Hello all,

After reading hundreds of posts on the subject of the H2 315's on the CTD Rams, I'm looking for some input on long term results, especially with real fuel usage impact.

I have a 2003 QC SWB HO with 4.10 and the 48RE. Stock tires/gearing are way to low for highway speeds, with mileage dropping from over 20 at 60 to 17'ish at 70, and on down from there. There is a significant decrease in mileage as RPM's go over 2000. I suspect the turbo is spinning up.

So here is the challenge: Most of the posts on 315 AT's are from 3.73 and or 6 speed owners, and they usually report mileage loss with the larger tire. Which would make sense with the 3.73's, but not with the 4.10.

I also see that folks who recalibrated the tone wheel or pinion factor saw increased performance and mileage, where those who did not usually complained about lower mileage. So I wonder if shift points, etc are factoring into the mileage aspect.

With the 4.10's, even with the higher rolling resistance of the 315 AT, the RPM decrease at 70 may get me into the under 2000 rpm range where I see much improved efficiency.

The 285's seem a natural compromise, but at almost $200 a tire VS $500 for 5 new H2 tires & wheels, I'm very tempted to give the 315's a try.

I'd really love to hear from owners with 4x4 4.10's 48RE with the 315's to see what the long term mileage impact was, and if you had the pinion factor updated in the computer. I know offroad performance would improve, and braking, tread life, etc may be slightly worse. That's ok. It's the mileage/drivability aspect I'm interested in.

I know this has been hashed over many times, but in nearly every case people were comparing apples/oranges with no consistancy on the comparison. (gearing, tranny, etc).

Thanks in advance!

Alan

2003 3500 4x4 QC SRW HO 4.10 48RE

 

I ran 315s for the past couple years. Yes your rpms drop way down on the hwy but the mileage doesn't go up. In fact my city mpg fell one point and hwy seemed to stay the same. Slowing down on the hwy will give you significantly higher mpg numbers. If I could drive 60 mpg sustained, my truck got a best of 23 mpg hwy. That's very hard to do. At my normal of 66-70 mph I usually got 19-20 mpg. My rpms were just shy of 2000 at 70 mph.
I too wanted 285s but 315s were much cheaper and that's the only reason I ran them. I finally found a cheap set of 285s and that's what I run now. No numbers yet as I just put them on....

Your poll is a bit hard to understand so I did not vote... I had my pinion factor reset for the bigger tires and I have performance boxes.

 

I see the same with my bone stock 4x4 HO 4.10 48RE. 22-23 for sustained 60'ish driving. But every stop light drags it down.


I think 2000 rpm is the magic number, as that is where I see the dramatic change. What's interesting, is that it seems largely independent of load, empty or full!


So it sounds like having had both, you would probably lean toward the 285's if found for a reasonable cost.


Yeah, sorry about that. I'm trying to see if there is a significant difference between people who had their pinion factor/tone wheel setting updated or not. Hard to tell, but it appears that those who did saw less mileage reduction, etc. It could be as simple as folks not calculating the mileage correctly, but it could also be shift points, etc.

Thanks for the scoop, however. I'm curious, which 285's did you end up with and where did you find a reasonable source for them?

Thanks,

Alan