My goal is to get 25+ mpg from my 99 XJ with 30 x 9.5 R15 ATs - Page 31 - JeepForum.com
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Unread 08-16-2013, 10:10 AM   #451
Newtons3
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Narrower tires do help with rolling resistance. Wheel/tire weight primarily matters during acceleration. At speed they are just flywheels and in theory could have some positive effect. Just some food for thought, rotating weights effect decreases by the square of the gear ratio driving it. So, if you have a 4 to 1 final drive, 1 lb. of crankshaft weight makes as much difference as 16 lbs. at the wheels. That principle also means that regearing can offset wheel weight, to some extent. The x mpg/100 lbs. theory is flawed too and incomplete. Within limits, your weight wont noticeably affect your mileage on the highway. It does take more energy to accelerate it though. Conversely, that weight helps carry speed through hills. Also that ratio is neither accurate or absolute for all vehicles.

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Unread 08-16-2013, 12:30 PM   #452
Charley3
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Quote:
Originally Posted by bobthecatkiller View Post
So I alone decrease my milage by 1.5mpg.
Now we should start asking how much people weigh in "way is my mpg so bad" threads.
I hadn't thought of that. Ha ha.

I lost 50 lbs off myself. I guess that's a theoretical 0.5 mpg increase in city mpg, if the ratio is correct.

I think the 1 mpg per 100 lbs is referring to city fuel economy, and driving up long hills on highway. I don't think it could matter much on level highway.

I don't know how accurate the info is. It's just what I read at various websites, including I think I saw it at the gov website for gas mileage ratings for cars.
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Unread 08-16-2013, 12:32 PM   #453
Charley3
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Quote:
Originally Posted by Newtons3 View Post
Well, first, be aware that fuel itself can be inconsistant between fill ups ame between seasons/altitudes. This may have something to do with better power/lower m4leage in the winter and take the focus off of some of the other causes. Secondly, it may be possible to make smarter decisions about where we buy fuel in the winter to better meet our goals. Thirdly, what if we could mitigate all of this? Gasoline is a blend. We could add something to the recipe.
OK. I see your points. You're correct.
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Unread 08-16-2013, 01:45 PM   #454
Charley3
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Quote:
Originally Posted by Newtons3 View Post
Narrower tires do help with rolling resistance. Wheel/tire weight primarily matters during acceleration. At speed they are just flywheels and in theory could have some positive effect. Just some food for thought, rotating weights effect decreases by the square of the gear ratio driving it. So, if you have a 4 to 1 final drive, 1 lb. of crankshaft weight makes as much difference as 16 lbs. at the wheels. That principle also means that regearing can offset wheel weight, to some extent. The x mpg/100 lbs. theory is flawed too and incomplete. Within limits, your weight wont noticeably affect your mileage on the highway. It does take more energy to accelerate it though. Conversely, that weight helps carry speed through hills. Also that ratio is neither accurate or absolute for all vehicles.
I think regearing does recover some of lost acceleration/power with heaver tires/wheels, but I don't think it recovers lost mpg.

Though regearing will recover some of the lost mpg from taller tires, by getting the rpms where they need to be.

That is my opinion based on experimenting with my LJ with 3 tire/wheel combos and 3 different gear ratios.
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Unread 08-16-2013, 05:49 PM   #455
Newtons3
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All things being completely equal, that is true. I just cant see making a tire selection based on weight unless it came down to a choice between load ranges. I think my decisions are made and then they weigh what they weigh. It may be worth noting that a second set of tires for 80 percent of our travels could be justified. Either that or some of us may want to park our egos and just buy tamer tires to match what we actually do with our Jeeps.
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Unread 08-16-2013, 05:54 PM   #456
Newtons3
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All things being completely equal, that is true. I just cant see making a tire selection based on weight unless it came down to a choice between load ranges. I think my decisions are made and then they weigh what they weigh. It may be worth noting that a second set of tires for 80 percent of our travels could be justified. Either that or some of us may want to park our egos and just buy tamer tires to match what we actually do with our Jeeps.
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Unread 08-16-2013, 06:08 PM   #457
rebelbowtie
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That's why I avoid mud and run all terrains.
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Unread 08-16-2013, 06:21 PM   #458
mschi772
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Hell, I'm considering touring tires for my next set. I go off road, but rarely and somewhat tame conditions that I think even street tires could handle well enough; they just have to get me where I'm going and back again. Tires really are a status symbol/ego thing among Jeepers where highway/touring tires are considered "uncool."

