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

On 9/8/2018 at 6:20 PM, Mopar1973Man said:

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. 

 

O.K.  Super anyone have any experience with an Automatic Trans and this tire size?  I'm about to enter uncharted Waters.  I've ordered my Quad Adrenaline V2, to play with the fuel curves.

 

Thanks

Michael.

I like your idea of Buying Used Tires, to try it before committing.

On ‎7‎/‎10‎/‎2018 at 4:57 PM, IBMobile said:

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.

These are one new and four used Michelin tires that I got of a wrecked 3/4 ton Ford Econoline van for $180 mounted.

Edited September 10, 20186 yr by IBMobile

On 9/9/2018 at 9:29 PM, int3man said:

 

O.K.  Super anyone have any experience with an Automatic Trans and this tire size?  I'm about to enter uncharted Waters.  I've ordered my Quad Adrenaline V2, to play with the fuel curves.

 

Thanks

Michael.

I like your idea of Buying Used Tires, to try it before committing.

Same size tires, 4.10 axle, but apparently Allison transmission is quite the different beast than the 48. I love the combination myself.

 

My wife runs a thrift business on the side and she's always buying stuff from auctions. There's an auction house here that has tires often. I literally paid $13 for the set and mounted them at home by hand. If I knew what size I could ask her to keep an eye out.

Edited September 12, 20186 yr by Scottfunk

On ‎9‎/‎8‎/‎2018 at 6:20 PM, Mopar1973Man said:

I can say without a doubt I'm going to keep the 245's for future tire size.

 

I am thinking the same thing.  With the 245's, I towed my tractor with implements from Salem to Baker City via I-84 last week (GCVW over 16,000 lbs) and the truck had all the power I needed and delivered 13.5 mpg.  Yesterday I towed the tractor back (minus a couple of implements) weighing in at 15,650 lbs via Hwy 26 and 22 at 15.2 mpg.  I checked the miles per gallon from John Day (filled up with B20) to home near Salem.  The power and the fuel economy are now the best they have ever been since the truck was new.  Still on original injectors and I will pass the 300,000 mile mark on my return trip to Baker City tomorrow with the mini-excavator..

 

- John

Here are the changes to the 1996 Dodge 1500 now that I've done the 215/85 R16 tires. I'm working on shaving off some of the cost per mile now and getting it down closer to the 17 cents a miles like the Cummins. 

 

Now for the 2002 Dodge 2500 Cummins... Last month was AVG MPG of 18.87 and Cost per mile was 18 cent a mile. The smaller tires did improve the economy!

On ‎9‎/‎11‎/‎2018 at 11:47 PM, Tractorman said:

Still on original injectors and I will pass the 300,000 mile mark on my return trip to Baker City tomorrow with the mini-excavator..

 

Just finished another round trip to Baker City and back hauling the mini-excavator both ways with the new 245 tires.  Fuel mileage ranged from 13.8 to 14.4 mpg and the truck performs great!  So far, I have not experienced any negative effects from switching to the 245 tires.  Also, another noted performance improvement was during two of my trips through the Columbia River Gorge with gusty winds.  When semi's passed me or I passed them, there was no longer a push to the side that I felt before with the 265 tires.

 

I just crossed over the 300,000 mile mark on the odometer.  The other photo is the 5 acre parcel of land we just purchased looking at the Elkhorn Mountains.

 

- John

Looking good.

Being the Cummins is shredded in the shop I've been driving the 96 Dodge half ton. I love these 215's tires on this truck awesome performance. With the 46RE transmission having a tall overdrive gear you still find that you are grabbing the OD Off button in some areas. It pulls up the power great and backs off on the cruise again. Last tank I still hit 16.34 MPG even with hopping on the interstate and running 70 MPH to Boise to drop the head off in the shop. I could of pulled a bit better numbers if I was stuck in traffic and stop and go. Oh well... Still not complaining this is awesome looking back at the old numbers of 12 to 14 MPG it a good increase in power and economy.

 Thinking about getting a spare set of rims ( steel ) for winter use, to keep my 4th gen wheels nicer longer. I found a set from 2003 with265/70/17 ( BF Rugget Trail-junk? date code 2004 about 1/2 tread $250 )which is kind of what I'd like to have on my aluminum rims with different rubber  of course. So I thought about getting the steel ones and trying them out since I never had that size on my truck and then later if I liked it I would put a set of 265/70/17 on the 4th gen wheels and then find a set of 245/70/17 and put them on the steel wheels. Just not sure of having two sets sitting around is worth it. Or if I should just sell the tires I got now and get a set of 265 and be done with it, I just don't have money to spend at the moment on new tires, but for $250 I get to try out that size and keep the rims. 

16 minutes ago, Dieselfuture said:

I just don't have money to spend at the moment on new tires, but for $250 I get to try out that size and keep the rims. 

 

I say give it a try. You won't be sorry. The RPM difference is small but the economy and power difference is pretty moderate. 

