Mileage

[michaelsgreene]

Here is some more interesting information from TST. Look at



http://www.tstproducts.com/power_kits.html





"Thousands of power kits have been sold, with nearly all customers reporting fantastic power gains. Most Kit owners report no difference in fuel mileage.



--->>> A few owners who tow heavy loads have reported the ability to tow in a higher gear, obtaining better fuel mileage. <<<---



Those customers reporting ability to cruise at higher speeds often report poorer mileage.



--->>>No secrets here, for a given horsepower the lower the engine speed (down to about 1500 rpm) the lower the fuel usage. <<<---



Also, higher speeds require more horsepower and more horsepower means more fuel used. TST Power Kits give you much more power and torque on tap:



--->>>using the torque to reduce engine speed can improve fuel mileage,<<<---



using power to increase road speed will reduce mileage. Either way you have much higher performance just a pedal away. "





Michael

 

[DEZLPWR]

Michael,

Are you running go cart tires on your truck? How the heck are you only running 63mph @ 2400rpm?

 

[michaelsgreene]

5 sp trans

4. 11 rears

215/85 or 225/75 tires



No, really!



I didn't know any better at the time and until recently, it did not occur to me that changing the tire size could make that much difference in the total ratio,



Michael

 

[Powder Extreme]

My old '94 with a 5 speed and 3. 54's would get about 18 to 19 empty and 14 to 15 towing a 14k 5th wheel. Not bad mileage at all. Then I added a US Gear overdrive (personally I feel is much better than a gear vendor). My mileage at 65-70mph went up from 19 to 21, I saw as high as 23. The biggest reason I added the overdrive was to cruise at 85mph, be spinning only 2000rpm, and still get 18 mpg, which I did. My towing mileage didn't really change with heavy loads because 5th gear and overdrive was too tall for towing 14k at 65mph. Towing my car at 70mph the mileage did increase. I think your best bet is to buy an overdrive unit. Then you'll always have the right gear and with your motor turned up, you'll always have enough power.

Hope this helps!



Jerry



PS. my 94 was a 3/4ton, when I went from 245/75 16 to 235/85 16 I saw another . 5mpg increase, not much, but worth it. Also if you are towing bumper pulls at times, having a tonneau cover will be good for . 5 to 1 mpg increase.

 

[zjones]

I run 235\85 R16 on my 97 (see sig) & get 85 mph at 3000 rpm.

get 12-13 mpg pulling a 26k lb. trailer (man I say that in every post ) running 70-75 mph, 13-14 mpg unladen.



cetane boost (fuel additive) & TST #11 kit gave me the best mpg increase. (I can stay in 5th gear )

 

[Mick2500]

Michael,

Try this site:



http://www.thisoffice.com/calc_tire3.html



It's BMANS gear ration calculator site. Just

after I got my truck I sold the 265X75X16 to

my riding buddy and put BFG TA KO's on. 315X75

X16.

Granted I only have 8,155 miles on this truck but I almost always get 17-18 MPG (calculated).

Mostly it's in-town stop and go, 45MPH'ish with

occasional 75MPH on the freeway (AZ is 75MPH).

On two trips I have seen 17-18MPG cruising at

1,900RPM just slightly over 75MPH.

One of these days I 'might' try keeping the

speed down for a whole tank on the freeway but

I'm not sure when I will have the patience to

do that. I would be considered a traffic hazard

around AZ.

I'm never loaded and about the only thing I

ever tow is a 1,000 MC trailer.



Mick

 

[michaelsgreene]

Thanks for the calculator page, but now I'm even more confused.



My present LT225/75R16 Michellins are just under 28 1/4 inches, which according to the calculator would be correct for a 205/75.



It DOES prove my theory that the height of the tire is inversly proportional to the engine RPM.



Thanks, still thinking.



Michael

 

[Oil Ape]

Be careful using the strict ratio tire method for determining size of a tire. Although that is basically how they are designed, due to differences in # of belts, tread patterns, etc... that will actually vary slightly dependent on tire size, application, and manufacturer. The tire once inflated, has a different aspect ratio due to width of rim, bulging of sidewalls... . you get the picture.



