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I'm looking for definitive physics for tire/lift vs. fuel efficiency

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Old 02-01-2011, 09:56 AM   #1
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I'm looking for definitive physics for tire/lift vs. fuel efficiency

Everyone I talk to says if I lift and put bigger tires my fuel efficiency would decrease. Can anyone prove this?

Logically, having a bigger tire should increase your fuel efficiency by increasing the gear ratio of your tire to your axle. Is it a lift thing, or a tire thing?

Note: I'm still a newb, and very limited auto-knowledge, but I'm a math guy and understand the physics.
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Old 02-01-2011, 09:59 AM   #2
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Larger tires = more mass to turn thus giving you less mileage
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Old 02-01-2011, 09:59 AM   #3
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Bigger tire weighs more, more energy required to get it moving and keep it moving.
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Old 02-01-2011, 10:01 AM   #4
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Lifting increases frontal area, thus resulting in more aerodynamic drag.......to add to what the others have said about the increased rotational mass with larger tires.
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Old 02-01-2011, 10:04 AM   #5
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Quote:
Originally Posted by Mr G View Post
Everyone I talk to says if I lift and put bigger tires my fuel efficiency would decrease. Can anyone prove this?

Logically, having a bigger tire should increase your fuel efficiency by increasing the gear ratio of your tire to your axle. Is it a lift thing, or a tire thing?

Note: I'm still a newb, and very limited auto-knowledge, but I'm a math guy and understand the physics.
Quote:
Originally Posted by JLee View Post
Larger tires = more mass to turn thus giving you less mileage
Quote:
Originally Posted by Jester243 View Post
Bigger tire weighs more, more energy required to get it moving and keep it moving.
Quote:
Originally Posted by chris4x4 View Post
Lifting increases frontal area, thus resulting in more aerodynamic drag.......to add to what the others have said about the increased rotational mass with larger tires.
yes, yes, yes, yes, yes, yes. These are all correct.

Logically, your initial thinking is correct. But all the comments above will help u understand better.
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Old 02-02-2011, 05:57 AM   #6
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ok, so that answers that. What kind of effect are we talking here? 1-2mpg? more? I've got an 09 V6 Access Cab that's my daily driver, and would love to lift and put better tires on it, but I'm afraid my 30min commute each way would make it not worth it.
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Old 02-02-2011, 06:00 AM   #7
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Old 02-02-2011, 06:05 AM   #9
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Quote:
Originally Posted by duckcmdr View Post
If you are worried about MPG's then don't do it. You will average 12-16mpg depending on your set-up and driving style.
exatcly
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Old 02-02-2011, 06:12 AM   #10
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One other factor, in addition to the others noted above.

Adding larger tires will make for a higher final drive ratio, what affect this has on your mpg's though depends on your driving habits. If your driving is more lower speed, light-to-light type driving, the higher ratio will negatively affect your mpgs as it takes more power to get the truck moving. If your driving is more highway, constant speed driving, then the higher ratio should positively affect your mpgs.
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Old 02-02-2011, 06:14 AM   #11
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Quote:
Originally Posted by duckcmdr View Post
If you are worried about MPG's then don't do it. You will average 12-16mpg depending on your set-up and driving style.
wow. lots of good knowledge from you guys.

here's my dilemma: I really want to get into off roading, but with my 30 min drive to work, mpg is fairly important. I guess I'll ease into off road with my AT's and no lift, and if I really love it, then possibly get a set of rims/MT's and switch them out before I go out.
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Old 02-02-2011, 06:16 AM   #12
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Quote:
Originally Posted by Lurkin View Post
If your driving is more highway, constant speed driving, then the higher ratio should positively affect your mpgs.
my commute consists of 2 mile's of stop and go, and about 25 miles of 70mph on cruise control
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Old 02-02-2011, 06:18 AM   #13
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There's so many factors that bring you highway miles down. In my case, I regeared to make up for the new tire size (not a Tacoma, a Jeep XJ). In city driving, I didn't notice much of a change. There was a little drop due to increased weight and/or rolling resistance between "all terrain tires" and BFG MTs.

On the highway, the new gears (4.56) put the RPMs a tad higher. This contributes to a significant drop in MPG.

The rolling resistance of agressive tires is greater. This contributes to a significant drop in MPG.

Any factory aerodynamics were gone with fenders cut out, all front plastic faring crap removed, high-clearance front bumper and a Rubicon Express 4.5 inch suspension lift (nearly six inches higher before it settles). This contributes to a significant drop in MPG.

This goes from a combined 18 (under the new way to calculate it) down to a combined 12 (under the new way to calculate it).

You don't need physics at this point. If you want stock MPG, leave it stock and drive it like an egg is under the gas pedal.
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Old 02-02-2011, 06:19 AM   #14
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Quote:
Originally Posted by Mr G View Post
wow. lots of good knowledge from you guys.

here's my dilemma: I really want to get into off roading, but with my 30 min drive to work, mpg is fairly important. I guess I'll ease into off road with my AT's and no lift, and if I really love it, then possibly get a set of rims/MT's and switch them out before I go out.
it seems you dont want to be spending the extra cash on gas after lifting but off roading costs money...
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Old 02-02-2011, 06:20 AM   #15
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Just go with some AT's

and plan on budgeting for more gas.

I bought a truck because I needed it to haul stuff and be able to go off-roading. I went from an accord getting 27-28mpg to getting 17-18mpg in the truck. I knew that getting into it and budgeted for gas expenses accordingly.
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Old 02-02-2011, 06:27 AM   #16
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Quote:
Originally Posted by Mr G View Post
wow. lots of good knowledge from you guys.

here's my dilemma: I really want to get into off roading, but with my 30 min drive to work, mpg is fairly important. I guess I'll ease into off road with my AT's and no lift, and if I really love it, then possibly get a set of rims/MT's and switch them out before I go out.
Sounds like a smart move to me! When you have competing priorities, prioritize the best bang for the buck moves and add 'em one by one.
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Old 02-02-2011, 07:15 AM   #17
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Quote:
Originally Posted by 808matt View Post
it seems you dont want to be spending the extra cash on gas after lifting but off roading costs money...
ahem..

with current A/T setup:
Price of Gas 3.15
MPG 21
MP tank 357
Cost/tank 53.55
Cost/mile 0.15
Miles/yr 15000
Cost/yr 2250

with duckcmdr 12-16 range, averaging 15 since I drive mostly highway
Price of Gas 3.15
MPG 15
Mi/tank 255
Cost/tank 53.55
Cost/mile 0.21
Miles/yr 15000
Cost/yr 3150

That's a difference of $900. If I have to replace those mudders after 30k (i have no idea for MT highway life), then that's a $1800 difference I could use on a nice set of mudders, rims, and jack stand and just switch before I hit the trails.

EDIT: several assumptions are made, such as the price of gas is constant over the next 2 years, no other magic MPG device actually works, and my daily commute remains the same for 2 yrs. ALSO, the second figures are excluding the initial price of MTs. that would another $1000 or so spread over 2 years
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Old 02-03-2011, 03:46 AM   #18
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wow, your gas is cheap
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Old 02-03-2011, 05:53 AM   #19
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Quote:
Originally Posted by 808matt View Post
wow, your gas is cheap
costco has it for $3.07
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Old 02-03-2011, 12:22 PM   #20
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Question for you... With those calculation did you take into mind that with the bigger tires you would have actually gone more miles then what the trip computer would read?
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