Goes with my plan to increase my tire size on the DRW when it is time for tires

 

interesting... could you fix the data so its consistent..?

the second row has the slash & dash in the wrong place
and the two dually +1.5 and +2.5 have the wrong diameter (70?)

 

OOPS, Fixed.
Thanks

 

Question for the Math Majors..........

I understand that a larger OD tire will lower the rpm for the same speed. Assuming the truck is already 17 mpg at 65 mph with the standard 17" DRW tires......what would be the projected mpg with the larger OD tires..??

 

I have 4:30 gears and get 15mpg empty and 9-10 pulling 16K to 17K at 70mph.

 

I doubt the mileage difference will be seen towing. The mileage difference will be seen traveling empty. Have to decide which you will be doing more often. I tow 95% of the time so the 4:30 works great for me.

 

That is about what I get. I tow at 65 mph and tow 17K.

 

Some interesting info. Using Torque and GPS, my RPM is 1810 @ 65. So I'm off by 180 Rpm. Still glad I did the 3.73.

Keith

 

Incredibly complex answer to that question:

ALL things being equal, if you increased the height of the tire at the same speed you would be a fewer rpm, theoretically you would see an resultant increase in mpg...because the engine is turning fewer rpm, in other words not breathing as hard.

Now the world becomes very complex and you get into torque and Hp curves, application of power in order to overcome rolling resistance and wind etc etc etc.

In theory you could see a 13% mpg increase (4.30 vs 3.73) which would translate out into about 1 mpg, in reality unless you made a long trip chances are the end of month fuel bill would come out about the same or so close you would not the difference.

Of course taller tires will weigh more, thus more effort to spin up.

Based upon my observations of the '15> 6.7 I think a 4.10 would be the best choice.

 

Don,
I am in total agreement on the 4.10 ratio for the dually. Back in 99 it was the Dually option.

I also found out my analog speedo needle is 3 mph fast..., but the ECM is right on the money with the GPS. I just can't figure out how I can be off by 10%. I get a few on either side, but 10%.... My OCD is kicking in. When I have the wheels off I will most likely count rotations. Maybe Ford slipped in a set of 3.55.

When someone has a free moment can you confirm RPM at 60, 65 and 70 in 6th gear please. Reading off the ECM is preferable.

So if I end up doing my tires I will be spinning about 1700 @ 65.

Paso,
Can you draw a tape on your rears unloaded overall and approximate center of hub (radius). Thanks

Thanks to everyone.

Keith

 

mostly insignificant difference. The 4.30 might get better mileage if/when towing heavy loads at lower speeds/rpms, but again, not really enough to matter in my opinion unless your planning to max out towing capacity and tow most of the time. Id go for 3.73 given those choices. personally i have 3.55 but i only tow around 9000 pounds less than half of the miles i drive. My unloaded average is pretty well right on 15.5mpg if i dont reset the meter for a few hundred to a few thousand miles, If i do reset it I get 17-19 on flat roads no wind at 70mph, 22-24mpg at 55mph flat roads no wind(but i never go that slow for long, speed limit on all highways is 65 in my state). I get 10-11mpg average towing 9000 pound 5th wheel going 70mph for 1500 miles from ND to NV through the rockies. Worst ive seen is 7mpg going 70 against a 40mph wind and best is 13mpg going 70 with flat road no wind.

 

You guys and your gear ratios lol.

IMO with the gazillion gears in the tranny there is no reason to go for the lowest gear possible anymore. No one said you have to use top gear when towing.

My 3.31's get the same mpg when towing as others have mentioned BUT my unloaded is much better than others.

 

But the lower gears(higher numbers) will put less stress on the rest of your drivetrain. Just physics. But I dont think most of us pull enough weight to make that much difference.

 

I agree with you Don...

Unless you need to pull at max tow ratings, I don't see getting a 4.30 rear gear. Especially if your concern is MPG running empty on the highway at highway speeds. I've never heard of anyone going to higher number rear gear for the mileage. Better performance/get up and go off the line and towing capacity, yes...

 

I recently picked up a new '15 Jeep Rubicon, it has a 6 sp manual and 4:10 gears. In my last Rubicon I had a 5 sp and 4:88 cogs, but it was mated to the inline 6, my new one has the V6 and does not hit peak torque till about 4000 rpm, my old inline 6 prob did not even wind up to 4000 rpm. Driving the two is like day and night, with the inline 6 giving much better performance around town.

My '11 F 350 w/3.73 gears got good mpg, good performance (I carry a camper in the bed that weighs in about 5500 lbs) and sometimes pull a trailer also will provide improved mpg and performance with 4:10 gears than either 3:73 or 4:30