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

5 hours ago, Mopar1973Man said:

 

California models had EGR valve and Catalytic converter.

 

Mine just has the catalytic converter. No EGR.

1 hour ago, 04Mach1 said:

Mine just has the catalytic converter. No EGR.

Can't believe you still have it on

58 minutes ago, Dieselfuture said:

Can't believe you still have it on

 

If I was in California I would take a rod and beat that piece of trash out. Then leave it as an empty can. 

6 hours ago, Dieselfuture said:

Can't believe you still have it on

I had to do opacity testing every year to register it in Denver, CO. I figured the catalytic converter may have helped keep smoke output down. Don't know if it did any good or not but the truck always passed the opacity testing with ease. Colorado's opacity testing consists of strapping your truck to Dyno and running the coon dog sh*t out of it to see how much smoke the engine makes. They basically drive it like a jackass. Opacity is measured by a machine hooked to the exhaust while they run the truck on the Dyno.

 

5 hours ago, Mopar1973Man said:

 

If I was in California I would take a rod and beat that piece of trash out. Then leave it as an empty can. 

This thread has me strongly considering it to see what would happen with fuel mileage and performance. I don't have any complaints as it is right now but there is always room for improvement. I live in Cibola County, New Mexico now and thankfully no emissions testing for gas or diesel.

Edited July 7, 20186 yr by 04Mach1

I put engine load on my quadzilla for the commute home today. At 65 mph the load is ~34%. I don't see low 20's until I'm well over 80 mph. That's with the 265/70/17's on. So I guess the sweet spot is the point where lowering the rpm's and lowering the load meet? I wonder what the math looks like for computing engine load.

 

According to the Spicer calculator if I go up to 4.11 (or down I guess, technically) and up to a 34" tire I can hit 1960 rpm's just below 80. Sounds like I'll be hunting for some gears. Does changing ratio above 3.73 require changing the carrier also like in the gm's?

I take it back...4.56 will get me to 1960 at 72 mph and I'm positive that requires a carrier swap. Good thing one of my top 10 things to do is junk yard research?

41 minutes ago, 04Mach1 said:

They basically drive it like a jackass.

Idk if I'd let them monkeys in my truck, I'd move out of that he'll hole statw and be done. 

10 hours ago, 04Mach1 said:

I had to do opacity testing every year to register it in Denver, CO. I figured the catalytic converter may have helped keep smoke output down. Don't know if it did any good or not but the truck always passed the opacity testing with ease. Colorado's opacity testing consists of strapping your truck to Dyno and running the coon dog sh*t out of it to see how much smoke the engine makes. They basically drive it like a jackass. Opacity is measured by a machine hooked to the exhaust while they run the truck on the Dyno.

Depends on the shop I've found.  I had one in golden test mine like you describe, and I've never gone back.  Others have put it on the rollers, ran it light for 30 seconds and handed me a sheet that said all 0's.  So that's my preferred shop now lol.  Oh and they didn't care about the additional turbo or lack of anything in the exhaust pipe.

14 minutes ago, trreed said:

Depends on the shop I've found.  I had one in golden test mine like you describe, and I've never gone back.  Others have put it on the rollers, ran it light for 30 seconds and handed me a sheet that said all 0's.  So that's my preferred shop now lol.  Oh and they didn't care about the additional turbo or lack of anything in the exhaust pipe.

 

I wish I could have found a shop like that to test mine. I used Progressive Diesel in Englewood most of the time because they were always the lowest price for diesel emissions testing. I went to J&J Auto in Aurora some too because they were not far from the house. Both always ran the trucks balls to the wall during testing.

I wrote an emissions tune for my truck. You can floor it and it will only slowly increase rpms and peak at about 2700 :-). 

 

I would have thought there would be a market for 12V emissions fuel plates but I don’t recall ever seeing one. 

 

Can the quad quad go low enough on fuel for a emissions tune? 

3 hours ago, AH64ID said:

Can the quad quad go low enough on fuel for a emissions tune? 

 

Most definitely. Can pull fuel back to 50% of stock duration. I was running 7x0.012’s with my HX35 for a while and it was pretty manageable with the quad pulling fuel.

5 hours ago, AH64ID said:

Can the quad quad go low enough on fuel for a emissions tune? 

 

I think the deepest it can cut is 50%. I've never bothered to try.

 

As for the 245's this next tank of fuel should be pretty good numbers. 

 

On ‎7‎/‎3‎/‎2018 at 9:34 AM, Mopar1973Man said:

Talk about a huge difference 1 inch of tire makes.

 

EGTs are lower.

Engine load is lower.

Transmission temp is lower.

Exhaust brake performance is better.

Brake performance is way better.

Can hold 5th gear wider speed range.

