Best mpg with 35s - Dodge Cummins Diesel Forum
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post #1 of 22 (permalink) Old 01-19-2017, 04:00 PM Thread Starter
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Best mpg with 35s

Just curious what everyone's running with 35s and what mpg you're getting. I'm feeling like 14-15 mostly highway isn't exactly ideal..but I don't have many upgrades, either.
I guess it's worth noting I drive up and down a huge grade twice a day, too..which doesn't help.

So what inj, tires, rims, etc are ppl rocking, and is there anything that made a noticeable difference?

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post #2 of 22 (permalink) Old 01-19-2017, 04:22 PM
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I am assuming you have 3.55 rear end? If so your effective gearing is 3.05, which is stupid low and really inefficent for a truck.


Timing vs load plays a pretty large role in MPG. As soon as you increase load at cruise state, IE: big tires, timing drops like a rock....which in turn means MPG drops like a rock. Just switching out lighter tires, same size, netted 1* of timing increase at cruise.


With the Quad we are able to set desired cruise timing. This has really helped keep MPG in the 20+ range regardless of MPH and load.
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post #3 of 22 (permalink) Old 01-19-2017, 06:07 PM
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Same here just dropping from the 265's to 235's netted me a good jump in MPG's. My buddy has 35" on his 06 Dodge and also netting a low 14-15 MPG because of the big tires. More rotational mass the lower your MPG's will be. I'm right at 62 pounds for both the wheel and tire.

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post #4 of 22 (permalink) Old 01-19-2017, 10:01 PM
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with my current setup (sig w/3:55's and 315/70/17 extreme country's), i got 22.1 mpg on a 4.5 hour drive, about 80% highway. all hand calculated, fill up to fill up, and speedo corrected.

that being said, last fill up netted a little under 7mpg. my commute is <.5 mile and i whoop on my truck regularly.

'02 2500 ECLB, 4x4, NV5600 EJWA(hot)/Smarty, Industrial Injection HO VP44, FASS 150, DAP 7x.011's, ARP Studs, 64.5/68/14 SX-E, Kenny's triple disc, 110# springs. 291k and still ticking. 526/1152 as of dec '16
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post #5 of 22 (permalink) Old 01-20-2017, 01:47 AM
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It's been a long time since I've calculated mileage. My tanks are so varied anymore, there really is no common factor to bother even trying to keep track. Most of my last highway trips with the truck in the past year or so have been towing my flatbed with a lead foot. And I feel compelled enough to add that one time I was towing with such a lead foot at 75 mph on 5% grades towing only about 4500 lbs that I was able to successfully overheat my manual transmission. It felt shameful having to drop to 5th gear and go 60-65 on the hills because the transmission was overheating...

However I will say that back when I was commuting 70 miles round trip per day about 75% freeway at 65-70 mph, and 25% in town, I was netting 19-20 mpg with 33" Toyo M/T tires. Same tire netted me 22.5 on one very long all highway trip at 55-60 mph. Now that I am running 35" Toyo M/T tires, the fuel economy has definitely fallen off. I get around 18 all highway and 15 mixed. With what I do around the farm and other miscellaneous stuff I would bet I'm only getting 12 mpg.

Another side note, I've never tried yet, but I am 100% sure I could still get over 20 mpg with the 35's if I had the opportunity to make a long trip entirely highway, and kept speed at 55 mph in 5th gear. I'm 90% sure I could net 20 mpg at 70 mph in 6th gear with cruise control set and relatively flat ground.

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post #6 of 22 (permalink) Old 01-20-2017, 10:41 AM
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Quote:
Originally Posted by ganzey View Post
with my current setup (sig w/3:55's and 315/70/17 extreme country's), i got 22.1 mpg on a 4.5 hour drive, about 80% highway. all hand calculated, fill up to fill up, and speedo corrected.

that being said, last fill up netted a little under 7mpg. my commute is <.5 mile and i whoop on my truck regularly.
I would verify against a GPS. Rarely does larger tire ever do good on MPG's. Most people when verifying against a GPS tend to report lower numbers even with "corrected Speedo's".

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post #7 of 22 (permalink) Old 01-20-2017, 10:47 AM
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I would verify against a GPS. Rarely does larger tire ever do good on MPG's. Most people when verifying against a GPS tend to report lower numbers even with "corrected Speedo's".
it is correct and reads exactly what a gps does, ive verified it.

'02 2500 ECLB, 4x4, NV5600 EJWA(hot)/Smarty, Industrial Injection HO VP44, FASS 150, DAP 7x.011's, ARP Studs, 64.5/68/14 SX-E, Kenny's triple disc, 110# springs. 291k and still ticking. 526/1152 as of dec '16
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post #8 of 22 (permalink) Old 01-20-2017, 10:57 AM
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Originally Posted by Mopar1973Man View Post
I would verify against a GPS. Rarely does larger tire ever do good on MPG's. Most people when verifying against a GPS tend to report lower numbers even with "corrected Speedo's".
@ganzey With his fueling mods it is not hard to beleive. If he is able to keep engine load below ~%24 timing will stay high enough to keep mpg up.

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post #9 of 22 (permalink) Old 01-20-2017, 11:00 AM
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Maybe? Still doubting it... As many large tire truck I've driven and worked on really hard to see it being the engine load is much high than a stock tire truck so the throttle is typically deeper by another 5% or more all depending on road speed.

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post #10 of 22 (permalink) Old 01-20-2017, 11:18 AM
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He's got a ton of fuel though, so that offsets the tire size. No doubt it would be better with less tire, but if your injectors are big enough to allow the engine to cruise at a lower load, then timing will stay in the cruise range of the oem map.

Just like IAT, as soon as you hit that %23-%25 load range OEM timing falls like a rock.


Key for getting the best mileage out of any trucks configuration.

IAT above 90*f
Load below %20 at cruise / or being able to hold timing where you want it.


Doesn't mean that swapping out tires wouldn't help overall, but a lot of guys are not willing to. The above will at least get them to the best mileage for their own trucks current configuration.

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post #11 of 22 (permalink) Old 01-20-2017, 11:13 PM
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22.3-23.8mpg with my signature truck

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post #12 of 22 (permalink) Old 01-21-2017, 08:49 PM
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16-16.5mpg with 6x.013s, compound twins, 4.10 gears (would love to have 3.54 but nobody wants to trade me locally that has compatible axles) and 315/75R16s and I live in quite the hilly area.

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