Ive only had my truck a few months and checked combination Highway/around town mileage Is about 11 mpg

I went on a 3500 mi trip across nevada, Idaho etc, Open road milelage With a 8'6" Lance camper about 2500 lb dry wieght .

The hole trip tring different speeds I only got 11-12 mpg

Truck has 3.54 gears automatic , bone stock with a K&N filter.It has 305/70 nitto tires and the trans is rebuilt and reprogramed. I think for the tire size.

I also found a old Dealer work order from the previous owner in the glove box,That complained of Poor milage ,10mpg, . It just said "cause over size tires".

I have not took a long staight highway trip with the bare truck (no camper/load) But I dont think I would even get 14 mpg.

I thought this truck sould get 17 -20 mpg

Whats causeing this crappy milelage? Something isnt right ... Map sensor ?? Or...???

Im going remove the exhaust resonator and stock muff and put on a 4" system . But I think this truck how it sits should get beter mpg than 11-12 .

The truck is in emaculate condition and the previous original owner took good care of it.

Any ideas?


Thanks Rick

 

How tall is your slide-in? You are probably poking a big 'ol hole in the air. Even though, I would think you should be getting at least a couple more miles per gallon. I get about that pulling a 28' enclosed tag that is almost 10' tall. I did notice a 2-3 mpg increase when I installed injectors and running the Comp on level 1.

 

Mkubacak,


Yea the Lance camper Is Tall . I Know that capover camper pushes alot of air, compared to a trailer back behind the truck. It looks like If I was pulling a lower , even heaveyer travel trailer Id have better airodymamics.

My truck doent have the fuel milage over head computer deal. So I cant see what mpg its getting at an instant when Im cruiseing down the highway. I just check it with a calculator when I fill up at the station.

 

verify the mileage is correct for the big tires, it's probably off by 7-8%

 

305/70 s arent realy big. Not even tall. The odometer seemed right on when I checked going by Milage marker checks on the highway. There is a trans reprogram sticker under the hood, I called the dealer and they said its programed for the tires.

Is that going to set the odometer too?

 

You may want to find out how many revolutions per mile your 305's turn and compare that number with whatever size was stock on your tuck. If I am correct, stock on mine was 679 revs per mile and my 19.5's are like 620 revs per mile. My local dealer changed mine for about $30.00. I had to walk them through the procedure on the DRBIII though.

Here is a link to stock revs per mile:

http://dodgeram.info/tsb/1999/26-11-99.htm

 

305/70/16 = 615 Revs @ mile
245/75/16 = 661 Revs @ Mile

McMopar is right....7.5% difference. Getting maybe 1 mpg more if your speedo is not corrected.

Have heard others talk low teens with a slide in...LOTS of wind resistance and 1000 lbs +/- over Gross wt.; 12-13 mpg doesn't sound that bad.

Is the 11 mpg around town with or without camper?
RJ

PS: Mcubacak - something appears wrong with that chart (link). They list 245/75/16's from 652 to 691 revs? Can't be that much difference between brands, can there?

 

I noticed the same thing. I found that on Fritz's Ram page. I am guessing the info was pulled straight from the TSB, but if it was keyed into the page, then there could be a typo. I called Kuhmo directly to get the revs per mile for my 19.5's. I have noticed on Rickson's website that different manufacturers tires may all be say 245/70R19.5, but have different widths and heights, and thus different revs per mile. This may explain some of the differences.

 

Rjohnson thanks for the imfo.

Do you know waht sixe 75 series tire will be the same revs as the 305/70.

I only ran one tank full through with out the camper on just local driveing . Combination runing down the freeway many times and stop and go in town, Plus I was doing oil changes, lift pump install,fuel pres gauge /filter install. milage was about 12.69 mpg no camper on.

With lance camper on I was getting 11.9 -12.6 open highway running 60- 70 . My speed didnt realy have affect on mpg. and pulling grades didnt seem to make a difference much either. I has fighting a stiff head wind from Jorden valley Id to winimucca nev and it went down to10.7 mpg . Wind was the biggest factor. And then 11.2 -12.2 with lots of stop and go .

I have the camper off again now so Ill have to run another tank through and check the mpg again

 

Check these two sites; Look under Revs @ mile column.

http://www.michelinman.com/assets/pdfs/doc_ltxms.pdf
http://www.bfgoodrichtires.com/asset...rain_ta_kd.pdf

Mkubacak - You'll see that both brands have about the same # revs.+/- 1 or 2.....per size.

GSP - check BFG page...Michelin does not make a 305/70/16.

RJ

 

To figure out the rev.per mile just measure around the tire and divide that number of inches into 63,360. That will give you the exact rev.

 

Yes...approximately. But # of Revs per mile decreases as speed increases and tire elongates. On a larger street tire, difference from 10 mph to 80 mph can be up to 10 revs @ mile. On a Top Fuel Dragster...probably 1/2 the # at 300 mph as sitting still.!

RJ

 

rjohnson,

I agree with you totally. The chart I was referring to is here:

http://www.ricksontruck.com/tires_24570R195.html

All tires are 245/70R19.5 (The size I am currently running) and the widths vary from 9.4 to 10.2 inches, diameters vary from 33.0 to 33.8 inches, and the revs per mile vary from 612 to 629.

I also concur with you on the difference in diameter based on speed. The other difference would be over the life of the tread. These particular tires have tread depths of up to 22/32nds of a inch. Double that number and the difference from new to bald is over a inch in diameter.

I guess there is no constant here just a variable.

 

Towing 30 ft eclosed trailer, TST on 7, and 70 MPH I currently get 14mpg. Empty, same settings and speed on hwy, I get 23mpg. With the large tires my speedo is off 5mph.

I had the same problem that you are describing and it turned out to be the wastegate not closing all the way. When I fixed that I just spent the money and did the rest of the upgrades.

JB

 

Any tips on checking if my waste gate isnt closeing all the way, Fixes? Working properly?

Ive only played around feeling the waste gate shaft and I couldnt make it move with my fingers. Dont know how stiff it is but I was thinking I could push or pull on the rod and it would move or wiggle. Nope.

Rick