I just got a pair of used 245/75 R16 tires from a friend. So I mounted them up on my old aluminum mags and mount the 245's on rear axle of the truck. 

 

 

They are a bit shorter in height. The gains are great!

 

Engine load is reduced by 5% to 10% roughly. 

EGT's are about 50*F lower.

Acceleration is way better and faster. 

Cruising RPM's are right about 1,960 RPM at 65 MPH.

 

I've got to reset my cruise timing limit on the Quadzilla I need to drop from my current 25% to 20% it was holding cruise timing climbing about 2-3% grade. 

 

I'm going to document MPG usage as well in the coming days. 

Edited July 2, 20186 yr by Mopar1973Man

245s would be better for the 4 speed automatics. Your OD is 0.68:1 vs 0.75:1 for my 5 speed in OD.

I changed out a set of bald 265/75 R16 Goodrich KOs for slightly used 245/75 R16 Michelin a couple of years ago.   I use the truck 90% of the time pulling my 5er and have gone on two 7,000 mile trips this last year with this size tire.   Yes, the sweet spot for towing with a 4.10 is right around 2,000 RPM.  At that RPM I cruse in 4th at 65 MPH indicated.  The truck pulls very well when going up hills and I drop down to 3ed, this keeps the exhaust temp down.       

The change to a 245/75 R16 tire will increase your finale ratio to 4.26 and the speedometer reading at 65 MPH indicated will really be 62.4 MPH 

 

https://www.discounttire.com/learn/tire-size-calculator

 

https://tiresize.com/gear-ratio-calculator/

 

2 hours ago, Mopar1973Man said:

245s would be better for the 4 speed automatics. Your OD is 0.68:1 vs 0.75:1 for my 5 speed in OD.

Well that is interesting.  I just checked the door jam and the truck came with 245 75 16.  Imagine that Chrysler knew what  they were doing!  Is the Ratio still listed on a tag on the Pumpkin?  I want to double check.

 

Thanks

Michael

Or the glove box or under the hood.

Finally it has been done. Fresh rubber in 245/75 R16. Ill admit the trucks much better and steering is lighter with 245 compared to the 235s. Running the Hankook ATm again being I'm getting 60 k to 65k from a set. I'm ready for winter time bring it on.

Wow civilization...

Hey your balls are showing 

18 minutes ago, Dieselfuture said:

Wow civilization...

Hey your balls are showing 

That's just OLD AGE catching up!!!

Just now, int3man said:

That's just OLD AGE catching up!!!

Good one

OMG I was laughing my  for that one... 

11 minutes ago, Mopar1973Man said:

OMG I was laughing my  for that one... 

You learn to be careful when you sit down!  Or slide on to a Creeper!!!!!

 

And Don't ask me how I know these facts.  I keep wondering who the old guys is that keeps watching me shave in the mirror.

Edited September 5, 20186 yr by int3man

Just now, int3man said:

You learn to be careful when you sit down!  Or slide on to a Creeper!!!!!

 

... 

Since were talking tires...I'm trying to figure out what the ideal pressure is but everything I read says check the door jamb. Problem with that is my Chummy is much more like your guys' trucks than what it was originally designed as. The tires themselves say 80psi max and right now I'm running 38. My contact patch is almost a whole square foot. I feel like a few more pounds would be easier on the fuel but if the trade off is premature wear then it's probably not worth it. What psi are you guys running?

Here you go...

 

38 minutes ago, Scottfunk said:

everything I read says check the door jamb

 

Door jamb is for max capacity weight to pressure. What about if you not to gross vehicle weight well my formula will figure that out for you. 

I run 58-60 in front and about 54 in back, that's empty. Average 18-19 on hwy if I'm easy on it.

I run 55 in the ftont and 45 to 50 in the rear. If I saw a dquare foot of contact patch on mine I would be under inflated. That will wear a tire faster than over infalted. The 80 psi on the tire is the pressure you need for the tire to carry its rated load.

I run 65 psi all the way around on both my 2nd gens. I never know when I'll throw 1000 or more lbs. of truck parts in the bed so I figure 65 is the middle of the road for good sailboat fuel hauling tire wear and when I do actually have a some weight sitting in the back. 

Guess I'll run the Chummy across the nearest cat scales this weekend. Frankly I have no idea whatsoever what she weighs. Front, back, or total. Thanks for that info. When my wife bought these tires for me they were used, and had a wear ring right down the center from being overinflated so I erred on the side of underinflation to avoid making it worse. 

Idaho keeps most of it's scales turned on all the time, even if they aren't manned so it's a free trip to the scales. 

 

I use the one in Horseshoe Bend on ID-55 quite often, as well as the one east of Boise on 84. The one on 84 isn't closed as often thou. 

 

On my 17's I run 65/45 most the time and adjust the rear as needed if I'll be heavier.  

There is a scale in Nyssa, ID also that I hit as well. Then in Council, ID the Shell station has a scale just ask before using she'll write down your numbers. 

I can say without a doubt I'm going to keep the 245's for future tire size. I'll never look back at 235's or 265's. 

 

You know how people whine about 5-speed transmissions and you have to wind it up tight to get from 3rd to 4th. Then people claim this is why the 6 speed came out for better overlap of gears. Well, guess what? With 3.55 axle gears, 245/75 R16 tires and NV4500 transmission, the gear has serious overlap now. I'm in 4th gear as early as 25 MPH and 5th gear by 35 MPH. No joke. Way better power and spread of gears. No need for winding uptight anymore. I can do the majority of my trip now in 5th gear that includes winding through the canyons. City stuff tends to be mostly 4th gear. 2nd you basically launch in and 3rd gear is long gone by 15 MPH. 

 

As for fuel mileage, I've got to grab my fuel logs and crunch some numbers but I'm loving the idea I might start skipping the fuel station on Thursday. The last trip There and back I was right at a bit below quarter tank used. 

 

Power wise if I downshift one gear, pound the throttle allow the Quadzilla to hit the 15 PSI limit for the wiretap when fuel comes on the whole rear axle starts to wrap up and tires start to break loose on dry pavement. The power is quite impressive. Even in 5th gear, it builds speed very fast. Downshifting is not required anymore. 

 

Steering wise it feels much lighter like my 1996 Dodge 1500. Kind of steering where you can hook your single finger on the spoke of the wheel and control with one finger for miles. No double grip, no saw steering, no fighting, straight as an arrow and smooth. Easy to steer with that Bluetop quick ratio and the 245's.