On 9/18/2018 at 9:23 PM, Mopar1973Man said:

Being the Cummins is shredded in the shop I've been driving the 96 Dodge half ton. I love these 215's tires on this truck awesome performance. With the 46RE transmission having a tall overdrive gear you still find that you are grabbing the OD Off button in some areas. It pulls up the power great and backs off on the cruise again. Last tank I still hit 16.34 MPG even with hopping on the interstate and running 70 MPH to Boise to drop the head off in the shop. I could of pulled a bit better numbers if I was stuck in traffic and stop and go. Oh well... Still not complaining this is awesome looking back at the old numbers of 12 to 14 MPG it a good increase in power and economy.

On the 1/2 ton have you bumped static timing up a few degrees? The computer didn’t offset that timing advancement till 99 when the total timing map was introduced. Give it 2* at a time till you hear it ping then drop back 2 for safety. Also unplugging the EGR vac line and capping the PCV and running a tube to the intake filter assembly will help a little also. It still burns the crank case emissions but not via vacuum draw which on those would richen the map at part throttle. 

Already have Mopar Performance PCM and the timing is running a full 40* cruising down the highway. It requires 91 octane now I'm sneaking by with 89 octane.

On 9/22/2018 at 1:32 PM, Mopar1973Man said:

Already have Mopar Performance PCM and the timing is running a full 40* cruising down the highway. It requires 91 octane now I'm sneaking by with 89 octane.

Oh ok, so the timing sweep is much further then. Stock is 30-32* total I do believe. Very cool. Exhaust I assume isn’t stock either? Cat back systems help some just don’t remove the cats. Beyond that it doesn’t matter as much. 

 

Before my 12v I had a 93 Dakota with the 3.9 5speed 4wd and I’d get 20-23 empty with it so your doing pretty good! On those engines they used a stock single roller timing chain, they go slack and kill power and MPG, you may want to get the parts for a dual roller chain and replace it. It’s a easy job. That’ll help your economy quest a lot, I’ve got a lot experience in that department lol

1 minute ago, Tittle Diesel Performance said:

Exhaust I assume isn’t stock either?

Yes. Hollow kitty.

 

1 minute ago, Tittle Diesel Performance said:

On those engines they used a stock single roller timing chain, they go slack and kill power and MPG, you may want to get the parts for a dual roller chain and replace it. It’s a easy job. That’ll help your economy quest a lot, I’ve got a lot experience in that department lol

Yeah it could be due for timing chain but right now my focus is getting the head gasket done on the Cummins before I dig deep in the V8.

27 minutes ago, Mopar1973Man said:

Yes. Hollow kitty.

 

Yeah it could be due for timing chain but right now my focus is getting the head gasket done on the Cummins before I dig deep in the V8.

Yeah I came across the post about the HG failure. Running that kind of timing will do that. My dually is in danger of it as well. I cranked down the head bolts but it’s gonna get studs soon anyways, it’s just a matter of time...plus warm up heat is the biggest contributor.

I just put these 265/70/17 and drove around a bit. Can definitely tell it's easier to take off in 2nd now and seem to be causing a little easier down the road. But these are on steel wheels and waight 84lb and my 285/70/17 are on 4th gen mags that waight 72lb so I'm not sure if I'll gain any mpg and it looks goofy being smaller, not sure how you guys do it with 245. 

 

My 96 had 245's on it and they definitely looked tiny for  them to be 1" shorter. Thats why I wanted the 265 on the 02

Should see the 215s on my half ton. Those are nearly razor thin. Best part is now reaching the high MPG number since I bought the truck back in 2001. High mark of 17.05 MPG.

 

As for the 245s I'm just right there at 21 MPG now.

So what about using steel wheels vs aluminum, they are smaller but much heavier. Will it be counterproductive, meaning I'll see same mpg with smaller heavier tire vs my lighter aluminum rims with bigger tires.  

56 minutes ago, Dieselfuture said:

So what about using steel wheels vs aluminum, they are smaller but much heavier. Will it be counterproductive, meaning I'll see same mpg with smaller heavier tire vs my lighter aluminum rims with bigger tires.  

 

I don't think that the increased tire weight will be an issue.  It's more about operating the engine in an RPM range that gives you performance and fuel economy. 

 

It is too bad that car and truck manufacturers don't provide engine performance charts that show engine horse power, engine torque, and fuel consumption in lbs/hp per hour at every RPM in its operating range.  Years ago when I purchased a Cummins 4BTA 3.9 and installed it in a 1991 Ford F150, I was provided with this performance chart from Cummins.  On that engine the peak torque was at 1700 RPM, but the lowest fuel consumption per hour was at 2100 RPM, so it gave me a good idea of what the final drive ratio should be.

 

The Cummins engines in our 2nd generation trucks probably closely fit this performance chart.  This is why the smaller tires will give a significant gain in fuel economy as well as performance

 

Attached is a performance chart for a mid '80's 4BT3.9 (no aftercooler).  Note the fuel consumption information (the horizontal line at the bottom of the graph)  If you save the picture, you can zoom in on the graph for better detail.

 

- John

Edited September 24, 20186 yr by Tractorman
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