The physics beginning to be discussed above are astronomically complex, and the moral of any of these stories put extremely simply is "weight = bad." I have to agree though that rarely is weight ever a deciding factor on tires or other parts (tires especially though) for me. Usually the decision is made long before weight even hits my radar.
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Unread 08-16-2013, 06:43 PM   #459
rebelbowtie
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Unless it rains most of the nearby trails can be completed with all seasons but I can't be seen with those! Lol for real though most people underestimate the traction many quality tires can provide or traction the surface you're driving on can provide.
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Unread 08-16-2013, 06:52 PM   #460
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I thought this was going to be a diesel swap thread...
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Unread 08-17-2013, 12:07 AM   #461
Charley3
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Quote:
Originally Posted by rebelbowtie View Post
That's why I avoid mud and run all terrains.
Get some Cooper AT3 and you can run some mud and an AT and get good gas mileage from one tire.

That's what I'm doing. I've driven them in 4" deep mud up a slight hill (through a muddy creek bed and up and over the muddy bank) in 2wd with open diff with only slight occasional wheel slip (like 1/4 turn at most) and no wheel spin. It was easy.

In addition to great tread design, the AT3 has silica in the tread. This increases wet traction, ice traction, gas mileage, and tread life.
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Unread 08-17-2013, 12:26 AM   #462
Charley3
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Re gas mileage...

I always consider tire weight when choosing a tire. It's not my only priority, but I do consider it.

Wheel and tire weight are important to me, along with having a narrowish (9.5 or narrower) tire, and a tread that's not to aggressive.

For tread I look for aggressive enough for my traction needs, but no more aggressive than I need. For me, that's Cooper Discoverer AT3, Hankook Dynapro ATM, or Hercules Terra Trac AT2. The Cooper and Hercules are cousins and both have similar tread pattern and silica in tread.

For size, I'm really happy with 30 x 9.5 R15 on stock 15 x 7 aluminum wheels. I find them great on road and good off road. I've owned and tried 28, 29, 30, 31, & 33 inch tires over 3 Jeeps. That includes 2 sets of 30x9.5, 33x12, 33x10.5.

The 30x9.5R15 are my favorite size so far for DD. They offer great on road and very good off road performance, and good gas mileage. I might want to try 31x9.5 someday.

===

Narrow tires (9.5 or less) have the additional benefits of being ideal on wet highway (very wet here) and ideal on Winter roads (which is also important here).
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Unread 08-17-2013, 09:55 AM   #463
Newtons3
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I think checking our egos and buying tires that really reflect our driving needs would definitely help our mileage.
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Unread 08-17-2013, 01:19 PM   #464
Charley3
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Quote:
Originally Posted by Newtons3 View Post
I think checking our egos and buying tires that really reflect our driving needs would definitely help our gas mileage
Macho attitude is very expensive in many ways, including (gas) mileage.

I can't avoid rain, snow, and ice; but I could avoid most mud. I don't need to off road at all, except my cousin's nasty long steep rugged driveway, but all season tires could handle that.

I really only need all season tires for transportation, but I sure love my Cooper AT3 for hobby offroading.

This is one reason I run 30" ATs these days instead of 33" MTs like I used to. I'm getting wiser, more conservative, and more realistic with age.
There was a young guy in another thread awhile ago who claimed that 35" MT don't affect gas mileage enough to matter (compared to a smaller tires), and he claimed he needed 35" tires to guarantee he could get home everyday. I called B.S. on that, and flames ensued. Some people are morons. If he showed up spouting that baloney in this thread, I wouldn't say anything because you guys would beat me to it.
There's nothing wrong with running big tires if you want, but it affects gas mileage (a lot). Likewise with aggressive tread.

The older I get, the smaller and less aggressive my tires get. Having tried an assortment of tire sizes and levels of aggressive tread over the years, I conclude that I want/prefer 30x9.5R15 AT for fun, but I could get by just fine with a 225/75R15 all season tires, if I'm honest with myself.

I really don't even need a Jeep. I could get by fine with my Buick. However, my XJ gives me a second car, which is useful, a lot of fun which I need, and it allows me to (someday) switch my Buick from snow tires to touring tires, which will help the Buick's gas mileage. So my XJ makes it possible for my Buick to become a better hypermiler.

I need two cars so I can drive one while modding the other. It's near impossible to do much mods on an "only" car. A spare car is needed while modding the other car. So I do need my Jeep! Ha! I'm keeping it!
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Unread 08-17-2013, 02:21 PM   #465
JMH21814
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Quote:
Originally Posted by Charley3 View Post
I need two cars so I can drive one while modding the other. It's near impossible to do much mods on an "only" car. A spare car is needing while modding the other car. So I do need my Jeep! Ha! I'm keeping it!
Cannot argue with this impeccable logic. Well played, sir.
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