An example we ran into while working at a tire location was the difference between a 235/75 R15 Truck tire vs a 235/75 R15 Car tire. The truck tire, even though having the same exact ratio on paper, was a taller tire by over 1" and probably closer to 2"



Once again I must state that I doubt a tire change is going to give you any appretiable gas mileage advantage and if you are indeed running a dually the largest you might get away with would be the 235/85 R16's.



I think it would be to your advantage to start looking for a truck with the 3. 54 rearend and sell yours off to someone who thinks they need the 4. 10's.



If you are pulling a trailer and you don't have an excessive amount of weight in the actual bed nor need the side to side stabilization helpful for a camper, you could probably gain the advantage of going to a regular bed vs. the dually. We use our trucks alot pulling loads via gooseneck trailers pushing the 30,000 lb barrier and have never needed a dually nor the 4. 10's in these particular trucks.



Good luck in whatever you end up doing... .

 

[Boldt's Wagon]

Michael:



You probably should go to 235x85 tires first.



You didn't mention what timing you set when you replaced the cam gear/KDP cover. A couple degrees of timing advance has reportedly given 1-2 mpg (particularly with the higher rpm you are operating at). When timing the TDC should be set by piston measurement, the plastic TDC pin has been known to be off.



The last change might be trading gears with someone.



Also get the gov spring kit to fill in the power holes between gears.

 

[pwknapp]

I run 4. 10, 5spd and 235/85's. At 2450 rpm I am running 71. 7-72. 3mph with the gps or 70 on the speedometer. I consistently get 13. 4 to 16. 5 empty with the average around 14. 8. This is with a flatbed. Pulling my trailer at 32k gross I get 7. 2 to 9. 3 usually around 8. 4 directly proportionate to the wind load and wind direction. Best tank unloaded was 19. 85 mpg running with a group of big trucks from Indy to Memphis at a "good" rate of speed. ( ie; no wind)



I would buy 235/85's and consider changing gears later, and keep the truck you have. It sure seems like it would cost a bunch more to sell one and get in another any cheeper, much less loosing all the mods you have done and the confidence in your previous maintenance. I have wrestled with the overdrive unit, tire size, gear change and which additives for some 400k and just keep pumping in fuel. If funds would permit I want to add 19. 5's and some tall skinnies. JMHO

 

[Rambling]

Just a thought or two..

At any specific rpm the stock engine has a given hp and torque. A change in the drive ratio doesn't change the hp at the specific rpm but it does alter the torque at the wheels.



That is, with higher drive ratios (bigger tires, 3:55 vs 4:10, O. D. ) there will be lower torque. . lower torque at the same rpm means more pedal(fuel) to regain the reduced torque because it can't pull as well. This might be why there is little gain from these modifications.



Adding more fuel (injectors or boxes) increase's horsepower but usually isn't burnt as efficiently (even if you can't see the smoke). Increase in hp increases torque but most likely not on a one-to-one ratio. Which also might explain no great leap in fuel economy (excluding the fun factor of course).



I know someone will help me see the error of my ways on this.

 

[Lsfarm]

I agree, But:

Rattlin: I agree with your points in the above post, but I think there is another issue here that has a big effect on mileage.



It is torque that pulls the load, and HP is just a multiplication of torque times speed or time. The 12v engine makes it's best torque for fuel consumed at much lower revs than 2400 rpm.



I haven't yet seen a post from anyone saying that they have lost significant mileage from there truck when they went overboard with tall tires or gear ratios. I think some are running 3. 08 gears. And others are running the additional overdrive boxes.



The 12v Cummins is near [when in stock form] it's upper rpm/HP limit when running 2400 rpm. If I remember correctly my '96 would stop revving at 2650, pedal flat to the floorboard.



