Mpg is down after changing to G614's

[woodman]

Switched from the Marathons to the G614's just before making our big trip and they're all pressurized at 110 psi. We've got about 650 miles logged in right now, however; my gas mileage has declined by about 15-20% with the same cold conditions, vehicle weight and driving habits as last year. Anyone else had similar results?

[bigskyjimmy]

WOW that is quite a hit in mileage ,I have not noticed any change since I switched ,the G's are heavier but it should not make a difference

[rohrmann]

The only way you can get an accurate comparison would be running the exact same route at exactly the same speeds under the exact same conditions. What I found, now that I'm not restricted to under 65 mph, which I was staying under 60 mph with the Marathons, is I'm going faster when conditions allow, and that will cut your fuel mileage which may be what you're seeing. On good interstates in good weather, we will travel between 65 mph and 70 mph.

[mlh]

You may be using winter blend fuel. That will cut your mileage about 10%. Your mileage should be better running 110 PSI but probably not enough to measure. rohrmann is spot on.
Lynwood

[awaywego]

Run mine at 100# and get better mileage than with the old tires but only a couple MPG.

[sambam]

I can't say the G614's are getting me better mileage, but if they were getting me worse, especially 15-20% worse, I'm sure I'd notice. It can't be an apples to apples comparison. Something isn't right.

[Tom S.]

There are so many things that affect mileage that you can't really blame the tires. While it's true, they have more mass to get moving, once moving there should be no appreciable difference. Add to that their stiffer sidewalls, thus less flexing, I'm betting they are pretty even from a rolling resistance or maybe even better. I suspect weather is what really caused your difference. Just a 5 mph head wind vs. a 5 mph tail wind would make a huge difference. Even air density (humidity) can affect your mileage.

As mlh pointed out, you may also be comparing winter fuel vs. non winter blend which will also effect mileage very negatively. Winter blend contains kerosene to prevent the diesel fuel from gelling at low temps and kerosene is not nearly as efficient as diesel fuel.

[TLightning]

Since the tires are a different size, does there need to be an adjustment to the speedometer to give the correct MPH and MPG?

[Overlord]

quote:Originally posted by TLightning

Since the tires are a different size, does there need to be an adjustment to the speedometer to give the correct MPH and MPG?
Ummmmm, the different tires are on the trailer.[:o)]

[Captain Joe]

Gauges are marked with a +/- 10%. If yours is a + 10%, you are overinflating your tires. I run at 100 psi and they handle the weight just fine.

[JandC]

quote:Originally posted by woodman

Switched from the Marathons to the G614's just before making our big trip and they're all pressurized at 110 psi. We've got about 650 miles logged in right now, however; my gas mileage has declined by about 15-20% with the same cold conditions, vehicle weight and driving habits as last year. Anyone else had similar results?


My last two Montana's both had G614's (thanks to all the stories on this forum) so I can't really make the comparison.

What effects my MPG when towing is wind, my speed, road conditions (flat/level), and then blend/type of fuel.

Just a slight head wind will knock 10% - 15% off my MPG. I can pick up some mpg by towing at 60-62 instead of 66-68mph.

Our longest trip in 2014 was 7 weeks and almost 6,000 miles. Conditions were different almost every day towing. I would not base my mpg on a 600 mile plus segment. Wait and do more of an average.

[DQDick]

First time we towed any distance with the 614's my milage went from 11 to 9 and I was concerned. Then I realized that from OK city to Albuquerque it's mostly up hill and normally against the wind. Coming back I got 14.6 so I was happy. Now that we have a couple of years to examine we are getting 11.5 so the 614's are getting us a half an MPG.

[TLightning]

quote:Originally posted by Overlord

quote:Originally posted by TLightning

Since the tires are a different size, does there need to be an adjustment to the speedometer to give the correct MPH and MPG?
Ummmmm, the different tires are on the trailer.[:o)]


Don't confuse me with facts![:I]

[woodman]

The tires were mounted on the trailer, not the truck; therefore won't have any impact on the speedometer. I agree that there could be other factors that could influence mpg, but as of now, can't think of any and I've eliminated everything else and can only conclude that the tires are harder to pull and therefore have reduced my mpg. We pulled the unit in super cold conditions last winter and were getting great mileage. Granted, I'm less hesitant about traveling over 65 with the G's, but from the very beginning I saw a decrease in mileage with the on-board computer when traveling closer to 55 mph.

[Mark N.]

quote:Originally posted by Captain Joe

Gauges are marked with a +/- 10%. If yours is a + 10%, you are overinflating your tires. I run at 100 psi and they handle the weight just fine.


Well, that sorta depends on the gauge, right? My electronic digital gauge has a +/- 1.5% tolerance. So, at 110 lbs., that is only a 3.3 psi. window.

[Mark N.]

