas up to about 60F in South Texas (430-miles), at 57-mph. Coolant temps ran around 188-194F the whole trip (grille block removed for towing portion). Still, saw 14.9-mpg on that southbound leg. Would have been just above 15 had I refilled prior to hitting Corpus Christi versus a couple of cold starts a day or so later.

Pics when I get a camera.

MPG on the initial northbound leg on IH-35 where a solid 23-mpg was seen (grille block in place) at 57-mph/1,750-rpm. Returned via US-281 50-miles to the west (hilly, rolling two-lane), but the yuppies who've moved into the country-side west of Austin ruined that for steady mpg (treating a country highway like a commuter freeway: dense-headed drivers unaware of others); a far sight different than when I used that road to travel to college back in the late 1970's and the relative cost of gasoline was even higher than today. 22-mpg

The second northbound leg was at just below 1,900-rpm (the likely "high" for reasonable mpg) at 63-mph on IH-35 and mpg was 25.

The overall was 2,190-miles at 21-mpg. At $3.90/gl (102-gls; or, $400) the fuel cost per mile was 18-cpm which is on track per history, overall. Fuel use prediction is key to my ecomodder interest: changes to the baseline mpg as percentage increases where expressed as cpm.

Truck solo weight was:

CAT Scale

FA = 4,220-lbs
RA = 3,760-lbs
TTL = 7,980-lbs

With TT:

FA: 3,820-lbs
RA: 5,340-lbs
TT: 6,540-lbs
TTL: 15,700-lbs

As you can see, the TV "lost" 400-lbs off the FA while adding 1,580-lbs to the RA. The TT was nose-down and the TV just slightly nose-up (hitch height was low). A WDH "restores" the FA to the solo value while also transfering some the TW rearwards back onto the TT axles. This improves braking & handling in all respects when done correctly (using a certified three-pad weight scale to leverage per derived values). This is a direct and indirect help to mpg.

The approximate TW of 1,180-lbs is high due to TT nose-down attitude, but will still be in excess of 1k. On an empty TT like this, a 12.5% TW would have been around 820-lbs. With a TT GVWR of 9k -- and an estimating GVW of .92 -- for calculating/planning purposes the TT may weigh around 8,280-lbs once loaded/outfitted. An estimated TW of 13% = 1,075-lb. Close to the actual number above.

Thus, when the TV FA is "restored" via leverage we'd expect to see about 800-lbs on the TV RA and 270-lbs added to the TT axles once the WD is set properly (versus all 1,070-lbs on the TV RA plus 400-lbs from the TV FA). This preserves over 1,400-lbs of TV payload capacity as well (which will be needed with the addition of a larger fuel tank and greater load in bed, as planned).

I should like to see 17-mpg once TV & TT have a better mechanical baseline and TV sees a few improvements as well. This would be low-altitude, level Interstate at under 60-mph. A range of 15-17 mpg would be consistent, overall, with at least a dozen others pulling aerodynamic, all-aluminum TT's of 28-34' at 8-11k with DODGE CTDS (pre-2008) at around 14-16/mpg.

This will be a near-to-the-legal-limit 65' combination rig weighing above 17,000-lbs.

(Current sig pic below shows the first of the three Silver Streak TT's I've owned; that one was a 34'. Appearance of the latest is quite different: radius curves, etc).

.

[ron]

thanks Slowmover I will use your set up info/advise as a baseline for my trailer when purchased . I am pleased to see the tow mpg numbers as well

[DieselX]

We are full timing now too, glad to see mpg's can be so good. Been watching this thread we are going from NC to Fla in a few weeks.

[slowmover]

I'll help as I can, fellas. Thanks

Mechanical baseline on both vehicles needs to be top-notch and the proper weight distribution hitch needs to be set up on a certified scale. This is basic, and minimum (and fewer than 10% of all RV'ers do it).

My towing average thus far is 25-cpm assuming $4/gl diesel. That's a more accurate way of looking at tow or solo miles than mpg figures.

Solo has been 15-cpm.

My previous combined figure was 20-cpm . . so the above, at 18-cpm, it is in the ballpark at the start.

.

[DieselX]

Towing I have been getting from 10-11.5 mpg. But I usually drive around 65 mph because if I don't the transmission wants to downshift out of overdrive on the rolling hills. On flat ground I can go 58-60 without issues.

[ron]

aren't you suppose to drive with the OD off to save the trans while towing

[DieselX]

Originally Posted by ron

aren't you suppose to drive with the OD off to save the trans while towing

I tow with the OD on unless the hills get too long and the transmission shifts in and out of overdrive. Fuel mileage wise I get better with the OD on than off at 60 ish.