ive got the stock 3.55s in my 360 and im running on 265 75 r16s at 70 im running about 2000rps. my question is wat is the optimal performance rpm for this setup. i ask because ive read a thread that said about 2200 was borderline performance and economy loss. so am i losing performance and economy with the gears an tires

 

I believe optimal rpm is related to driving conditions.
So, how much do you drive over 60mph and how many hills and what size and do you haul anything and how often?

 

let me clean this up a little just for these purposes lets say that 2500 rpms is the rate at which hp vs fuel economy are equal. lets also say if you go in rpms that hp increases but economy decreases. and vice-versa when rpms decrease. so what is the rate with 3.55s and 265 75r 16s at which fuel economy and hp are equal for my truck with the 360

 

I was always told there is a "float point" when driving the truck at highway speeds. The point where at speed the truck seems to "float" and thats where I assume your fuel economy will probably peak. I for some reason have never actually felt my truck float LOL but if I had to guess, for 3.55 and 245's, I say 60-65 is the good spot for me. For this case, I'll call it 63 mph.

 

265X75X16 is 31.5" or so. The best way to make the truck "feel" like it supposed to with the stock 225X75X16 tires is to re-gear to 3.92. That's the closest option available. You'd be amazed at how "torquey" the stock gears are when you use the corporate recommended tires. Most owners don't like a tire that small and my Dodge even came with 245X75X16's from the dealer.

 

I have 245/75 LT tires with 3.55 gears and my truck struggles to accelerate under 65mph. So, I have been thinking about smaller tires vs changing to 3.92 gears. I haven't changed yet because most of my driving is 500 mile roundtrips on the weekends on the interstate at 75-80mph. However, there are several 15 mile long hills that I can't maintain the speed limit and stay in overdrive because I am geared too tall. My rpms drop below 2000. So, my current thinking is changing to 3.92 gears and increasing the rpms might give me better gas mileage going up the hills. And it would be more fun to drive because my engine really comes alive above 2200 rpms.

 

how to you mod a pickup to get better MPG for the least money?

https://dodgeforum.com/forum/off-brand-news-concepts-and-rumors/172127-xfe-silverado-with-6sp-3-08-a.html

 

I think gearing is your best shot. I was VERY suprised how sizing my tire size down dramatically still did not make much of a differance.

I was running 35/12.5/17 mud tires. I took the lift off, and sized down to a 285/70/17 all-terrain tire. I figured I'd at least regain fuel mileage and some power. Well much to my suprise, I experienced a very small differance in power, and almost nothing for fuel economy. Even with a very big tire size change, I still am getting pretty much the same fuel economy, and very little differance in performance overall. I have 4.10 gearing by the way.

My suggesstion is either live with what you have, or buy 4.10 gearing for the most dramatic change for yourself.

 

Something doesn't sound right here. 35's to 33's and no mpg improvement? Did you have the computer recalibrated for the different tire size?

 

Yes. I have reset the computer several times. What I have found is that my mileage is quite a bit better when I can stay in overdrive such as backroads and the highway. But city driving is ultimately the same. With the 35" tires, I flirted with 10-11. Now I flirt with about 11-12.5. It did give me about a mpg differance, but I was suprised how similiar my truck is still. Still drives pretty the same, just without the noise of a mud tire. Goes to show these rams don't let much phase them. I'm still only getting about 240 miles to a full tank of a fuel though.