I can just say point blank: There is no way going from Marathons to G614s will hit your mileage 15-20%. In theory, they are a percentage heavier than the marathons, so technically you are pulling a heavier load. But, the added weight you are now pulling is so inconsequential, it will be un-measurable in mpg calculations.
A bigger factor in tires and mpg calculations is the rolling resistance. I seriously doubt the difference in these two tires is even measurable on a heavy towed vehicle like a Montana. Rolling resistance barely makes a change on a Prius I drive, and it's designed to take advantage of everything it can to get 51 mpg.

[jlb27537]

OK you folks......

You need to quit worrying about anything.

Need to remember that what ever you spend, it is money the kids will not get, and they will not be fighting over, SO, you are saving peace in the family and that is a good thing.

I have a friend with a Ford that gets about 1-2 mpg more than I do. But do I care? Nope. If you have to worry about 10% less mileage, you need to get a different hobby or life style.

[DQDick]

The other thing to remember is the reason to go to a better tire than the Marathon's. MPG isn't much of a concern when you're having tires explode and repairing trailer damage. Even if I wasn't getting better milage with the 614's the peace of mine would be worth it.

[psomers]

If you have a diesel 2007.5 or later you more than likely have a DPF filter in the exhaust. Your truck will go into regen mode about every 30 gallons of fuel ( not exact as the computer decides when }. My truck normally runs around 11.2 MPG while towing but will quickly drop to 9.5 if a regen occurs. I couldn't tell any difference after G614 install.

[PackerFan]

I was told a long time ago "If you are worried about fuel mileage buy a Prius...Not an RV!" :D :D

[RKassl]

Don't blame the tires they are not the problem, believe me we are on second set.

[woodman]

We've now traveled another 700 miles and the numbers have improved ever so slightly, but definitely still less than on the Marathons. That's a total of 1350 miles so far on the "G" tires. Weather is warming up as we head south, so that may have contributed to a bit better fuel efficiency. The G614's are a wider tire, which means there's more contact surface meeting the road, hence; more resistance. I know they're a heavier tire, but believe it or not, we've actually lightened our cargo, so our GVWR is actually less than last year. I was initially just trying to figure out why my mileage was down when all the other variables seemed essentially the same. This is the perfect forum to find out what others have experienced and determine if this is just some anomaly or if it's consistent with what others have found. Thanks for all your input and thoughts.

[Tom S.]

I still think it's winter fuel. It's notorious for dropping fuel economy.

[drsmart]

If you keep this up, you'll have everyone switching from G614's to Marabombs :D

[DQDick]

I still say, based on the number of Montana's I've seen by the side of the road or pulling into a campground with side damage, that I'd give up a good deal of mileage to get rid of the OEM tires if I had to.

[Phil P]

Hi

We have about 80,000 miles on the Montana and all but about 3,000 of that on G614s.

The truck was new when we change to the G614 and still getting 6 to 7 miles to the gallon. At about 30,000 on the truck our mileage started improving rapidly.

We now average 12 MPG on the highway with the Montana at 60 MPH and 18 MPG on the highway bobtail at 75 MPH.

I haven’t found any difference in mileage between winter diesel and summer diesel. The Cetaine in diesel doesn’t change like the Octane in winter gasoline.

I find this compares closely with most of the folks here on the forum.

Phil P

[Mark N.]

quote:Originally posted by PackerFan

I was told a long time ago "If you are worried about fuel mileage buy a Prius...Not an RV!" :D :D
And remember: It's not and "either/or" proposition. I did both! I have a 1 ton diesel AND a Prius. :)

[clarkandsheila]

If you have a turbo boost guage on the truck, become familiar with it. On my own I have found that at ~ 10# boost at 55-58mph that we are running on a relatively flat road, no up or down grade and no wind.
If I notice either less or more then something outside is affecting operation. Wind, or grade, dragging brakes.
But it will take some time and attention to learn where the boost guage will reside on a flat road with no wind.

[richard66]

Run what you can afford and are comfortable with. If you tow 20 miles to the lake on weekends and then home your requirements differ greatly from a full timer or folks who take 10k trips. Buy all means get rid of the ST tires. If buying trailer from dealer make tire replacement part of the deal.

[jcurryii]

Changed to G614's last fall, seem to be getting the same mileage as before on same round trip to Gulf.

[Goin 4 Broke]

What is the approximate cost to upgrade? I am still working the numbers with my dealer on a 3900FB. What would be a good price for them to change out to G614?

[rohrmann]

I paid about $1900 a little over a year ago for 5 G614's installed. If you can get them all replaced for $1000, I would consider it a good deal. Of course, I would start at a lower price, not sure what their price is for those tires, and they are also trying to sell the trailer too. Whatever deal you work out, you are wise getting started with the right rubber.

[Goin 4 Broke]

Thank you for the prompt response. The tires and axles are my biggest worry having read lots of forum posts. I am saving a good amount on a non-current model and I will convince my wife that the extra for the tires is worth it... Now if she will just approve the slide toppers, the satellite dish, the TPMS, the rear camera AND the BD3...

[DQDick]

You won't go wrong taking the tire worry out of the deal.