Dodge Cummins Diesel Forum banner
  • Hey everyone! Enter your ride HERE to be a part of October's Cummins of the Month Challenge!
1 - 20 of 28 Posts

·
Registered
Joined
·
222 Posts
Discussion Starter · #1 ·
Ok, so how big can I go w/o a lift and on the stock size wheels? On my Chevy gas powered dually I increase the size by a couple inches or so and it got my RPMs down and increased my HWY MPG a bit, same be said on this 4x4 DRW Cummins?

Thanks
 

·
Registered
Joined
·
178 Posts
It should help going to a taller tire. Assuming you have 4.10 gears, going to a 315/70-17 would bring the RPMs down close to what 3.73's and stock tires are. Not sure if you can clear those on the front of a dually without some kind of lift or level kit. You would definately need spacers for the rear wheels to maintain your gap between the sidewalls.
 

·
Registered
Joined
·
222 Posts
Discussion Starter · #3 ·
It has 3:73's in it so I may be able to get them down to where 3:42's would be I guess, not sure if I need to be aware of getting them too low with this Cummins or not, is there a sweet spot these like to run down the road at?
 

·
TECH SPECIALIST
Joined
·
294 Posts
There are people running 37" tires on stock wheels without a lift.
 

·
Registered
Joined
·
222 Posts
Discussion Starter · #5 ·
There are people running 37" tires on stock wheels without a lift.
HOLY COW!!!! way bigger than I need, I was thinking a couple sizes taller lol
 

·
Registered
Joined
·
59 Posts
I get my best MPG at 1900 - 2100 RPM.
 

·
Registered
Joined
·
265 Posts
you can run 35s or 37s with the only rubbing being on the control arms. My 35" toyo MTs didn't help mpg's but I attribute that to the 75 pounds each tire weighs. If you went with a more streetable tire I would imagine you would see gains.
 

·
Registered
Joined
·
178 Posts
It has 3:73's in it so I may be able to get them down to where 3:42's would be I guess, not sure if I need to be aware of getting them too low with this Cummins or not, is there a sweet spot these like to run down the road at?
Keeping RPM's under 2000 is what you want for mileage. With 4.10's, 6 speed stick, and 315/70-17's (34.5") I have to run around 68mph to keep the RPM's under 2000.
 

·
Registered
Joined
·
353 Posts
I just installed a 35" M/T and found my MPG's drop slightly. I was previously running a 265/75/20 which was a smidge taller than my 35's, but they were street tires. RPM wise, I find that I get better milage around 70-75 vs 60-65, or 1600-1800 vs 1400-1600. I am sure it has to do with the tire diameter and the proverbial "Sweet spot". I fit a 35" tire with only a 2" leveling kit. I am sure I will need to do some minor pinch weld modification for wheeling, but for street driving, they fit just fine, and in my opinion look really good!:thumbsup:

 

·
06 Cummins
Joined
·
1,620 Posts
I installed BFG 315 AT KO's on my 2006, lowered my rpms quite a bit put it in the sweet spot for sure, I got better fuel mileage as well, couple mpg's. I had a slight amount of rub at full lock, but you remember it's there and just stay out of it. Now no rub, got 5/8" longer control arms and installed a KORE leveling kit. I guess mud terrains might not get you better mileage, or at least that is what I have seen when my friends have put them on.



CD
 

·
Registered
Joined
·
85 Posts
i just orderd some 18x9 rockstars with 5in backspacing, and 325/65/18 feirce attitude mt. my question is with the tire being 13in wide will it fit with jus a 2.5in leveling kit.
 

·
Retired Old Fart!
Joined
·
8,489 Posts
IMHO it depends on how heavy those bigger tires are. The simple math say the larger tires "effectively" change my 3.73 up to about 3.42. That should have helped. Nope.

I put some really HD Maxxis off-road tires on mine. Went from 31 to 34" 315/70/17. The tires are hella HEAVY. I lost about 2 mpg. I'll probably drop to maybe 295/70's for the next set.
I have a stock set on wheels that I can swap back to and may do so again when I'm ready to do some direct comparisons.
 

·
Registered
Joined
·
503 Posts
I am running Goodyear Silent Armor 285/70/17s (33" tall) on stock wheels. They did not effect my mileage at all. One of my friends is running 315/70/17 Goodyear Dura Tracs on stock wheels. He claims little to no mileage change as well. Neither truck is lifted.
 

·
Registered
Joined
·
11,230 Posts
I'm running 285-75-17 Toyo Mt's. No rub anywhere,but I lost 1 mpg over the AT version of the same size. Additional rolling friction with these. They also create a right pull which was corrected by my Carli Highmount ss.
 

·
Registered
Joined
·
222 Posts
Discussion Starter · #15 · (Edited)
Turning 1900 RPMs at 75 MPH with the 235/80/17's that are on it, guess I'll make a few runs as is and see how it does
 

·
Registered
Joined
·
689 Posts
I am running Goodyear Silent Armor 285/70/17s (33" tall) on stock wheels. They did not effect my mileage at all. One of my friends is running 315/70/17 Goodyear Dura Tracs on stock wheels. He claims little to no mileage change as well. Neither truck is lifted.
Do you have a picture you can post with the 285 SA's? This is what I am looking to put on my truck.
 

·
Salty Squid
Joined
·
769 Posts
You also have to keep in mind that a taller tire is usually wider which creates additional resistance in the wind and on the road.
 

·
Premium Member
Joined
·
0 Posts
Another thing to consider. You already have 3.73 gears, right? And you want lower. Less RPM, same speed. Your sig shows a 45 foot 17k + toy hauler. I would bet loaded up it weighs more than that, but just consider that you may be getting your engine OUT of its sweet spot for towing and start raising your EGTs. Just a thought. I know there are guys on here that tow heavy with 3.42s, especially the 10-11s.
 

·
Registered
Joined
·
222 Posts
Discussion Starter · #19 ·
Thats what I was wondering too, after cruising around last night on the e-way I noticed it like to be at around 70-75 and 18-1900 rpms on the liar gauge, if I lugged around at 60-65 the liar gauge went down on MPG so I'll try this out and see what happens on the first run to GA. I need to weight this camper, it says on the tag 13200 lb dry weight and I figure we add 3-4000lbs in water, lp gas, quads, tools, parts and so on? its heavy :(
 

·
Registered
Joined
·
1,972 Posts
Thats what I was wondering too, after cruising around last night on the e-way I noticed it like to be at around 70-75 and 18-1900 rpms on the liar gauge, if I lugged around at 60-65 the liar gauge went down on MPG so I'll try this out and see what happens on the first run to GA. I need to weight this camper, it says on the tag 13200 lb dry weight and I figure we add 3-4000lbs in water, lp gas, quads, tools, parts and so on? its heavy :(
I have found my best mpg at 58-62 with my 3.73s now im not sure if it would changed when your towing that much weight but i would suspect that it would.
 
1 - 20 of 28 Posts
Top