Mileage Drop ?? - Montana Owners Club

tjuhl · 06-25-2009, 06:30 AM

Anyone ever hear of this? Had been getting 12.4 MPG consistently over the last 1 1/2 years (actual mileage,no bogus computer) pulling Monty with '06 Dodge CTD. Just prior to this 4500 mile trip I put new Michelin Ribs on the Monty and mileage dropped to 11.4 MPG. Same type roads, same speeds, same 80# pressure. Even checked axels, do not appear to have moved. Only difference was the new tires. Empty mileage appears to be the same.
The Michelins couldn't have more resistance, could they?

jjackflash · 06-25-2009, 07:05 AM

Are the new tires the same size as the originals?
If their smaller,that could make a difference.
Jack

tjuhl · 06-25-2009, 07:42 AM

Michelins are the 235/85 R16 instead of the Mission 235/80 R16, so they are slightly larger.

KTManiac · 06-25-2009, 08:25 AM

Must be more rolling resistance due to the radial sidewalls of the LT tires. Did you have ST tires on it before? That may be it, or it could be an alignment issue.

Art-n-Marge · 06-25-2009, 01:49 PM

I have heard of differences in trips because of different tires, and I imagine that the size of tires could affect the MPGs. 1 MPG doesn't sound like much until you've driven 4500 miles! We always hope for this number to go UP not down.

Could it also be the trip? Have you done that same 4500 mile trip on the old trailer tires? That would be comparing apples to apples.

For example, two years ago I drove from California to Florida via I-10 and got 20.1 MPGs driving the same speed in both directions. The load was predominantly the same in both directions except that we had a few souvenirs by the time we were done.

Last month I took a trip across the United States starting in California Eastbound via I-40, I-44, I-70 (predominant route) to Maryland. I got 19.0 miles to the gallon Eastbound (and lost 3 hours of sleepy time). Westbound, the same route got me 17.2 miles to the gallon - but I was also carrying an additional 900 lbs in the truck bed and we had a lot of windy or rainy weather. I attribute the decline in MPGs to the load and the wind and. But when compared to the first trip at 19 MPG, there were way bigger and longer altitude changes versus I-10.

I hope we can learn a little about size and type of tires and how it affects MPGs by someone here.

LonnieB · 06-25-2009, 03:36 PM

My guess would be the weight of the XPS Rib. It weighs about three times what the Mission weighs and will have a higher rolling resistance. The ST Mission and the LT Michelin are both radial constructed tires.

Art-n-Marge · 06-25-2009, 06:34 PM

So LonnieB, would that actually make the Michelin a much stronger tire and hence while losing only 1 MPG there would be a huge gain in reliability and number of miles? I like that tradeoff, because then getting 11.4MPG but much better dependability might be a worthwhile tradeoff.

helmick · 06-25-2009, 07:01 PM

Lonnie, Please don`t say that. After buying new XPS RIB tires
We are getting ready to take off on a 6,500 mile trip.

LonnieB · 06-26-2009, 12:03 PM

Quote:

quote:So LonnieB, would that actually make the Michelin a much stronger tire and hence while losing only 1 MPG there would be a huge gain in reliability and number of miles? I like that tradeoff, because then getting 11.4MPG but much better dependability might be a worthwhile tradeoff.

Art, the Michelin XPS Rib is a much stronger tire by far than the Mission ST, or any other ST rated 10 ply tire. It is also stronger than most LT rated 10 ply tires.

Quote:

quote:Lonnie, Please don`t say that. After buying new XPS RIB tires
We are getting ready to take off on a 6,500 mile trip.

I don't know for certain that the weight of the tires caused the drop in MPG. I do know for certain its harder to roll a heavy tire than a light tire.

Art-n-Marge · 06-26-2009, 12:25 PM

Thanks LonnieB, but is my reasoning following my strength question a good reason to justify the 1MPG loss - the point being, do you want strength or 1mpg? Member's choice.

Helmick, just tell your family you thought safety was more important than 1 MPG. They'll love you for it.

Let's face it. We are towing 10, 11 or more tons or rig down the road. As long as we strive for safety, comfort, comformance and good times, 12-14 MPGs is great for a rig combination and we shouldn't be too worried about MPGs. It could be a lot worse. You could be using a gasoline truck at 6-8 MPGs.

I think the rolling resistance is a strong possibility for this issue, but justified because of the benefits.

helmick · 06-26-2009, 01:34 PM

Art, Safety is a lot more important for both my family and others on the road in my path.
Ron

sreigle · 06-26-2009, 02:00 PM

Tjuhl, any chance your trip included areas of the country that have winterized diesel during the winter months and some have it through the spring months? Winterized diesel drops my mileage by 1 to 1.5 mpg. Just a thought.

tjuhl · 06-27-2009, 03:57 PM

Thanks folks. The peace of mind is even greater then I expected it to be. More trips will verify if that mileage difference continues. But a lot of people have gone from Missions to Michelins and after reading this great forum for over 2 years I never saw anything like this mentioned.

Tom S. · 06-30-2009, 01:25 PM

Tom, there are so many variables here! As has already been discussed, the tires have more rolling mass. Since they are slightly larger, they also stick the trailer higher into the wind. Maybe you had a heavier load than previously? Also, unless you fueled at high usage stations, you may also be seeing the effects of the remnants of winter fuel. Speaking of fuel, how old was the fuel filter and air filter on your truck? I have heard people claim a dirty fuel filter can effect mileage, but I don't know it for a fact. I am pretty sure a dirty air filter will negatively effect mileage though.

Just some things to consider.

But if you want some Missions back, I'm sure someone would be willing to swap!

sreigle · 07-01-2009, 07:12 AM

I think Tom may have hit on something about the fuel filter. I keep an eye on ours to make sure I change it every 15,000 miles. When getting close to that I have noticed a small drop in mileage. And it improves after the fuel filter change.

tjuhl · 07-03-2009, 03:19 PM

Just had the oil, oil filter, fuel filter and air filter changed before that trip and I always fuel at high volumn truck stops and the trip was mid-May-June. I still can't think of anything that changed except for the tires and the oil and filter changes.

garyka · 07-05-2009, 02:17 AM

Are you sure it's the tires? I had my mileage drop returning from snow birding in Florida to NY and it seemed the closer I got home it returned to what I usually get 11 to 12 mpg.

sreigle · 07-05-2009, 08:20 AM

Gary, if you look at your map in your signature, when you leave Florida for anywhere north of there, you're going uphill. The trip to Florida then is downhill. I would think that would impact your mileage.

(Can't believe I really said that.)

garyka · 07-06-2009, 07:23 AM

Thanks for the response,now I know why your the MOC wizard

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