Anyone else running 285/75R16s on a 2nd gen? I'll tell ya the dangedest thing happened to me this weekend. Just got my 285's put on and pulled my first trailer since doing so.

Empty: drove 180 miles, 4 lane divided highway, 24 foot stock trailer EMPTY, 6th gear, 80 miles per hour. Average econ according to overhead.....9.9 mpg.

Loaded: drove 180 miles back, same road, loaded with #10,500 of steers, 5th gear, 65 miles per hour. Average econ according to overhead....10.5 mpg.

Huh? I know head winds, speed, and grade play a large roll in this. Delete grade...I'm in Oklahoma. Wind or no wind....I had more than an extra 5 tons of weight! Yes I drove a little slower coming back, but 10,500 pounds!!!

I do like how these over size tires run 65-70 at 2000-2300 rpm in 5th gear. 6th gear is worthless on this truck unless bob-tail anyway. Any trailer at all and the EGT gets too high on hills in my opinion.

Will a smarty help econ AND give more power while pulling with these bigger tires, or will it just give me more power and shot the econ to Hades? I don't know if I can afford road diesel for pulling trailers if I'm going to get less than 9 mpg.

 

If you didn't correct your speedometer, you were going around 84mph,
no wonder your mileage sucked.
(unless your stock tires were 245's, then you were going 86+)

The smarty will help, if you use the speedometer recalibrator function.

Best thing to do is not go so bloody fast, especially when towing a trailer.
Keep it at the speed limit and you'll get wonderful mileage, comparatively speaking.


phox

 

I feel ur pain, hoss. I replaced the stock Michelins with 285/75/r16's Trailbuster At's and didnt see a noticeable increase in mileage. Since me and abuddy installed my BHAF and 5'' straight pipe, I just cant keep my foot off the throttle. I am not running a programer yet, but I am gettin around 15.65 MPG which kinda blows!! I am not disciplined enough to drive sensibly i guess

 

Did you hand calc the mileage at all??? Pulling a trailer is for sure going to cut your mileage but not as much as the 80mph speed....

I run 285's on mine and on the highway I still see 20mpg unloaded...

 

4x4dually
I would say recalibrate the speedo and hand calculate your mileage. Did you ever hand calculate your mileage before the new tires?

And in response to BigBruno, I have no freakin idea how people get such good mileage. I have filled the tank full and ran down near empty, roughly 480 mi when the low fuel light comes on. So far, I've ran the truck from completely full to near empty six times in a row. I have NEVER beat 16.01mpg hand calculated. I've ran with truck fuel here at our farm, which I think is 11%bio. I've ran truck fuel from the truckstop. And for some reason I get terrible mileage with red fuel from the farm.

 

Yes. I had dodge recal the speedo. I jewed them down to $20 to do so. I had them enter 630 revs/mile. The Kumho website didn't offer the actual info, it just said "na" in that column...thanks guys...nice support. So, I researched all other 285s that I could find and found that to be the average. I also took the diameter and figured it by hand...I'm sure that is still not exact. I haven't had the chance to actually time it for a mile at 60 and see if it is right on yet. I didn't have anything with me with a second hand.

Now, reguardless of whether the over head is exactly correct, or my tire size is entered right, or any other un-calibrated device, I just found it funny that I could get better mileage pulling a completely loaded stock trailer than I could empty at any speed.

It seems that the larger tires take a lot more ponys to turn in 6th gear. My egt runs a lot higher even bob-tail when pushing the speed up.

Will smarty help decrease the egts or just make them worse when it boosts my power? I know I need it to dial in my tire size and get everything to read correctly.

Thanks,

 

getting a smarty will only add to your egt problems,it fuels hard down low and egts skyrocket without boost,see if you can try one before you buy one.they work well but they do add alot of egt down low.i have 285s and unloaded just playing i can get it to over 1100,with out the smarty i barley seen 900.

 

Soooo...I need a 4 inch stack first....is that what you're saying?

 

if you're ever up in Wichita, you could give my Smarty a try...

 

Just so you know "Jewed" as a verb is considered a racial epithet by some-- I'm sure you have no such intentions.

A typical 285 tire will actually be around 624-625 revs/mile, so your speedo is actually reading a little high. Unfortunately, that means your mileage is actually less, too-- by a tiny amount.

Keep in mind that you are pushing a LOT of rubber down the road with 285s on a dually. Your empty mileage is going to suck, too.


The other thing here is that you bought Kumhos. Kumhos are not bad tires, but they aren't the top of the line, either. A lower priced tire like the Kumhos could very well have a LOT more rolling resistance relative to a more "premium" tire like the Michelins.

So when you swapped tires, you killed you mileage because you took steps backwards in tire rolling resistance (both quality and tire size) and tire weight. NOw add in that you have a dually and things get worse.


Under the conditions you note, your MPG seems about right, but definitely on the low side. I assume you've checked all the normal stuff-- fuel filter, fuel pressure, IAT sensor, etc??

 

Absolutley no ethnical reference meant....I talked them down....how's that?

Yip. I bought cheap tires. I got them for $120 each.

I still crack up everytime I see your avatar. MORE COWBELL!!

I think I'll watch that clip again.......peace.

 

i feel your pain.. i've done about everything i could do to try to keep the mileage the same as stock or better. running the 1.6's it stayed the same but since i switched to the 4's i lost about 70 miles per tank!! all mine is hand calculated, the overhead is worthless it showes me getting 20.6 mpg with the 4's. i run 255/85's and we recently came back from MO with a 25k load of hey, and i had to run 55 mph in 5th or 75 mph in 6th to keep the turbo lit. mileage has never been over 16.5-17 on my truck even when i first got it. that's not bad considering it weighs 8500 lbs. the next load i'm going back to the 1.6's and back to 235/85's to gear it down some and see if that helps with egt's, mileage, and smoke control. with the TX heat the 4's have to come out (too much smoke) or i need some twins.