Acceleration is quicker.

Less stress on the clutch during launch.

 

Just in the 120 miles I'm loving 245's over my 235's. Very impressed with the changes. Now I'm having hard time understanding people with 35 or 37 inch tires with 3.55 gears. I'm going to start fuel logs on my next tank.

 

I have noted that for a number of years you have used 235/85R16 tires on your truck and you have liked their performance – less stress on the steering components, less rotating mass, better snow traction, etc.

I have run 265/75R16’s for the life of the truck and was going to make the change to 235/R8516’s because I agree with your observations.  I am ready to buy the tires now, but I just read about your testing of the 245/75R16 tires on your truck and your positive performance observations.

So, I am holding off purchasing tires until I read about your fuel economy with the different final drive ratio using the 245 tires.  I rarely drive over 65 mph (especially when I’m towing), so the benefits of 245 tires would seem to be excellent.

I am looking forward to hearing the results of your fuel economy test.

- John

Lets say. I'm already planning on running 245s on the Cummins then 215s on the 1/2 ton. Really like the performance. Just about mustered 21 MPG on the last tank. Plan on towing the RV home on Thursday. So ill get some tow experience.

2 hours ago, Tractorman said:

So, I am holding off purchasing tires until I read about your fuel economy with the different final drive ratio using the 245 tires.  I rarely drive over 65 mph (especially when I’m towing), so the benefits of 245 tires would seem to be excellent.

I too had 265/75R-16 tires and came across a deal for five 245/75R-16 That I switched to the smaller size.   I too drive at 65MPH or less and tow 90% of the time.  In the last 9 months the truck has towed over 12.000 with only seeing exhaust temp increases going up steep grades like route 16 out of Rapid City, SD up into the Black Hills.  I just took it out of overdrive and backed off a hair.

 

 

2 hours ago, Mopar1973Man said:

Just about mustered 21 MPG on the last tank.

 

The MPG's sound good along with the overall performance benefits.  Tomorrow, my wife and I will be leaving with the travel trailer to Baker City - we purchased a 5 acre parcel of land there right at the base of the Elkhorn Mountains, about 14 miles northwest of Baker City.  We will spend about three or four days there figuring out where to put the well and septic system and to find out what is required from the county to build a house there. 

 

This will be the last trip with the 265 tires and the next set of tires will be the 245's.

 

Thanks for your prompt response about the fuel mileage.

- John

 

1 hour ago, IBMobile said:

I too drive at 65MPH or less and tow 90% of the time.  In the last 9 months the truck has towed over 12.000 with only seeing exhaust temp increases going up steep grades like route 16 out of Rapid City, SD up into the Black Hills.  I just took it out of overdrive and backed off a hair.

 

It sounds like you are happy with the 245 tires, as well.  Thank you for your input.  Having the 6 spd manual transmission, my overdrive is not quite as tall as yours, so I think that I will be able to climb most grades in overdrive - my combined truck and travel trailer weight is 12,500 lbs.

 

- John

Edited July 11, 20186 yr by Tractorman

28 minutes ago, Tractorman said:

 

Thank you for your input.  Having the 6 spd manual transmission, my overdrive is not quite as tall as yours, so I think that I will be able to climb most grades in overdrive - my combined truck and travel trailer weight is 12,500 lbs.

 

- John

 

You should have zero issues. Aside from 2 hills I can run from Pendleton to Boise on OD at 17K GCW with my TT with my much taller tires.  245/70R19.5 are about a 34” tire, or closer on diameter to a 285/75R16. 

Edited July 11, 20186 yr by AH64ID

I'm happy with the fact the 65 MPH RPM is 1960 on the tach. Now that I've taught myself to leave the transmission in high gear I find that majority of my travel now I can do in top gear empty. I plan on hauling my RV back on Thursday so I'll get a good test run on that.

I have always liked how mine drives empty with the 265's. But towing I always wanted a touch more rpm for the 65 mph towing. I guess all I need is extra st of towing tires.

I just made a run at 80 MPH down a short blast of the interstate. 245's on the rear yet. In 5th gear at 80 MPH it's turning 2,400 RPM. not bad yet you can safely blow down the interstate at 70 MPH and still but reasonable like 2200 RPM (IIRC). I know previously 70 MPH was a touch over 2,100 RPM.

 

@dripley Basically the RPM difference if you drive 5 MPH faster that is what you new RPM will be. So if you want to see 70 MPH on 245's drive 75 MPH that is your RPM at 70 MPH on 245's. 

Is there anyone here that can chime in about 4:10s and tire size? Seems like everyone has 3:55s. I am getting 18.5 mpg with 4:10s and 265/70/17 right now and would like to get 20. For 4:10s do I want to go bigger to bring the gear ratio down or not?