There is a lot of internal friction that every engine has to overcome to run and this friction increases rapidly with rpm. If Michael's truck was able to run say 2000 rpm at the same speed,[63mph]. I believe that he would see at least a 10-20% average increase in fuel mileage. His 12v Cummins likes lower rpms, and much less fuel would be consumed overcoming internal engine friction.



Note: I said average fuel milage. There will be tanks consumed where the headwinds, and uphill climbs may result in the same or slightly lower mileage, but from Michael's description of his driving, I believe he should see a mileage increase.



JMO Greg L

 

[Oil Ape]

You're right on... .....



Granted running around empty these trucks have untapped potential so adding a larger tire, higher ratio etc. . may snare you some extra mileage. That is only if you don't increase the ratio to the point that you begin to work the truck...



The problem rests with a load. Once a load is placed onto the truck, not necessarily a large load but one that would normally show a mild change in fuel mileage even running empty up a hill, the truck is being taxed. Any modification to this ratio at this time means the truck has to demand more fuel to obtain the same speed. If you put a yard of sand in the bed of your truck, you can't move as fast or accelerate without giving more pedal..... more pedal more fuel... . more fuel lower mileage... .



That is why the 3. 55 rearends get superior empty mileage, then drastically reduced mileage(6-7mpg) under a load whereas the 4. 10's don't get very good mileage to begin with but only lose a couple of miles per gallon under the same load. The 4. 10 rearends are virtually designed with a lot more untapped potential empty... .

 

[Lsfarm]

That's Why

Oil Ape: That's why I like 3. 54 gears! I can run 70mph @ 1900 rpm, then if the hill and load are significant, I can drop out of OD, and turn 2700 rpm up the hill, maintain speed if I want, and still drop back into OD when on level or downhill. And either save some fuel that would be used up in friction, or pick up the speed.



When I had 5 speed and 6 speed CTDs I used 4th or 5th [Direct ratio] when pulling a heavy load. The ratio is about the same as having 4. 10 gears, and there is no heating of the transmission since there is no gear multipication [or reduction] in the gearbox.



With my stock trucks I've never seen less than 12 mpg towing at up to GCVW of 20K. And I run hard! 75-80 towing if the traffic is light. I haven't had the opportunity to tow much weight very far yet with my latest truck [see Sig. ]



Greg L

 

[michaelsgreene]

OK, so I put on the new tires and a funny thing happened: The radius of the

tire is 20% bigger, the diameter is 20% bigger, the circumference is 20%

bigger, so far so good? The speedometer is off by? ... No, you would be wrong.

It is off by 10%.



I was pretty much awake during math class and this just doesn't make much

sense. There are no exponents or logarithms here, just straight linear ratios.

I am very confused about this. Oh, well, at least there is some improvement.



Oh, more good news. I found a guy up in the middle of BC who has the gears I

want (3. 54) and he wants the ones I have (4. 10). That makes the gear ratio change now cost

$200 for labor rather than $2200 for parts AND labor.



I will run like this (with the bigger tires) for a month or so and see what the

difference is. If it is as I expect, then in July I will do the gears. If

that turns out to be TOO much, then I can always keep the gears and go back to

the smaller tires.



Michael

 

[Oil Ape]

Nice looking truck, I think you'll like the bigger tires... even if they don't give you any better mpg.



I would just assume the difference in size will account for "about" a 5 mph difference in your speedo. That will be close enough.



After you have run it for awhile report back on your findings... Most of us are very interested in the conclusion...

 

[pwknapp]

I measured the circumference of the original stock 215's and the 235's and came up with 5%. The GPS shows 3. 3% at 70 mph. This has bothered me for a while because I charge by the mile. I think the stock setup is not as accurate as it should be for a baseline. I think that you wil be getting the mileage every else brags on after the tire and gear switch. Plus as all of us 4. 10 owners know triple digits without sounding as if it is going to blow up may be a reality for you. What a deal!!!!!

 

[Chipstien]

I think the tires will help. Glad you got them. what size did you end up going with... . 235 or 255.