Effective gear ratios

[Fader]

Hello all... I am looking at various tire size options for two Cummins powered pickups & am curious about what gear ratio works best.

I am guessing that the factory ratios are ideal..?

Here is what I have going on....

I have a '97 Ram 2500, 6bt/nv4500, 4x4 that came stock with the 3.55 gears. It currently has some 18" later model ram wheels on it essentially giving it a effective ratio of 3.21:1.
I would like to get back closer to the stock ratio but 245/75s look so small on anything... this pickup is also pretty far down the totem pole of available project cash that changing gears probably isn't going to happen.
I'm assuming that I'm giving up a lot of grunt with 321s...I have a nice set of 265/75/16s that I could swap onto some Dodge steel wheels. That would get me to an effective ratio of 3.42:1.
Is that exponentially better than 3.21:1 or should I get myself back to 355s or even higher?

Likewise I have a old Chevy c30 also wirh a p-pump 6bt/nv4500... it has factory 4.10 gears & stock size tires... I am boring & don't plan on lifting or lowering it. I've considered throwing a set of steel 19.5 wheels but 225/70/19.5s are nearly identical in diameter to a 235/85/16 so no real change.

I guess what I am looking for....is your personal experiences with what is the ideal gear ratio for a 12 valve/nv4500?

Both of these vehicles are generally just driven around with no huge loads behind them. Both also will be called on to tow heavy trailers on occasion & need to be ready for such a task.
I guess that I like MPGs but don't drive either enough to make a decision strictly based on that.
A combo of MPG & towing power in the ideal range is what I'm after...probably leaning towards the power.
I don't want to preach the old mechanical Cummins gospel & not be able to get the job done when I need to move something.

Thanks in advance.

 

[Cummins12V98]

4.10's and be done with it.

 

[BigPapa]

A gear change, especially on a 4x4, will be very expensive. If I’m thinking right, your truck also has the D80 and will require a new carrier to go to 4.10.

 

[Fader]

It does have the dana 80... probably not going to get anywhere close to 410s on the Dodge.
Thinking I may just go with 235/85s or the 275/65s that I already have both of which leave me around 342s...

Interestingly enough...the guy who swapped & sold me the Chevy included a set of 354 gears for the dana 70 that be had planned on installing. I believe that he was in it for the fuel economy...which we may all be if diesel begins to rise drastically.

 

[jffmaz]

fuel economy...which we may all be if diesel begins to rise drastically.

Which is bound to happen with the new regime. They want us to be short vegetarian bicycle riding cat people. SHORT - take up less space on the planet and exhale less CO2, VEGETARIAN - So we don't eat beef and they don't have to deal with cow farts methane gas, BICYCLE RIDING - we will no longer be energy independent so fuel prices will skyrocket (by design) and no one can afford to drive fossil fuel burning vehicles and will resort to riding bikes, CAT PEOPLE - So we can see in the dark when the lights go out at night because the sun went down and there is no available solar power till morning daylight.

 

[Fader]

I've never ate Cat... but I suppose I'd try it in a socialist utopia.

 

[BigPapa]

Did the 4th Gen 18” wheels bolt up with no problems? Were the hubcaps deep enough to fit over the hubs? Any chance of a pic?

 

[Fader]

Probably the best pic on my phone...I could run outside but we are experiencing a windstorm/whiteout at the moment.
They bolted right on...I need to track down different lug nuts for the center caps. I utilized the chrome aftermarket ones that came on the pickup.

I realized one thing today... these Ram factory Firestone transforce? 18s off of a 2018ish have a lot of tread but are pretty poor in slick conditions.

 

[BigPapa]

Nah, that pic’s good enough. Those are steel wheels, right? So, the hubcaps will work with the stock lug nuts?
Thanks.

 

[Fader]

I believe so but I'm not 100%. The caps clear everything for sure.

I got the lugnuts that came off of the 4th gen but they are for a smaller stud if I recall correctly.

Everytime that I go to the salvage yard I forget to start collecting lug nuts.

They are soon coming off... probably going back to 16s. I'm not too worried about the appearance as much as the function & getting back closer to a decent gear ratio.

 

[jffmaz]

Did the 4th Gen 18” wheels bolt up with no problems? Were the hubcaps deep enough to fit over the hubs? Any chance of a pic?

I found a set of 2015 alloy wheels for my rwd 1998 12v for cheap in my area. Picked them up from an older gent (like me) who had taken them off the first year he owned the truck in 2015. Perfect condition wheels. He said they were 17s, I didn't check till I got home, they were actually 18s. The wheels made me aware of 2 issues - 1st, if they had been 17s they wouldn't have worked on my 2wd. The deeper offset (if they had been 17s) would have made the inside of the rim hit my upper control arm (rwd), but the 18s cleared. 2nd, the cap is only about 3" diameter, the wheel body necks down to fit the smaller cap, so they won't fit over the rear hub by about 3/4". So either wheel spacers or maybe cut off the end of the hub section on the wheel to fit my 98 Dana 70 hub. I had already bought a set of 2020 take off 17" tires, so i didn't use the wheels and found a set of 3rd gen chromes I used instead. Now I have a set of mint 18" allows taking up space in my shop.

 

[BigPapa]

That’s what I was looking for. There’s a fellow on another forum asking if they’ll fit.