Interesting Articles concerning tire size and it's effect on fuel economy

http://www.barrystiretech.com/rrandfe2.html
http://ecomodder.com/forum/showthread.php/tire-width-vs-drag-cd-7475.html
http://www.alliedoil.com/2011/03/the-benefits-of-wide-base-tires/
http://www.greencarcongress.com/2006/06/single_widebase.html

 

I cannot believe that... A wider tire consumes less gas, huh.

Then why is it that when people get larger tires to accommodate lifts, their MPG goes down? Yes you could say it's the lift itself but I don't think it can be denied that most TWers report lower MPGs with bigger tires (265/75/16 or 285/75/16)

 

I get no MPG any more. 35's with 4:88's and a ton of plate under my truck I am happy to see 14mpg. But that the price you pay to play...

 

You would think the less contact with the road surface would = more mpg, we built a car in college that got 125-150mpg, all the wheels together had a total of 1.1 inches of contact with the road. If we used regular tires from a car or truck we would've had i think 6-12 inches of road contact and 6-12 times more friction.

 

Unless you are looking closely at each factor (frontal area, rolling resistance, weight), then you will probably not have a clear understanding of the effect your tires are having on your mileage.

 

The decrease in frontal area and rotational mass/weight, are exponentialy greater than the rolling resistance factor in your situation. You have to measure each variable separately in order to come to a solid conclusion about which tire will serve you best in each application.

 

I'm guessing that is the answer to my question, why do bigger tires get less MPG

If that's the case the author of that first article shouldn't have really said bigger tires=more mpg

 

Yeah, the answer really is, that it depends. If you put 33'' muds on your truck and do all city driving, I wouldn't be surprised to see a 3+mpg loss. But if your doing 90% highway driving you could see a slight gain, even though you've effectively doubled your tire weight over stock

 

I am putting probably 32"s on and doing mixed, don't need offroad. Dilemma is finding street 32"s that look aggressive as muds.

 

[SIZE=+2][SIZE=+0]3) Inflation pressure has a lesser effect: 10% for the first 8 psi - and diminishing after that. Be aware that increasing the inflation pressure also decreases the size of the footprint. While it seems logical that a decrease in footprint size ought to lead to a reduction in traction, and have some adverse effects in treadwear, there just aren't any studies to help clarify the situation

So a 1" wide tire has the same traction as a 1' wide tire. Sounds legit Now we just have to convince every off-roader that they should be running bicycle tires instead of 40's and they'll do better in the rocks. Think of the money the nhra could save every race by getting rid of all the extra rubber.
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There's more to that scenario than just tire size.

The height of the vehicle usually allows more air underneath and therefore more drag.

Each tire itself weighs more, so more hp needed to just get you rolling.

The increase in diameter lowers your effective gear ratio, so again your engine has to work harder to turn the tire. You can compensate by adjusting your gears, but lots of people don't regear after going larger.

Put together and you've got lower mpg. Gears will help but generally even with gears you will lose a bit to drag and weight.

 

He's talking about how contact patch size changes at different inflation levels. There is no reference to tires of differing sizes having the same traction..

 

How much does a regear cost? And I am hoping to do a belly panel now that I have seen a few of them to compensate that drag.

 

Which gears are you hoping to run? Generally speaking taller=better for fuel economy.

 

I don't know much about gears and have limited time to research things lately and I don't know what gears I am hoping to run. Whichever is required for 32" tires (or whatever else I choose)

 

How do these numbers affect performance? I know taller gears are better for MPG but is does regearing the truck to your tires make it faster? Correct the MPG loss from additional power needed to get them rolling? Prevent engine damage? Fix odometer?

 

torque vs speed

 

To run 32s I wouldn't worry about regearing in your situation. Once you factor in parts and install at a GOOD shop, you probably won't be saving much. Gears aren't something you want to take to the lowest bidder. Usually only want to hit the specialty shops so you know it's done right. Specialty shops = $$$

 

There are a lot of different ways to take that

That's a good point. Can you please list all of the positive/negative effects of getting taller tires without regearing?

 

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